Yamaha TRX850 Enthusiasts Forum

Hi all. Checked the clearances today on my 96 bike and it looks like it has the 'soft' inlet valves. All exhaust valve clearances were within spec, whereas all of the inlet clearances were well under - in fact I couldn't get my smallest feeler gauge (0.05) into 4 of the 6!! The problem I now have is working out what shims I need on the valves which have closed up. Presumably I'll need to remove the cam, measure the shims and put in a new thinner shims to at least create a gap and then work out exactly the sizes needed before repeating the process. Now shims aren't cheap and I don't have a pile of various sizes sitting around so, in this instance, am I better off taking the bike to a local workshop?

Shims are cheap compared to a workshop. Buy a set with more than you could ever use from eBay. Easiest thing to do is remove current shims, check size and go smaller so you get within specs calculated. That will most likely get you close enough in real world.

Say clearence should be .25 (don't remember but let's pretend). You find a "85" shim, and you have no clearence at all now. Just get a "60" shim that would put you good enough around the desired .25 clearence.

Or get one of these
https://www.kedo.com/products/40068.html

Sometimes you can figure it out by shuffling the shims you already have, by switching the position.

How many Km’s on the motor?? (60,000km??)
If the inlet shims are already around 165’s ( std from factory is usually 185-195 ) you may want to look at saving some pocket money for 4 new inlet valves soon.
Just remember 10Nm. on the cam caps because a number of TRX owners have destroyed their motors by not using a torque wrench.

cobbadiggabuddyblooo wrote:How many Km’s on the motor?? (60,000km??)
If the inlet shims are already around 165’s ( std from factory is usually 185-195 ) you may want to look at saving some pocket money for 4 new inlet valves soon.
Just remember 10Nm. on the cam caps because a number of TRX owners have destroyed their motors by not using a torque wrench.

And double check if the cam shaft rotates freely! Very important.

Thanks for the advice guys. Called into the bike shop today just to check cost/time and they quoted what I thought was a very reasonable 1 to 2 hours for the job (remember the bike is already stripped). Unfortunately they can't collect the bike so I've decided to do the job myself. It will be interesting to see what shim sizes are in there currently - I can see from some paint marks on the chain that someone has been in there before me. The bike has done almost 30K miles (48k KM's) so could still be on the factory shims but you never know. I only use the bike occasionally now so mileage is creeping up very slowly so I'm hoping I'll never need to change the valves (x6). I'll let you know what I find

A bit more dismantling today so after double checking the gaps I removed the cams. Exhaust cam came out easily but the inlet cam was a little more awkward but got there in the end. Then I removed the exhaust buckets and shims and did the same for cylinder 2 inlet. However, I couldn't remove No 1 cylinder buckets - the problem is that the cam seems to have 'bound' with a couple of the cam journals. As well as some scoring the edges of the journals have burs which are sufficient to stop the 3 buckets from being removed. This is the cylinder which had zero valve clearance. I'm not sure how far off standard the other shims are but this is what I found. Cylinder 1 exhaust 184/184. Cylinder 2 exhaust 182/184. Cylinder 2 inlet 175/145/165. So I guess I now have 2 options - have the head reconditioned (any recommended companies in the UK) or try to pick up a good 2nd hand one (anyone got one they would sell). Advice appreciated.

When there is no clearance the cam doesn't get time "off" the bucket to cool down, so expands and contacts the journals that it runs in.. It's a well known problem and the head is scrap. I highly recommend getting a 1997 or later head and fitting that, TDM850 heads are a straight swap.

I do have a head, it's the one I took off my 4NX - the inlet valves need replacing. If you see how much the valves are you probably wouldn't think about bothering with it though..!

Yeah I didn't realise how expensive the valves were, so I don't think the engineering solution is a viable option. I have already emailed a couple of firms for estimates so it will be interesting to see what they come back with. I think I'll need to be patient until I can find a good used head, complete with 'hard' valves. There's actually a TDM head on ebay now but it's located in Germany; also the pics don't show the journal surfaces.

Pieter sells oversize valves (1mm inlet/2mm exhaust) and has a shop in the Netherlands.
You may be able to pick up the 1mm oversize inlets cheaper than new valves from Yamaha.
If you remove the head you can de-burr the cam journal and clean it up when you get the inlet valve seats cut.
So money saved with oversize inlets will be spent + a little more to cut seats.
In saying it may be cheaper to buy 4 inlets from Yamaha and lap them in.
Finding a 2nd hand head may cost as much as 4 valves and you don’t really know what your getting until you pull it apart.
Better the devil you know than the devil you don’t....
You can de-burr the inlet cam journal with a little wet n dry as many have done successfully before with no issues and lap in new valves.
Replace the valve seals at the same time.

Note...
2nd hand head may have been off the bike for a while and valves seals may have dried and cracked.

Cheers cobba' - food for thought. Think I'll spend a few days looking at my options and costs before deciding what route to take but I'd like to get the bike back together sooner rather than later.

Who's Pieter - is there a company name to make him easier to find? I've seen from an old thread that forum member sanddune51 was selling oversized valves so I've PM'd him to see whether he has any left.

I've noticed when looking for a used head that they've generally had the cams removed (presumably more profitable to sell separately). Also, I think you can buy after market replacement cams. I assume that heads were line bored to match the camshaft originally but the fact that heads are being sold without cams and after market cams can be fitted to used heads, it's OK to mix and match so no problem fitting my existing cams to a replacement head?

Tealman wrote: I've noticed when looking for a used head that they've generally had the cams removed (presumably more profitable to sell separately). Also, I think you can buy after market replacement cams. I assume that heads were line bored to match the camshaft originally but the fact that heads are being sold without cams and after market cams can be fitted to used heads, it's OK to mix and match so no problem fitting my existing cams to a replacement head?

As long as the cam caps come with the head, you're good to go.

Rod.s wrote:

Tealman wrote: I've noticed when looking for a used head that they've generally had the cams removed (presumably more profitable to sell separately). Also, I think you can buy after market replacement cams. I assume that heads were line bored to match the camshaft originally but the fact that heads are being sold without cams and after market cams can be fitted to used heads, it's OK to mix and match so no problem fitting my existing cams to a replacement head?

As long as the cam caps come with the head, you're good to go.

Brilliant

I'm getting a little ahead of myself here but when I removed the cam chain tensioner I needed to loosen the bottom oil pipe fitting for clearance. I've since noticed that on both the TRX and TDM this pipe has a steel lower part with a flexible upper section. Mine is fitted with a steel braided flexi hose. Is this because it's an early (96) bike or has the original been replaced at some point. Also, does the steel pipe allow clearance for the cam chain tensioner to be removed? Does the TRX and TDM use the same pipe?

Mine is only half braided, yours is not original. But I've never had to remove the pipe to get the CCT out, it comes out past the frame pretty easily??

Also can't believe it will bolt in upside down..