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Blow By on a fresh rebuild.

44K views 187 replies 26 participants last post by  68NovaSS 
#1 ·
A week ago or so I posted a thread in regards to my car smoking a little bit. I thought It might have been running to rich so I adjusted the fuel mixture screws with no success. Well yesterday I took her out for a drive and I noticed there was oil coming from the passenger exhaust pipe. My heart sank !.....First thing that came to mind was a blown piston rings... I looked under the hood and noticed there was black residue coming out of the #2 cylinder. I had actually noticed this 2 weeks ago but figured it might be normal b/c the header bolt was a bit loose on the # 2 exhaust manifold...

So I spent half the night searching the forum and reading up on other articles. Seems like there are other possibilities than just blown piston rings. For example, one member stated that he experienced the same problem just after replacing his valve covers for some chrome Holley's. He didn't replace the PCV valve and he was experiencing "blow by". Another member had bad valve seals.

So here I am wondering what the worst case scenario is.....

Specs:
SBC 350 rebuilt winter of 06'
Installed July 08'
Running synthetic oil

When I installed the motor it never showed any signs of smoking. In fact, I would drive the car up and down my alley with open headers and it never smoked....It started smoking only after I had the full exhaust done (3 weeks ago) and I installed some Edelbrock Elite valve covers. I didn't replace the PCV valve. During this time I also attached the tranny vacuum line and tinkered with the timing.


Pics:




 
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#54 ·
Regal Beagle said:
I have the exact same valve covers and have had a similar issue.
Send an email to Edelbrock and ask them to send you a couple of baffles.
I did that offering to pay and they replied the same day stating they were in the mail to me already. Sure enough, 5 days later (I live in Canada) they were in my mailbox. No Charge. Tremendous customer service in my opinion.
Best of all my problem was solved.
Give it a go and good luck. :D
Will give them a call tomorrow morning and hopefully they will send me a pair...I obtained these valve covers and air cleaner on a trade. I never bothered asking for the baffles...
 
#56 ·
carsavvycook said:
You do not have to remove all of the other plugs.
making sure I got this right....

disconnect the distributor battery lead, and remove the spark plug for the cylinder i'm trying to test. Install the fitting and give it a crank... 4 compression strokes or until the needle stops rising, Correct ?
 
#59 · (Edited)
Just in case you have trouble getting some baffles from edelbrock..
Spectre makes a rubber grommet for the valve cover with the baffle molded in.

http://www.spectreperformance.com/#CATALOG.5333


A quick googly search for "baffled grommet" showed me that moroso and mr gasket make them too.
Sometimes the grommet type will clear big rockers and high lift cams where the baffle won't always clear. (the grommet fits between the rockers.)

You can also make one from 20 gauge steel or aluminum..It's just a plate with the edges bent up.

Later, mikey
 
#60 ·
If you are doing a compression check, remove ALL PLUGS, lock throttle wide open, pull off BATT wire off HEI, screw in compression gauge into each hole and do all cylinders noting, pressure on first stroke and then best compression on that cylinder.

First stroke tells you the kind of volume the cylinder is displacing and condition of compression rings. Subsequent strokes will deminish pressure per stroke as test goes on, and gauge reveals total pressure. An good compression engine with minimum wear should be within 5 to 8 % of the best and worst cylinders. Spiking indicates different problems.

The problem you are having with #2 cylinder could be anything from a guide to a cracked cylinder wall. Look at the compression test first.
 
#62 ·
alittle1 said:
If you are doing a compression check, remove ALL PLUGS, lock throttle wide open, pull off BATT wire off HEI, screw in compression gauge into each hole and do all cylinders noting, pressure on first stroke and then best compression on that cylinder.

First stroke tells you the kind of volume the cylinder is displacing and condition of compression rings. Subsequent strokes will deminish pressure per stroke as test goes on, and gauge reveals total pressure. An good compression engine with minimum wear should be within 5 to 8 % of the best and worst cylinders. Spiking indicates different problems.

The problem you are having with #2 cylinder could be anything from a guide to a cracked cylinder wall. Look at the compression test first.

will removing all the plugs drastically affect the readings?
 
