Topic: cycle -x pistons

[Terry in Australia]

Geez Frank, good side-shift mate! Your "On the road to Bonneville" story has convinced me that you weren't taking a cheap shot at Big Bob's mechanical ability, but of course, I'm easily convinced, ha ha!  

[Big Bob]

Geez Frank, good side-shift mate! Your "On the road to Bonneville" story has convinced me that you weren't taking a cheap shot at Big Bob's mechanical ability, but of course, I'm easily convinced, ha ha!  

The weird thing is - I'm not the one that assembled the engine that ate the piston in question.  Said so several posts ago.

He still hasn't told me anything.

[754]

What I am saying is if you dont find the root cause, it could happen again.. then do you quit racing, or find the cause.

 I dont hnow what happened for sure..

 Look at the Facts,
was broken in and did run well..

 then, something changed.

 could be higher temps that day,  oil level problem, ignition  changing, or perhaps a different cause, but something happened that day, that did not happen on the other days
.
 To me it looks a bit like the ring was seizing as it broke as the material above top ring is pushed Upward, not just eroded/burnt away. .. but that is just a guess..

 What kind of oil were you running, and did you always run that brand?

 I am getting the feeling that roadracing is harder on the motors than I used to think.

 My cast pistons went a long long time and saw a lot higher RPMs than those.

[ymracing]

Used to see similar on CB250K4 way back when if the engine was "thrashed" from cold. Best reason we ever came up with was that warming too quick nipped the ring causing it to shatter then a piece would work its way out upwards but that was just an unproved theory

Same as mentor Jan Svensson stated about his 500/4 that he raced in Europe.  I am pretty good about doing a warm up and heat sink prior to heading for the track, but Roebling Road and Daytona were very cold and I may have not allowed long enough of a warm up.

BTW Rings were gapped, done several hundred of them. 

[lucky]

....it might be OK for light duty work, but I'd definitely not use 'em for racing, and I wouldn't expect a real long life from them, either.

Y'all might be interested to know that I've got a 1976 CB 750 K in the garage right know that's equipped with a CycleX 850 kit.  After being raced at Roebling Road and Daytona last February it suffered some sort of failure in the #3 cylinder at a track day in May.  No compression on that cylinder.  Spark plug was bent closed.  Oddly enough the engine still runs and pulls very strong.

I hope to have the time to get into that engine in the next month or so.  I will share the results of the autopsy here.

Spark plug bent closed. You were lucky the rod did not let go completely!
I would at least check that rod bearing on that cylinder.

Sometimes if the rod bearing or bolts fail/stretch, the the piston comes up too far and then it can hit things and get broken. I have seen it before.
I do not see any other reason.
If it was that hot to cause that damage, it would have seized .