Dyna

Hello gentlemen. I have been out for a while, and am glad to be back. I have a '66 coupe with a 1968 0.030-over 396 in it with an internal oil leak. Since I rebuilt it, it consumes approximately 1 qt every 200 miles. I can't find the problem...and I hate that. Cylinder cranking pressure is 170-180 psi in all cylinders. No blue smoke. There is also a lot of blowby coming out the pcv system. I have changed pcv's twice with no improvement. The intake manifold has a light uniform oil coating in it everywhere, from the plenums on down to every port. My only mod to the engine is an Edelbrock Performer. I have taken it off twice to check the manifold seals and can't see a problem there. Cracks in the engine are possible, but unlikely, as I know this engine's entire life history. Otherwise, the engine runs absolutely great. Does anyone have an idea here?

SWCDuke

Do you have a properly configured PCV system?

Duke

Dyna

Yeah, I believe it is set up properly. It is a closed loop from the air filter to the rh valve cover, through the crankcase, and our the lh valve cover, throught the pcv, and into the plenum of the intake manifold. Does this sound right?

SWCDuke

Sounds basically correct. The valve covers should have built in liquid/vapor separators. Is it possible that they were removed?

I think most BB applications had the PCV outlet (downstream of the valve) routed into the base of the carburetor, not directly into the inlet manifold.

Also, make sure the valve you are using is correct for your application. Valves have different flow rates at different manifold vacuums

If you are seeing a lot of oil in the inlet manifold, then I suspect something is amiss in the PCV system.

Duke

Dyna

Thanks for you input, SWCDuke. I mis-stated the connection from the pcv, it is connected to the base of the carb, as you said. Is the oil separator in the valve cover anything more than some baffles? I can see the baffle in there when I pull the pcv out. Does all the blowby hint at anything to you?

SWCDuke

I'm not sure what the exact configuration of the liquid-vapor separators are, but there should be one welded into each valve cover and they may be different right and left - specifically configured for flow direction, which means reversing the covers right and left could cause problems. You might want to pull the covers and inspect them for signs of damage, repair, or modification. Take a picture if possible and post so someone can compare them to a set of covers they have laying around.

If the engine had excessive blowby past the rings, the compression would probably not be so high. The other source of blowby could be valve guides.
Is there oil in the air cleaner? What PCV valve is installed and how did you select it?

Duke

Dyna

I'll take the valve covers off tonight after work and photo & post. No oil ever shows up in the air cleaner. The three pcv's I have tried were from GM, Fram and than GM again. No change from those. They all looked the same, with the same opening sizes and spring tension. I checked the fit of the valves to the guides, they all have 0.001 +/- 0.0005 in clearance, and all the rubber boots are new.
Thanks for the ideas, and more are welcome.

JL66REDCPE

Before I respond I have to ask. Do you have oil in the exhaust ports ??? Pull the exhaust manifolds and take a look. Also, what do the plugs look like ? Is there oil on them also ??




[Modified by JL66REDCPE, 3:24 PM 12/29/2003]

SWCDuke

My Delco catalog lists CV746C for nearly all '68 V-8 engines, both BB and SB. It is "style 307", which has and inlet side designed to insert into the valve cover grommet and the outlet side equipped with a nipple for a hose. Both the inlet and outlet are on the same axis. Beginning in '69 the CV736C replaces most 746 applications. It is the same style, so I assume it has different flow characteristics.

There are problems with several GM PCV designs, though the basic architecture of your system is good. It comes down to having proper flow, which is managed by the valve and effective liquid-vapor separators.

I had to redesign the PCV system on my Cosworth Vega TWICE before I finally came up with a design that didn't suck oil into the manifold and pump it into the air cleaner as did the OE system.

The PCV design on my SWC never passed oil, but since the flow is from the oil inlet tube to the back of the block it didn't ventilate the rocker boxes very well. That's why GM went to the valve cover to valve cover system. With that architecture the entire internal engine volume, including the rocker boxes is well ventilated.

Duke

Dyna

Hello JL66REDCPE,

Glad to have you jump in to the fray.
I have had the manifolds off recently. They and the ports are bone dry on the inside. Plugs are all uniform, dry, and dark tan colored on the electrode.

