vettef6

Oil consumption 1quart/100 miles

Like the title says, my oil consumption is very high. The engine is a 397 with .040" over forged pistons and normal tension Perfect Circle rings. The engine has run about 500 miles up to now since it was rebuilt.

This is the third time I have taken off my intake because I thought it might come from a not so good sealing intake manifold gasket. The second time I changed gaskets I used some sealer around the ports and thought if it were leaking this would solve my problem. Looking at the gasket and sealer around the ports it isn't coming from the gasket as I see it.
What I have done so far prior to changing gaskets was:
Removed the PCV valve, so therefore no oil being pulled through the valve.
Checked CR, it's around 230 psi
No hoses connected to the TB
The heads were ported and put together from Lloyd Elliott with new valve guide seals etc.
Rocker studs mounted with sealant´

Looking at the picture below you can see oil on top of the closed intake valves. The left port is cyl.# 7, the right # 5 which is the worst. The amount of oil in port # 5 is about 2cm³ and # 7 should be about 1cm³. I really don't know how that much oil can gather on top of the valve dish in about 2-3 hrs of time before taking off the intake. The driver side bank is worse than the passenger side with cyl. #5 being the worst when looking at the spark plugs. Can't see how plug # 5 can fire at all, plug # 7 being a little better.

glntom

The picture makes me believe the oil is coming past intake gaskets from lifter valley. What intake gasket are you using? Have the heads been cut? Was the intake cut to match?
Are you using the rubber/cork gaskets at the front and rear of intake, if so toss them and try just silicone.

383vett

I'm just throwing this out there, but it might help you. Years ago, when I had a 383, I couldn't figure out why I was using so much oil. Like you, I had oil puddling on top of the intake valves. I had a fresh motor refreshened after only a thousand or two miles. Finally, I found that the dipstick I was using (an aftermarket driver's side stick) was mismarked and the oil level in the crank was too high. This along with the stroker crank allowed the crank to slosh too much oil onto the cylinder walls and overpower the oil rings. Got the sick recalibrated and all has been well.

vettef6

I'm using the off road GM gasket # 12367777 which I have been using for several years now. The heads have been milled but the LT4 intake hasn't. I checked the clearance and there is still enough clearance between the china wall and intake. As far as I know the LTx engines don't use rubber gaskets at the front or rear. Mind you, I'm not loosing any oil because of leakage, it's just being burned. The intake is soaked with oil.

I thought it could be the rings but my CR is real good.
I've been using this dipstick ever since I built the engine several years ago.

bill mcdonald

I installed AFR heads and was burning a qt in almost 100 miles.

I later pulled the heads and found the back of the valves were covered in what would appear to be carbon, but it was very hard to get off, not all black but yellow like clumpy material that needed a wire wheel to remove.

I pulled all valves. cleaned them, lapped them in, and replaced my valve seals.
I opened up my return for oil on the head by grinding the hole bigger and shaping it to aid in return oil flow. I smoothed it out after. I already removed casting flash from the block in the whole galley there, and smoothed it all out.

after doing all this, I still burned oil but not as bad. I lost a piston, removed the heads and they were actually clean this time compared to before. But the pieces of the piston were pushed up in the intake and put into the other cylinders and left in the super ram plenum.

My spark plugs never looked as bad as yours.

vettef6

My AFR heads were done first by AI 286/216 then from Lloyd Elliot 314/236. I've been using these same heads for quite a few years.

