Questions about compression and blow by.

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Questions about compression and blow by.

Post  Bigred69 on April 16th 2014, 7:00 am

Ok, here's my situation. I bought a used 429 from a friend who pulled it out of a 72 Torino with 65k miles. I brought the nSty beast back to my place, and went to work on it. First thing I did was to do a simple compression check on all cylinders. All seemed to be good enough to run it for a while. I averaged about 165 psi on all cylinders. Well, I put rebuilt C8 heads on it, along with Edlebrock performer intake ,straight up timing chain, and HEI distributor. We cranked the motor up and noticed when I hit the throttle it smoked. White smoke , and smells like gas. The biggest thing is that I have blow by out of where the PCV valve plugs into the valve cover. The crazy thing is, this engine pops off at the slightest turn of the starter. But the exhaust smells like gas. Fast forward to tonight. I cranked her up and let her warm up , then shut it down and pulled all the plugs. Below is what I got checking the compression. The first number is the first puff of that cylinder, the next is after 5 hits on that cylinder.
1 -95-170
2-110-165
3-90-170
4-90-160
5-95-160
6-110-165
7-100-170
8-110-160

Now, I know that blow by means rings , but what should I do next ? Leak down? Before I yank the motor back out of it.
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Re: Questions about compression and blow by.

Post  dfree383 on April 16th 2014, 7:08 am

Have you tried tuning the carb? And tuning the timing?

What plugs? New old? New wires? Coil? Ignition up to snuff?
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Re: Questions about compression and blow by.

Post  Bigred69 on April 16th 2014, 7:42 am

I do suspect my carb is wongo. My plugs smell like gas , and the carb has no adjustment air or fuel. This I already knew when I cranked it up, but didn't think it would affect blow by. I plan on pulling the carb and going thru it again. The plugs are new , and new HEI distibutor, along with new wires. Just a touch of the key and she starts and runs smooth. One other thing, it won't blow smoke unless I give it half throttle or better. I fear that I will be pulling this motor, but just wanted to ask the gurus before doing so.
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Re: Questions about compression and blow by.

Post  Dave C. on April 16th 2014, 8:33 am

I'd drive her for a while then leak it down....

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Re: Questions about compression and blow by.

Post  Bigred69 on April 16th 2014, 8:53 am

Yeah, I thought about that. But, man she smokes like crazy when you hit the throttle. Haha. I think I'm going to pull the carb and have it redone, while I'm doing the body work on the car. Then drive it around close and see what happens.
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Re: Questions about compression and blow by.

Post  cool40 on April 16th 2014, 8:56 am

You may have some stuck rings.get it warmed up good and dump some atf through it.
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Re: Questions about compression and blow by.

Post  kim on April 16th 2014, 11:21 am

If its cylinder washing the oil away do to raw gas in cylinder, your accelerating ring/cylinder wear and affecting cylinder seal. No oil and the rings got nothing to seal against. TUNE the carb.

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Re: Questions about compression and blow by.

Post  Bigred69 on April 16th 2014, 11:28 am

Thanks for all the replies. Tuning the carb will be done this week. Thanks again.
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Re: Questions about compression and blow by.

Post  supervel45 on April 16th 2014, 11:28 am

Fix the carb issue, and drive it and give the rings a chance to loosen up.

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Re: Questions about compression and blow by.

Post  Bigred69 on April 16th 2014, 11:30 am

Coolio, will do!
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Re: Questions about compression and blow by.

Post  Bigred69 on April 16th 2014, 6:43 pm

Pulled the carb tonight and after I removed it , I looked down into the. Intake. Soaking wet with gas from two days ago. Taking it to a good carb guy tomorrow.
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Re: Questions about compression and blow by.

Post  Foxfire85 on April 16th 2014, 8:38 pm

I recently had a problem like this. Motor ran too rich, smoked (sometimes seemed white), had steam coming out of the valve cover breather. I did numerous tests to check for a blown head gasket, comp tests, and a serious rejecting of the carb and an oil change cured it all. Get that carb right, change the oil, and drive it like you're on cops.
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Re: Questions about compression and blow by.

Post  nuclearcobra on April 16th 2014, 9:14 pm

My motors not a smoker at all , but I tried out a different carb last year I bought and it was a instant smoker when I nailed it or revved it in the driveway but it idled fine and started good.
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Re: Questions about compression and blow by.

Post  Bigred69 on April 18th 2014, 1:20 pm

I think while I have it apart I may go ahead and check to make sure I'm not sucking oil out of the galley thru the intake ports on the manifold.
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Re: Questions about compression and blow by.

Post  Bigred69 on April 22nd 2014, 6:45 am

Ok, so Saturday I installed the new properly tuned carb. I also decided to check into the intake gasket to make sure all was well there. I noticed some oil between the gasket and the head, at the bottom part of the gasket. I thought to myself maybe I had nailed the smoking problem. Still didn't explain blow by , but I installed the new recommended intake gasket anyway. It does idle way better than it did before, meaning it would idle down . But, I here's my problem, I still have no adjustment on fuel air mix. With both adjustment screws all the way in the car still idles. My carb guy says I have a vacuum leak somewhere. But, it seems like I have checked very possible hose. I'm just wondering if I could be sucking oil from the galley thru the bottom of the intake gasket. The engine still smokes , and now at idle. Before I had nothing. Let me ask you guys this. Why would my PCV valve be humming after the engine is warmed up? I mean, damn it sounds like I have a locust inside my engine compartment. When I pull the PCV valve out of the valve cover the idle does change. I think I need to yank this motor and just rebuild it. I would kick myself in the ars though if I found out after I pulled the motor that it was something very small . Thanks for any input.
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Re: Questions about compression and blow by.

Post  Foxfire85 on April 22nd 2014, 7:37 am

It sounds to me like you're still just retardedly rich. When mine was pig rich, the idle mixture screws wouldn't do anything until one of them were all the way in and then It would idle up a hair. It was pretty useless to try and tune it with a vaccum gauge because it wouldn't show anything really.

Also if you're still rich, it requires more air to run so you may want to check your primary transition slot and see if too much of it is uncovered. That can sometimes cause the mixture screws not to jive.

You said you installed the "properly tuned" carb, but was it properly tuned on this motor? Every motor is different and they wants what they wants. Take some starter fluid give a quick burst into the carb as it's idling and see if the idle goes up or down. Up means it's lean, down rich. Or take a piece of cardboard or something and start to cover up the secondaries on the carb and see if the idle goes up or down. If it goes up it's lean, down it could be good or rich. Of course these little tests will just get you in the ballpark. The best way is to put a wideband on it and see exactly what's going on or give it the old full throttle run and kill the motor and read the plugs deal. Myself I struggle with carb tuning so a wideband afr gauge makes a huge huge diference.

I'd say get it dialed in precisely, squirt some ATF down in the tubes, and drive it a while to at least give it a chance to reseat the rings or whatever. You'd know the diference in gas smoke and oil smoke just by smell.
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Re: Questions about compression and blow by.

Post  Bigred69 on April 22nd 2014, 8:01 am

Yep, the smell I'm getting I believe is oil and not fuel. Gonna take the carb back and let my guy check it again. Thanks.
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