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Its no secret that I’ve some kind of energy problem. What is less known is how horrible the effects can be, or how plain weird the pattern is. People see me manage the motorcycling, the mountain biking or cycling but they don’t see what happens afterwards.

My current working model is that exercise generates some kind of toxin. That toxin builds up in the body and its effects peak around 24-28 hours after the exercise that generated it. The symptoms of that are best described as “flu like”, lethargy, feeling cold, a brain fog, inability to concentrate, feeling washed out, muscle and joint pains, tinnitus, teeth nerve pain and general mood changes. Those feelings can go on for around 2 weeks. There is no respiratory side to it and it never seems to be actual flu.

How serious is it? At its worst, after two days of motorcycling I collapsed semi-conscious and was out of it for 18 hours. My body had run so low on energy it lost the ability to regulate its temperature properly (thankfully I collapsed onto a duvet).

Whatever the toxin is, it appears to attack the nervous system, hence the various joint/muscle pains, tinnitus, teeth sensitivity and so on. If I’ve kept going and not given in to it either (through shear willpower or pain killers) I ended up with a permanent hand/limb tremor. Thankfully I also discovered biotin (Vitamin B7) appears to accelerate healing of that and after around a year, I managed to stop shaking, a major win.

The closest thing in medical knowledge that matches is paracetamol overdose, the key match being the timeframe. You don’t see symptoms of that for 24-48 hours after overdose. This lead to the realisation that its treatment also seems to help me. Its treated with NAC (N-acetyl-Cysteine) which is thankfully freely available and is a non-essential amino acid so its comparatively safe with low side effect risks.

Have I talked to a doctor about this? In short, yes, a lot. They have run a ton of tests over around a decade and there are few types of specialists I’ve not seen at some point. There are a ton of things we know it isn’t and some abnormalities. They don’t match anything they recognise. The two interesting data points are that my liver is unhappy about something (always raised GGT and sometimes raised ALT/AST/ALP) and prolactin is elevated. No idea about the prolactin (a story in its own right) but the liver fits the toxin poisoning model.

Its taken me that decade to figure out the pattern and to come up with the current coping strategy which takes the recovery from two weeks to 2-3 days. At one point I felt like I was accumulating damage (the tremor in particular), I’m pleased to say that it feels much less so now.

There are swings and roundabouts as the NAC appears to help a huge amount but may expose/cause other vitamin deficiency (B2?).

I personally suspect there is some genetic glitch somewhere, not enough to threaten life but enough to mean backup pathways which are less efficient are being used. There is solid science behind NAC increasing levels of Glutathione which is a master anti-oxidant and the way the body cleans up toxins. B2 is needed for recycling Glutathione and biotin is being studied in nervous system disease.

I guess I’m putting this out there in case it helps anyone else or that someone with knowledge of biochemistry could give any further insight into this.

I think by now people realise there is some “fatigue” thing going on with me.

I spent a couple of evenings last week doing strenuous wall paper stripping (woodchip), to the point I was trembling when I took breaks. On Saturday I took my new cyclocross bicycle for an 18 mile ride, I’ve been talking about buying one for years so I was determined to try it while the weather was good. Compared to my previous 40 year old bicycle with non-indexed gears and ineffective brakes, its a complete revelation and I love it. There is an 10 mile “time trial” section on the route I picked, Nov 2013 I was doing ~45 mins, Nov 2014 on the old bike, ~39 mins, on the new one, under 34 mins. I was pleasantly surprised!

I spent the weekend in a bit of a daze induced by the exercise which is par for the course, I’m used to that along with the muscle aches.

On Monday night, I became extremely cold and shivery with the “flu” aches and pains and basically didn’t sleep, oddly wide awake yet more unwell than I’ve ever been with proper flu. There were no respiratory or digestive symptoms. It could be a virus although the pattern of flu like symptoms 36-48 hours after exertion with varying intensity makes me lets say suspicious.

The medical profession? They basically don’t have a clue what is going on :(. Lots of tests up to and including muscle biopsy and some interesting results (like spinal nerve damage I seemingly recovered from?!) but nothing which explains it.

