New engine blowby

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harvenator

harvenator

A fish called Wanda
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I recently rebuilt a 273 and had a multitude of problems with carburetion and timing. I finally got it to run and fixed my timing issue with a new distributor. I ran it at about 2500 rpm for about 30 mins to break in the cam and drove it about 40 miles, with 18" flexpipe on the stock manifolds for some back pressure, to check for leaks and take it to an exhaust fabricator.
After i got the exhaust done, I drove it home and readjusted the valves.
Next morning I cranked it up and tried to drive it into town but about 8 miles down the road, after a few second boot to 4000 RPM, it started smoking.
I pulled over and found my breather cap gone and smoke coming from the valve cover.
I nursed it to AutoZone and replaced the breather, got it home and rechecked the valve lash.
What gives?
PCV valve feels as if it works (rattles and idle changes when it's pulled).
Wires weren't touched.
Rings weren't gapped but were installed properly.

Anyone have any ideas?
 
More info is needed. Was the block bored? Or did you hone it and install new rings? Sounds like the rings don't have a good seal.
 
Your breather cap fell off.
 
The primary causes of blowby are improper ring// piston fit (or worn) or out of round bores or excessive taper

Loose valve guides, especially exhaust

and.... if you re-used a "good" crank and the bearings are a little loose and maybe you have a nice hig-vol. pump, a "lot more" oil in the "air" in the crankcase can add to the problem

Then there's things like a leaky head gasket blown into the crankcase (valley) area, or a crack in a block / head casting somewhere.

Depending on what rings you are using they may just not be seated yet. I'd give it as much a 500 miles before I get too concerned, unless it's ridiculous

Might try a different PCV "just because" and make sure the manifold/ carb end of the fitting is unrestricted.

Watch the oil--level, viscosity and smell--to be sure it's not getting diluted by something like a leaky mechanical fuel pump
 
To quote-"Rings weren't gapped but were installed properly."
If you did not gap them how can you say they are installed properly?
What other short cuts did you do?
 
Put the breather cap back on and drive it. If it keeps doin it you might have a problem. But if it does not. Drive it. The rings ain't even broken in yet. Don't get excited just yet. It might not be a damned thing. Give it time. And no, rings don't have to be "gapped". If they are a regular available oversize and the block was bored competently, the ring end gap will be correct when assembled. Modern rings are machined to pretty good tolerences. Usually, only custom or race engines require a ring to be filed fitted. It is not necessary for probably 90% or more of street engines.
 
slant6/4speed said:
To quote-"Rings weren't gapped but were installed properly."
If you did not gap them how can you say they are installed properly?
What other short cuts did you do?
Click to expand...

can only hope he means they were pre fit ootb and not file fit, then as long as the machinist did his job and the installer didn't twist/crack the rings, cool.

oh, scamp alrady said this, lol
 
To answer a few questions:
Push on cap
bored .030 over and appropriate iron rings purchased, personally installed and never twisted.
crank turned .010 and appropriate bearings purchased
no other inappropriate noises
 
harvenator said:
To answer a few questions:
Push on cap
bored .030 over and appropriate iron rings purchased, personally installed and never twisted.
crank turned .010 and appropriate bearings purchased
no other inappropriate noises
Click to expand...

Iron rings are the easiest to seat. I don't like using them because they promote fast cylinder wear. Do you think you might have broken a ring or two?
 
Were they moly coated iron rings, or just plain iron faced? If they were moly, the honing job should have been very smooth and they would have seated right away. If you have a picture of the bores during assembly you can see if they are smooth enough. If they were iron face rings, they will take some time to seat, but they should not, in my opinion, be leaking so badly the breather pops off or the dipstick blows out. If they were moly, but the bores were rough, then the rings will take a while just like plain iron to seat. At this point, I'd say try driving it easilly for a few hundred miles, limiting the idle time, and see if it improves. If it doesnt, do a leak down test or std compression test and see how things look.
 
SGBARRACUDA said:
Iron rings are the easiest to seat. I don't like using them because they promote fast cylinder wear. Do you think you might have broken a ring or two?
Click to expand...


