Yamaha TRX850 Enthusiasts Forum

So I'm attempting my first valve clearance check at 95K (got a mechanic to do them when I first bought it at about 52K and had it shimmed to spec).

I am a bit confused.

I rotated the crankshaft to align the TDC mark and the cam lobes on cylinder 1 are facing out as per Haynes and Yamaha manuals, but the lobes didn't seem to be exactly mirrored/opposite in their positions. I looked at the camshaft sprockets and it looks like the inlet cam is a tooth out!



Is this a result of the inlet cam being installed a tooth out by the mechanic? There is bugger-all clearance on the inlet (just squeezed in the .001" feeler) when I measure in this position, but should it be measured with the inlet sprocket marks aligned to the head? Or would I be better off removing and re-installing the cams so that the marks line up with each other and are parallel to the head before taking clearance measurements? Any help greatly appreciated!

I never had the marks line up 100%, although it got better after I changed the cam chain. It could be that it's one tooth out, but it looks like one tooth would make a greater difference. The exhaust cam could be turned clockwise a bit more, and then the inlet would line up a little better too. Hard to say from the picture as one doesn't see the second mark of the inlet. I am pretty sure the cams are mounted properly. A camchain that's served a long time will be slightly longer, and hence the marks won't be spot on.

As for the gaps, they should not be measured with the cams in this position. I can't recall exactly, but a rule of thumb is that one measures when the lobes are furthest away from the valves, i.e. 4 positions of the crankshaft. But in the manuals you'll find the description as to how the crank should be positioned.

JL wrote:So I'm attempting my first valve clearance check at 95K (got a mechanic to do them when I first bought it at about 52K and had it shimmed to spec).

I am a bit confused.

I rotated the crankshaft to align the TDC mark and the cam lobes on cylinder 1 are facing out as per Haynes and Yamaha manuals, but the lobes didn't seem to be exactly mirrored/opposite in their positions. I looked at the camshaft sprockets and it looks like the inlet cam is a tooth out!



Is this a result of the inlet cam being installed a tooth out by the mechanic? There is bugger-all clearance on the inlet (just squeezed in the .001" feeler) when I measure in this position, but should it be measured with the inlet sprocket marks aligned to the head? Or would I be better off removing and re-installing the cams so that the marks line up with each other and are parallel to the head before taking clearance measurements? Any help greatly appreciated!

One thousands of an inch clearance Think i'd be doing a cylinder leakage test - the valve may be starting to burn!

dandywarhol wrote:One thousands of an inch clearance Think i'd be doing a cylinder leakage test - the valve may be starting to burn!

Definitely, if, and that's a big IF, he measured correctly. If I understood him right, he measured with the cams in the position in the picture.

Yep i agree,if the motor`s been run with such small clearances then a compression check should be carried out for sure.
As Dandywarhol said,valve faces could have already been burned.

I couldn't take a picture that showed all 4 marks on the sprocket, but the left mark on the inlet was below the head in the above picture. I have rotated the crank counter-clockwise a little so that the exhaust and inlet marks all line up pretty much parallel to the head now, so I think my fear of being one tooth out was wrong as suggested.

The problem now is that with the sprockets in this position, the timing marks do not line up!



I have tried to take the photo as straight-on as possible, but still show the "T" timing mark. It clearly does not line up

I took clearance measurements on cylinder 1 in this position and they were the same as when I took them with the timing marks lined up and the sprocket marks slightly misaligned as per my previous post.
Exhaust 1 & 2: .009"/.229mm - just under
Inlet 1 & 3: Couldn't even squeeze the .0015"/.038mm - oh crap
Inlet 2 (middle): .002"/.051mm - pretty crappy too

HansJ wrote:...
As for the gaps, they should not be measured with the cams in this position. I can't recall exactly, but a rule of thumb is that one measures when the lobes are furthest away from the valves, i.e. 4 positions of the crankshaft. But in the manuals you'll find the description as to how the crank should be positioned.

I'm not sure if I understand you here - I've gone by the workshop manual with the lobes facing away from each other on cyl 1 like below...

... so I think I'm doing it right, but have just been thrown off by having the timing marks out.

It's a '96 model, so I'm guessing this could be the inlet valve stretch which I've read about in other posts. Apparently there was barely any clearance on the inlets when I had it done last time.

