Yamaha TRX850 Enthusiasts Forum

Bozo that I am, I've lost the crank timing since starting the rebuild. Now I've set the crank at the TDC mark for cylinder 1 and timed the cams as per Haynes (#1 intake and exhaust cam lobes pointing away from each other, index punch marks vertical and finally "I" and "E" exactly horizontal) but I can't see how I could not be either correct or 360degrees of crank rotation out, meaning the ignition will fire at the wrong point and cylinder 2's valves might contact its piston.

I am also farked if I can work out how to get the cam tensioner bolt back in!!! Very annoying.

Help please!

Edit: ok, got that last one sorted, you take the clutch cable off and the engine mount bracket.

Still not convinced on the timing issue though, unless the engine fires each pot "wasted spark" style - twice per 720 degrees then I guess it wouldn't matter how you timed it. Otherwise, it's just not going to run. At least I can turn it over without valves meeting pistons. Guess I better analyse the ignition system to determine how it fires.

Not real happy with the cam sprocket alignment, exhaust seems spot on, but intake is slightly out. Going one tooth the other way is worse. Can't be cam chain stretch, it's only the bit between the 2 cam sprockets! Would have to be waaay stretched for that to be the case.

Will keep fumbling on.

Edit again: Hang about though, if the punch marks are perfectly aligned (at #1 TDC), then surely it doesn't matter what the gear positions are?

Edit again again: It runs perfectly (well as far as I can tell thus far), now understand the cylinder phasing and ignition timing. Aaaaah. Long weekend.

There a few past threads relating to valve timing. Ive been through the same process as you and found the the two cam sprocket marks to not be in synch. Dont worry about that, that's the way they are. I relocated one of them to try and get closer agreement between markings and the valve gear rattled like a bastard but the engine went well.... it might have even given it a bit of top end extra zap. I changed things back and the old girl runs beautifully.Its just one of those TRX endearing traits I reckon...... chain stretch doesnt account for the disparity between markings. Cheers

Yeah cheers Smithers, been out on a couple of runs now, done nearly 50k and the timing's spot on. I swear it's running smoother than it used to, dunno if I'm imagining it - result of all the hard work maybe. Vernier sprockets wouldn't be a bad idea?

Well, the two original 7mm (clearance) holes through the cam sprockets could be slotted Dave. Then the back of the cam sprockets could be drilled to accept a hardened drive pin and the cam flange faces radially drilled to accept the pin in several positions. Obviously the hole in the back of the cam sprockets would need to be a blind hole to keep the pin retained.
In this way a few degrees either side of the Yamaha timing could easily be applied. The drive pin would mean there was less torsional force applied to the `hold` the cam sprocket fixing bolts have on the sprockets too.
I`m surprised no-one`s talked of it on here before, maybe they have and I`ve just never seen it?

Handy info ........ Ive got this particular task to look forward to when I build my new engine

Chris