Dyna

Dyna

Duke,

That CV746C number sounds familiar. I will confirm that it is the one I have when I get home from work.

JL66REDCPE

I thought this sounded like a classic case of two problems 1) bad valve guides on the exhuast side - especially on a BB I would have bet a hundred bucks that the exhuast ports would have had oil in them. 2) bad intake manifold to head fit whereby oil is being sucked into the intake manifold and that is why there is oil in the intake runners and under the carbeurator. You have stated that there is no blue smoke. You may want to take the car out and hammer it somewhat while a freind looks for blue smoke. Were the valve guides knurled by chance as part of a rebuild ??? This much oil consumption sure sounds like bad valve guides and perhaps also seals to me. All respect to Duke who's opinion I and just about everyone else respects -- this seems to be an awful lot of oil to be a pvc valve.

Dyna

JL,

The valves and guides were recently replaced with new, not knurled, bronze guides and new Manley valves. Boots are also new. I'll try the "hammer" test tomorrow (even if it doesn't tell us anything, the entertainment value is very high).

Thanks again for your ideas.

Dyna

Plasticman

Dyna,

You stated that you have a lot of blowby coming out of the PCV. I take it that this is at idle? If it is, then blowby at idle is a definate sign of poor ring control. Sounds like the rings are not seated (or installed incorrectly) or the gaps are excessive. If the engine had not been rebuilt recently, I would say your oil control rings are "stucK" (very common during the 60's & 70's with some brands of high ash content motor oil). Understand that you have good cranking compression, but compression reading are very variable depending on cam timing. Recommend that you do a Leak Down test instead. This is the application through a metered orfice into the cylinder while at TDC with both valves closed. A presurre gauge both before and aft of the metered orfice reads out the percentage of "leakage". 100 PSI in, while 80 PSI downstream (cylinder side) is a 20% leakage. Leak Down testers are available for around $66 from Summit or Jeg's, but require a constant 100 PSI air supply (air compressor). You can also tell the condition of the valve sealing (if any air leakage from either the carb or exhaust pipe, then the intake or exhaust valve is not "sealed".)

I am not discounting the need for a properly working PCV, but sounds to me that the PCV system is being overpowered by excessive blowby. The fact that this occured after the engine was rebuilt, says something was not done correctly. The oil coating in the intake tracts agrees with my theory that the PCV is being overpowered (but also agrees with Duke that the PCV system may not be properly baffled). This is not a case of the intake manifold not sealed correctly (vacuum level would be down, poor idle, and one or more plugs would be fouled, but excessive blowby would not occur).

What type of rings were used in the rebuild, and what was the bore/hone finish used?

Good luck,
Plasticman


[Modified by Plasticman, 5:04 PM 12/29/2003]

Dyna

Hello Plasticman,

Thanks for the ideas. Hmmm. The blowby theory makes sense. I'm thinking that the leakdown tester would be a good addition to my garage right about now. Can't hurt, that's for sure. Another oddity is that the blowby is about the same flow rate regardles of which or how many cylinders I kill off by grounding. I am also thinking of the possibility of the exhaust crossover system having some type of sealing problem. How does that theory smell to you? I do not have the ring reciepts here right now, so I can't tell you the ring type, other than that they were pretty run-of-the-mill cast iron. I believe the honing pattern was a 60 deg helix with a medium stone.

Dyna

Plasticman

Dyna,

Don't think grounding out a cylinder (or 2) would change blowby all that much (even grounding 2 cylinders still leaves 75% of them firing). As for the crossover leaking, I have not seen that unless the intake ports next to it was leaking also. Since the engine runs OK with no loading up of plugs and no "poor" idle, I doubt that is the cause.

Cast iron rings are pretty much "old" tech. Standard these days are Moly rings (they are faced with a coating of moly). These rings seat almost immediately, whereas cast iron rings do take a little while and require a coarser honing pattern (your medium stone is about right for cast iron, whereas Moly likes a finer stone).

Did you do the rebuild, or a shop? If a shop, I would take it back ASAP.

