Not A Skyline But An Engine Is An Engine.

[Abo Bob]

What do you guys think is going on with my bike engine? Basically it's a two cylinder engine and each cylinder has it's own carby.

Cylinder 1:

Cylinder 2:

And here is the underside of the head. Does this mean cylinder 2 is running lean?

Cylinder 1:

Cylinder 2:

These are my camshafts. Anyone care to comment?

These are my bores. You can still clearly see the hones marks but I measured the bores by eye and they are 89.5mm x 89.1mm at the top of the bore and 89.5mm x 89.4mm at the bottom. Ok I used a Vernier Caliper as I didn't have a bore scope thingy.

I was hoping to get away with new rings, bearings and gaskets. What do you all think? The pics there show that the piston skirts are wearing the bores.

I haven't got the bearings out yet so don't know their condition.

[Guilt-Toy]

to me it looks like filings of some sort, possibly aluminium has broken and found its way in the oil & on the top of the piston?

in the oil are there any filings or chunks of anything ? cos if there are small filings of anything going through the cam while its spinning it can mark it like that or it could be a oil supply issue but the bits of metal on the top of that piston does not look good.

[Abo Bob]

Sorry that's not the bit I was asking about. That's just crap from a bolt I had to grind off cos someone before me had completely rounded it.

What I'm curious about is the condition of those two different coloured valves and also the condition of the bores.

[STATUS]

give it a fresh hone, fit new rings into bores without pistons and meaure the ring gap. do this in three spots (top, middle and bottom) and check to see if it is within spec. As for the valves i would check to see if they are sealing correctley (drop thinners down that port and see if it leaks past valves... bit dodge but it works) and then check the spark plug colors, if the second cyl has a light plug too it could be the mixtures... bikes are easy to tune what carbs are on it? check to make sure both needlles are on the same "clip" if they are and cyl 2 is still lean lift the needle up a clip on cylinder 2 and recheck plug.

i would get heads cleaned and checked anyway while they are off for safety sake myself.

[Abo Bob]

Thanks Trent. I am starting to think those two valves aren't sealing properly. I will try the thinners trick. Plugs were fairly similar.

[MBS206]

I've been told unleaded burns that colour that those two valves are, but I've never pulled a head off to tell.

[Dale FZ1]

Being a carb'd engine, I'm presuming it is the TRX850 or an earlier TDM900? Good fun machines both, in the right environment.

The wear on those cam journals is a bit of an issue I think. What condition are the mains and big ends in?

What sort of mileage and service schedule on the engine? And what was the reason for the pull-down? The different colour of exhaust valve deposits indicates a difference in mixtures (to my eyes anyway).

It might be worth checking to see if Yamaha plated the bores with Nicasil in those things too.

[Abo Bob]

Well spotted. It's a TDM850. You know what's funny is that now that it has dried off a bit, the exhaust valves from each cylinder no longer look quite so different from each other. The erstwhile lighter one have no deposits on them though and the others do, it's just that those ones have lightened up a little.

Haven't got to the bottom end yet but that's what I think it's problem was. Rattley big end or main bearing.

[R34GTFOUR]

i would of though oil supply issue aswell. Thoses cams show oil stavation, and if you spun a big end that explains it.

before you put it all back together, see why it was staving of oil

[Abo Bob]

Well not the carnage I was expecting. No time for a long post just shitloads of pics.

[Lunatikk]

I'd say it's more oil breakdown than starvation- not changed often enough or simply the wrong oil used.

The joys of buying second-hand toys

[Abo Bob]

But what do you think about the surfaces and what it means in terms of things needing to be replaced or machined or whatever? I'm a noob when it comes to reading the surfaces.

[BOZ22N]

How much fun is pulling stuff apart. Ha Ha

I hope you have marked every thing?

Make sure that you plasta gauge all bearing clearances when you put her together so that you don't build in the same problem. And measure your piston ring to piston gap with some feeler gauges just to make sure that you don't need to replace the pistons as well. I would just linish all your bearing running surfaces give her a hone and replace all your bearings, gaskets and either pistons or pistons and rings.

Check the cam chain tensioner cause they can make a hell of a noise when they are about to shit them self’s, if it is cheap i would replace it.

Get the carbies balanced and checked by a motorbike mechanic cause they can be a pain in the arse to get right on older well worn bikes.

Good luck,

Ryan