brown7373

Tried this on the Small Block Forum. Got 81 views and no replies, so I'll try it here.


I was in a terrible traffic jam trying to enter the Daytona Speedway last month, and idled for almost 2 hours. The engine started running rough at idle, but seemed fine once off idle, and ran perfectly on the 125 mile drive home. The temperature never exceeded 190 degrees. When I got home, I pulled the drivers side plugs because I know number 3 gets oily. The other 3 were dry and slightly tan, but 3 was oil covered and crispy oil and hard black crud was down in the plug around the electrode, but the gap was open and fine. A new plug improved but it still is a little rough.


Does this sound like a bad valve seal? I have not as yet done a leak down or compression check and would do that before I tear into it. The oil issue has been on going, but the engine has run perfectly for the past few years and 10K on these plugs.


Any "magic additive" to clean a possible fouled valve?

D. Yaros

Sounds like a bad ring to me?

brown7373

I was thinking either ring or valve seal, but do you think it is likely that only one cylinder would have a ring failure, or a broken ring, when the other cylinders are bone dry and nice light tan in color. I guess you could ask the same thing of valve seals...would just one fail.

droldsmorland

Before you do anything run a legit compression and 3 position leakdown test. This will pinpoint the problem rather than guessing and tossing parts at it. If both the above tests pass then it's likely valve seals. They can be done with engine in the car, heads on the block.
Be sure everything fuel and ignition related is functioning properly
Mileage on engine? Ever been rebuilt? Original seals? How much oil does it use between changes?

redoldsman

What kind of ignition are you running?

brown7373

Pertronix Ignition. Not sure of the mileage, but it has turned over twice, so 200K+. I don't know if the seals are original. I have owned the car for almost 10 years and other than a Q-jet rebuild and a new balancer and timing chain, and plug and wire changes, nothing has been done to the engine. It uses maybe a quart of oil between 3000 mile changes, and has always run perfectly and can and is driven all over Florida with never a breakdown. Starts on the first twist of the key, and still does, but runs rough at idle(slow).

Octania

Pour a can of Sea Foam into the tank/ carb and see if it helps.

Can't hurt, except for the cost of the attempt.

oldcutlass

This is the best direction, pinpoint the problem and go from there.

brown7373

I bought some Rislone to try in the oil to see if it might help a cartboned up valve. I have had the oil on the plug since I bought the car in 2006. Other than changing plugs at 10K instead on 12K, it hasn't been a problem. All the other plugs are dry and tan. The engine never smokes and has run great, and I have put nearly 60K on it in almost 10 years. It is a nice driver, not a show car, that gets driven regularly, and isn't going to get an engine rebuild or other extensive work unless and until it is needed.

droldsmorland

Likely a valve seal. Cheap to fix especially if you DIY. Not so sure the snake oil will help do anything other than lighten your wallet.

brown7373

I am not sold on any snake oil either, but Rislone and Marvel Mystery Oil has been around forever, and some people swear by it. I have no illusions that it will repair a bad seal or broken ring, but if I developed crud on a valve, maybe it will help.


Any suggestions on which valve seal to use?

oldcutlass

The Felpro valve stem seals are inexpensive. When I went to change mine in the 330 as I pressurized the cylinders I found a blown head gasket which lead to a full blown valve job.

brown7373

I'll get some seals and hope that fixes it. Thanks

Sugar Bear

Worn/cracked valve seals would very likely cause a problem on more than one cylinder. The mentioned leakdown tests are the way to go.

If compression is low or ring leakage is found you could try a solvent directly into that cylinder for a day or more, blow the solvent out, reinstall a fresh plug, then take the the car for a ride accelerating at full throttle up to about fifty MPH and then coasting down to about about twenty MPH. Repeat the accel/decel process about ten times. This is how new rings used to be seated/broken-in and may work them back forth enough to free up a clogged oil scraper or stuck rings.

It could also be a leaky intake gasket sucking in oil to that cylinder from the bottom of the intake. Thoughts or comments on the leaking intake theory anyone?

gs72

I agree with either rings or intake gasket. Valve seals will show themselves when you start the engine after a hot soak, you will see a puff of blue smoke upon starting it. This is due to the hot oil running down the valve guide and into the cylinder as it sits. To check the intake gaskets, pull the pcv valve out of the valve cover and the breather from the other side. Plug both holes (with the engine running) in the valve covers with your thumbs and see if any vacuum builds in the crankcase. If the gaskets are good the crankcase will build pressure instead of vacuum.

brown7373

Thanks for the additional suggestions. I hope to be able to dig a little deeper today.

Sugar Bear

"To check the intake gaskets, pull the pcv valve out of the valve cover and the breather from the other side. Plug both holes (with the engine running) in the valve covers with your thumbs and see if any vacuum builds in the crankcase. If the gaskets are good the crankcase will build pressure instead of vacuum."

Nice, I like it...learned something today!