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Engine SwapEverything about swapping an engine into your Third Gen.....be it V6, V8, LTX/LSX, crate engine, etc. Pictures, questions, answers, and work logs.
I rebuilt 1974 350 and put it in my 91 formula. Only got a couple miles on it. I’m getting a small amount of oil, maybe a cup out of the valve cover breath on passenger side.
pretty sure it only happens on hard pulls cause on a hard pull I can smell oil and nothing seems to be coming out the tail pipes.
a little background on the build. Bored .30 over, decked block, raised flat top with valve relief pistons. Should be in the 10:1-10:5 comp area. New Aluminum heads. Edelbrock intake. Edelbrock carb. Cam is 224 at .050 single pattern with .525 lift roller with 1.5 roller rockers. Vacuum is right around 10 at idle.
my thoughts on the problem.
It might just be a blow by issue cause the ring haven’t sealed yet. Might be the cheap valve covers (they do have balffles). With the low idle vacuum I don’t think a stock type pcv valve is the right thing to use, I have one and tried it, I also have one that just has a tiny hole in it, neither make a difference. maybe my valves are not adjusted properly. I have a high volume normal pressure oil pump and my bearing clearance is tight as F so my oil pressure nears 100psi on hard pulls. Maybe I’m just pumping too much oil up there. High compression is giving me too much crank case pressure and I don’t have the right setup to handle it.
anyone have similar issues they’ve dealt with or thoughts? Thanks
There are a few threads on this although you've touched on most of the content. Discussions including the right PCV valve to use and also on the fixed orifice type you described. There's also an adjustable version.
That said, IMO, a PCV system is essential and your combination doesn't sound out of the ordinary. I'm at 10.5:1 and when the short block was fresh, oil control was handled by a stock arrangement. Now, as the block aged and blowby increased (along with a decrease in cranking compression) the oil control became an problem. In line between the intake and PCV valve, I installed a catch can. It helps.
I'd think that with a new engine blowby shouldn't be an issue unless your application is high RPM for extended periods of time. A quick blast down the quarter shouldn't show up as "a cup of oil" out the breather. Here's hoping you haven't wasted the ring seal on your new build.
What is your idle vacuum? What's your peak RPM? And what was your crank ventilation arrangement?
I’m at about 9 or 10 inches of Vacuum at idle. The highest rpm I’ve hit in the 10 or so miles I’ve ran is 4,500 maybe 5,000. Originally I put a standard ac delco pcv valve on the passenger side with a standard breather on the driver side but then realized when I was having trouble really fine tuning my idle mixture that I’m pull too much vacuum through the pcv.
during this time I was only getting a small amount of oil around the pcv grommet.
so then I fell down the rabbit hole of pcv research. Signs mostly point to the need for an adjustable valve but at $125 I, at least for now want to find a different avenue.
Seem that the early 70’s late 60’s cars with radical cams such as the solid cammed 427’s used a pcv with just a really small hole.
and the pcv should be on the driver side cause that’s what crank rotation dictates.
so I got the fixed hole pcv, moved it to the driver side and picked up one of those breathers that looks like a mini k&n filter.
after a little drive. The hardest drive yet. Even a couple nice black marks on the road. I noticed the small amount of oil that came from the large open mesh type breather.
hopefully I have good ring seal. Moly faced rings and running standard 10w-30. From what I understand moly faced rings break in quick. If nothing else I’m gonna ride it hard as sh*t for awhile and then check compression.
what are thoughts on maybe getting rid of the pcv and in its place an open tube that goes to a catch can, then to the bottom of the air cleaner with a breather on the other side? That way I’d be pulling air flow from the top of the carb, no vacuum loss, removing crank case pressure and catching any residual oil.
or what is the best configuration for a catch can? In-between the pcv and carb? With higher flowing pcv or low flow?
I also think there’s a chance the combination on high oil pressure and possibly a crappy valve cover baffle system could be a factor here too.
You mentioned having valve covers that may not have the best baffles. That's something I'd address for sure.
As for the catch can arrangement you described, I'm inclined to think that a functioning PCV system is still the best arrangement. The thread posted above has a few part numbers for some old school muscle car engine valves. Something I was pursuing but I can't recall what I ended up with. In my case though, a thoroughly trashed shortblock with terrible leak down test results doesn't warrant my chasing this any further. I don't go WOT anymore (sadly). Check the test procedure that Sofakingdom proposes. Perhaps you'll gain some insights from that.
As for the catch can arrangement I'm running: Starts with a breather on the passenger side valve cover (excellent baffles by the way) then a PCV valve on the drivers side, to the sealed catch can and then returns to plenum at the back of the intake. Seems to work OK.
Did a compression test cause the thought of glazed over cylinders was making me loose sleep.
They all range between 185-195psi.
So based on that it seems the rings have sealed well. Maybe some will say cranking compression doesn’t tell the whole story and a leak down test will. I don’t know.
All the plugs look like this. I’m no pro but I’d say they look pretty good, a little rich maybe. The oil on the threads isn’t as bad as the pic makes it seems.
