How to "do" the valve clearances on a TRX850

So your TRX is getting a bit unwilling to start, or you've just bought it and have no idea about its real history and want some peace of mind, or it's running a little rough. Reading up on the subject reveals that pre-1997 TRX's (and TDMs) have soft, rubbishy inlet valves which close up their clearances.. And here you are. Come with me as we explore a world of strange design choices and the particular foibles of working on an engine which was originally meant for a different frame..

Step 1

Play some Road Rash. This will get you in the mood and hopefully give you enough enthusiasm to finish the job. You can revisit Step 1 at any time if you need a bit of a boost or to be reminded why this needs to be done. If you can't play Road Rash it is somewhat acceptable to watch the following video, but it is not a true substitute for playing the real thing:

Step 2

Sort out a way to get Soundgarden pumped into your work space. This is important for morale. Growing your hair and wearing three quarter length trousers with Doc Martens is optional but recommended.

Step 3

Admire your own taste in bikes.

No one has a bike as cool as you do. Well done you. Mine is better though, a 1995 4NX version from Japan with pumper carbs, Brembo front calipers and a couple of warnings written entirely in Japanese. Oh and the best paint scheme ever.

Step 4

Decapitate it. It's a shame but you have to break some eggs to make a reliable road bike and all that.

Step 5
You need to empty the coolant. A washing up bowl works well.

There is also a 10mm bolt (with a posidrive cut out for some reason? Who would use that?) on the front of the engine which drains the block and maybe some more of the head, take that one out as well. Not a lot will come out of that one but the manual says do it, so do it.

Step 6
Use the lock on the left side of the bike to unclip the passenger seat, and remove it. Then pull the hook in the uncovered compartment and unclip the rider's seat, remove that too. Then remove the two bolts at the front of the tank which hold it to the frame. Now move the clip that holds the relatively fat petrol pipe on to the stupid and unnecessary fuel pump. Don't try and remove the pipe from the fuel tap as the barb has been known to pull clean out.

At this point, with that clip squeezed together and moved along the pipe, you will need a clamp for the fuel pipe. In theory the fuel tap will not let fuel through without a vacuum on it and you should be fine, but in reality these taps do not work. Some dribble fuel constantly, some let it pour through. I have a small thumbscrew affair which is very handy for this. When the pipe is clamped, screwdriver it off the pump and then simply lift the front of the tank up. Try not to let the pipes catch on anything underneath, you are exerting a lot of turning force doing this and could damage something.

At last!

Step 7
By now you're probably well into the Superunknown album, but that's okay. Taking your time is good. The next thing in the way is the airbox - pull the small breather tube off that seems to go into the frame for reasons and try to undo the clip holding the fat crankcase breather hose onto the rocker cover. You will find the frame is in the way, best of luck not scratching it to buggery with your pliars. Pull the hose off the rocker cover and then undo the screws in the jubilee clips holding the airbox on to the carbs. A little pull and away it should come, revealing twin BDST38s, a nice sight.

Step 8
Because this stupid bike is water cooled, like a car or any decent computer, there is a stupid radiator that we have to remove before we can get to the rocker cover. Undo the little breather hose, loosen the jubilee clips, twist/break the hoses free, remove all four bolts and just pull the thing off.

We're getting somewhere now!

Step 9
Because this stupid bike is water cooled there is a stupid thermostat that we have to remove before we can remove the rocker cover. What is the deal with water cooled motorcycles? What's it all about?

Pull the electrical connectors off the stupid thermostat and undo the screw that clamps a wire in place, then put the screw back before you lose it. You've been putting all these bolts back before you lose them, right? Then undo and remove the single allen bolt that is holding the thermostat to the frame (it's probably rusty as owt, good luck) and possibly remove the hose from the metal pipe that goes into the top of the head. You will have to remove that pipe to get the rocker cover off but it's up to you how you do it.

Simply wrestle with the thermostat, its hoses and all the wiring just above it until the thing pulls out through the hole in the front of the frame. Throw it on the grass in disgust at water cooled motorcycles.

Step 10
You could be on to the Down On The Upside album by now, fed up with how much work this project is and disheartened at the direction Soundgarden chose to take. Try not to think about either of these things because we can see a rocker cover!!

Pull the plug caps off (you may need to free the coils so that you can get enough slack/movement on the HT leads to allow you to actually pull the caps free. Mine have had their screws chewed up by some gorilla, and one of the frame mounting points has even been snapped off - that special Yamaha build quality is shining through all the time). With the plug caps freed, undo the bolts that hold the rocker cover on..