There seems to be a finite amount I can do, if I exceed that, there is a price to pay. I still feel horrible 24 hours on, nowhere near as bad as I did but still “not good”, sitting wearing half my wardrobe to keep warm (trail riding base layers are wonderful). I have no idea which events to commit to and need to be careful about being in a fit state for things. On the plus side, the price comes later, not during activity and I guess I have some handle on the pattern. Its also always been there I think, I’ve just tried to be more active/fit and provoked it.

So really, I don’t know whether to laugh or cry :/. If you see me having disappeared a bit from some things, this is why though.

Sunday morning was an early start but despite the fun of the previous day, I was basically ok and the swelling of my leg has massively reduced overnight. I made my way back to Bellingham in time to put fuel onto the fuel trailer and then made my way leisurely to the far checkpoint and my section. Unfortunately I was on my own today, it is more fun when you have someone to ride with and talk to.

Eventually bikes turned up and entered the section and then I followed the pack through to make sure there weren’t any issues. It was all quiet so I cut back to the special test and refueled finding the riders weren’t yet back to there. I therefore waited around. The end of the special test has an interesting detour through a ditch and there were a number of people falling off there who I ended up helping. There was one person who decided to head off the line everyone else was using and buried it in liquid mud up to the mudguards. I didn’t enjoy pulling that out and getting covered in mud. Another went off line, planted the front wheel into a hole and went over the bars head first, thankfully he was shaken but ok as it was slow speed.

There were people having fun on the enduro loops but my back tyre wasn’t up to it, nor were my energy levels to be quite honest. I had something to eat/drink and eventually the closing marshal turned up which marked the start of my main work. I headed back to my section via a short cut along with a local rider who was wanting to retire. There, I had a wait for the closing marshal again, he arrived and it was time to demark.

I was supposed to be with a team of another two however they weren’t there and I decided to get started without them, leaving word with the checkpoint to send them on. I hadn’t gotten too far when they showed up and joined in. We worked as a team, person in front gets the first arrow they come to and the team rotates. Demarking can be interesting as you never know quite what kind of terrain you’ll have to park on to reach the arrows. Obviously you try to do it without getting off the bike, although if the ditch is marsh/water with reeds growing out of it, you quickly learn not to ride into it (I’d remembered from last year).

We made it around the course to the next checkpoint and demarked to the road there, then also demarked the route back to the camping field. The far section with the second special test was being handled by another team. By the end of the few days, the bike was rather coated in mud/dust and rather sorry for itself with its missing headlight:

The forest fire roads are hard on tyres, particularly when you do use the power to accelerate and my rear was paractially a slick at this point:

So all in all a good weekend and some good fun. The bike is going to need a good check over after all that vibration from the fireroads.

Saturday dawned and I found I could roughly move. Various locals started arriving, either entering in the rally or marshalling. I was given the top section of the course to look after where I’d run out of fuel the day before. One of the local TRF was to be my partner in crime.

We had a leisurely ride out to the special test, then short cut to our section. We did a sighting lap of that part not least so my partner had some idea where we were, then watched a load of bikes through the special test since that was our way back to the start of our section and the checkpoint there. We headed back there to find nobody has entered it yet and managed to push our way through the crowds to the front. The spot has a lovely view over the reservoir.

After a good few bikes had set off, we started a check through and stopped to take some photos of some friends. After that we came across
a breakdown, a 690 that wouldn’t run. We spent a while pooling tools trying to diagnose the problem. It had a spark so it had to be fuel related. We left to go and find a tow rope. We swept through our section, then went back to the special test and fuel point to refill and find a tow rope. On the way back to our section we passed some other breakdowns but there wasn’t anything we could do to help and they were in a good place for recovery.

Whilst my two stroke wasn’t up to towing, my partner’s four stroke was and we were able to get him out the forest using some creative use of shortcuts and into a position he could get recovered from. Greg did well particularly given he’d never tried this before.

After Greg refueled at Kielder and I’d eaten my sandwiches, we went back around our section, stopping for photos and so on, hovering near the end so we’d hear of any other breakdowns or problems. When it was clear things were winding down we headed back to the test/fuel area and found the course was closed. All that was left was for us to head back to base which we did without incident. Our section was clear as far as we knew and would get checked by the closing team anyway.

