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Discussion Starter · #1 ·
I am fighting an oil leak that appears to be coming from the base of the distributor. I believe the oil leak occurs at higher RPM. I know it is not the rear engine seal or valve covers and I don't think it is the intake manifold. I have been reading a lot of post that say I could be building up pressure in my crankcase that could be forcing oil out the distributor, dip stick, etc if the crankcase is not vented properly.

I have a PCV and breather/filter both on the passenger side valve cover. The driver side valve cover is not vented. The PCV is new and I am changing the breather that sits over the PCV and the breather/filter as well. My understanding is the breather/filter allows air in while the PCV is sucking the pressure out and into the intake. I have good vacuum so that is not the issue. One question I have is do I need to have a breather/filter on the driver valve cover as well? The driver valve cover has nothing at this point.

I am also changing the distributor lock down bracket to provide more even downward pressure on the distributor. I am concerned that my current bracket is pushing down on one side of the distributor which could be contributing to the leak.

My oil pressure is around 70 psi when cold and 38 psi when hot and idling. The engine is a 1996 355c.i. with vortec heads fully roller engine putting out about 350 to 375hp. Distributor is a new MSD Street Fire. Intake is a Edelbrock Performer RPM for Vortec.

Any wisdom on whether I need to add a breather to the driver side valve cover or whether my existing PCV and breather/filter is fine. Any other ideas on what would cause oil to leak at the base of the distributor would be appreciated. I am a rookie when it comes to engines so I am checking to see if I am covering all my bases.

Thanks
Todd
 

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Oddly enough I have this same issue and I am also running a 9-s centerbolt style SBC mine is a 305. I have the exact same leak at higher rpm I thought my pcv was nto working but I canged than and put in new breathers to no avail. Please let me know what you find to stop this issue. I was actually getting ready to pull the intake and replace it with a edelbrock one along with new valve cover gaskets to see if that woudl stop the leak. did you try double gasketing the distributer?
 

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I would check the oil sending unit that leaks at the rear of the motor and if its not that then it maybe the rear intake seal, on the vortec it dont use a seal it has a bead of RTV sealent on the rear of the intake, but check the oil sending unit first. Later Bill
 

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Discussion Starter · #4 ·
Oddly enough I have this same issue and I am also running a 9-s centerbolt style SBC mine is a 305. I have the exact same leak at higher rpm I thought my pcv was nto working but I canged than and put in new breathers to no avail. Please let me know what you find to stop this issue. I was actually getting ready to pull the intake and replace it with a edelbrock one along with new valve cover gaskets to see if that woudl stop the leak. did you try double gasketing the distributer?
I have new breathers and a different distributor lock down bracket arriving hopefully tomorrow. I have a new gasket coming also but will try the new lock down bracket first to see if applying hold down pressure more evenly on the distributor will make a difference. I also checked my valve covers and they are not leaking. I will keep you posted as I make progress.
 

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Discussion Starter · #5 ·
I would check the oil sending unit that leaks at the rear of the motor and if its not that then it maybe the rear intake seal, on the vortec it dont use a seal it has a bead of RTV sealent on the rear of the intake, but check the oil sending unit first. Later Bill
My oil sending unit is actually on the driver side block below headers so I have a plug where the rear oil sending unit goes. I did remove the intake and applied new seals and RTV. I am not positive but pretty sure the leak is the distributor. I will check it some more this weekend.
 

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You did install the distributor gasket didn't you?
 

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I like to use the Moroso distributor clamp that's real thick with flanges, it also has a stud instead of a bolt.

If the distributor can't be turned easily by hand, your clamp is working good enough.

A double gasket might help. The Mr. Gasket distributor gaskets are a bit softer and may seal easier.

You don't want to use any sealer because that would interfere with setting the timing; or the other way around, setting the timing would break any seal from the sealer. But a dab of grease might help.

Leaks in this area are not always what they first appear to be.
 

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It would be best to have a breather anywhere but on the same valve cover your pcv valve is connected to. Your pcv system is probably doing a real good job of circulating air through that valve cover, but maybe not so good at the rest of the crankcase.

But here's the other thing - at high rpm you aren't making as much vacuum, so the pcv system can't evacuate the crankcase as well as it does at idle. Add that to the fact you have more blowby at high rpm.
 

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Discussion Starter · #9 ·
It would be best to have a breather anywhere but on the same valve cover your pcv valve is connected to. Your pcv system is probably doing a real good job of circulating air through that valve cover, but maybe not so good at the rest of the crankcase.

