Atomic 4 Engine RPMs

[sailingdude]

I have just completed moving the Atomic 4 engine controls from the cockpit wall up onto the steering pedestal on my 1980 Catalina 30. I notice that I seem to have substantially more throttle travel that I had with the old arrangement. With the new throttle cable, I seem to be able to run the engine to higher rpms than before, to the point where I am hearing what sounds to me like valve lifter slap. That is, the engine rpms are such that the valves don't have time to close before the next lifter cycle. This is not unreasonable, but my problem is that according to my tachometer, this is occurring at approximately 1450 rpms. This seems somewhat low to me. The Atomic 4 book I have says the maximum engine rpms is 2500 and recommends not running sustained speeds above 2000. Is the 1450 rpms reasonable, or should I look to some other problem, like the tach being incorrect or a problem with the engine?

Thanks in advance for any suggestions you might have.

Bob Boller

[Don Moyer]

Bob,

It would help us if we knew how fast 1450 RPM moves you through the water
and what your maximum achievable RPM is while underway.

You're correct that real valve slap shouldn't occur until RPM well above
1450. In the Atomic 4 fleet, valve noise is more frequently caused by
valves hanging up slightly for any number of reasons, usually related to the
effects of water or elevated exhaust pressure causing caramelized goo on
valve stems. You might try a couple Marvel Mystery Oil (MMO) treatments (5
or 6 squirts of MMO in each spark plug hole aiming away from the manifold
side of the engine). If your valves are a bit problematic, the MMO should
make an immediate improvement.

Don

[sailingdude]

Don

Thanks for your reply. Unfortunately, since I moved the engine controls, I haven't had the opportunity to get the boat out of the slip. So, I can't answer your question about top speed and rpm. Perhaps this weekend. I have owned this boat for a little over 2 years and whenever I add gas, I always add 1-2 ounces of MMO per gallon to the fuel. I'll try putting MMO in the spark plug holes and let you know the result.

Thanks again.

Bob