Crank Cases: paint inside Vs paintless and oil impregnation.

[TLCbobber]

Yamaha put a thin coat of paint inside the cases, if it's removed should it be replaced? Looking for opinions and thoughts on this and whether oil impregnation is an issue or not if there's no paint inside.

 

[TwoManyXS1Bs]

Hey, TLC. My vote would be to NOT paint inside the cases. Reasons, for one, like you said, 'oil impregnation'. There's the risk of paint separating, especially in the turbulent crank area. Wouldn't want that. There's also the tiny crank squirters that could get clogged. And, I prefer to avoid configurations that may impede heat transfer, with certain exceptions like exhaust pipes to legs...

 

[650Skull]

In 82/83 Yamaha painted the cases black. I haven't seen it but some say this is on the inside as well as the outside. This paint is not normal, as in peeling as paint does. No..... painting would be a no no for the reasons 2M outlined above.........

good pics of cases here no factory paint........81 motor http://www.xs650.com/threads/my-engine-rebuild-from-scratch.30786/

 

[XSLeo]

I think they make paint especially for inside of engines. It has a very slippery surface. This helps the oil slide off and return to the crank case faster. As I recall racers used it. It helped keep the engine oil cooler as well as much of it as it can in the oil pan.
Leo

 

[TLCbobber]

Hey, TLC. My vote would be to NOT paint inside the cases. Reasons, for one, like you said, 'oil impregnation'. There's the risk of paint separating, especially in the turbulent crank area. Wouldn't want that. There's also the tiny crank squirters that could get clogged. And, I prefer to avoid configurations that may impede heat transfer, with certain exceptions like exhaust pipes to legs...

so you're saying oil impregnation would be a good thing? or that new paint may not stick due to oil impregnation? I wouldn't think it would be impregnated yet since it had paint on. I was thinking of oil impregnation being an issue later on once it's built and running. I actually washed right through the paint with thinners while cleaning it out, I didn't have anything milder and didn't realise it was painted inside... just looked like really smooth casting... which it is now lol. Oh well, I shan't worry about it then, one less job to do lol... but I'd rather have left it on.

Thanks guys, much appreciated.

 

[TwoManyXS1Bs]

...or that new paint may not stick due to oil impregnation?

Yes, I was thinkin' of that one.

Engine build tips show internal casting surfaces being smoothed and painted, like XSleo noted, to improve oil flowback. But, I've only seen that done on liquid-cooled auto engines. Heat management on air cooled engines is different. Honestly, I haven't any idea why our case innards would be painted. Open to learning here...