Intake sucking oil ???? C-1

[Al R.]

Short of pulling heads or intake and looking at the backside of the intake valves, is there a way of detecting if the intake is not properly aligned with the heads and allowing oil to be sucked into the combustion chambers. I have excessive oil usage on a recently rebuilt 283 (approx. 225-250 miles on it) and am trying to rule out all possibilities. This has been suggested as 1 possibility, especially if the heads had been milled for straightness several times (know of at least 1 time, not sure if it was done previously thru the years). A compression check revealed 6 cylinders with 160 PSI, 1 with 165, and 1 with 145 and a leak of the intake valve on the low cylinder. Help will be coming over on Sun to do a cold and hot leak down test, and I just want to cover all the possibilities while I've got the help

[Richard M.]

Re: Intake sucking oil ???? C-1

I'd look at other more easily observable clues first. Is this a solid or hydraulic lifter engine? What are the conditions of each spark plug? Do any give a clue of black oily deposits?

The leakdown test could give you a better idea of the issue.

I'd back off the rockers on that low reading cylinder and recheck compression.

Rich

[Al R.]

Re: Intake sucking oil ???? C-1

Rich, they are solids. There is a gap of .014 and .020 cold on the int and exh valves, so a partially open valve is not an issue here, most likely a poor job of re-working the heads. Yes, there is an oily deposit on the plugs, but not heavy. Machine shop owner keeps saying the rings may not be fully seated yet, drive it for a total of about 500 miles and if still doing it, he'll look at it. I'm tired of the BS from him and am trying to come up with the problem and simple solution, if there is one. If not, it's court time.

[Michael H.]

Re: Intake sucking oil ???? C-1

Machine shop owner keeps saying the rings may not be fully seated yet, drive it for a total of about 500 miles and if still doing it, he'll look at it. I'm tired of the BS from him and am trying to come up with the problem and simple solution, if there is one. If not, it's court time.

Al

It amazes me that some engine builders are still trying to hide behind the "it ain't broke in yet" story. With properly prepared cylinders and today's rings, there is no such thing as lengthy break in. A few minutes of running and rings are as broken in as they will ever be.

[Richard M.]

Re: Intake sucking oil ???? C-1

Al, What exactly is "excessive" oil usage. Are you seeing it in the exhaust AND on the dipstick?

I've been troubleshooting a 283/270hp myself for the last month, re-built twice due to combustion gasses in the coolant. In the process of teardown the first time, cylinders 1,3,2,4, were very oily and plugs were fouled. I'm still uncertain why it is that way again.......on the 2nd go around. I pulled plugs and those four are still more dark than I'd expect them to be.

Rich
edit....p.s. totally agree with Michael. I'm still not out of the woods with my 2nd rebuild.

#2 Sparker & #2,#4 cylinders
PA030002.jpg PA060075.jpg

[Edward J.]

Re: Intake sucking oil ???? C-1

Al, if you pull the intake off you can see the intake valve stems to see if oil is running down the guides, this is the best way to tell if you have a guide or seal problem. machinist are not always perfect. In my 40+ years in the automotive repair business I have had some problems. Its generally from overlooking a problem, more so with cylinder heads guide issues. If nothing is found, next step would be to pull the head off on the side that has the deposits on the plug and look at the piston, If its using oil, The piston will be wet around the outter edges if piston( pistons will appear to be washed), that is a dead ringer for a problem. Good luck. I do agree with Mike todays piston rings only need a few hundred miles to seat. and even at that I think that a new engine it may not even use qt. of oil in a thousand, if the cylinder walls are prepped correctly. Another area to look maybe the intake belly they have had some problems cracking and drawing oil into the cylinders. And the mating of the intake and cylinder head. sometimes the engine cylinder head surfaces can be machined to much and cause a problem with the take ports will be peeking into the engine block.

[Al R.]

Re: Intake sucking oil ???? C-1

A cold leak down test had the following results 1) 39% 3) 39% 5) 42% 7) 47% 2) 46% 4) 40% 6) 46% 8) 45% The # 3 plug has the heaviest oil deposit on it , caking up kindly heavy in only 225 miles, approx. #4 & # 6 plugs also have heavy oil build-up, other plugs do have oil residue on them. As far as oil usage, it used about 3 qts to 4 qts in this 225 mile break-in period. There is no oil leakage underneath the car from anywhere about the engine. I do have a question, This is a 290 FI engine that I using an intake off a 66 327 on. The oil filler tube cap is the breathable one like is used on the carb engine. Is this OK or should I use the non-breathable one that is used for the FI engine, even though I'm using the carb. Oh, there is not an signs of oil dripping down inside the road draft tube either

[Gary R.]

