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Topic Review (Newest First)
03-19-2013 09:26 AM
oldbogie
Quote:
Originally Posted by stegman View Post
I have a fresh 383 stroker in my roadster and after tuning and general cam breakin with a couple of short drives iam getting some blowby with and without the pvc. i know i should get some until its broke in, but it seems a little excessive to me. i pulled the plugs and they look even and pretty good telling me no broke rings. could timing effect blowby, iam running 76cc heads on 8cc dome pistons with a compression ratio of about 10.5 on 93 octane. does anybody think race gas or 100 octane avfuel would help. total timing is only 32 advance. thanks agian........
You need to break the engine in, short drives will not accomplish that. The engine and the oil need to get up to operating temps and stay there for a considerable period. You need about five 100 mile drives or one 500 mile drive at mostly moderate RPMs, with a few blasts on throttle to ge there. If you don't, it is easy to have an engine that will always have high blow by and perhaps oil consumption, though these are two different issues with their own as well as some common causes. What was used for rings is very important, chrome rings can be hard to seal up, these take more aggression on the throttle to bed them in than moly and certainly plain iron. A good engine builder would keep track of these things and advise the engine's owner/operator accordingly.

Short drives are very hard on an engine especially a fresh one. You can get a lot of blow by till the rings and cylinder walls get seated into each other. No 100 octane fuel will not help. If this doesn't settle down after a handful of long drives then you can start to consider problems in parts and/or machining.

Bogie
03-19-2013 08:57 AM
ASE Doc Are the rings gapped correctly? Easy to check once the pistons are out.
03-14-2013 05:41 AM
cobalt327 Detonation or ring ends butting would be the top two. Rod bearing damage could point to detonation. Inspecting the rings might show if they butted.
03-14-2013 04:17 AM
64nailhead
Quote:
Originally Posted by stegman View Post
Yes sir i found the problem two pistons with cracked lands. Time to put flat top pistons and not trust someone else. My figures with my heads should be about 9.5 to 1 much better for the street. Good news is bores still look good. thx and surprise it ran as good as it did.
Stegman,
When you say not trust someone else, are you implying that the installer, that wasn't you, broke the pistons when they were installed?

I'm curious of the ring gap on the bad cylinders?


To the rest of you,
Do you think these are broken due to install, detonation or something else?
03-13-2013 11:44 PM
1Gary Thanks for the sense of reason post.We have taught our driver a good "seat of the pants" dyno on new builds is invaluable.After all your in that situation can't hear much over open heads.Same applies to street rods.So let the fun begin after the first 1,000.
03-13-2013 06:15 PM
ASE Doc Yep. I was just going to comment that as a general rule, 9.5:1 for cast iron heads on pump gas. 10.5:1 for aluminum. Aluminum heads allow for more compression due to their inferior thermal efficiency. I generally stay down at the 10.2 mark even on aluminum just for safety and to allow a little more flexibilty with fuel trims and timing. Remember also, the Vortecs are a "fast burn" design, meaning that they want less ignition lead by design.

As far as what happened in your engine during those 90 miles, I am concerned for you that you didn't hear that. It had to be ringing pretty hard. I would urge you to pay very close attention to the tone of the engine as you run it. No radio. And remember also, unless you break a motor in on the dyno, you generally want to run it easy for the first 1,000 miles anyway, focusing on seating the rings so you don't end up with an oil burner.
10-19-2011 10:06 PM
stegman Yes sir i found the problem two pistons with cracked lands. Time to put flat top pistons and not trust someone else. My figures with my heads should be about 9.5 to 1 much better for the street. Good news is bores still look good. thx and surprise it ran as good as it did.
10-17-2011 09:11 AM
T-bucket23 When I broke mine it was not obvious until I removed them. Dont forget to mark everything
10-17-2011 07:14 AM
stegman Thx Bud, ya i was expecting to see rough looking bores or damaged piston. thx for the ring advice.
10-17-2011 02:41 AM
cobalt327
Quote:
Originally Posted by stegman
Moly rings, i resorted to tearing it down and the bores and top of the pistons look good. ill push the pistons out tomorrow. thx again........
In case there was a ring installed upside down, be careful to pay attention to the pip marks or chamfers that show which way is "up". Most times these can be seen w/o removing the rings from the pistons but the pistons do need to be out of the block.

There's a slight chance that a ring could have broken and still not tore up the bore. And the bore/hone job can look OK and still not be good- it sometimes takes a close look to see the 'high and low' spots that are witness to a bore that isn't round.
10-16-2011 11:00 PM
CNC BLOCKS NE Here is a pic of some cylinders that had poor ring seal and blowby issues,

[IMG][/IMG]
10-16-2011 08:37 PM
stegman Moly rings, i resorted to tearing it down and the bores and top of the pistons look good. ill push the pistons out tomorrow. thx again........
10-16-2011 05:39 PM
cobalt327 Are the low holes next to each other? What do the plugs look like from the low holes? Besides the chance of bad ring seal, you might have inverted rings in the bad holes.

Was a torque plate hone done on this engine? What type rings were used- moly or plain cast iron, or ? Normal width rings or 1/16"/metric? Low tension oil rings or standard?
10-16-2011 12:37 PM
CNC BLOCKS NE
Quote:
Originally Posted by stegman
thx for all the good advice, i ran it up and down the highway a couple of time and its still blowing oil excessively. so i did a comp test and 2 of the cyclinders show about 90 psi max, i then squirted a couple of drops of oil in the spark plug hole and it came up a bit. also blew air in and could hear a little air in the bottom of the case. should i pull the motor and see if the rings are broke or wait for them to break in???
I would do a leak down test at TDC to find out whats going on if your block was machine corrcectly the rings should be seated by now!!

I have seen circle track engines that were not prepared correctly and after 3 years or running they still had rags wrapped around the breathers because of blowby issues.
10-16-2011 12:21 PM
stegman thx for all the good advice, i ran it up and down the highway a couple of time and its still blowing oil excessively. so i did a comp test and 2 of the cyclinders show about 90 psi max, i then squirted a couple of drops of oil in the spark plug hole and it came up a bit. also blew air in and could hear a little air in the bottom of the case. should i pull the motor and see if the rings are broke or wait for them to break in???
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