Cylinders were improperly honed. There should not be any noticeable ring break in period. The engine should just work. Cranking compression just means there's plenty of oil getting flung around to seal the rings. Running compression is blowing by them which indicates a poor seal (crankcase pressure). The way this happens is incorrect cylinder finish, incorrect rings, wrong gap, etc.
Machine shop work was done by a reputable shop. They used torque plates and had the pistons and rings.
that’s a very interesting article but, is just one persons opinion. 999,999 out of 1,000,000 will say that honing and break-in process are important and necessary
Last edited by FormulaGTArs; Apr 30, 2020 at 10:09 AM.
Machine shop work was done by a reputable shop. They used torque plates and had the pistons and rings.
that’s a very interesting article but, is just one persons opinion. 999,999 out of 1,000,000 will say that honing and break-in process are important and necessary
Not anymore. And it's not just one persons opinion. OEM's, including GM, routinely issue service instructions to replace pistons without touching cylinders. This has been the case for more than 40 years. Unfortunately there's still the ingrained belief among many that honing is necessary when it's not and it's not even a good idea. Here's a section from the official Chevrolet Power manual. 5th edition published in 1984:
You can see the dyno chart in my recent post on my L31 rebuild. The bores were not touched. 177k on the block. Many other machine operations were performed. Honing wasn't one of them. No blow-by present at all. Here's my post:
I own a performance shop with a chassis dyno. I build engines for a living. Haven't honed a cylinder in 15 years and not planning to start anytime soon. Number of engines with blow-by or oil consumption: ZERO.
Your engine almost certainly has the wrong finish for the rings. Probably too aggressive and it overheated the rings.
This is of course assuming the accuracy of your statement that a CUP of oil was lost through the breather. That's an absolutely $HITLOAD of oil to lose through a breather from crankcase pressure. I got a few droplets - like a mist - out of my brand new engine build with NO breather in the grommet. I literally didn't have one on hand. For 3 days I drove it with a 1" hole in the valve cover and got only the slightest *whiff* of a mist on the valve cover around it.
GD
Last edited by GeneralDisorder; Apr 30, 2020 at 05:56 PM.
I suppose a leak down test would settle that.
But, assuming that you do have a good ring seal (and assumptions are dangerous) all I have to go in is how your build compares to mine. A few engines back I ran 10.2:1 with a 224@.050" cam and also had 190 PSI cranking pressure (or better). That engine had no oil control problems whatsoever. It didn't even have a windage tray. RPMs were 6K max. What it did have was better than 13" of idle vacuum. Timing was in or around 16 initial. Valve covers were GM's standard fare centre bolt style with the factory baffles intact. You had mentioned possibly have a poor baffle design. I'd settle that first.
A question for you: How much oil are we talking about? You had mentioned a "cup". That's a lot. Some sweating around the grommets I feel is inevitable. I've seen racers take there valve cover breathers and wrap them with microfiber cloth. Seems this helps with the accumulation on the covers themselves (and consequently onto the headers). Once the cloth is saturated, they're replaced. This doesn't solve the issue but it does keep things manageable.
Ok so I started it today. Nicest day so far this year (68). Pulled the breather. Nothing coming out, fumes or air of any sort. If anything maybe a slight suction. So I put the breather back on, put a rag around it and went rippin. Ran great, no oil smell. Got back home and checked the rag. Dry. Pulled the breather. No drips or nothing.
so. This is my first motor build. It seems I might not have had good ring seal at first but maybe hopefully it’s pretty well set now. Add to that the confusion (which I’m still sorting out) of the pcv thing and properly vacating crank case pressures.
As far as the vacuum goes. If I screw in the idle mix screws all the way (edelbrock 1407) I can get around 12/13 inches at 850-900rpm. Shouldn’t it die with them screwed all in? That’s what led me down the pcv rabbit hole. Throttle blades closed of course. Still runs. No vac leaks anywhere. Maybe the brake boost line is drawing to much? Or my fuel pump is over ridding the floats.
Still fine tuning. Still dialing it in.
Another thing to add to the pcv, vacuum, oil pressure, compression thought. From the first start I’ve been battling a small oil leak on rear oil pan right by the starter. Cheap oil pan and 4 piece cork gasket. That leak has gotten slightly worse and another at front oil pan/timing cover. So soon enough I’ll pulling the pan, getting a better one and a 1 piece high quality gasket. I’m sure my crank case pressure issues with pcv and ring seal didn’t do me any favors with these leaks.
Can high oil pressure effect oil pan gasket? Or rear main seal? I wouldn’t think so.
High oil pressure should not affect any seals. Mine is wicked high. Off my gauge. Hot idle is 50.
The mixture screws regulate *fuel* to the idle circuit. Not air. The throttle blades would need to be open a *little bit* to keep it running. If you screw in the idle mix screws and it doesn't die then you are sucking fuel through the primaries. Without air it will not run so *something* is open, and there's a fuel source too.
Are you setting the throttle blades with the choke plates propped open? If not they aren't closed they are on the fast idle cam.