I think if there was a broken ring the cylinder would have low compression and mis fire. I like strokerscamps Idea. Engine isnt broken in yet
 
Well, I did a compression check today and had 110 -120 lbs on all cylinders except #8. It has "0". Even after squirting some oil in the cylinder there is not even a quiver on the needle. I do feel a little tug on the intake stroke when I put my finger over the hole but nothing in the compression stroke. Guess I'm gonna have to pull the head and take a look. I might be in the market for a flat top .030 over 273 piston if it's broken or othrwise defective.
I'm hoping it's just a ring issue and I've not done any damage to the cylinder wall.
There's a lesson here: I thought I was going to save some money by rebuilding an old 273 rather than buying a crate motor. I think I was wrong. Between the expense of the rebuild and the frustration of finding ancillary parts, I believe I've equalled or surpassed what I would have spent had I just bought a 360.
More to come this weekend.
 
Also 110 -120 is pretty low. Maybe 8 to 1. Not going to make much power that way. Those 273 flat tops sit down in the hole too far. I had to mill the heads and deck my block to get 9 to 1.
 
The 110-120psi is about right for a stock type rebuild. If you want performance it takes more because there's a lot of blueprinting that has to be done to get more compression, and special parts, like head gaskets. The goose egg is your problem, and if I had to guess, zero means you may have broken a ring putting it together, or perhaps forgot a ring altogether. Usually you'll have something even if it's low if the stuff in close to right. Dont lose faith. Stuff happens.
 
Do a leakdown test on #8 and see where the air is leaking. 0 psi compression should not be hard to track down the problem.
 
Don't have to do a leak down -- with blow by and "0" compression in #8, I know where my problem is. I just won't know exactly what the cause of the problem is until I pull the head.
"moper" -- I know I didn't miss a ring because there were no parts left and this problem didn't occur until I had some miles on the engine -- maybe 150 or so. I'm inclined to believe that either the piston had a 'comeapart' or a ring broke or all the ring gaps got lined up. I'm not too keen on the last 2 because that would still give me a few #'s of compression.
I'll know more when I pull the head.
 
harvenator said:
Well, I did a compression check today and had 110 -120 lbs on all cylinders except #8. It has "0". Even after squirting some oil in the cylinder there is not even a quiver on the needle. I do feel a little tug on the intake stroke when I put my finger over the hole but nothing in the compression stroke.
Click to expand...

That would lead me to look more into your valvetrain. A valve hung up would explain you not feeling anything on the compression stroke and zero on your compression reading. I would put air in that cylinder with the valves closed and have a listen.
 
camd64 said:
That would lead me to look more into your valvetrain. A valve hung up would explain you not feeling anything on the compression stroke and zero on your compression reading. I would put air in that cylinder with the valves closed and have a listen.
Click to expand...


Also very true. I was stuck on the ring deal... Might also be valvetrain related. See if the tip of the exh valve is lower than the others on that head when you pull the rockers and shafts. That would indicate the valve hung open. A hung intake would push back up the carb.
 
harvenator said:
Don't have to do a leak down -- with blow by and "0" compression in #8, I know where my problem is. I just won't know exactly what the cause of the problem is until I pull the head.
"moper" -- I know I didn't miss a ring because there were no parts left and this problem didn't occur until I had some miles on the engine -- maybe 150 or so. I'm inclined to believe that either the piston had a 'comeapart' or a ring broke or all the ring gaps got lined up. I'm not too keen on the last 2 because that would still give me a few #'s of compression.
I'll know more when I pull the head.
Click to expand...

You could have at least one ring broken and still have compression. You could have all the gaps lined up and you MIGHT not even notice the difference.

This is something serious like a broken piston, but it could be

A VALVE problem. Pull the valve cover. If you spit out the intake pushrod, it won't have compression and would probably use oil--trying to pull a vacuum on the rings.
 
Yeah buddy. snatch that valve cover off. you might have somethin stupid and cheap like a broke or bent pushrod.
 
You mentioned earlier you readjusted the valves so I'd check the valve adjustment on #8 first before I condemn the rings or piston. You may just have a valve too tight. That of course won't affect the blowby but it may answer the 0 compression on that cyl.
 
Valve adjustment is good. Pushrods are good. Head coming off this weekend for a look see. Sure wish AutoZone rented borescopes.
 
With a piston ring issue you'll feel suction and blowby at the pcv gromet if you block off the filler neck, wet yer finger and cover the pcv hole and rev the engine.

when on intake it will pull in oil and make suction, then on compression will push out pressure past rings/through hole in the piston [worst case]

an intake gasket leaking could add to the oil consumption.

fwiw
 
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