Yamaha TRX850 Enthusiasts Forum

So, I have an old engine that's thrown the left big end bearing...

I want to swap the head over because my new engine has some damage to the cam journals, what else should I do at the same time?

I am thinking:

Probably swap bores too?
Hone bores
Skim head (?)
clean up inlets/polish outlets (or have I got that backwards...?)
Hone valves
Replace rings & valve seals...
Worth doing a cam grind?

Any other thoughts?

I don't want to spend a bundle, but I DO want to stop the oil burning! & maybe pick up a few HP as well...

Measure those bores before swapping them, your originals may be fine with a good hone.
Skim head, to increase compression ratio or just to be sure it`s flat? To increase your compression don`t take more than ten thou / 0.254 mm off with stock pistons.
Clean up inlets / polish exhaust ports? Again if you`re wanting better gas flow yes, but don`t go mad or brightly polish anthing, you could actually slow gases down. Matching diameters is important though.
Hone valves. You mean lap / regrind valves into their respective seats surely? If that`s right then again, yes.
Valve stem oil seals, definately!
Again if you`re after more bhp then a camshaft regrind will also help too.

Other thoughts?

A real good check over of the ignition circuit, plug leads, caps, etc. Really just making sure all the connections are good and clean for the least path of resistance for those sparks.
Maybe new drive chain and sprockets if you`re feeling flush, you would be amazed at how much a worn chain can take from the power output.

Leave the pistons out and head off and grow plants in the old barrels! Good talking point.

Dave E

slow codger wrote: Leave the pistons out and head off and grow plants in the old barrels! Good talking point.

Dave E

Well, I will have a spare set of barrels & I do need a herb garden...

Thanks for the info Mince, will be a longish term project so just getting the ideas together at this stage!

Skim for higher comp & to make sure it flat & yes, lap the valves (forgot what it was called).

I remember lapping the valves in my old mans MH900 as a kid, I should still be able to do it!

Clean up the inlet so it all joins nicely & give the exhaust port a slight polish should be the go, right?

The good thing is, I can do most of the work on the spare head as money dictates & then just swap it over when it's all done.

My chain & sprockets are still in good nick, less than 5K on them roughly.

So, I think I have a plan put together!

Replace valve stems seals, lap valves, replace rings & hone bores, swap bore & head from old engine onto new head & fix my oil burning problems.




This might have to be in liue of flatslides Oh well.

Given I have 3 month off riding, it should be enough time to get it all done!

I moved the engine onto the bench last night, anyone got any tips for an engine stand?

2 blocks of wood. thats what I have used!

If you`re handy with a jigsaw, some chipboard cut to fit the contours of the cases and a few bits of 2" X 2" can be fabricated up to support the motor sufficiently.

I wanna knock something up out of steel, need some welding practice!

A few bits of square section should do the job.

slow codger wrote: Leave the pistons out and head off and grow plants in the old barrels! Good talking point.

Dave E

Wine rack for two bottles

Cal

Hey, that's not a bad idea! I'd need more capacity though...

Im sure Ive seen it somewhere with a V8 !