[John F63]

Looking to see if I am on the right track. I have a '70 GTO with a RAIII motor that runs very well. At idle you can see a very small amount t of smoke, which is not visible while driving. However, after the car sits for a bit I get a big cloud of smoke on startup.

My first thought was valve seals but the slight smoking at idle was still concerning. So, I got out my trusty 1980 Sears Compression tester and got these results, rounded to the nearest 5psi marker:

1. 155
2. 150
3. 180
4. 175
5. 150
6. 145
7. 150
8. 155


The least is only about 80 percent of the highest, so those numbers are not ideal, but is the low cylinder low enough to burn oil?

I have owned the car for a couple years and know nothing about the engine history or internals.

At this point I think valve seals are still a safe bet, especially since I am on a budget. All opinions are welcome!

John

[i82much]

"after the car sits for a bit I get a big cloud of smoke on startup."

Easy fix - drive it more often!

[geeteeohguy]

You need to follow up with a cylinder leakdown test to verify the condition of the rings. Then you'll know for sure. You have more variation between cylinders than is preferred. That could be due to wear or carbon build up or both.

Puff on start up is valve seals/guides. Oil smoke out of the valve cover breathers on acceleration is piston blow by. Do a leakdown test.

[25stevem]

Blueish white puffing at idle once the the oil temp starts to chase the water temp, or after 15 minutes or drive time is a clear indicator of dried up and busted valve stem O-ring seals, if not worn valve stems and guides also .

When you have blow by passed the rings that is seen coming out the breather tube if you have a stock 1970 set up and or the oil filled cap.

As posted a leak down test will confirm what percentage of leakage you have, and those cylinders you have testing out below 160 are a sure bet for 20% leakage!

If you pull your intake manifold and look down into the runners I will bet you will see some burnt oil piled up on the back side of the intake valves, indicating bad valves seals in the least.

I have seen plenty of motors that leak down tested bad when taken apart had near perfect cylinder walls, but the motor had been overheated once or twice and the two compression rings had lost there tension.
Just think of how well your motor would run with all cylinders at checking in at 175!

[Schurkey]

Originally Posted by John F63

At idle you can see a very small amount t of smoke, which is not visible while driving.

Verify PCV system--not drawing oil mist into PCV hose via ineffective or missing baffles.

Check for excessive blow-by.

Originally Posted by John F63

However, after the car sits for a bit I get a big cloud of smoke on startup.

Likely valve stem seals/worn valve guides

Originally Posted by John F63

I got out my trusty 1980 Sears Compression tester and got these results,

3. 180

6. 145

The least is only about 80 percent of the highest, so those numbers are not ideal, but is the low cylinder low enough to burn oil?

Low compression does not "have" to result in oil burning.

Oil burning might result in "high" cranking compression test results, due to excess carbon build-up.

I would run the engine at 2000+ rpm, and drizzle a urine-stream of water alternating between the two primary venturis. When it's me, I use about a gallon of water, other folks probably use less. The water steam-cleans the cylinders. Does a wonderful job, and costs almost nothing besides your labor. Doesn't create clouds of smoke like petro-chemical carbon cleaners, so the neighbors don't call the fire-department.

Change oil when you're done. There'll be excess moisture in the crankcase, contaminating the oil.

When you're done, perform the cranking compression test again. See if they're more even.

You could also squirt about two ounces of GM Top Engine Cleaner (TEC) into each cylinder of a fully-warmed-up engine via the spark-plug hole. With the plugs screwed in loosely, turn the crank by hand (so you don't push the TEC out the plug hole) to distribute the solvent. Let the engine soak overnight. Sometimes that can free-up sticking rings. When you re-start the engine, it will smoke terribly until the TEC residue is gone.

[mgarblik]

I like to combine what Schurkey has suggested. I would also de-carbonize the engine and repeat your compression test. I combine a full bottle of GM top Engine cleaner, Techron, or Sea Foam with an equal amount of water in a coffee can. Stir the mixture. Get the engine nice and warm and hold the throttle at 2500 rpm's or so. Attach a small vacuum hose to the little fitting on the front of the intake where the hose from the air cleaner usually attaches. then with the rpm's up dip the hose in the can and draw the mixture through the engine. DO NOT let the engine stall. It will smoke like hell but hopefully won't bring any fire department out. The whole thing takes 10 minutes or so. Then I run a 1/2 can of just water through it the same way. change oil and re-check your compression.
i also agree valve seals are almost certainly shot. They were not great when new. Much better seals are available now. Good luck.

[Schurkey]

Originally Posted by mgarblik

...Attach a small vacuum hose to the little fitting on the front of the intake where the hose from the air cleaner usually attaches...

Unless that vacuum nipple supplies both planes of a dual-plane manifold, only four cylinders are getting "treatment".

Might work OK on a single-plane manifold, though.

That's why I pour directly down the two primary venturis. Nicely atomized, and distributed as evenly as practical.

[John F63]

Thanks so much for the advice and suggestions offered so far!

[Tom Vaught]

Originally Posted by Schurkey

Unless that vacuum nipple supplies both planes of a dual-plane manifold, only four cylinders are getting "treatment".

Might work OK on a single-plane manifold, though.

