Yamaha TRX850 Enthusiasts Forum

Measured my cams up today before swapping cylinder heads.

Journal OD should be 24.967 to 24.980mm.

Exhaust is all ok at 24.971 but inlets are all 24.967 with one at 24.961.

Was going to have these reground by Kent and feel that being on the lower end of the tolerance shouldn't really be an issue for lubrication to remain effective.

Then measured journal clearances and things look slightly worse than above suggests.

Clearance should be 0.02 to 0.055mm.

Plastigauge gives most on the inlet at 0.075mm with the exhaust at 0.05mm with caps torqued to 10Nm.

Can't go to the expense of complex machining of the head to tighten these up to spec and so I think I'm gonna run it as it is and fingers crossed it stays in one piece.

If oil pressure is good from my recent crank regrind, my feeling is that the top end should survive even with these loose clearances. Oil pisses out of the M6 gallery bolt now when spun on the starter motor where as before the crank went it was a mere dribble.

Could try for a used inlet cam and hope journal diameter is towards the upper limit which would improve things but I will still be towards if not outside the upper limit. Doubt many breakers would have the patience to mic one up for me but I'll give it a go.

Anyone been through the same procedure with positive results?

Ever hopeful; has anyone (UK) got a decent pair of unwanted cams that measure up close to 24.980mm (or even a set of Kent cams )?

I don't want to be the one that says ''it'll be fine'' & then your engine 5h1t5 itself but i'd say all of those clearances would (just about) be ok - the only one that would give me any concern would be the journal clearance on the inlet. It's your engine & your budget so ultimately your call?

Just don't be tempted to tighten the caps a 'little more' or you'll be back to square one

How about plating offending journals and grinding to size?

Probably possible but all comes down to the most cost efficient option.

Sandune51 thankfully may have come to the rescue with a good set of used ones.

Hmmm, the wear should be mostly in the cap ..... be tempting to employ ancient fitting skills and carefully take a thou off the cap mating face using fine wet&dry paper, on a flat machined surface, ie. mill table. To even halve the present clearance, compared to spec, would give piece of mind ... the crap hits the fan if you remove too much off the mating face of course...... this solution wouldn't be difficult and is kosha (in the circumstances) as long as wear exists in the cap and it is that amount of wear that is removed from the cap face....... the clearances you have now are not too diabolical but if it were my engine I would go for the faced cap trick as long as the cam shaft wasn't being deflected off center-line by taking material off the cap face without the equivalent amount of wear being present in the cap itself..... good luck