Here is a question for our engine people out there. I have a L48 engine in my 1980 vette. I am noticing that there is a bad clattering sound coming from the engine when it is running around 190 - 200 degrees. It is especially bad when I step on the gas. I never hear it when the car is cool or when it is idling. I am not sure if I have a valve train problem or a cooling problem, possibly with the water pump. Before I bring it to a shop and get raped, I thought some of you may have a similar experience and a possible fix to correct the problem.

Thanks,
Chris


[Modified by Chris80, 7:42 PM 4/20/2003]


[Modified by Chris80, 7:43 PM 4/20/2003]

 

You have a case of pre-ignition. This comes from any or all of the following: low octane gas, too much initial timing or too much advace, higher than normal water temp, too lean fuel mixture, deposits in the combustion chamber. If you can turn a wrench start by checking the timing. 190 degress is not bad for an AC car. Try a mid grade gas (or premium) and see if it goes away.
Mark :cheers:


[Modified by mbeeman350, 8:58 PM 4/20/2003]

 

Has the Car been sitting with the same fuel in it? Try some hight test fuel and see if she acts up.

 

Yep all these suggestions ring true. Yank the dist cap off, and see if you can move the ignition rotor a quarter turn or so in one direction. If so, the mechanical advance is not frozen. THis is very common ... the spark in the HEI cap creates a lack of ozone which causes the parts to rust together. Strange but true. Check for this along with the other suggestions. If the ign rotor is not able to be turned at all, then it will be frozen...which can be fixed. Mark the dist position and pull it out of the engine. A hot rod shop should be able to spin it, set the curve, and free the mechanical advance if frozen. :flag

 

While diagnosing sounds without actually hearing them is far from the best way to do so, my best guess is the same as mbeenab's. The fact that they don't occur at lower temps is more evidence pointing to pre-ignition. What is the timing set at? What's the condition of the engine and it's tune?

 

Hey, thanks to all for the replys to this post. I'll follow your suggestions and check for pre-ignition problems. But I also have another problem that I stumbled onto after writing my original post. Took the car out for a short cruise and when the engine reached 200 degrees, and the knocking sound started, I let off the gas to slow down for a signal light and the oil pressure went to zero. As soon as I get on the gas the pressure rose to 40. I had just put some oil in the car a day before. My oil pump may be failing or I have a very serious leak along with transmission leak I have. I don't see any evidence of an engine oil leak when it is parked, only the transmission fluid.

I have a feeling that rebuild or a new crate motor is around the corner!

Thanks again guys.

 

to zero??? o.k. here's what you do. at the address bar, type in http://www.summitracing.com and get your credit card handy.
scared yet? well, i'm assuming you have rechecked and confirmed your oil level is good. is it possibly you have an incorrect dipstick causing you to underfill the sump but still think your o.k.? i would perform the same test again but this time shift the car into neutral when you are stopping. if the pressure drops to zero again, raise the RPMs and see if it comes back up at all. BTW, what RPM does the engine idle at? it may very well be time for a new oil pump which is actually not that bad a job with the engine still in the car.
then again, like the others have said about your pre-ignition problem, you have work ahead of you. depending on the mileage, you may want to start concidering an overhaul. first, i'd suggest using a carb and choke cleaner with the engine at high idle. these have a tendancy to blow out a lot of crap. then follow that by using a small bottle of water and pouring that slowly down the carburator air horn. just a trickle, stop if the engine begins to really fall off. this has somewhat of a steam cleaning affect and you can get BIG chunks of crap coming out if it's never been done before. this is something i do every year as part of my annual maintenance. if that doesn't work, you might need to switch to a cooler plug and/or a cooler t-stat. after that, heads gotta come off.