Re: Intake sucking oil ???? C-1

Al, this seems to have been a common complaint recently. I just resolved it and you can check my threads to see if they would help you. I had the same issues, fouled every plug in 800 miles, used 1 qt about 600-700 miles, smoking, no leaks, good compression-190-200 lbs, and a suspect leak down- gauge is not the best. My case it was the valve guides not having the correct positive seals, I have 800 miles on the engine now and oil level is perfect, no smoke.

[Domenic T.]

Re: Intake sucking oil ???? C-1

Al,
what pressure are you using on the leak down test? We use 80 lbs on the first gauge and measure the leak down on the second gauge thru the orifice to determine the amount of leak.
You can then listen for the leak past the rings at the crankcase breather, the exhaust valve at the exhaust pipe, and intake at the carb.
A bleed down on the second gauge below 60 lbs is not good.
The rings move and WILL line up gaps at times but a good oil control ring will stop the oil burning till the gaps stagger again. What was the ring end gap when they were installed?

DOM

DOM

[Al R.]

Re: Intake sucking oil ???? C-1

Dom, have no idea what the gap was other than the shop owner said everything was in tolerance. The inlet pressure to the test assy is 45PSI but from what I understand with this assy, it only allows 15 PSI thru it into the cylinder. The 2nd gauge has a dial with ranges on it in percentages, not PSI, so that is where I was getting the 0/0 from. You can hear air thru the oil filler tube and dipstick, but not thru the intake or exhaust pipes , nor see any in the radiator. I'm also wondering if the compression PSI is high enough (1@145, 6@160, and 1@165) with it having 10.5 CR pistons in it. I did hook the air line from the compressor to 3 cylinders with the 45PSI going into the cylinders w/o hearing any air other than in the oil pan.

[Edward J.]

Re: Intake sucking oil ???? C-1

Al, I would take your oil usage problem one step at a time. Have you checked to see if the PCV valve is not sucking oil. Is the PCV located in the oil fill tube or valve cover? if in the valve cover, is it shrouded from the oil by a baffle? 2to 3 qts. in so few miles indicates its really sucking the oil down. If at this point your sure you few comfortable that its not, Then I would start by taking the intake off and look at the belly for cracks ( there is a shield under the carb area thats were they crack) and look at the intake valve stemsin each one of the ports, If there are traces of oil leaking down the stems you found your problem. sloppy guides act like a vacuum when the engine is running regardless of the new seals. Al I missed the post on the road draft tube, forget about the PCV valve. since you don't have one.

[Joe L.]

Re: Intake sucking oil ???? C-1

Al, I would take your oil usage problem one step at a time. Have you checked to see if the PCV valve is not sucking oil. Is the PCV located in the oil fill tube or valve cover? if in the valve cover, is it shrouded from the oil by a baffle? 2to 3 qts. in so few miles indicates its really sucking the oil down. If at this point your sure you few comfortable that its not, Then I would start by taking the intake off and look at the belly for cracks ( there is a shield under the carb area thats were they crack) and look at the intake valve stemsin each one of the ports, If there are traces of oil leaking down the stems you found your problem. sloppy guides act like a vacuum when the engine is running regardless of the new seals.

Edward-----


Al's car has a road draft tube so I don't think it has a PCV system.

[Edward J.]

Re: Intake sucking oil ???? C-1

I missed that thanks Joe, I will edit my post.

[Joe L.]

Re: Intake sucking oil ???? C-1

I missed that thanks Joe, I will edit my post.

Edward-----

Actually, to be 100% accurate, there was a situation in which a car could have a road draft tube and a PCV system. Although no Corvettes were built this way, once-upon-a-time California required that PCV systems be retrofitted to certain vehicles under certain conditions ( I've forgotten what they were). In those cases, the PCV system was field-retrofitted and the road draft tube was left in place but plugged with a permanent plug.

[Al R.]

Re: Intake sucking oil ???? C-1

Edward, in a previous post, I saw where the underside of the intake was cracked and pulling oil up into the intake ports. This may be something I will take a close look at this weekend. I'm gonna try to see if the shop owner will bring his video scope over to try to look inside the intake ports and possibly the back side of the intake valves first and if not, then pull the intake. I was also told to look for loose rivets on the underside of the intake as a possible source for sucking up oil.