Topic: Cb750K2 Oil Pan Surprise

[LarryR]

I purchased my K2 a year ago as a project bike. It ran decent last fall and I'm just getting around to working on it. I wasn't planning to rebuild the engine, just tune, clean, polish, rebuild carbs, etc but upon removal of the oil pan I found a few surprises. Appears to be a piece of a piston ring?, gasket material from a prior repair and a piece of aluminum fin.

Prior owner did say he had the transmission repaired as second gear was slipping. Any chance these pieces might be the remains of that failure and a sloppy repair? Looking for input before I tear down for further inspection.

Thanks!

Larry

[Terry in Australia]

Yep, it's amazing what can break off and yet our bikes still run fine. I found one gear tooth in my oil pan, my engine has never been apart, and it still runs sweet with no transmission noise or false neutrals. If yours is running well, leaving it alone isn't a bad thing.

[kmb69]

I purchased my K2 a year ago as a project bike. It ran decent last fall and I'm just getting around to working on it. I wasn't planning to rebuild the engine, just tune, clean, polish, rebuild carbs, etc but upon removal of the oil pan I found a few surprises. Appears to be a piece of a piston ring?, gasket material from a prior repair and a piece of aluminum fin.
.....

The aluminum piece looks like the tab off the center main that sits under the cam chain.
If the "ring" breaks versus bend when you bend it, probably a piston ring. If it bends versus breaks, it's probably a piece of one of the transmission bearing alignment rings.

[LarryR]

Thanks. The ring is rigid so as you point out its likely a piston ring. Im not sure how a broken ring gets into the oil pan unless the piston also failed which is not the case. Either left over from previous repair and left in the pan or broke on install?? I didn't compression test but wouldn't I have had noticeable blue smoke with a broken ring?

[kmb69]

.....
I didn't compression test but wouldn't I have had noticeable blue smoke with a broken ring?

One would think so.

[FuZZie]

Think I'd do that compression test, and cross my fingers that it's just sloppy leftovers.  

[disco]

+1 to a left over from a sloppy repair. I don’t see how a piece of piston ring that large, can depart from a piston that is still in one piece.

[Terry in Australia]

It's easy, when the "mechanic" lowered the cylinder block on to the pistons he didn't have the rings correctly compressed, a piece of the ring snapped off and fell into the engine. It's too big to be sucked into the oil pump, so it just lived in the sump with those pieces of the cylinder base gasket.

The "fin" looks like one of the fins cast into the lower crankcase, are there any chipped off? If it's a compression ring (the early bikes had one piece oil rings, so it could be an oil ring, but I think it looks more like a compression ring) it won't blow smoke, it'll just be down on power a little, probably.

If it's running well with plenty of poke, (for a 45 year old bike) then it's probably not worth digging into it, it's probably been like that for years.  

[disco]

Hi Terry, Yeah I get that can happen.

What I meant was, a perfectly good working intact piston ring can’t just shed a huge piece like that unless the piston has also self destructed.

But yes, your scenario of the ham fisted ‘mechanic’ poorly installing is likely how it occurred. 

[Terry in Australia]

Of course I'm not speaking from experience, er, because you'd have to be a real moron to do that, and, er, I'm not a moron........

[disco]

Ha ha 

[LarryR]

Thanks for the responses. I think I'll take it down far enough to at least inspect / replace the rings. I'll post my findings

Larry

[strynboen]

im have missing my red schrecdriver..så please send it to me..must have forgotten it vhen i made that gearbox..

[TwoTired]

How thick is that piece of ring?

Doesn't the transmission have snap ring position locators?  Those would be thinner than piston rings.

Cheers,

[ekpent]

How thick is that piece of ring?

Doesn't the transmission have snap ring position locators?  Those would be thinner than piston rings.

Cheers,

By the look of its size compared to the screwdriver handle and the radius bend it looks pretty pistony- my new word for the day    Jagged edge looks like a brittle break also.

[Terry in Australia]

im have missing my red schrecdriver..så please send it to me..must have forgotten it vhen i made that gearbox..

Bullsh1t Lars, that's MY screwdriver mate, I distinctly remember using it to push the rings in, until it just disappeared?