I have to say I was pretty tired at this point. I decided that rather than camping, I’d head home for a shower and so on in comfort and I wanted a better look at my leg. I arrived home without incident, had a shower and re-bandaged the leg and then started to feel extremely unwell. As far as I can tell I was losing my ability to regulate body temperature and was very shaky and shivering with a fast pulse. I tried various quick food/drink options and it wasn’t helping, if anything I was getting worse, extremely cold and shivery. An idea struck me and I tried a can of coke which thankfully hit the spot and pulled me out of it within 10 minutes.

This is very similar to what happened to me a couple of years ago. In that case I ended up near enough unconscious for 18 hours so this was an improvement on last time. I’m now pretty sure these were both cases of hypoglycaemia. Readers are probably thinking diabetes come to mind or a thyroid problem etc. For the record, I’ve had a ton of tests and its not any of the “usual” suspects. It does seem to be exercise induced, delayed effect and some kind of metabolic muscle issue is prime suspect. I have my theories and investigation is still ongoing.

So I opted to stay at home for a good night’s sleep and to see how I was in the morning. Any sensible person would perhaps of opted to rest the next day however I believe I’m actually starting to understand what was going on with energy levels and all my instincts told me I would be fine to ride.

The K2 rally is this weekend in Kielder forest. It was fairly eventful so I’ll split these day by day.

Marking out a 65 mile course in the forest takes quite some time so I’d offered help to the organiser with that as well as marshalling in the rally itself.

As things worked out on the Friday, the course was pretty much done but it did need sighting, a check that all the signs were present in the right places, hazards marked etc. for the perspective of someone coming around the course.

Having arrived and secured a flat piece of ground for the tent, I therefore set off with someone who I won’t name on a DRZ400 on semi tyres, not off road ones. He assured me he would go steady but he’d finished X rallies, considers himself a retired enduro rider etc. He did have a good medical reason for not wanting to fall off too and wanted someone with him.

So we set off and it was soon clear that when he said we’d go ‘steady’, he didn’t half mean it. I was on the YZ with its road gearing on, not the enduro gearing since this was a rally. It’s engine is a handful at the best of times and it didn’t run well at this (lack of) speed :(.

Back in the karting days, I prided myself on an ability to limp broken two stroke engines back to the pits so somehow, I managed to keep the YZ running and not oil the plug.

When we found the special test, I ended up having to go past for one section since the YZ requires commitment and the 10mph simply wasn’t going to work. I was wishing I was on the CRM which would have been much happier at this pace.

We did put up a few arrows in places to make things clearer and there was only one confusing section where some tape wasn’t out. At this point it became clear that whilst we had a map, I’d have to read it. I also had the GPS and some idea of what the forest looks like by now, thankfully.

Somehow we made it to the top of the course and after a biscuit break, we dropped down onto the road by the reservoir and then turned back into the forest. He commented that his speedo had stopped working.

At this point I noticed his front wheel was unwell. At first it looked like he’d lost a spoke which had snagged the speedo cable and wrapped it around the wheel a couple of times. The bike was basically unsafe to ride.

So, first up, what tools did we have? He seemed very unkeen to try and get them from the sealed package on his bike so we tried mine. Unfortunately I’d picked up my favourite multitool, not remembering it was broken so we were without decent pliers. The speedo cable was at quite some tension and therefore not easy to undo. We could undo various mounting clips to try and slacken it off and then using the broken pliers, very slowly inched the top end of the cable undone.

When it did come undone it did so with quite some force and could have done nasty things to my fingers but I had anticipated this. We found it wasn’t a spoke that was wrapped around the wheel but 12″ of fencing wire. We pulled that off and then rather than disconnecting the speedo from the other end, managed to simply sever the cable. Great, we could continue.

The course is supposed to be a 2-2.5 hour lap. I think we were 4 hours in at this point, maybe more and not even half way. We looped around the next section of forest and then suddenly, my bike started sounding odd, the kind of odd that means the fuel is running out. I sounded my horn, waved arms and he took not notice of me and continued off into the distance as I coasted to a stop.