..And, after removing the metal water pipe, pull the cover free!

Try not to let too much oil fall out the lower corner and on to the floor, or too much grit from that metal pipe fall into the head and cam/bucket surfaces. The manual never mentions that. I got quite a lot of grit in there, a most marvellous design feature from Yamaha right there. Of course if it was sensible and air cooled there wouldn't be a pipe to collect grit like that..

Step 11
Grab your biggest, meanest flat headed screwdriver and undo the inspection/timing/whatever plugs on the alternator cover. If some pillock really tightened these up previously then I am sorry for the way you just wiped a chunk of value off the bike by leaving big scars on the engine. Can't be helped though, blame the Japanese for sticking with that bizarre design. With the caps screwdrivered/hammered/whatevered off get a 19mm socket and a ratchet of useful length and turn the flywheel/crank anticlockwise until the T mark is next to the little notch in the small hole. This is supposed to be TDC, with the cam lobes on the left cylinder facing away from each other. if it's the compression stroke. This seems to be okay, I did quickly try with the lobe facing straight away from the bucket and the measured clearance was the same. Then turn the crank 270 degrees and measure the other set of valves.

Stick the thickest feeler gauge you can  in the gap and record. To be in spec you are hoping to find the inlets are at 0.15-0.2mm and the exhausts at 0.25-0.3mm. Mine came out at this:

This is as you look at it from the front. The zero is disturbing and quite annoying as it means I have to take the cams out and everything to change just one clearance, but I must do it before this causes major damage, if it hasn't done so already. Zero clearances are very bad because the cam lobe never comes off the valve/bucket and so never gets to cool down, which can make the cam expand enough to pick up on its sliding surfaces on the cam caps and on the head. Zero clearance is Bad News. Having said that, this looks a lot healthier than the first time I did it, when I found this a mere 11K miles ago:

That was awful. I have a feeling the inlet that has zero'd twice is going to cause me some big hassle at some point! This is a good point to put it back in the garage and have a rest too, while wondering why that last Soundgarden album was a bit weird and disappointing.

 Step 12
Right, a quick rest from this (I had two weeks) and then straight back into it. For this next section I recommend the Dragline album by Paw, it's really good:

With shouting in your ear it's time to perform some serious engine surgery. The workshop manual says to put the engine to TDC, this isn't all that necessary but it's a starting point. This does sadly mean that the right inlets will be pressed down so there is a lot of pressure on the inlet cam caps, but there's not a lot you can do about it. The timing marks on the cam gears will be roughly flat with the top of the head like so:

With the marks like that, it's time to curse Yamaha for using any old engine they could get and stuffing it in a frame that covers useful bits because you'll have to remove the clutch cable in order to get any real purchase on the inner bolt of the cam chain tensioner. See, it's right behind where the cable is held to the frame:

With that silly thing out the way stick a 12mm spanner on the bolt in the middle of the tensioner and undo it.

Pull out the bolt and the strange double spring thing that it crushes inside there. At this point I wussed out slightly and decided it would be best to mark the cams and chain with some Tipp Ex so that I could be relatively sure everything goes back together timed up. This is an old trick, some say it doesn't help if the chain skips around the sprocket on the crank but if your marks are the same number of teeth away from each other on the cam sprockets you're still good to go.

With the springy innards of the tensioner out the way you must do your best to undo the two allen bolts that hold the body of the tensioner in place. I used two different allen keys for this, they had the flats in different places to each other so I could use one to twist the bolt slightly then get the other one in. You need to do this because there is no room. Once again, thanks Yamaha.. Have I mentioned the valve clearances on my 1994 CB250 take 20 minutes and are tappet and locknut so can be done for free? I don't even have to take the tank off. And I don't have to do them any more often than with this thing.. Anyway, pull the tensioner out and take note of how extended it is - if it doesn't have much extension left you need a new cam chain. Have fun with that.

That is pushed back in, mine was quite far extended. Maybe I'll put a new chain in next time..

Step 13
Are you a fan of Paw yet? Next is to free the cams because they're in the way. Undo the bolts in a criss cross manner, a bit at a time so that the silly weak aluminium things don't warp horribly. I took the right one off first because if you remove the one next to the chain there may be a lot of leverage on the far cap, but the manual gives no pointers on how to do this so just, like, undo it. Because my exhaust valves are all in spec I only want to remove the inlet cam, which left me with this:

 While removing the cap near to the chain the chain skipped round a tooth on the sly, this is what the Tipp Ex is for!

