Smoking at idle
 

I have a 428 that I recently rebuilt that smokes at idle once the engine warms up. When you 1st start the engine, it doesn't smoke at all. The engine starts very easy and the throttle is very responsive with no flat spots at first. Once it gets up to operating temperature, it starts smoking at idle and there is a noticeable flat spot when you hit the throttle.

A few things about my engine:

.030 428, TRW pistons, Speed Pro moly rings, hyd roller cam (224 230 .502 .510 112), Lunati HR lifters, 16 heads with positive viton seals (about .040 seal to retainer clearance), Edelbrock RPM intake (can't remember if I used Fel Pro or Victor/ROL intake gaskets), stock valley pan with PCV at the front of the pan running to carb at baseplate. Both valve covers have breathers in them. The PCV valve and hose does have some oil in it. I can run without the PCV valve and it still smokes. There is no smoke or oil coming out of the breathers in the valve covers. I can take the breathers completely out and there is no smoke or blow by coming out of the valve cover.

What could cause this thing to act like it does? I am running out of ideas.

Thanks

What is the clearance on the valve guides?

Whenever I have worked on motors with this issue it was always due to the valve seals.

Everything is fine and dandy until the oil warms up enough to drip down passed the seal and down the stem.

In fact I did a set of heads a few years ago and assembled them with new what I thought where the correct seals for 11/32” stems, and it turned out they where for 3/8” stems.

I would get a known correct 11/32” seal even it it’s used and then remove one spring , pull the seal and compare the friction you feel on the stem.

Thanks for the replies. I am running Ferrea stainless valves and the clearance was in the .0017 range. It sounds like I may need to take a look at the seals.

Agree valve seals are the most likely cause. There are others, but I would start there. .040" clearance between the retainer and top of valve seal is a little tight, depending on the style of seal. The Viton seals I use have a garter spring around the OD of the seal and a metal jacket below. They work fantastic and are very compact. But .060" the bare minimum clearance I run because the garter spring can be knocked off by the inner spring or retainer if too tight in there. Do you have a pic or better description of what the seals look like and the spring package?. Did this situation start right after the engine build or after miles or years of use?

A secondary cause could be small amounts of oil could be getting in the intake track from a gasket leak. Idle is when vacuum would be the highest and the most likely to have oil getting into the combustion chamber.

You can probably tell which cylinder by looking at spark plug condition.... .... .040 isn't much clearance if you only checked one, ..... another unchecked cylinder could be much tighter and damaged, .... .one time i had replacement guides that were smooth and some seals slid off, ...... ... any time i had bad valve seals it smoked a lot on start up

Thanks for the replies. This situation started right after the engine build. I attached a picture of the type of seal that was used. The valve springs are Lunati dual springs and the retainers are Comp. I checked each retainer to seal clearance and all were in the .040 range at full lift. Some were slightly more but none measured less. The guides had all been replaced with a .500 press in cast iron guide, which was done before I bought the heads. I will double check to see if any of the seals have slid off. Also a good thought on the intake gasket. I don't recall any issues bolting the intake up but I may try another intake/gasket just to rule that out. I will say that it doesn't smoke at all on cold startup, only when the engine is up to operating temperature. That is also when my off idle flat spot shows up. On warm startup, it smokes.

Did you assemble the heads, if so did the seals just slide onto the tops of the guides or did you need to use a installation tool / or a small deep socket?

A off idle flat spot when warm is a separate issue.

I did assemble the heads myself. I didn't use an installation tool or socket to install them. I wouldn't say that they just slid on but I installed them with just strong finger pressure on them. The fit seemed as tight as many others that I have put together this way with no issues.

Another source is a bad vac. modulator on the trans, easy to take line off at carb to evaluate.... .. those valve seals you used are not the best for staying put, do you have a pick of your heads and guide tops before assy. ?? the seals with a metal shell are better

I did have a pick, now I am second guessing that pick, though. Good idea on the modulator but this one is a 4 speed. I do wish it would be something easy that I am not thinking of.

Sure sounds like its sucking oil past the guides. Its possible to cut the seals on the valve lock recesses on the valves. When I've done vitons, I use a large soda straw over the valvestem to prevent seal cutting. I also use a little tool that goes over the valve and drives the seal down.

I also use the style of seal that has the metal shell and not the garter as shown.

You did the exhaust valves too right? right?

These are the only type of positive seals I use.

You will need a installation tool or 1/4” drive deep socket of the needed OD to get these on.

Be sure to use the included clear plastic stem guide and lube up this stem guide and the guide itself to end up with a good installation.

Them valve seals can be easily damaged while passing the valve tip, without the "plastic protector" to smooth the process.

The basic valve seal problem is the seal being off the guide & riding the stem.

The seals Steve 25 shows in his pic is the only style I have been using for about 10 years now. They stay tight on the guide, are low friction on the stem and have a small OD that won't snag the inner spring. That's not to say there is anything wrong with the Viton seals the OP used. The smoking only when hot is the tricky thing to answer. Is the engine actually using some oil you can read on the dipstick?

I did install the same style of seal on both the intake and exhaust. I would be surprised if I have put 1,000 miles on the engine. It is just off the full line on the dipstick. So it has used a small amount.