Not entirely able to believe it I checked the tank and yes, it was extremely low and now on reserve. Eventually he noticed I was missing and came back to look for me. Basically, my lack of fuel was extremely frustrating for him and his advice was we split up and I make my own way back on the road, I could always hitch a lift and then pick the bike up. That way I was no longer a problem for him. Against my better judgement, I decided that yes, I’d have to sort myself out. I knew where there was an automated fuel station, perhaps within range of my reserve however I had neither two stroke oil to mix new fuel, or a credit card with me (not many places take them deep in the forest).

We also had a little disagreement about the cause of my lack of fuel. He was keen to point out that as any idiot knows, running slower doesn’t use more fuel. I suggested that rule may apply to a point but that the YZ actually runs more efficiently at more than 10mph however he wasn’t having it. Regardless, it wasn’t going to change anything.

I therefore left, in full fuel economy mode and headed for Bellingham. Making it was never going to happen and I coasted to a stop completely out just past Falston. On the plus side I knew exactly where I was. On the downside it was a fair distance to where I needed to be (9 miles as it turned out).

I stashed the bike down a side road in some bushes, I also stashed the bike helmet, the arrows, stapler, body armour and anything else I wasn’t going to need under a handy plastic sheet over some firewood. I should mention at this point that there is no mobile phone signal apart from occasionally a network I wasn’t on, nor was I expecting any signal any time soon. Any houses around there are holiday lets or second homes and nobody was around.

So still wearing the knee braces and bike boots, I started the walk to Bellingham. At least this way I knew I’d get sorted out eventually. I was passed by lots of cars and I’d imagine someone wearing MX clothing and big bike boots looked a little out of place walking along a verge. One oncoming car did stop and ask if I was ok and did offer me a lift in the wrong direction but I politely declined. I wasn’t taking too well to walking in the heat with that gear on, “dripping”, doesn’t quite cover it.

After 3 miles a car going the right way did stop and gave me a lift into Bellingham for which I was extremely grateful. I tried to find the organiser to tell him I was ok but he wasn’t around. I figured my friend was still riding around the forest so far so nobody probably knew I was stranded yet. I therefore jumped into the discovery and went to collect the bike and stashed gear. That went without incident and when I got back to the site, the organiser also arrived back having been looking for me. My friend had got a message from his phone to his wife. Anyhow, I+bike were back and all was well.

It was now late afternoon and I opted for a tea break. Thinking I was just popping out for three hours, I hadn’t taken food with me although I’d had a drink. The organiser was apologetic for my trip out and said if I wanted, I could go and check the other half of the course with him if I was up for it. So we set off and all I can say is that this trip was opposite extremes to the first one. I mostly kept up and we got the other half of the course done on half a tank of fuel (including riding out to it). So perhaps it does use more fuel at 10mph, who’d have thought it! I did get to see the second special test although I much preferred the first.

Unfortunately, just as we were coming to the end of the course, I relaxed a little too much, ran wide on the exit of a corner, ran onto the edge of and then into a gravel drainage ditch and spent a short while sliding along said ditch under the bike.

Once I was sure we’d actually stopped, I have a distinct memory of the self test of various pieces of me, concluding that all appeared to still be attached with one area of pain on my thigh which wasn’t structural. I therefore extracted myself and inspection showed a hole through the clothing on my thigh and some rather red raw looking skin, 3×2″ in size. I wasn’t leaking and inspection tallied with the previous conclusion, not structural so I turned my attention to the bike. It appeared not to be too bad and so while the adrenaline was still kicking in, I hauled it out the ditch through shear will power. The organiser therefore found me sitting in the middle of the track looking a little worse for wear. I was thankful the bike started without too much faff for a change and we went the two corners out the forest and the few miles of road back to camp.

Once back, someone helpfully pointed out the headlight was smashed. That was the least of my concerns, I dug out the first aid kit from my backpack which I’ve been carrying around for literally years, some water and paper towels and went about seeing how bad the damage was to me. I still can’t make up my mind if its a burn or a graze, I suspect its a burn from the exhaust. The first aid kit had the right things in it thankfully and although the first attempt at a bandage didn’t work too well, it did after supplementation with gaffer tape. It was clear at this point there was ‘some’ bruising too. I suspect that I hit my knee hard but the brace deflected the damage into my thigh muscle which is a good thing and working as designed. I’ve a link here to a picture of said injury, don’t follow it if you don’t like gruesome graphic detail.