#63 ·
powerrodsmike said:
Just in case you have trouble getting some baffles from edelbrock..
Spectre makes a rubber grommet for the valve cover with the baffle molded in.

http://www.spectreperformance.com/#CATALOG.5333


A quick googly search for "baffled grommet" showed me that moroso and mr gasket make them too.
Sometimes the grommet type will clear big rockers and high lift cams where the baffle won't always clear. (the grommet fits between the rockers.)

You can also make one from 20 gauge steel or aluminum..It's just a plate with the edges bent up.

Later, mikey
Good lookin out Mikey :thumbup:
 
#64 · (Edited)
Those compression readings are a bit low for a somewhat fresh motor, 170-200 is a good reading for a fairly stock, fresh motor. I'm guessing that either the rings didn't seat, or got gummed up with oil from the unbaffled pvc, or you have some loose valve guides, which let the valves get burned. Or maybe the valve seats got all gummed up from the oil, and they burned from trying to close on the carboned up smegma from burnt oil..As your problem occurred over time, I'd bet valves are the culprit.

You can put a couple of squirts of engine oil in the spark plug hole, and re test, if the compression comes up 10 or 20 PSI, that indicates rings are the prob, if the compression does not come up, then it says valves are leaky.

You can also make a poor man's leakdown tester to isolate or confirm/disallow those theories., Take the hose from the compression tester, connect it to your air compressor,(if you have one), then put the cylinder at exactly top dead center, with both valves for that cylinder closed...Put some pressure in the cylinder,(if the crank turns, reset it back on TDC and try again..sometimes I leave the breaker bar on the balancer bolt and jammed into the frame to keep the crank from turning), ..Once the cylinder has pressure, you can listen for the air leaks at the carb throat, with the throttle open,(intake valve is NG,) the crankcase,(listen with a tube at the oil return holes with your valve covers off, that will say rings), or at the exhaust port....(ex valve leaking).


None of this sound good.


Mikey
 
#66 ·
carsavvycook said:
Hey Mikey, You forgot to mention, that to use the hose from the compression tester, you have to remove the schrader valve from the end of the hose so the air will pass through it.

I was testing sin7...... :rolleyes:

Good call :thumbup: I forgot about that.

Does the rest of my post sound reasonable? To me, although the unbaffled PVC is creating an oil burning problem, it's sounding like something the machine shop might have done, especially if it's found that the guides were too loose, (or a smidge too tight), it's hard to tell that though, without knowing how many miles since the rebuild, and what kind of assembly lube was used,(did the bores get dry after sitting for 2 years?).


He said it ran good, but how much driving was done on the open headers..I know that long tubes are usually no prob, but shorties could let cold air back up the header, and mess with an exhaust valve..He said the prob started when the exhaust and valve covers got put on, was that a short time into it's life, or was the motor run a bunch before with no problems.


The second part of the compression test will reveal alot.


You are way better at the motor stuff than me, I'm just tossing the things I'd think of out there.


Mikey
 
#67 ·
well

looking at the spark plug, it's kinda clean so it's probably coming from other than the intake runners.

i mean if you were trying to ignite an oily mix the plugs would tell you about it. And this stuff is pouring out the pipe, looks unburnt on your finger.

what's the color code/brand for that engine paint ? if you don't mind...it's the same color as my chris craft 327's.

take it easy with the carb spray on the rockers, too. if you are using the o-ring valve stem seals, the carb spray could eat them up a little and you'll get oil runnin down the valve stems.

And the compression may very well be low on #2 because the gunk around the exhaust valve is preventing a seal.


I'm leavin now. Good Luck.


