340 Oil Burning Question

[HawkRod]

We discovered an issue with my Son's 1973 Roadrunner :sad10:. Some specs:

• 340; 727 Slap Stik; 3.55 Sure Grip; Original A/C
• Engine Modifications: Edelbrock Performer 318/360 dual plane manifold; Crane Cam; 10.0:1 compression; stock crank, but balanced differently than original (on flex plate); “medium” ported original heads; larger 2.02 / 1.60 valves; headers; 2 ½” exhaust, 8qt oil pan.
• Cam Specs: Lift Intake = 454; Lift Exhaust = 480; Rocker ratio 1.5; Intake duration = 272, Exhaust duration = 284.

The engine has 12,000 miles on the rebuild. About 10,000 miles were since 1992 until about 6 months ago, then I gave it to my son and he has been driving it more regularly.
The problem is it suddenly burned through almost the entire crankcase of oil. One suspicion was the PCV, so we temporarily plugged the line and "think" it was OK. We then replaced the PCV and I drove it on the highway about 250 miles. It burned through 4 quarts of oil. The car generally runs OK.

Can the PCV really do this? Of course, I am worried about the oil rings and/or compression rings. I still need to pull the plugs this weekend and do a compression check, but suggestions and things to check (and potential theories) would be greatly appreciated.

Thanks in advance,

Hawk

 

[70rr-brian]

Is there a baffle in the valve cover hole the PCV is connecting to? Even if there wasn't I would find it hard to believe it is getting sucked out at that kind of rate. I would think it would be smoking like a mfer if it is burning that fast. But if the rings were shot it would be smoking good too.

Run a compression test. Do it normally the 1st go around and record the numbers for each cylinder. Then go back and do them again after misting oil into the cyclinders through the plug holes (One at a time and do it right before rerunning the test) and see if the numbers improve. If they do....it is your rings that are shot.

 

[HawkRod]

Is there a baffle in the valve cover hole the PCV is connecting to? Even if there wasn't I would find it hard to believe it is getting sucked out at that kind of rate. I would think it would be smoking like a mfer if it is burning that fast. But if the rings were shot it would be smoking good too.

Run a compression test. Do it normally the 1st go around and record the numbers for each cylinder. Then go back and do them again after misting oil into the cyclinders through the plug holes (One at a time and do it right before rerunning the test) and see if the numbers improve. If they do....it is your rings that are shot.

Brian,

Thanks for the feedback. The car does have aftermarket valve covers, and I did add a home made baffle. Of course now I am thinking (perhaps hoping ;-) that that baffle could potentially contribute to the problem as well. It is very close to the opening, so could oil be laying on top and then getting sucked through? I think at this point it would be good to put the original valve covers back on just to eliminate anything stupid.

I'll see what the compression test this weekend tells me and see if that gives me any insight. Thanks for the reminder about misting the cylinders with oil. I had forgotten about doing that...

 

[HawkRod]

Update

Did a compression test this weekend and all the cylinders registered between 170 - 190 PSI without oil and with the engine cold. Unless I am mistaken, these numbers seem pretty good.

We also did a leak down test on a couple of cylinders whose plugs looked worse than others. They were solid as a rock, with no leakage we could hear or detect (my gauge has a one way bleeder valve, so we couldn't use the gauge).

The plugs looked horrible. Some were worse than others, and it made them hard to read. Some seemed to indicate the timing was good others not. Some were black, others were more tan. Since they had been in there awhile, we installed a new set of Autolite 65s into the car, and I'll see what they look like in a week or two.

We replaced the aftermarket valve covers with the original Plymouth valve covers and they seem to fit much better. This should take care of the valve cover oil leak and should rule out any issues with the PCV baffle.

I am now feeling more hopeful that we won't need to tear into the engine...

Hawk

 

[70rr-brian]

Yeah those are decent numbers. Hopefully the valve covers will do the trick.

 

[pistol_grip_polara]

Have you found out the issue yet? I had a 360 in a 68 barracuda that ran amazingly well and I put it in my polara 2 yrs later, and it burns through oil like crazy, smokes like a b*tch as well. I had another 360 that was bored .040 and some X-heads I was rebuilding and just put that in the polara (was going to anyways just wanted to get it goin real quick) My spark plugs all looked good and couldnt find anything majorly wrong. messed around with the pcv but didnt help any. I didnt do a compression test just chaulked it up to a broken ring and pulled it out. Figured I would rebuild it anyways before it goes in my wifes '56 stepside dodge. But if theres something else I overlooked, other then the comp test, that might help...

 

[451Mopar]

Check for leaks, spark plugs should be really oily if using that much oil?
Compression test, or better, a leakdown test. If compression/leakdown check good, lower intake port may not be sealing and sucking oil into the mainfold. Also check valve guide wear and seals?

 

[HawkRod]

Update #2

Thanks for the replies.

We are still in a "holding pattern" and checking for oil usage. At first glance the car seems to be better, but we have also done some other work on it.

It had a 750 Holley, which was really too much carb for the engine. Yes, it can be made to work, and so we started poking around with it because the car was running very rich. Long story short, it has some kind of leak in the secondaries. I pulled it to rebuild it and replaced it with an Edelbrock 600 cfm carb. The car now runs much better and is not running as rich.

So the bottom line is the car now runs great, is reliable and doesn't smoke at all. We need to continue to monitor oil usage, but the car isn't driven very far and seldom at highway speeds where the oil usage really appeared to be an issue.

I remain hopeful...

Thanks again for all the replies. :headbang:

Hawk

 

[green1]

Valve seals or intake; on intake, what is vacuum? erractic?

 

[HawkRod]

Valve seals or intake; on intake, what is vacuum? erractic?

I just remeasured the vacuum with the new carb to ensure that I could give you accurate numbers:

The vacuum is pretty steady; between 14.5 to 15". The needle certainly does bounce between those two values, but that seems to be a small enough difference to NOT be called erratic.

It has a Crane cam with 454 intake lift and 480 exhaust lift; 272 intake duration and 284 duration. I would expect vacuum [FONT=&quot][/FONT]would not be 20" with this cam, but please let me know if anyone feels this vacuum reading seem too low.

Thanks,

Hawk

 

[green1]

Check for oil out exhaust after letting of gas=valve seals. Oily plugs(not the ceramic, the end threads- intake valve seals or rings.

 

[HawkRod]

Good News Update!

Just an update on this issue:

First the bad news: The valve cover changes did NOT help the problem.

The Good News: However, one of the other suspects was the intake manifold (Aluminum Edelbrock dual plane Performer). We decided to pull the intake manifold and replace the gaskets. Lo and behold, when we took off the intake, there was OBVIOUS intake gasket failure and even mis-alignment. (Sorry, I wasn't smart enough to remember to take pictures of it as the manifold came off.)

My son and I carefully installed new gaskets and let the car sit for over 24 hours to "cure".

The final proof is that we just drove the car over 250 miles, and had next to ZERO oil usage. This included driving the car around Pocono Raceway as part of the Bertil Roos driving course this past Thursday and Friday. My son was drivin' her hard around the corners and straights, and it performed perfectly!

Once again, thank you to all the folks on this forum who reply with helpful advice, suggestions, etc. It is really helpful and MOST APPRECIATED!

Hawk