What followed was a pleasant evening on the campsite, cooking dinner and then talking to various people as they arrived, I eventually had to call it a night as sitting in the cold was causing my leg to seize up.

But hang on, what became of my friend you might ask? Well, he did complete lap one but proceeded to follow the arrows and start a second, not realising where he was. He did think some of the corners looked familiar! At some point he ran out of fuel. The only remaining detail to complete to story is that that he was rescued by a passing postman!

Back in August 2010 I blew the MG’s engine up. I did get around to taking that one out and fitting the spare. The battery was too flat to start it and winter came along before I’d got any further. With moving house, the work on said house and garage and 101 other things, the MG just never happened and its been sat looking sorry for itself ever since :(.

Today, I thought I’d see what state it was in. It was changed overnight so the battery should either be good or knackered. The bonnet release cable was snapped but I found a way in.

Whilst stiff, the controls all seemed to roughly do what they should. First try at ignition on saw petrol explode over the engine bay as the fuel line between the carbs gave way. At least the fuel pump works I guess.

After a small new piece of fuel pipe was fitted, take two. Ignition on, fuel at pressure, no overflow from the carbs which was a pleasant surprised as I was expecting a carb rebuild. Trying the starter, the engine turned over at a reasonable speed, it even make a hint of a cough of life. The lack of oil pressure stopped me at this point. I took the plugs out, then ran it on the starter and after what seemed like an eternity, the oil pressure climbed to normal. Ok.

Plugs back in, try the starter. Nothing. This was the point I was at after the rebuild but with a charged battery. I noted the distributor was loose and I’d never set the timing. Ok, twiddle it one way, try again. Still nothing. Ok, lets try the other way.

This time, you could hear it trying. After some further gentle nudging, it started coughing into life, first on a single cylinder then quickly onto approximately two. At this point I just gently tried to keep it running. The other cylinders kicked in intermittently at first, then it was running on all approximately four. I looked around for Dad who’d run off to try and stop the clouds of smoke a two stoke would be proud of from getting into the garage (too late). I gestured for Dad to check nothing was on fire on the exhaust (probably just the petrol from the earlier spillage).

I decided not to run it too much more since there was no water in it. We stopped and then rectified that, cue a comedy moment where there was water pouring from a hole in the cylinder head with us wondering “what’s missing?” until we realised it was the water temperature sender unit.

Emboldened by this, we wondered “could it move?”. My Dad carefully moved vehicles out of the way in case the brakes failed in some catastrophic way and made dire predictions about whether I’d destroy the clutch trying this. It started and then we managed a controlled lurch forwards as the brakes unbound with not nearly as much issue as we’d expected. At this point I drove it off the drive and did a couple of loops around the T junction. Everything felt seized up but it was none the less moving, stopping, starting and turning.

At this point attention turned to the driveway which needed a good clean and with the car missing, this was an ideal opportunity. Later, the car started first turn of the starter and reversed back on relatively happily.

Sadly the bodywork is in a bad way but at least now its known to vaguely function and move under its own power :).

I took the CRM to bits back in September. It was making various rattling noises that said the engine was tired and in need of a rebuild. Upon dismantling it, I found that not only was the piston chattering but the power valve was also not in the best of health being rather loose on its shaft. I managed to get a secondhand part for that but getting a new piston proved tricky since I wanted a forged one rather than cast. I ended up going for a .4mm oversize after much playing with feeler gauges and vernier callipers to map out the barrel wear. As expected it was more worn in the centre of the bore and less at the top/bottom.

As a family we’ve long since used an engineering shop in Blyth for rebores. A lot of our engines now have nikasil liners which mean sending off the cylinders but this one is a cast iron liner and hence can be done locally. When I dropped it off, there was much sucking of teeth about a 0.4mm oversize piston as it was not leaving them a lot of room for the rebore. They’d do the best they could, complaining the standard bores were never actually straight. It had been given to the “old man” by the son since he has more patience with these silly motorcycle things. We use the place due to their attention to detail. A joke from my school’s karting association days about their local competitor springs to mind: “Where did you get the rebore? Armstrongs?! How do you square up the barrel then? Yellow pages [telephone directory] under one side?”.

