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Old 08-05-2007, 01:40 PM
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Chevy 350 Blowby Suddenly

I have a chevy 350 Crate engine with about 3000 miles on it. Today when returning from a show I noticed a lot of blowby comming out of the breather. It still seems to be running fine. I have a pvc and baffled breather. It doesnt make sense to me why this is happening. Im thinking mayby I broke a ring or something. I am going to run a compression test as soon as it cools down a little.

Anyone have any thoughts on this.

Thanks
Chet

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Old 08-05-2007, 02:50 PM
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Chet, other than the possibility of fuel being in the oil, the only other thing is pistons or rings. However, I did see one time where a kid used diesel oil as it was all he had and the engine had alot of blow by until it was changed. unless your running a electric fuel pump, give the dip stick a yank and see what it smells like. The only other possibility I know of is condensation. I would also suggest checking over the pcv system and filter. Depending on the cruise RPM vacuum lowers and the valve doesn`t pull much, so it comes out the filter, the only place it can. I`ve noticed this many times on past projects when I held the engine at any kind of RPM. Check the filter, if it`s oil soaked, the pressure at cruise rpm is just pushing it out so it appears to be alot more than it really is. Hope this helps.
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Old 08-05-2007, 05:20 PM
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Well there is no gas in the oil. I pulled it all apart and I didnt find anything. I ran a compression check and cylinders 3 and 5 were low. The cylinders look fine. I was hoping to find a blown head gasket or something but it doesnt look blown. I dont know if I should pop out a couple pistons to see what the rings look like. I will try to post up some pics of the cylinders but I am not great with the camera. I was hoping to find something obvious.
Do you think a blown head gasket could cause blowby. It seemed to do it at idle, it would go away at light acceleration and then come back.

Any help or insight would be appreciated greatly.

Thanks
Chet
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Old 08-05-2007, 06:46 PM
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I don`t think a blown head gasket causes blow by, but it does enhaunce it, as the water content evaporates and the steam, condensation, looks just like blow by. If it comes out at idle, and I`m assuming you checked the pcv, and the vacuum line to make sure it`s not collapsing, then it only leaves the rings left, As I honestly can`t think of anything else that would cause it. Perhaps the guys have more ideas than I have. Hope you find the problem.
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Old 08-05-2007, 07:15 PM
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I think I am going to knock out a couple pistons tommorow to have a peek. It is in my t-bucket so it is fairly easy. Lots of room. Heck it only took 1 1/2 hours to tear the heads off. I really want to find something. I hate to replace the gaskets and put it together and have the same issue.

Any of the engine guys have any thoughts on this. This is my life lately, nothing is easy.
It has a small blower on it so a broken ring is possible. The tops of the pistons look fine, no detonation marks at all. All the spark plugs looked ok and the same.
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Old 08-05-2007, 09:00 PM
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I guess I`m not considered a "engine guy" lol.
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Old 08-05-2007, 09:21 PM
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Sorry, I thought that was what you meant earlier when you said one of the guys. I appreciate any and all help. This one is just weird. I though for sure I was going to pull the heads and find a roasted piston. Do you think a ring could break and not mark the cylinder. There are a few shinny spots in the cylinders but they all seem to have them and it is very light. You can still see the original hone lines
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Old 08-05-2007, 09:58 PM
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No worry Chet, It was just a joke. While I have alot of posts, I know about enough to get by. Most times I use what I`ve experienced as guidelines. I`ve been at it most of my life, and all my builds have been a success but one, which the machinist goofed, it ran fine, but smoked like a train.
Shiny spots in the bore will always be present, as they are usually high spots that get more wear due to them being higher from the head bolt stress. If a ring has broken it may not have had enough time for it to do any damage. It`s also common to find some cylinders lower than others, but they shouldn`t be that much lower. While you certainly can overheat the ring lands and cause breakage, the cylinders with the highest heat concentrations will likely be the first culprits, and 3 and 5 as in your case, are side by side, and so are there exhaust ports so heat is highest there.
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Old 08-06-2007, 12:22 AM
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Doc here,

While your in the, look for tiny cracks BETWEEN the piston ring grooves..oil can track up that way on a good ring set..and will be subject to more or less travel depending on the demand (torque) on the engine.


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Old 08-06-2007, 05:26 AM
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Please be sure to tell us what you find and if your repairs work out.
This post could be very helpful to some of us.

