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Discussion Starter · #1 ·
Hey everyone,

Had my engine start, run roughly, then die last fall before I started a rebuild on the carbs, thinking it was only due to some plugged up jets. Jets were one of the issues but after cleaning my engine and moving it onto my workbench I heard a small rattle in the lower case. I guess I had never heard the noise before when moving the engine around because it still had oil in it. Long story short, I ripped into the engine to find the P.O. had lied to me (of course, right?) and one of the pistons and connecting rods had blown apart and cracked the cylinder wall. I am devastated. I'm practically ready to reassemble the bike for the year and now this.

I've found a piston/ring set on eBay for a decent price, but for a 78/79 CM400 and they are oversized at 71.00mm. Will these work?

If not, I have spare 400 engine but having no exhaust on it I fear the elements may have done some damage. If the pistons just need some cleaning, will a hone of the head and some new rings for 70.50mm do the trick?

Thanks in advance!

PS - I can throw up a picture if anyone is interested in seeing the damage
 

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Discussion Starter · #4 ·
Oh wow, didn't know they even had domed pistons. Thanks guys.

Lots of info in those links as well HamHock, thanks.
 

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I'll take a guess that the crankshaft on the engine with the bad rod/piston is toast as well. It sounds like you'll be better off working with the spare engine.
 
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