Enjoy
 
#69 ·
I've been following this whole post, and there's 2 things that kinda stick out which haven't been addressed. #1- How much actual running time is on this engine so far -namely;is it even "broken-in" enough yet for the rings to have fully seated? and #2- I saw the mention of "only synthetic oil" which makes me wonder if that was (attempted to be) used for break-in. I only mention these two things because of the fact that I see no further explanation on either of these matters after the first casual mention of either one. Both could have a significant impact, but obviously a baffled valvecover issue will need to be addressed. Also, what compression ratio was this engine built to? If it's a 10.5:1 then yes that 120-125 psi comp.test reading would be terrible, but if 8.0:1 then a 120-125 reading wouldn't be so far off the norm. I don't mean to interfere at all, I'm just wondering if this engine has been broken-in all the way yet, or at least enough for the rings to have fully seated, and if perhaps it was attempted to break it in with full-synthetic oil (which most folks would consider to be a pretty big no-no!). I hope that it doesn't turn out to be a major problem for you, as I know what a P.I.T.A. that can be, so here's hoping it turns out alright for you. -Jim
 
#70 ·
seven up said:
well

looking at the spark plug, it's kinda clean so it's probably coming from other than the intake runners.

i mean if you were trying to ignite an oily mix the plugs would tell you about it. And this stuff is pouring out the pipe, looks unburnt on your finger.


And the compression may very well be low on #2 because the gunk around the exhaust valve is preventing a seal.


Two excellent points! Give the man a gold star. If the oil was coming from the rings it would be burned during combustion and the plugs would show it. The valve stem is heavily ladden with oily crust and the exhaust port is just as bad. The engine just never got hot enough in the open header mode because they were probably just short sprints and the oil exited really fast out of the engine and never got a chance to burn it like it did with the full headers and exhaust on.

Your next step will be removing the head, like it or not. This isn't some external fix where you force a can of DR. Good Stuff down the carb , and its fixed.
 
#71 ·
powerrodsmike said:
I was testing sin7...... :rolleyes:

Good call :thumbup: I forgot about that.

Does the rest of my post sound reasonable? To me, although the unbaffled PVC is creating an oil burning problem, it's sounding like something the machine shop might have done, especially if it's found that the guides were too loose, (or a smidge too tight), it's hard to tell that though, without knowing how many miles since the rebuild, and what kind of assembly lube was used,(did the bores get dry after sitting for 2 years?).


He said it ran good, but how much driving was done on the open headers..I know that long tubes are usually no prob, but shorties could let cold air back up the header, and mess with an exhaust valve..He said the prob started when the exhaust and valve covers got put on, was that a short time into it's life, or was the motor run a bunch before with no problems.


The second part of the compression test will reveal alot.


You are way better at the motor stuff than me, I'm just tossing the things I'd think of out there.


Mikey
I agree with you on all of these things, those are very good possibilities, The compression readigs are low, but we don't know if it has run long enough to seat them yet. If the compression comes up by 25-35 psi after putting oil in, then we will know.

Years ago I found a cracked baffle in a 302 Ford, that was blowing oil. Then remembering that was how I thought about using clear plastic hose to help diagnose this problem. Then finding the same problem on this blown 383, my first thought was no baffles. After pulling one valve cover, I decided to install a set of tall valve covers. After running it for 30 minutes it quit smoking. The engine builder had spent 2 years trying to get it to stop, I had it fixed in less than 4 hours. :D So this is why I always list this as a possibility.

Stephen
 
#74 ·
Sin7 said:
Inside of the valve cover:


The other 3 exhaust ports. They look good and dry. Looks like they're burning right:

The photos that I looked at in Post # 41 show 3 fairly dry ports. In post # 42, it shows an exhaust port with oil oozing out of it. Do you honestly think that a PCV without a baffle is just picking #2 cylinder to blow oil through!!!

If the oil was being picked up in the valve cover and sent down the hose to the base of the carb and then being injected into the intake plenum to be returned into the engine, DO YOU NOT THINK 'ALL' CYLINDERS WOULD SHOW OIL AND BURNING OF OIL????
 
#75 ·
Sin7 said:
This is what the #2 port looks like :eek:



Here's Post #42. That port and valve has more crud on it from burnt oil then BK's bar-b-que had all last year.

There is also appears to be a light fluffiness of burnt oil on the other 3 ports, but I haven't taken the liberty to run my fingers in it and determine that, maybe Sin7 can do that for us and report back. I would imagine that he's not to happy right now and will spend some time digesting all this info tonight.
 
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