Topic: Maiden voyage, disaster!!

[CB750R]

well, after triple checking the timing, and valve clearances, assuring that proper oil flow was getting to the head, I took the old girl out for a ride, nice and mellow, kept it under 5grand, no faster than 100km. but steady at 80 for most the time, all of a sudden it sounded like a grinding gear, so I pulled in the clutch and coasted to a stop, was with two other riders incase of such an event, so they went back for the pickup, and when I got home I popped the valve cap covers and tried spinning the crank in reverse to see if the cam chain was the culprit, but it held, and then I discovered that the #1 intake was stuck down, and when I fully removed the plug, she's all mashed in!!!  the only good news is that I didn't find any metal frags in the oil, so there's a very small silver lining in this!!!

Just thought I'd share my misery

[Harry]

Jeez, why did that happen, d'you think?

[Raul CB750K1]

That's very unlikely to happen. What can the reason be?

[Bodi]

Either the guide is undersize and seized or the valve spring retainers failed. Or the clearances were tight and Mr. Piston met Ms. Valve; I've had that happen on a new"hot" cam install when inexperience led me to check valve/piston clearance before setting tappet clearance. On a tight setup only a few thou makes the difference between vrooom and kerrrunch.

[CB750R]

my best guess, is that mr piston met mr valve, cuz mr head was machined, cuz mr dumbass previous owner took a wire brush to remove the old head gasket, and pooched the head,

[Lumbee]

...I rebuilt a donor motor I got this past spring, and it had a bent valve exhaust valve.  It was only bent slightly, and not enough to damage the piston.  I am assuming it made contact with the piston, or how else would it have become bent?  Anyway, it happens...

[Philly550K1]

when I fully removed the plug, she's all mashed in!!! 

was the spark plug mashed?

[Lumbee]

...I don't think so..however, now that you mention it the #3 plug (which was the damaged vavle) was kind of hard to screw in..but how would the valve hit the plug?  As I said it was only a slight bend in the valve...enough that it was not sealing...

[Trevor from Warragul]

I had this happen to me THREE times!  Turned out to be crap case-hardening on the valve retainers!  Got the ones I had nitrided and the problem went away.

[CB750R]

haven't had the extra body to lift the engine outa the frame, yet so I haven't been able to diagnose the failure, but that one is interesting to look out for, thanks.

[nomadwarmachine]

Would love to see some photos of the problem, once you get the engine out. Hope that the problem is nothing major and you are back on the road soon!!

[CB750R]

Will definatly post some pics of the carnage, not only for the gore factor, but hopefully to gleen some input from all of you, I think the engines' commin out this weekend, if I can muster up a sucker (um er friend, I mean) to help me lift it onto my bench
hehee