The above shows a mark left which they were very apologetic about but they had warned me. In reality this won’t make any difference to the running.

New shiny parts and some less shiny power valve bits.

Crazy amounts of plumbing. The question is could I remember how it all goes together from back in September?

An interesting aside, these photos show the exhaust port with the valve open and closed. It makes an amazing difference to the port size and position. This allows the engine to have low down grunt and decent top end rather than having the port timing fixed to a specific engine speed.

The new shiny piston fitted and ready for the top end. I nearly forgot to fit the new base gasket but did thankfully remember.

It went back together with nothing unepected left over which is always good. So did it start? Kind of. It did fire up, smoke a lot then stop. It reluctantly fired up again, stopped and lost all compression. At this point I was some what panicking and also out to time to work on it further.

There are a limited number of ways a two stroke can lose compression and most of them are not good. This morning I took the exhaust off and peered into the barrel as best I could, all looked well. No signs of the power valve having hit the piston which was one worry. I tried turning the engine over under load and the compression came back suggesting the thing was just full of oil which was seizing up the piston rings. I spent an age kicking it over trying to get it started and did manage to get it to fire up occasionally once managing to get it onto full throttle with clouds of smoke coming out, then it basically stopped dead again. The plug was clearly oiling up and its a 10 minute job to remove, clean and refit it.

I gave in and called in Dad to drive the discovery whilst I was towed by it on the CRM. I am reluctant to do this having destroyed engines like this but I was confident the thing was just clogged up with oil. It took half the block for it to turn over enough to clear, fire and then run under its own power. A couple of more trips around the block, probably much to the enjoyment of the neighbours and its running! So it lives again, just need to get it out and gently run it in now.

Never let it be said I don’t believe in preventative maintenance. Admittedly this is a little just in time!

This is the YZ’s clutch cable in case that isn’t clear. The first one that arrived was for a 250F (a four stroke) despite me clearly buying one for the YZ250 (a two stroke).

Back in August I found the YZ’s engine needed “a bit of attention”. Its taken a bit longer to get back to it than I’d hoped, partly due to building work but I can now complete the story. I stripped the bottom end down and concluded the easiest way forward was to buy a complete new crank shaft. This was slightly more expensive than just a conrod kit however it meant I didn’t need to press in the new rod and rebalance the crank, both things I could probably do but would need to buy/make tooling for. Luckily the wear on the top end was to the piston, the barrel looked fine. Bottom and top end kits were therefore duly ordered and turned up.

I started to reassemble the engine only to find the replacement crank was right, apart from the taper and thread on the ignition side. It had an M10 thread, I needed an M12 for my ignition. The bike is a 2002 model, the engine is a 2002 engine however it appears to have a 2003 crankshaft. This is probably due to the aftermarket alternator and weight. I ended up deciding to get another 2003 model crankshaft.

Since I was doing a complete overhaul I put new main bearings and seals in:

The photo shows some scary looking “cracks” in the casings although every two stroke I’ve ever rebuild looks like this to some degree so I’m doing my best to ignore them.

One nice feature of modern Japanese engines is the gearbox stays as one lump. Trying to put those back together and getting all the thrust washers in the right places is “fun”.

The crankshaft installed and casings mated back together. Of course life isn’t simple and whilst taking the engine apart, I found the likely cause of the scary sounding rattle. A worn power valve linkage. The part looks like this:

and the wear is in the first joint next to the coin in the photo. Its very hard to photograph “play” however this gives a better idea, after I’ve ground off the weld and separated the joint:

You shouldn’t be able to see light through there! Yamaha wanted a sum of money I considered excessive for this part so I decided I’d have a go at a home “oversize rebore” repair. This means drilling the hole in the outer piece larger (to make it square) and then machining a new oversize internally collar/bearing. The only lathe available to me was a little bit overkill for the job, weighing in at about 3.5tons:

however I did manage to get it to machine something that small, just about anyway:

Its hard to tell any difference from the final part however it has much less play:

After putting the crankshaft in and mating the cases, the clutch basket, plates and primary drive gear on the RHS of the engine can be installed:

A view of the ignition side of the engine showing the ignition and aftermarket flywheel weight in situ:

The clutch casing/cover can now be installed and the lovely new shiny piston can be connected to the conrod. You can see the power value linkage on the bottom left of the green base gasket. It sits in the clutch cover where there are spinning weights which control the power values depending on engine speed. The main bearings, both ends of the con ron, piston and rings were all liberally coated with two stroke oil as it was assembled.

