mike tkach

iTrader: (3)

pro comp[speedway] is a chinese company that makes junk and floods it into the american market,the people who buy it soon realize the did not get such a good deal when the parts break and trash their engine.comp cams is an american company that makes good quality parts.their is no connection with the two company,s.

F-2 Speedy

iTrader: (6)

Im so glad you said this

1MOSES1

We re-used our crane gold rockers. It was the only thing we re-used. Valves, springs, locks, and lifters got replaced. People that talk about fatigue don't know material or structural analysis. Parts are designed to 10x6 cycles. That's 2500 hours at 4000 rpm. Sure there are pre-mature failures on used parts but there can also be premature failures on new stuff too. Just my 0.02.

mike tkach

iTrader: (3)

not sure if i follow,are you saying a crane rocker arm is designed to go 2500 hrs at 4000 rpm.that equils 300 million cycles.NO WAY!

1MOSES1

Sorry long night at the office. Typos and bad math. Fatigue life is designed to 10x7. That's roughly 500 hours at 4000 rpm. Id imagine that's 1000 hours or more of real time running.

kevinb230

So based on those #'s with an average rpm of 3500-4000 its time to replace the whole set. I'm sitting at 325hrs now. Where does one find that information? Or do you have the numbers for other rockers?

mike tkach

iTrader: (3)

i don,t know the cycle life on the crane gold 1.7 ratio rocker arm but bob madera mentioned to me that the aluminum shaft mounted rockers on a mercury marine sc1075 has a life of 11 million cycles,they translate that to 80 hours.

1MOSES1

These are typical design values commonly used not hard numbers. Nothing is 100% when it comes to mechanical parts. In my field we design for 10x7 fatigue as do most companies. We always derate material allowables accounting for temperature. Usually it's a -3 sigma 99%. Obviously all this math goes out the window when there is mis-alignment, higher than designed spring forces, etc. likely the contributing factors to early failure.

I highly doubt your average rpm is 3500. Read your ECM and I would be willing to bet 75% of your run time is at idle. Just trying to point out that many people replace things way before they should be replaced.

1MOSES1

It's conceivable that they use 10x6. I'd be a little surprised as there would be a lot more failures out there.

mike tkach

iTrader: (3)

i believe they did a cycle test and had first failure at 11 million cycles.i am not telling you what to do but when i error i do it on the safe side.a new set of rocker arm,s is peanuts compared to xtra damage when a rocker takes a chit at 5000 rpm.