So did you have valve piston meeting? What was the damage?

 

Yep, just renewed my plates today!

Yes, the valve and piston had a glorious, explosive meeting. The exhaust valve was stuck open and lodged in the piston.

 

So exhaust valve stuck open. Do you know what caused that? Valve float from high rpm?

 

Jhoffy22, it is important to know how long - miles or hours of use - did you run the bike with the 351+MCM combo before failure..?

 

You see, as far as I know , you are the only member to run MCM+351. After your engine failure, no more information was gathered - as far as this thread is concerned - on 351+MCM.. With no actual measurements or other factual data, everyone just assumed the worst, labeled the MCM wrong for the 351, and the subject was dropped..

I have read and researched this thread many times.. Correct my determinations if I'm wrong - Only you did full MCM on a 351. You reported fantastic power. Right?

 

Yes, I did. I bet I put 5+ hours on the bike before it happened. The bike didn't blow up on first start or anything.

Yes, but fantastic power is relative since my point of comparison was the jetted bolted on 250. The power felt great though, I distinctly remember thinking to myself, wow, I'm going to hurt myself on this thing.

You're correct, my approach to the situation scared many people off of even trying to do it with the 351 and I don't know of a single 351er that has the MCM done. I don't knwo if you ever saw my pictures or not, but my valve completely went through the piston and into the bottom end. It was a nasty explosion. I had to replace the cylinder head (with valves, springs, and retainers), sleeve, and piston.

 

Yes I did see your pictures - but just barely caught them as they were removed shortly after I joined.. It is probably a good thing that they were removed because there is no way the MCM could have caused your issue (IMO).. Valve to piston clearance does not magically become a problem 5+ running hours later (after MCM mod completion)..

What I can't explain is how the propaganda got started about MCM and 351 not working well together? Have I missed finding this in here?

 

It's possible that someone else talked to Bill Blue and he told them the same thing that he told me - recommending not to do it.

 

I understood some others did the mod but didn't feel the change.

As for hitting valves, the only way the 351 piston would hit is if it is running less valve clearance than the stock piston. After all, it is using the same head and cams for most everyone. That alone makes me believe there isn't any risk of sticking a valve.

I will also say I dropped an exhaust valve in my Yamaha SR500 some years back, probably several hundred miles after I rebuilt the top end. All I can figure is a valve keeper wasn't quite installed properly, because if I remember right I installed a set of S&W heavy duty valve springs when I did the valves. Next time I put in new valves and keepers and verified the fitting of the keepers. If I do any other bike I will do the same, just to make sure everything seats in right.

 

Batter up! I'll sit in the bleachers and watch.