Yamaha TRX850 Enthusiasts Forum

If you're easily offended or have any semblance of mechanical sympathy, you should probably look away now.

Ok, on the weekend I started stripping down my old engine which died of oil starvation ~18months ago.
On the bench, my DIY engine stand works ok, hasn't fallen apart yet. (Don't look at the welds)

A bit of 50mm square section holds the barrels near enough to level for me!
Some scoring on the cam journal, I can feel it with my fingernail...

Q1.Any ideas on getting rid of that? Fine emery paper? Get a professional to do it?

Most likely from me running the engine after the big end went... like I said, look away now if you're squamish!
Bit of rust, lots of carbon!

Q2. What's the best way to clean the Valves, combustion chamber etc?

Right hand bore, can still see the crosshatching, (Q3) this would indicate the rings didn't seal properly yes?
This is my old engine, but was using about the same amount as my new engine.
Left hand piston, you can see where the piston skirt was rubbing on the bore, I can't really feel any scoring, I think the pistons has just deposited metal on the bore walls...

Remember my waring from before? Look away now.
I believe that used to be a bearing...

so what should i be aware about to not have this happen to my engine....is all this about not keeping the oil up to the sight glass, or can it be from a design fault...?..a lot could be said to Yamaha for not putting a basic oil switch on the bike somewhat...a sad thing you have..

The piston.
Bore from the other side.
I guess the next step is to see if the bores are salvagable, clean up the head, hone the valves, replace the valve selas, clean up the inlets, & lightly polish the outlets!

alextrx850 wrote:so what should i be aware about to not have this happen to my engine....is all this about not keeping the oil up to the sight glass, or can it be from a design fault...?..a lot could be said to Yamaha for not putting a basic oil switch on the bike somewhat...a sad thing you have..

Yes, check your oil religiously, some people are adding oil lights, I am suprised Yamaha didn't include one...

Most TRX's use oil, so you need to be aware of that, most engines take out the L/h big end bearing when they go, I think that is just the weakest point/first in line to fail, rather than a flaw.

Got pretty hot didn't it I can smell it from here YUK.

MM

Yeah, the L/H con rod has all kinds of rainbow colours on it!

The head might be salvageable M.V. a good engineering works will tell you.
The bores might well clean up with a good hone and to get the carbon off the valves it`s simply a matter of scraping it off with a craft knife or similar (they are hard, no ordinary steel knife should score them if used `sensibly`)
Alternatively if you have a lathe or even an electric drill you can polish them nicely with Scotchbrite pads.
Most folk are not aware of it but those crank shells if the motor is at the correct oil levels and the oil is clean, NEVER actually touch the mating crank surface.
In fact if you tried to get continuity across the crank to the shell when the motor is running and up to normal operating conditions you wouldn`t!
The crank actually floats in a film of oil, although obviously the tolerances between the crank and shells are tiny:

http://www.enginebuildermag.com/Article ... trong.aspx

Oil, all you might need to know:

http://en.wikipedia.org/wiki/Motor_oil