Took an engine appart and noticed some strange stuff on my crank. In the flywheel you can also see it. Is it corrosion and broken with taking appart the flywheel?

 

 

Furthermore there was some brown corrosion ''spray'' inside the plastic casing and some vapour.

Edited July 11, 201610 yr by crazybond700

Just Machine grunge IMHO  ! clean it seal it and do another 50 hrs ... No engine is spotless inside , and that one looks pretty clean to me...

Glenn

Looks like overspray varnish for waterproofing that just aged from long exposure to heat. That's unusually clean compared to any engine I've been in.

My question is about the crank itself. Notice the small area, almost looks like the flywheel welded itself to the crank.

 

Edited July 12, 201610 yr by crazybond700

I have seen this on most, if not all of my trial motors, from Bultaco days on. I think it is caused by galvanic reaction between two (slightly) dissimialr metals, there is always a minute emf (electro motive force) between two different metals, when connected together, this is how thermocouples work.

The crankshaft may possibly have a different mix of alloys compared to the flywheel, though both being basically steel, they are still a mixture of various elements. I usually smear grease there (on the crankshaft!) to prevent this.

Bye, Peter B.

Ah now I see. Yeah that is a little odd. Almost like a high spot on the crank caused by a casting defect in the steel. I'd love to throw that under a microscope.

Edited July 14, 201610 yr by dan williams

Agree with Peter B

This is common on the odd bike with a magneto. (not common but i have seen it on varied bikes over time in our workshop). When you look at them closely it is almost like a SPOT WELD.

Anecdotally I have found it is usually on the bikes where the tapered surfaces (crank to flywheel) are not a great match. 

The marks on the flywheel always correspond with the one on the crank - like there has been current flow across a small gap. Hence the look of a spot weld! Not sure if that is correct, but that is what it appears to look like without any other evidence.

 

Edited July 18, 201610 yr by arnoux

Agree with Peter B

This is common on the odd bike with a magneto. (not common but i have seen it on varied bikes over time in our workshop). When you look at them closely it is almost like a SPOT WELD.

Anecdotally I have found it is usually on the bikes where the tapered surfaces (crank to flywheel) are not a great match. 

The marks on the flywheel always correspond with the one on the crank - like there has been current flow across a small gap. Hence the look of a spot weld! Not sure if that is correct, but that is what it appears to look like without any other evidence.

 

Exactly like a spotweld yes!

 

Bike is back together, used some extra grease putting it together and runs like a champ.