Sadly it won’t look this shiny for long. You get a good idea of what the ports in a two stroke engine look like from this view:

A view of the power value chamber on the front of the cylinder. The repaired power value linkage rod connects to the end of the shaft on the left of the photo, turning it to different positions depending on engine rpm. The YZ has three power values, a main one on the centre exhaust port actuated by the springs in the centre and two secondary ports on the sides which are actuated by the cams and levers at the sides of the chamber. This was the only point throughout the rebuild I consulted the manual about since I’ve never actually tried to set up power valves before. The manual was a bit vague so I did what seemed right…

After all the access covers are installed, the engine is then complete. You can see the power value chamber on the front with the chamber on the side covering the repaired linkage. The cylinder head has also been installed.

All that is left is to fit it back into the bike. It took less time than I thought to do so and I’m pleased to report that whilst it didn’t start first kick, it did fire up pretty readily and whilst I didn’t run it for long, it sounds much happier!

As anyone reading would note, YZ hasn’t been happy recently. Its been making noises I didn’t like the sound of so I decided to pull the barrel off and take a look, the first time I’ve done so. You can do this with the engine still in the bike. The first thing of note was the piston, the exhaust side was unremarkable but the inlet side had fairly deep scoring, above what I’d consider normal:

Its a widely accepted fact of life that two stroke engines do need maintenance from time to time and with two years of (ab)use, I can hardly complain and I’d expected it would need a piston. The barrel didn’t photograph well but I think its probably serviceable which is a relief as getting a new coating put in is a pain. I had removed the piston so I turned my attention to look at the bottom end of the engine and specifically the big end bearing:

The big end was fine however in checking it, I thought the little end felt like I’d filled it with sand. A closer look revealed:

Which is something I’d not expected, the little end is to put it technical engineering terms, knackered. I’ve damaged two stokes in a multitude of different ways but I’d never broken a little end bearing until now. First time for everything I guess. Sadly, with damage like that a new con-rod is needed and that means splitting the casings to get the crank out. That in turn means taking the whole engine out the bike. To do that there are a number of serious nuts that need undoing. It was one of these that I previously managed to snap ligaments in my hand whilst attempting to undo. This time around with having the barrel off, its possible to rather robustly brace things to stop them turning:

This may look abusive but the little end is already broken so it can’t really damage much else. The bike looks rather sorry for itself without the engine. You can see from the photo how spindly the frame is which makes more sense when you realise the engine is actually part of the frame (a stressed member):

So I’ve found it needs a new piston and a new con-rod but why was the bike rattling? My best theory so far is the power valves are also in need of attention. The push rod from the bottom to top end is loose and the free play in it could account for the rattle. The fact it doesn’t work directly as engine rpm changes also matches well with the symptoms. In looking at the valves themselves on the workbench, it was clear the left hand valve was not completely closing. Wear in the power valve cams and the cam following pins would appear to account for this. In an ideal world, I would just replace all these parts however to do so looks like adding hundreds of pounds to the repair bill. I think there is adjustment which would allow the free play in the cams to be taken up, the push rod may need to be replaced however.

A photo of the engine partially dismantled on the workbench. I can’t split the casings until I find a puller to take the ignition off. The cams are on the left and right of the square oily opening on the barrel. The followers are on the ends of the forks on the black thing on the workbench on the bottom left.

It could be a lot worse, something could have seized whilst it was running and caused considerably more damage. Finding reasonable priced spare parts seems to be a bit of a challenge and I haven’t figured out what to do with the power valves yet. The YZ has some life left in it yet and will live again!