All my oil returns and the casting flash were done also quite a few years back. Never had such problems with oil consumption before. Now I'm using Ross pistons and Perfect Circle rings which make me wonder. But again, the compression test shows 230 psi.

cumbercr

The picture looks a lot like what happened to me. I was using about the same amount of oil and the back of the valves were covered in it. In my case it was oil from the lifter galley being sucked in through the intake ports. The intake gasket was slightly deformed from torqueing. I cured mine by reinstalling the manifold with a thin film of RTV around all the ports. I set the gaskets to the heads first. I installed the manifold with about 10 lbs of torque all around. I removed the manifold after 24 hours and applied RTV to the top of the gasket and reinstalled the manifold. This procedure assured that the gasket did not move during final torqueing.

vettef6

I might try that, even though I did use RTV the last time I installed my intake, see picture.
Since no one up to now said anything about piston rings, I'm inclined to think it must be the gasket.

hooked073

I have two thoughts, 1 with all the porting in the heads is it possible that you have hair line cracks along the guides. And the 2nd would be broken oil rings, it should not affect your compression infact if anything it will raise it just like doing a wet or dry reading.

bill mcdonald

I wish there was an easy way to find out of the bottom of the gasket is where it is leaking.

The last install I did, I put glue over the entire gasket, front and back.
Still burned oil.

All the years I have been here, the blame with AFR heads and burning oil has always been on the heads.

I remember one post where a guy said he added external drain lines to the bottom of the valve cover, that drained to the oil pan.

I had plugs that looked terrible before, on my truck 350 sbc. had a piston down, and it showed on a compression check. I would guess your rings are good with the numbers your turning.

Pete K

Compression tests show the ability to build quick pressure. The numbers are held in the gauge with a check valve. The compression test, in my opinion, is about worthless for diagnosing a bad ring seal.
I would do a leakdown test. Leakdown will tell you for certain.

vettef6

Pete, can you explain the procedure of a leak down test??

Another thing I don't understand is how can bad rings bring so much oil on top of the intake valve dish??

Pete K

A leakdown tester screws into the spark plug hole, and hooks to an air compressor. 100 lbs of pressure is placed in the cylinder, and the attached gauge shows how much air it is holding. The difference between the cylinder pressure and the air pressure applied is the percentage of leakdown. This test will confirm or deny ring seal as a problem. It will also tell you if the valves are leaking, head gasket etc.

cv67

Bet money its the intake gasket though...Get that pcv back in and working too.

vettef6

Pete thanks for the quick reply.
In what time span and which percentage is allowed??

Pete K

Leakdown will be in real time.
IMHO a street engine is 8-15 percent or so is common.
Over 20% is bad.
You always read about 3-5% or so as being a benchmark, but most real street builds are higher.
On a fresh, well sealed motor, I would expect somewhere between 5 and 10%

Real handy test though, as the air has to go somewhere. If you hear it in the intake or exhaust, you can assume leaky valves. Bubbly coolant points to a head gasket, and hissing in the valvecovers means it is blowing past the rings, into the crankcase.

ex-x-fire

Try & find thicker intake gaskets, that should help.
Some of these aftermarket heads w/ screw in rocker stud, they go right through the ceiling of the intake ports. Seal those studs good. That was one of my problems that caused oil consumption.

cv67

Good catch.....

If it were the rings Id imagine youd have noticeable smoke coming out the exhaust at some point (lotsa smoke coming out the valve cover too). Leakdown does tell a lot though for sure.

mike100

It's probably the rings. I once tried out some plasma moly rings with the wrong bore finish. It was recommended to use a rough hone and I used a fine one. It took about a 1000 miles to break those damn things in and it still used a little oil. Once that engine spun a bearing due to 8k rpm issues, the next refresh went back to conventional moly rings-problem solved.

What I ended up doing was beating the engine like a red-headed step child by revving it to 7500 rpm in second gear about 10 times in a row. This was done in accel and rev-down to load the rings both ways. I didn't exactly wait for it to warm up all the way either. It stopped smoking after I did that a few times.

mtwoolford

on the underside of your intake manifold are four pipe plugs that close off passages that were necessary during the machining of the manifold. If memory serves me right, you may have to remove the tin heat / oil splash shield on the bottom of the manifold to access these plugs. I suggest taking each out (on my lt4 they weren't very tight); apply sealant, and reinstall. costs nothing and may help.