But here's the other thing - at high rpm you aren't making as much vacuum, so the pcv system can't evacuate the crankcase as well as it does at idle. Add that to the fact you have more blowby at high rpm.
So if I am not evacuating the crankcase pressure at higher RPM, then is there a chance of causing damage such as blowing out a rear seal or something. I have concern that if I solve the distribute leak then I might be closing off where some crankcase pressure is escaping which could cause higher pressure in the crankcase.

Is there another type of crankcase venting system that I should consider over and above the PCV and valve cover breather?
 

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did this start when you put the new msd in? I have the same one and recently had to pull it out. I thought i had enough firewall clearance, but i didnt. when the motor revved hard it would hit the firewall and cause the gasket under the dist to rip.
 

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Discussion Starter · #11 ·
I moved my engine forward 3/4" and ensured the body was as far back as possible so my firewall clearance is good. I need to double check that I am not bottoming out on the pump shaft causing the distributor to not settle down enough. I will check this weekend.
 

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Good idea to check for bottoming out. A double gasket will cure that if it's not too bad. To check, when you pull the distributor to change the gasket, drop the distributor back in temporarily without one, see if there's a gap. If there is one, you can measure it with a feeler gauge.

I wouldn't worry too much about the high rpm stuff. It is what it is. Just find your leak and fix it. After seeing and hearing your engine run, I don't think you have a huge problem. This is just a detail to fix, you'll be good.
 

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An inexpensive black lite/dye kit goes a long way toward finding leaks....
 

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Discussion Starter · #14 ·
Yep, the distributor is definitely leaking along the gasket. I put the distributor back in without the gasket and I did have a gap so the distributor is bottoming out on the oil pump. I also noticed a couple of small scrape cuts in the intake where the distributor sits. I used two gaskets putting RTV between the intake and the first gasket. The felpro gaskets were too thin so I used a couple of other gaskets that were thicker to ensure I had enough spacing. I also changed my lock down bracket so downward pressure would be put more in the center of the distributor instead of on one side. I will put a timing light on it tomorrow and see if leak is solved.

Hopefully tomorrow will be productive and I can complete correcting my leak, installing my rear shock bar and solve my front brake lock up problem.

My front brakes are locking up after I drive a few miles and press the brakes a few times. My pedal is adjusted properly. Per Rick's advice, I put a spacer between the master cylinder and booster and it did help. I called CPP to see how to adjust the rod between booster and master cylinder and they said there is no adjustment. CPP said my problem is probably being caused by air in the master cylinder and recommended I bench bleed my master cylinder. I will bleed tomorrow and hopefully solve this problem as well.

Thanks to all for sharing your knowledge.

Todd
 

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I run a stock AC vented breather in each Cal Custom valve cover on my 396. No pcv no problems, same set up on my 13-1 roller cammed 454 Camaro drag car.
 

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If you ever looked at a 50s to mid 60s GM oil fill cap, you would find it vented with raised letters AC on it. I believe it stands for AC Delco. I guess sometimes I forget how old I am and think such things are common knowlege.
 

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But these filters you speak of are on engines equipped with a road draft tube. GM has set up non road drafted engines for one PCV valve and a twist on oil fill cap (not vented).
 

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I did not say Chevy, I said GM, I believe the ones I have came off a Pontiac V8 that used a vented oil fill cap. There were similar looking ones used of the push on varity on Chevy small journal 327s & 283s. They pushed on on a tube coming out of the intake. By the mid 60s they did not have road draft tubes a pcv hooked up on the back of block. An engine meeds 2 vents of some kind to function properly.
 

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It would be best to have a breather anywhere but on the same valve cover your pcv valve is connected to. Your pcv system is probably doing a real good job of circulating air through that valve cover, but maybe not so good at the rest of the crankcase.

But here's the other thing - at high rpm you aren't making as much vacuum, so the pcv system can't evacuate the crankcase as well as it does at idle. Add that to the fact you have more blowby at high rpm.
This makes sense. But conversly lefthand racers are set up the same (only opposite) and a well assembled one does not leak at all... Try swapping VCs side to side and using a good gasket just to make sure the leak ain't coming from blowby pressurising the VC and finding a leak.. Also if you are talking HIGH RPM (like 6K or upwards - you could be overwhelming the heads oil return and finding a leak that ain't there when the returns CAN handle the flow.
 
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