Before you remove the cam you must tie the chain to the frame somehow to stop it falling down inside the engine. Finally having a frame full of holes pays off!

Now use a magnet on a stick to pull the bucket off whichever valves you want to change the shim in, in my case #5 inlet..

The shim will usually come out and be stuck to the top of the bucket, like so..

Now read the number off the shim, in my case #175, write it down on your map of clearances and put it back with the bucket. You must put each bucket back where it came from as they may have worn in to match their hole in the head, do not mix them up.

With your existing shims read and written down, you can try going to your local Yamaha dealer to be told they look nothing like anything they use and no they can't help you or you can just buy some off the Internet. Because mine is a #175 (1.75mm thick) and I have no clearance but I need 0.15-0.2mm I need at least a #150, maybe #145 - I won't know until I have a clearance to check.
 Now is another good time to stop for a bit.

Step 14
Did you try the Yamaha shop? What a waste of time that was, eh? After a bit of searching I managed to find a #145 on ebay for £6, which is apparently a reasonable price. I still feel ripped off.

Do we need more Road Rash music for this? We're fast running out of decent albums, I don't care much for Therapy? or Swervedriver or Monster Magnet but Hammerbox are okay by me. Get it down yer!

Yeah that's better, let's put this stupid piece of Yamaha engineering back together. Slap your tiny overpriced shim in its hole above the valve stem (the manual says put it in with the number facing upwards, I have no idea why), put some oil on it, then put more oil around the bucket and put that back in place on top. Remember we Tipp Ex'd the cam and chain so we know where it goes back? Now is the time to bask in the glory of forwards thinking, pop the chain on like so..

Cover all the sliding surfaces with more oil (I just used the oil sat in the corner of the engine which keeps dripping on the floor) and place the cam caps on top.

Yes, the caps don't fit because the right side is pressing down on the valves. It doesn't matter, very carefully tighten the bolts down in a criss cross pattern, trying to keep both caps under equal pressure. The caps seem to be built for it, just be careful and even. End this madness when all the bolts are torqued to 10nm.

With the cam and caps all in place (including the top chain guide because two of the cap bolts hold it in place) put the tensioner back in the way it came out (I think the ratchet thing goes at the bottom?) and the big bolt into the end of the tensioner. With all this in place it is time to turn the engine over and see if it all still works - be careful! If it won't turn it is likely the chain is snagged around the crank sprocket, if you force it your engine could end up as scrap. You'll need to free it off however you can.. But thankfully this hasn't happened to me yet. Turn the engine round a few times and then measure your new clearance. Mine ended up as 0.25-0.3mm which is beyond the 0.15-0.2mm spec but I'm okay with that, it's a lot better than being tight. It does mean I needed a #150 shim though, but I'm not paying out for yet another tiny piece of metal.

If you're happy with the clearance you can carry on and put it all together, if not then you know what you have to do. Because I'm cheap I popped the rocker cover on, changed the plugs while I was there (to matching ones this time, thanks previous owner who fitted one DPR8EA-9 and one DPR7EA-9!), squeezed the thermostat back in and bolted the radiator in place. It's all so easy when you know what you're doing!

At this point I stopped again because I want to replace the needles and jets in the carbs, and since they're plumbed into the water cooling I didn't want to fill it up. If you are unaware of the maintenance needed on these carbs you should look into emulsion tube and needle replacement at this point, now is a good time to do it since it's in bits like this.

Step 15
We're close to the end now, so no real need for more nineties rock music.. Though you should give Gruntruck a listen. I took the opportunity to fit #140 main jets and new 5E185 needles with the clip in the middle position, it was easy enough to do and should make the bike run nicely. Onwards!

Pop the airbox back on with all its silly tubes:

And lower the tank down over it, then reconnect the fuel pipe..

Starting to look like a bike again innit? At this point I bunged 1.4L of tap water into the radiator (I'm switching from the red long life antifreeze to the cheap not long life blue antifreeze and want to flush it through with water before going for it, apparently the two don't mix well) and went around the bike checking for things I'd not properly tightened or forgotten about before the big test. I found I hadn't tightened the inspection caps back on to the alternator cover properly and the clutch cable wasn't tightened on to its bracket near the engine, but that was all.

Testing testing 1 2 3!

Aww yiss. I can hear the valve that is opened up past spec but I'll live with it, as long as I can hear it I know it's okay. If it goes quiet any time soon I'll have to take the head off and get the valve replaced, so noise is good for now. In a final burst of enthusiasm stick the fairing back on and you have yourself a properly serviced bike.

Thank God that's over. Until next time..