Bad Valves???
 

After having my engine rebuilt last winter we had a problem in the spring on the dyno of the exhaust valves hanging up at higher RPMs and Temperatures. The engine builder honed the guides and reassembled the heads. All seemed to work fine on the dyno with no more valves sticking open at RPM or temp.

Most recently while attempting to get some RPM (5000)out of the motor, (3) rockers came off the valves. I posted this previously:

http://www.offshoreonly.com/forums/s...highlight=whay

The valves were the only part reused in the rebuild of the heads. The engine builder and I cannot identify the brand of valves that they are.

He is convinced that the valves are creating the problem.
As I cannot come up with a better answer, I purchased new inconel exhaust valves which are being installed Monday.

Has anyone ever experienced a situation like this this?

If the valves are bad, he should be able to tell whats wrong with them:confused:

I really doubt the valves would cause the rockers to come off. They are set in guides and locked down. They don't or at least should not move from side to side.

I've bent a lot of pushrods but I've never seen broken guide plates.

I am a firm believer that most engine builders have the wrong attitude about valve guide seals. Preventing ALL oil from lubricating the valve stems and valve guides is wrong, especially on the hot exhaust valve guide/valve stem. There needs to be some oil getting in there.

The stock Chevy valve guide seals are fine but many builders use the Teflon seals that prevent ANY oil from getting in there at all.

If it really bothers an engine builder that some oil may get into the combustion chamber through the valve guide/valve stem (the intake port has vacuum and may suck some oil through the stem/guide) then he should use the Teflon seals on the cooler intake valve guide/valve stem only.

The exhaust port doesn't have any vacuum and will not pull oil into the combustion chamber while the engine is running (although some oil may run down the exhaust valve stem/valve guide when the engine is shut off, it is burned as soon as the engine is started).

Use the stock valve guide seals on the exhaust to allow some lubrication in there.

Dennis Moore

I'd rather burn a little oil through the valve guides especially on the exhaust side than have the clearances be too tight and have a valve get hung up in the guide.

Also, check for coil bind and make sure the lift of the cam is taken into consideration to make sure your retainers aren't bottoming out on the valve guides as well! Your engine builder should know all of this.

Dennis Moore, In a post a while ago, Budah recommended not using valve seals at all on the exaust side. That seemed a little extreme to me. What do you think?

I am not Dennis and do not have his knowledge and experience but Mercury recommends removing the spring tensioner on exhaust side valve seal if you use teflon seals. No seal seems a little extreme to me.

I agree with Budah, who cares if the engine smokes a little when you start it up? Oil is not going to seep into the exhaust ports when the engine is running, thats for sure! The amount of oil seeping past the valve guide/valve stem is really small, much less than gets past the oil rings.
I would rather have the exhaust guides lubricated really well, especially if you run a high lift camshaft.
Dennis Moore

I don't have valve guide seals on the exhaust valves on my 406 /.625 lift Dart aluminum head small block (per Jim V's recommendation)some times it will smoke for an instant if it has been sitting for a while,but other than that no problems I have yet to hang a Valve.

Rob

Thanks for the info.