questions about valve seals

[iamseth]

I think mine need to be changed. I installed new spark plugs a few months ago to help settle a rough idle, and it worked! However, slowly the rough idle came back and when I inspected the spark plus last weekend all but 3 (4,6 & 8) had a some build up and were pretty black on the inside.

So, my question is this; Would changing the valve seals fix this? And if so, should I attempt it myself? This would be something I've never done before.

oh yeah- it's a 1972 C-10 400 bigblk.

thanks!

[JimKshortstep4x4]

The build up on the plugs could be a rich mixture problem. I would check out the carb and make sure that it is not causing the problem before changing the valve seals.

Jim

[swamp rat]

You don't mention if you have a stock engine or not but assuming you have stock engine and stock guides its pretty common for the valve guides to wear a little and the stock seals are not the best to say the least..The oil tends to seep thru them and foul the rear plugs due to the fact that the engine is lower in the rear.

[iamseth]

yes, it's the stock engine. Would this be a DIY project if adjusting the carb is not the remedy?

[rsavage]

It would depend on your mechanical ability. On an engine that is not worn and does not have any worn or burned valve seats, you could do them with the heads on the engine. You would need a fitting to screw in the sparkplug hole, a compressor that will hold about 160 psi, and a pry bar type valve spring compressor. Obviously, all rocker arms have to be loosened so all valves are closed. Air pressure holds valve up against spring pressure so you can remove the two little wedge keeps, the retainer and the spring off the valve stem. The stock oil seal is a little o-ring that sits in the second groove down from the top on the valve stem. You do one at a time. You can buy "umbrella type " seals for about $16 which is what I would suggest. These slide down on the valve stem right to the head. Quite likely, the engine and heads are going to have enough wear that this "heads on" method won't work. I have never had it work successfully on an older motor with some miles. Best way is to pull the heads. You will need to drain coolant pull the intake, exhaust, distributor, alternator brackets etc. Keep the rocker arms and push rods in order for each cylinder so they go back in the same spot on reassembly. With the heads off, buy a decent adjustable clamp type spring compressor. If you have the heads off, you might want to take them in to a machine shop to see what kind of work they might need on any seats or guides. You will need an upper gasket set for the motor (head gaskets, intake, exhaust, etc) and still use the umbrella seals which are extra. You need a torque wrench for the head bolts. Everything, including all the bolts, has to be cleaned up prior to reassembly. All the rtv has to be cleaned off the threads so that they will torque correctly. It's a fairly big job. In either scenario, you will need to adust the lifter/rocker arms when done, and in the case of heads off, re time the distributor. Get some help from someone who is experienced if you can. It's good to have an extra set of hands. Oh, and a lot easier if you take the hood and hinges off just for working access. Good luck.

[Huck]

With the engine idleing at normal operating temp---hold a piece of white cardboard or heavy paper right up against the exhaust pipe--. If you are getting black drops---more then likely your carb is running too rich. Plugs will foul pretty fast with too rich a mixture. Setting the idle adjustment screws ONLY change the mixture at idle. My bet is that your carb need cleaning and adjustment---choke partially closed could also drive you nuts. The brand new edelbrock carbs out of the box are known for running too rich. Sometimes you need to change the mixture rods and jets to get them right.
Changing valve seals will not cure oil usage if the guides are warn. They are designed to keep the valve stems and guides clean more so then to prevent any oil going down the stems. How many miles one engine? What carb are you using. Are you using a lot of oil---a quart or so in a 1,000 miles?
Go for the carb fix first as it can be a whole lot easier and cheaper.

[redbaron69]

lots of good info posted above. if the valve seals are bad you should see a puff of smoke when you start the engine when its warm. this is from the oil leaking past the bad seals, and being burnt off at start up.

[iamseth]

It's the Rochester Quad Jet carb. This sounds like a good starting point. Thanks for the input!

[iamseth]

So, I held up a piece of paper to the tail pipe and got a bunch of black specs. Looks like i should tackle the carb first....

[swamp rat]

I would say absolutly, especially if its not plugs 7 and 8 that are fouled, why not go ahead and get the carb set right before chasing anything else.. Hard to be totally accurate on a forum but i do think your running a but rich.

[iamseth]

Will the exhaust stop spitting black once the carb is set right? How will I know when it's set right? You (swamp rat) left a pretty detailed reply about adjusting the carb on one of my other posts. I'll refer to that before i start. Thanks for all the great info!