Sorry if this thread is a bit 'newbish', just figured I should be able to do the clearances myself. Read the manual and it seemed straight forward (just time consuming), but it looks like I have uncovered more than I bargained for! I'll measure cylinder 2, but maybe I should start thinking about ordering a head gasket and some of those updated inlet valves...

Doesn`t sound good JL.
I think you might benefit from reading through this thread carefully:

http://trx850.motomaniac.net/forum/view ... lve+timing

You`ll find all you need to know I think.

Thanks Mincehead, it's been about 40K since clearances were done and cam chain was replaced. Clearances are out big time, stands to reason that the chain would be up for renewal as well. I was going to remove the inlet cam to see what shims were installed, but ran out of time. Have put the valve cover back on because we have an inspection on tuesday - don't want the garage looking too much like a workshop (from the missus). Just glad this new place has a sheltered garage!

Since finding out about the valve problems with the '96ers, I have been kind of expecting this. Will have to let it sit for the next few days and in the meanwhile will start to price up the valves, valve seals, cam chain, head & cam tensioner gaskets and any other parts it looks like I might need. May as well replace the valves with the 98 onwards ones rather than re-shim assuming that it will need to be done down the track anyway. Good thing I've spotted a head workshop a few minutes away that has a few vintage bikes in the window. Hopefully the price won't be too steep if I bring the head to him. For a first-time attempt at checking clearances, I've certainly been thrown in the deep end! All part of the fun I guess

Might see if I can get a mate to help me with a leak down test too. Thanks for the help so far guys!

I´m with HansJ, my camchain where 1,5 links longer than the new one i had to install....i set the cams 10 times and just could not understand why it was so off. Actually Hans who put me in the right direction. If your going to change, beware of the phillips screws...they´re made of butter!

Slightly off topic but still relevant - anyone know why the '96TDM doesn't seem to suffer from "valve stretch" - same engine..................

GOOD question!
I`ve nothing informative to answer with though.
Mine`s a 96`er,`N` reg and mid 20,000 miles too.I`m planning on doing my camchain,valve clearances & general top end check over before using the old girl again in anger next year.
I`ve got the usual `tappings` going on up top so at least I know that my valve clearances are still there,well at least some of them anyway.Plus the old girl makes 88 bhp at the wheel on a friends dyno that i know is accurate,it wouldn`t make those figures if there was blow by from burnt valve faces and seats sapping the power.
So,ANYONE know why the 96 TDM`s don`t have the same valve stretching issues?

Lets take a stab in the dark... The exhaust headers are slightly different also arent they??? The first bend out of the head as a lot mention being a restriction on the TRX ....and motors mounted at slightly different angles???

cobbadiggabuddyblooo wrote:Lets take a stab in the dark... The exhaust headers are slightly different also arent they??? The first bend out of the head as a lot mention being a restriction on the TRX ....and motors mounted at slightly different angles???

Must be a helluva dark over on your side of the planet cobb - why would that cause the valves to "strech" (if they do)?

Ok, so back on topic ( although it is interesting that TDMs don'e seem to be afflicted) here's a small update - haven't pulled the head off but have ordered the (genuine) parts.

- inlet valves (2+4)
- stem seals (10)
- cam chain
- ^^^ tensioner gasket
- head gasket
- coolant pipe o-ring
- new valve cover gasket (to replace buggered one in my other post)

Grand total $649 + shims when I get around to that part. Guess it has to be done...

Luckily got a mechanic mate with a spring compressor and lapping tool to help with the re-build!

More updates when the parts arrive...

Btw, it really paid to call around for prices. This isn't a plug but Peter Stevens were the cheapest by far. All the other Yamaha dealers prices were $10 - $30 more for the more expensive parts. Hope the parts prices are useful to anyone else thinking of doing this.

like I said takin a stab ... weather the head is different on tdm because of the different angle mounted and weather the flow causes heat building up on the ealier TRX... What mods did they do to stop this prblem...I'm not a mechanic, I'm an ex rock n roll sound engineer ... mmmm Have the same problems Put a bottle of Jack Daniels on the band rider in stead of some cheap arse bourbon and things flow a lot better for the guitarist that nite I always find Makes their heads work different I know that much...