Pontoon Boat & Deck Boat Forum

I have been told that my 115 hp four stroke Yamaha is called a NO CLEARANCE MOTOR and will bend the valves if my camshaft timing belt breaks.
I have ALSO been told the 150 hp four stroke Yamaha is a CLEARANCE MOTOR and it will NOT bend the valves if the timing belt breaks.
Questions...
(1)...Have you heard this, and is that correct?

(2)...How about a 90 hp four stroke Yamaha. What is it, CLEARANCE or NO CLEARANCE ?

I am pretty sure I heard this on this forum, and I have searched for it and all over the internet and I can't find the answer..

Thanks for your help..

Harry

That don't sound right to me, if the belt breaks that should shut down the motor just like a cars motor when that happens.

What he's talking about is if the timing belt breaks, will the pistons pound the valves and cause damage.

Some auto engines are destroyed, and some are not.

I have no idea on this one. The belts are a 1000 hour replacement, which is many, many years for most people. I'm not ready to think about it yet.

The term is "Interference" and "non-interference" engines. Yours is an Interference engine meaning the valves will be shot if that belt breaks. On the up side, as Bamaman said, the service life of that belt is 1000 hours. I've got over 700 hours on mine and inspected it when I did my last tune up. The thing looked brand new with no sign of cracking or drying. I'm not really to worried about it for now but I'll probably have is changed at 1000 if I still have it.

Thanks, good to know.

This is what I got back from a mechanic on the Bass Fisherman website:

ALL units should be treated as no clearence. If maintance is being performed as required you will never have a belt break. I have seen belt failure's however. In most instances, due to the idler pulley, or poor instulation per a mechanic. I had one example of a failure where the unit had so many hours that the cogs on the belt were worn to the point of "jumping time".I have also seen the plastic camshaft gear fail. Don't loose any sleep over it.



I guess that means deal with it in another 15 years--for me at least.