Germfree Adolescents

No photos for this update, mainly because I can’t remember where I put the camera, but also as there’s very little worth photographing at this stage. Hopefully once I get past the “cleaning the crap off and trying to catalogue the list of horrific bodges that need fixing” there’s going to be something worth taking a piccie of. So, first up… the head. As we saw last time out, it was in a bit of a state really, with a binding journal, and some tight clearances. While fixing that lot I also discovered that one of the exhaust studs has been snapped off at some point, and the helicoil bodge drilled off centre and at a rather jaunty angle. And, probably to mitigate the effects of an exhaust that wouldn’t seat properly any more, each exhaust port had two gaskets hammered into it. Fixing this would involve drilling out the helicoil, filling the hole with weld, and re-drilling and tapping the hole in the right place. I genuinely can’t be bothered with that, given that the rest of the head is pretty marginal. I may well look out for another head at some point in the future to see if it’s in better condition. Well, it’s unlikely to be any worse unless someone has set fire to it. For now, I’ll just re-bodge it, and see how it all runs.

The engine itself is now sitting on the floor next to the bike, ready to be handed over to the chaps at Cambridge Motorcycles for the gearbox work. Getting the engine out of the bike was one of the least enjoyable things I’ve done for several years. It should have all been a relatively simple process, but the lower rear engine mounting bolt wouldn’t shift. In the end, I was able to unbolt a little brackety-wotsit affair with the engine still in situ, and then allow the whole thing to slide forwards and out. It took three people though, and a not inconsiderable amount of tea. Once the engine was out, I could get to the bolt properly, and nothing I’ve tried so far has moved it. I’ve hit it with hammers, heated it, hit it again ,got a bigger hammer, soaked it in all sorts of nasty solvents and penetrating lubricants, heated it again, got the really big hammer, and even spent real money on an impact wrench. It’s still not moved. If I can get the engine back in the same way it came out, I think that’s what I’ll do. Last option for removal of the bolt is to weld another bolt onto the end of it, and get a big bar on there. Either that, or cut the whole thing out and try to pick up another brackety-wotsit from a breaker.

Which leads us nicely to the carbs. It’s fair to say that these carbs (Keihin FCR41s) were one of the main reasons I wanted to get my hands on this particular bike. I don’t think I’d have been tempted to swap the ZXR if it wasn’t for them. They suit the bike perfectly, and look great. Well, that’s to say they probably looked great. I couldn’t actually see them, as they had so much crud accumulated all over them. Honestly, when they came off the bike it looked like a massive ball of black tar with a couple of blue bellmouths sticking out of it. So yesterday I started to clean them up. And it took five hours of soaking in petrol, scrubbing, more soaking, running through the ultrasonic tank, scrubbing, cleaning etc. etc. But eventually they all came up clean, and it looks like all the jets are good. The throttle position sensor seems to be slightly out of alignment, but that’s something I can sort out once the carbs are back on. For now, they’re sitting on my bench looking lovely again. Now, seeing as my hand currently looks like this:


I’d like to say that all of the above work was carried out in an atmosphere of complete cleanliness and ruthless observation of hygiene protocols. Only that would be a complete lie. Luckily the stitches survived most of the work, and I only had one bloody moment when I tried clamping up some mole grips on the wayward exhaust stud. That was enough of a warning note though to make me hang up my spanners for a couple of weeks. Normal service will be resumed shortly.


Lovely Head

One of the things that I knew about the TRX when I picked it up was that it needed the gearbox output shaft replacing. Now, on pretty much every other bike I’ve owned, you can get to this by simply turning the engine upside down, and removing the lower engine case. I say ‘simply’, but obviously that’s a bit involved, as it means dropping the engine out of the frame, and all that entails. But still, it’s a reasonably straightforward process. So, I picked up a second hand set of gearbox internals, and read the manual. To get to the gearbox, I needed to remove:

  1. Valve cover
  2. Cylinder head
  3. Cylinder block
  4. Pistons
  5. Clutch
  6. Starter clutch and idle reduction gear
  7. Gearchange mechanism external components
  8. Oil pumps
  9. Cam chain and guides
  10. Oil tank
  11. Oil sump
  12. Balancer shafts
  13. Water pump
  14. Starter motor

Hmm. That’s quite a list. And to get at some of those things, I need to remove other things first. So, it’s a Big Job. And while I’m OK with Big Jobs for the most part, I don’t have the necessary tools for a lot of this. So I made a decision to strip the motor down to the bottom end, and drop that off with the super chaps at Cambridge Motorcycles to swap the gearbox out, while I take a look at the top end.

So, off came the head. That’s a very glib statement for something that took several really good cups of tea and quite a lot of grunting. But there were no stuck fasteners, and other than it being a bit of a squeeze to lift the head off with the motor still in the frame, I soon had it sitting on my bench. You may ask why did I pull the head while the motor is still in the frame, given that I’m going to be dropping the motor anyway. I’m sure I’ll think of a good reason soon enough. It soon became obvious that all was not well with the head. Firstly, the clearances on the inlet for cylinder #2 were, well, basically not there. So new shims on order to fix that. More worrying though, was the fact that the inlet cam was very tight to turn. I popped the caps off, and it was soon obvious why: the cap for the #1 cylinder was binding on the shaft. Now, the preferred way to sort this is to send the whole lot away to a specialist for re-boring and honing and all sorts of expensive stuff. I just got out a scraper and some wet and dry paper. Seems to be OK now. Now, the obvious question is how the thing was still running like this – and I’m not entirely sure. There’s obvious signs that the aluminium in the seat has picked up in a couple of places and burred a little. So I’m being optimistic, and thinking that it had only just started binding when the bike was taken off the road. The alternative is that the head is so warped that when it gets pulled down onto the block it was bringing things back into alignment. I don’t really want to consider that option right now. Anyway, even if that was the case, the seat and cap still needed deburring, so I’m not desperately unhappy.

This is the first time I’ve looked inside a Yamaha five valve head. And while there’s no doubt that it’s all very clever and everything, is there really any advantage over a four valve setup? I have my doubts. Still. It’s pretty, and I took a photo, so there you are.

I know that while I’m in here I should probably replace the valves, but that’s out of budget right now, so again, I’ll clean up what’s there, put new gaskets in, and putĀ it all back together. Now I know how simple it is to pop the head off, this is something I can work on in future.

I’d still rather be working on the TZR250 though.