I have a 1972 R75/5, 50,000 miles... I am rebuilding the engine. Crank is out, just pressed new bearings in and noticed a small crack at the front of the case through the bearing holder 'hole' at around 7 o'clock, passing downward about an inch, through the internal webbing. Looks like it has been there for a long time from the staining, and machine marks...maybe since 1972? Since it looks like it has been there a while and the forces from the front bearing are distributed pretty broadly due to the fit of the bearing holder, I am considering drilling the end of the crack and filling with appropriate epoxy. However that seems like a half measure since I am this far into it......on Ebay there are used cases that are cheap enough, is there any reason that the bearing holder, cylinder, etc parts off my old case won't fit a different serial number case? Any advice?
I have seen these types of optical illusions (I don't know what else to call them) on complex aluminum castings.
I would first make sure you have a real issue. Was oil leaking from/through this "crack" or some other indication that it was more than simply a superficial abnormality ? Can you blow air through it ?
There are dies and penetrants available that professionals use in "Non-Destructive Testing" (NDT) that can test castings for possible failure points. Shops that use these can be found around small private airports where aircraft engines are maintained.
Then there are secondary considerations, like the serial numbers.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks for the reply. Good points to consider but it is definitely a crack. On the machined surface of the bearing holder contact area it is displaced enough to catch your fingernail. Yes unfortunately would mean non matching numbers. Oh well never intended it for a museum piece but disappointed to find this. Not sure “the blocks cracked but the hey the numbers match” is much to brag about and dont want this in the back of my head every time O ride. This bike has been fun to rebuild but has turned into a freaking money pit. If I can fit everything on a different block I probably will do that. Do know of any components that aren’t interchangeable?
Sorry, I can't answer that.
Best of luck.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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