Good luck,
Plasticman

Dyna

Unfortunately, I would be returning the engine to myself. I did it in my own shop. After doing approximately 20 rebuilds in my life, I have never had this problem, so I am still currently stumped. I actually was grounding out 6 plugs at a time, and still seeing the blowby [?] blasting out of the valve cover. It didn't matter which cylinders were firing. Incidentally, it looks like we are expecting bad weather here tomorrow, so I may not get to do the hammer test right away. Another 'Vette engine that I just built using the same sealing techniques (I think) does not have this problem.

Still searching..and thanks for the insight,

Dyna

JL66REDCPE

What kind of oil pressures are you seeing when hot and cold at idle and at 3000 rpm ?? Are they excessive ??

Kid_Again

I've thought a while about this post, followed the thought posted by Duke and I've fixed the very same problem on my small block that you noteÂ….I am the first to admit that I MAY have a problem with blow-by but I think it's unlikelyÂ…here's the detail on the what I didÂ….

As background, I had both the small block and big block rebuilt at the same time, by the same guy who has an outstanding reputation as an engine builder that goes back over 30 yearsÂ…the big block is PERFECT, but the small block always fouled plugsÂ…I tried lots of fixes which were somewhat helpful but finally decided that the plugs were oil fouled and that the oil was coming in through the crankcase somehowÂ….I was using the factory carb and pulling in the crankcase vapors, per the factory specs, from the oil filler tube into an orifice-restricted elbow into the carb.

I plugged the factory setup and the car started to run better but then the oil filler tube started to push out and my oil pressure was ALWAYS over 60lbs - poopie. I then added a vent on the driver's side valve cover and a PCV valve on the opposite side and it was better but not really and now I had oil coming back out of the vent, onto the valve cover - poopie. Not having leakdown testers or anything funky like that, I looked at the PCV valve and internally it was coated with oil, which was obviously being pulled into the intake manifold. So I decided to see if I could trap the oil vapors before it got to the intake manifold and I added a large, clear plastic gas filter inline just before the manifold and it immediately trapped the oil and the car ran much better. OK, big deal, how do I fix this problem earlier in the process?

I should add that I have tall cast aluminum valve covers to clear the rr's and I decided to measure the inside clearance - I have almost 1.5" inside clearance - and not a baffle in sight. OK, I look at Duke's thoughts and decide that my problem is somehow, the tall valve covers are allowing a LOT of oil to aerosolize and head into the intake - providing a reasonable amount of obstruction (baffles) should cure that. I did two things - I made 2" long baffles from 1" wide aluminum 90* stock and attached them to the underside of the valve covers in a pattern that suggested the most turbulence possible (the vapors have to go to the ends of the heads so I installed the baffles at an angle, opposite of each next baffle). I then used some aluminum flashing to fabricate baffles for the vent and the PCV grommet, leaving enough room to allow air to pass but not close enough that I thought the oil adhereing to the baffle would be pulled up. I attached the aluminum bits with Ultra Black, cleaned the inside of the valve cover with solvent beforehand and let the sealer cure overnight.


Just came back from a pretty aggressive 50 mile run, pulled up to 5K on startup and cruised for a while at 70mph. Runs like a champ, oil venting has disappeared, the bottom of the PCV valve is not dripping with oil, the oil filler tube stays put and the oil pressure gauge has dropped almost 20 lbs.

Could I still have blow-by? Yes, but given the odds, I don't believe so. Me and my tall valve covers.

Thanks Duke!

[Modified by Kid_Again, 12:56 PM 12/30/2003]


[Modified by Kid_Again, 12:59 PM 12/30/2003]

Dyna

Kid_Again,

thanks for joining in. Well, that's a whole new wrinkle. I am confused about the connection between the oil pressure in the passages and your venting changes. How are these related? By the way, my pcv is only a little bit moist, not dripping when I take it out after a run. My objective is really to just get my stock system to work right. So I'll avoid the mod's for now.

I removed my valve covers and took some pictures of the pcv system and baffles per Plasticman's advice. I am not having any luck creating a website for the photos on the Forum, so I will email the pics to anyone who will look at them and tell me if the pcv system and the valve cover baffles look right.

Dyna