Yamaha TRX850 Enthusiasts Forum

Plenty of advice as to why, and plenty of entries with it on the "to-do" list, but has anyone successfully degreed cams on their TRX motor? The reason I ask...

When I went to check my piston to valve clearances today, I figured I'd throw a dial and wheel on to check timing as well. But I found that the size of the cam shaft prevent any access to the slim-buckets/followers for the dial gauge!

I thought about a tricky reverse reading from the top, but without a follower and a true centreline it would be inaccurate anyway.

Using a .2 mm gasket, the sprockets still seem to line up damn-near perfectly l if I use all the available play in the bolt holes, so it's probably fairly academic anyway. But I'd love to hear if anyone has a clever solution.

Hi Brett,
I know Mark.(sandunes ) dialed his in successfully.
have a look back through his threads on the valves over the last 12mths and you'll see something in there.

Thanks Cobba'. It might be there but I couldn't find it.

However... When I installed the Cams with the 0.2mm gasket it certainly was apparent that the cam timing had retarded by half a mark width. It seems that measuring timing with a dial & degree wheel just isn't practicable on a 5-valve head, so I've just sought adjustment going by the timing marks (I figure I can trust Mr.Yamaha on those).

The marks in the pic below shows the cam is retarded by a half a width. I'd estimate that to be probably 1-2 degrees at the crank.
So out with the rat-tail file to "slot" (or more "relieve") the cam sprockets. viewtopic.php?f=5&t=10047 I didn't need to remove much material from the front side of the sprocket bolt holes. Took me about 20 mins to do 4 holes.

Now the timing marks are able to be aligned perfectly before the sprocket bolts are tightened up. At 24Nm I figure they'll stay put ok.

Interesting stuff. As the marks are on the cam itself and not on the sprockets, it should be good now! I've never thought of this.
The only 'disadvantage' I can think of, is that the chain will get more loose (theoretically), but the tensioner should be able to compensate this easily.

So your head gasket is only 0,2 mm in thickness? Must be like a thin foil then?

QuickDraw wrote:Plenty of advice as to why, and plenty of entries with it on the "to-do" list, but has anyone successfully degreed cams on their TRX motor? The reason I ask...

When I went to check my piston to valve clearances today, I figured I'd throw a dial and wheel on to check timing as well. But I found that the size of the cam shaft prevent any access to the slim-buckets/followers for the dial gauge!

I thought about a tricky reverse reading from the top, but without a follower and a true centreline it would be inaccurate anyway.

Using a .2 mm gasket, the sprockets still seem to line up damn-near perfectly l if I use all the available play in the bolt holes, so it's probably fairly academic anyway. But I'd love to hear if anyone has a clever solution.

Brett,

As Brian rightly points out, I did go to the time and trouble of "dialling in" (or correctly phasing my camshafts position to that of the crankshaft).
I did not take photos or describe in detail how I achieved it as so few people are interested. I have looked for the brief post I made at that time, but I think it must have been posted in someone elses thread. The general consensus appears to be that near enough with the factory marks is plenty good enough.

Having spent so much time on my engine trying my best to coax every last ounce of power and torque from it, I decided to spend some (loads!) of my free time (but no cash )in making sure my Kent cams were installed bang on ; inlet fully open @ 105° after TDC and exhaust fully open 109° before TDC.

There are no tricks or short cuts in doing this and a good understanding of what is trying to be achieved is a prerequisite.... There is lots of great reading all over the web regarding this subject.

I used 6mm bar threaded at one end to screw into the relevant cam bearing caps. Further 6mm bars and dial gauge clamps and swivels were used to position the an extended dial gauge stylus on the top of the follower (albeit at a slight angle, but perfectly acceptable to show maximum travel). As you rightly point out this is not always possible due to the cam lobe interfering.

Having pondered this, I decided the only way I could ascertain full lift would be to measure the same camshaft on the adjacent cylinder. Due to the architecture of our engines the adjacent cylinder would either be trailing or leading by 90 or 270 crank degrees (ie. 45 or 135 camshaft degrees). This relationship is fixed and cannot change.

The dial gauge was thus set up to read max deflection when this valve on the alternate cylinder was bang in the middle of it's closed period ie eccentric lobe facing fully away from valve stem.

From reading the large diameter degree wheel that I had installed on the end of the crankshaft I was able to determine my camshaft phasing in crankshaft degrees. (Degree wheel fitted to crankshaft outboard or rotor using suitable spacers to leave degree disc flush with rotor) and correct as necessary by slotting the camshaft chain wheels and reinstalling.

During all of this the camchain tensioner was removed each time a cam chainwheel needed to be removed due to the tendency of the valve springs to try and rotate the camshaft and thus the cam chain to jump a tooth.


None of this was straightforward and the first cam I timed in took me no less than 12hours over 2 days The second camshaft took less than an hour and a half

I considered this task an integral part of the program of works I carried out on my Trx and wouldn't have been happy if I had omitted. It was painfully slow, but at least I have the satisfaction of knowing my cams are installed as specified anything else would have been a haphazard guess.

I hope the above goes some way to addressing your question.


Mark.

I've trawlled through my posts and found this:

viewtopic.php?f=6&t=9573

Mark.

Thanks for your well-detailed outline Mark. Certainly of interest and value to me

Was the dial-gauge extension you used an angled type? I did a quick Google but the only page I found was out of date. I may well make one up and add it to the growing TRX-special-tools box

Tarwetijger wrote:Interesting stuff. As the marks are on the cam itself and not on the sprockets, it should be good now! I've never thought of this.
The only 'disadvantage' I can think of, is that the chain will get more loose (theoretically), but the tensioner should be able to compensate this easily.

So your head gasket is only 0,2 mm in thickness? Must be like a thin foil then?

I wondered about the chain tension too. Taking the tensioner out to check, there was still a fair amount of adjustment to go, so should be aok.

And yes. My gasket's fairly thin; roughly 1/3 the standard. Looks radical but compression ratio will still be less than 11:1. I've used Hylomar sealant on both sides. First time I've used it. Interesting stuff and tricky to get an even spray. It looks and smells like PVC-pipe cement (It doesn't set though... dries to a rubbery state). It certainly appears it will give a good seal. I reckon it will have added a small but measurable difference to the gasket thickness overall.

QuickDraw wrote:Thanks for your well-detailed outline Mark. Certainly of interest and value to me

Was the dial-gauge extension you used an angled type? I did a quick Google but the only page I found was out of date. I may well make one up and add it to the growing TRX-special-tools box

No, didn't have an angled extension available to me only a std straight type. Good luck with it Mate.

Mark

I had a go at doing my cam timing with guidance and advice from Mark. My motor was out of the frame on the bench and it is still a reasonably challenging task. Mark did his with the motor insitu which must have been infinitely more difficult

I had a degree disc on the rh end of the crank with the oil pumps removed. Mounted a length of 6mm steel plate flat on the top of the head and used a magnetic base on this for the dial gauge mount.

Good luck! It's a rewarding process to go through.

This is my setup when I set my cam timing , looking at the marks on the camshaft and chainwheels doesn't say very much . (when I measured with non slotted original wheels , the timing was 5 degrees off)
The most difficult thing is to find a point where you can measure on the valve caps without the gauge pointer touching anything else , finding the exact tdc point was done with a stop made off an old spark plug .

Aaaaahhh this is the thread I was looking for..