Thanks !

454 RATTLER
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Old 08-06-2007, 06:16 AM
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Quote:
Originally Posted by 454 Rattler
Please be sure to tell us what you find and if your repairs work out.
This post could be very helpful to some of us.

Thanks !

454 RATTLER
Dont worry, I will keep you informed. I need to pull the pan and knock out pistons untill I find something. As I said the tops looked good and the combustion chamber in the heads look normal, Look s like I am laying on my back to pull the pan and some pistons. Probably wont get to it tonight, we will see.
Again, thanks for all the replys.
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Old 08-06-2007, 06:24 AM
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Couple Questions

What would you guys recomend for head gaskets for a SBC gen 1 with Vortec heads.

If the original hone marks are still visible do I need to re-hone it if I need to replace the pistons and or rings.

Thanks again

I Turned 50 last week and I thought is was me that was going to have problems not my car LOL
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Old 08-06-2007, 09:43 AM
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Quote:
Originally Posted by DoubleVision
Chet, other than the possibility of fuel being in the oil, the only other thing is pistons or rings. However, I did see one time where a kid used diesel oil as it was all he had and the engine had alot of blow by until it was changed. unless your running a electric fuel pump, give the dip stick a yank and see what it smells like. The only other possibility I know of is condensation. I would also suggest checking over the pcv system and filter. Depending on the cruise RPM vacuum lowers and the valve doesn`t pull much, so it comes out the filter, the only place it can. I`ve noticed this many times on past projects when I held the engine at any kind of RPM. Check the filter, if it`s oil soaked, the pressure at cruise rpm is just pushing it out so it appears to be alot more than it really is. Hope this helps.

Diesel oil is the norm for flat tappet cams now. Been using it for years.
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Old 08-06-2007, 03:11 PM
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I`m aware of that big, As I recommend to many on here to use diesel oil for new cam break in. The oil he used was some of the thinnest stuff I ever seen, it was almost like water, blowby was all over the valve cover and hood.
Chet, as for honing, even so you still see the crosshatch, you`ll still need to slightly hone the cylinder just enough to rough it. Then scrub it good, then use WD40 on a paper towel, if you get gray on the towel, it`s not clean enough. I`m also thinking and I`m sure you know, and this is just a reminder, if those 2 cylinders failed, it`s only a matter of time before the other side does it. And if the cylinder temps get too high and the rings butt it`ll happen on other cylinders, so it maybe wise to just do them all, and it`ll give you the peace of mind that it won`t occur again. If your reuse the pistons, make sure the ring lands are spotlessly clean. Good Luck.

Last edited by DoubleVision; 08-06-2007 at 03:30 PM.
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Old 08-06-2007, 03:43 PM
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Quote:
Originally Posted by DoubleVision
I`m aware of that big, As I recommend to many on here to use diesel oil for new cam break in. The oil he used was some of the thinnest stuff I ever seen, it was almost like water, blowby was all over the valve cover and hood.
Chet, as for honing, even so you still see the crosshatch, you`ll still need to slightly hone the cylinder just enough to rough it. Then scrub it good, then use WD40 on a paper towel, if you get gray on the towel, it`s not clean enough. I`m also thinking and I`m sure you know, and this is just a reminder, if those 2 cylinders failed, it`s only a matter of time before the other side does it. And if the cylinder temps get too high and the rings butt it`ll happen on other cylinders, so it maybe wise to just do them all, and it`ll give you the peace of mind that it won`t occur again. If your reuse the pistons, make sure the ring lands are spotlessly clean. Good Luck.
I wil definaetly change all the pistons if they are the problem. No more good enough for me. I think I am lucky I didnt damage the cylinders.I will get some forged pistons. Most dont list stock bore only 30 over and above. I am sure someone must have them. I really dont want to bore it if I dont have to. We will see. I have a meeting to go to at 7 maybe when I get back I will pop the pan off and pull them. I have a real small garage so it kinda sucks to work in there. getting up off the floor isnt fun anymore either lol. I might just tow it to the garage and put it on the lift. Depending on what I find, the spare engine may go in for a while.
Do you think a home hone job would be ok or should I send it out.

Again thanks for the help and advise.

Last edited by T-bucket23; 08-06-2007 at 10:01 PM.
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