That's why I pour directly down the two primary venturis. Nicely atomized, and distributed as evenly as practical.

Because the engine is a 400 cid engine it will have a fitting for the PCV at the front of the engine. This fitting is designed to get signal from BOTH PLANES of the intake manifold and then to the PCV valve.

In this case the treatment will go to all 8 cylinders and will do its job properly.

So you will be fine with Mikes suggestion.

Tom V.

[Schurkey]

Originally Posted by Tom Vaught

Because the engine is a 400 cid engine it will have a fitting for the PCV at the front of the engine. This fitting is designed to get signal from BOTH PLANES of the intake manifold and then to the PCV valve.

In this case the treatment will go to all 8 cylinders and will do its job properly.

So you will be fine with Mikes suggestion.

Tom V.

Yup, Pontiacs often have a vacuum fitting that connects to both planes of the dual-plane manifold, for use with a PCV system.

HOWEVER, that hose would be 3/8", not "little"; and it wouldn't go "to the air cleaner" as described by Mike. It would go--of course--to the PCV valve.

Originally Posted by mgarblik

...Attach a small vacuum hose to the little fitting on the front of the intake where the hose from the air cleaner usually attaches...

What Mike describes is likely a vacuum nipple intended to supply the thermal sensor in the air cleaner, and then supply the vacuum motor on the snorkel of the air cleaner for the heated air intake. And I'm pretty sure--but not positive--that that nipple connects to only one plane of a dual-plane manifold.

So...I drizzle down the carb primaries directly.

[Tom Vaught]

There is a nipple on the carb throttle front base that feeds upper and lower engine vacuum to the distributor vacuum can. But whatever works for the OP will be fine.

Tom V.

[78w72]

when i used to work at a GM dealership as a teenager, the mechanics would throw away cans of the TEC that were 1/4-1/2 full, i would always grab them to use on my t/a with a higher mile 455. watching them use it & reading the instructions on the can, they would always just spray it right into the carb or throttle bodies while holding about 2000rpms, then at the end they would drop the idle a bit & let the engine die from the spray. let it sit for 20-30 minutes then start it up & rev it up or go for a drive under hard acceleration blowing smoke out the exhaust. i noticed or had a perception of running & idling better when i used it but never did a compression test.

same basic instructions for using seafoam this way & have heard of using water too. if its the right vac hose it will feed all cylinders, some use the brake booster line that connects to the tree on the lower back of the carb.

[geeteeohguy]

All of this is well and fine, but the OP first needs to do a simple leak down test.

[mgarblik]

Originally Posted by geeteeohguy

All of this is well and fine, but the OP first needs to do a simple leak down test.

Honestly, I would decarbonize it first, then do the cylinder leakage test. But either way would work. The fitting I described would be the thermac supply and as Shurkey described, IS NOT ideal. Sorry. I was just thinking of the easiest way to get the caustic mix in there. Dribbling the mix through the carb is great but scares the hell out of some people. If using the PCV fitting, you would absolutely need reducers to get the hole size down to 3/32" or so. Do not put a 3/8" hose into the mixture in a coffee can. It will stall the engine and could hydraulic it. You just want a small amount going through at a time.

[Ram Air IV Jack]

Originally Posted by mgarblik

I like to combine what Schurkey has suggested. I would also de-carbonize the engine and repeat your compression test. I combine a full bottle of GM top Engine cleaner, Techron, or Sea Foam with an equal amount of water in a coffee can. Stir the mixture. Get the engine nice and warm and hold the throttle at 2500 rpm's or so. Attach a small vacuum hose to the little fitting on the front of the intake where the hose from the air cleaner usually attaches. then with the rpm's up dip the hose in the can and draw the mixture through the engine. DO NOT let the engine stall. It will smoke like hell but hopefully won't bring any fire department out. The whole thing takes 10 minutes or so. Then I run a 1/2 can of just water through it the same way. change oil and re-check your compression.
i also agree valve seals are almost certainly shot. They were not great when new. Much better seals are available now. Good luck.

Back in HS auto shop our instructor did this very thing. He said water would steam clean the inside of the engine and tried it on a carboned-up engine. He said the exhaust spit out black bits of carbon and soot and ran much better afterwards. Seafoam does this same thing as well.

[Dragncar]

Remember Edelbrocks old Water Injection ? I bought one and never used it.
It had a water tank, pump, controller and spray bar on top of the carb.
Same thing.

[PunchT37]

Originally Posted by Dragncar

Remember Edelbrocks old Water Injection ? I bought one and never used it.
It had a water tank, pump, controller and spray bar on top of the carb.
Same thing.

Had one of those. I used to put alcohol in it. Running a 455 with a single pattern cam, with 62 heads. Pinging machine.

[78w72]

a few places have made or still make water/meth injection systems. snow performance is a popular one for the old draw through style turbo engines, helps when running higher than factory boost psi.

[Schurkey]

Originally Posted by Dragncar

Remember Edelbrocks old Water Injection ? I bought one and never used it.
It had a water tank, pump, controller and spray bar on top of the carb.
Same thing.

I built my own. Windshield washer pump and reservoir, vacuum hose, windshield washer spray bars.

Dumped so much water in the carb that the engine bogged. I wasn't much of an engineer at 20.