383 cylinder scoring? Anybody have any ideas?

Old 05-08-2010, 09:53 PM
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josh4ku
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Default 383 cylinder scoring? Anybody have any ideas?

I am building a 383 stroker, ran for about 2 hours and started to hear a wierd noise, sounded like pistons slap so i pulled the motor back out and actually found the one of the pistons was dented in on the skirt, Found out somebody had knocked that piston off of the bench and didn't tell me about it, Anyway while I had that head off i noticed the cylinder walls seamed to be scored just a bit, But i had only ran the engine for a few hours all together. Just wondering if anyone would know why it would have scoring already. I have molly pistons. top end gap .018 and bottum end gap .021. 850 carburator, seemed to be running to rich.
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Old 05-08-2010, 09:58 PM
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josh4ku
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Default Re: 383 cylinder scoring? Anybody have any ideas?

Originally Posted by josh4ku
I am building a 383 stroker, ran for about 2 hours and started to hear a wierd noise, sounded like pistons slap so i pulled the motor back out and actually found the one of the pistons was dented in on the skirt, Found out somebody had knocked that piston off of the bench and didn't tell me about it, Anyway while I had that head off i noticed the cylinder walls seamed to be scored just a bit, But i had only ran the engine for a few hours all together. Just wondering if anyone would know why it would have scoring already. I have molly pistons. top end gap .018 and bottum end gap .021. 850 carburator , seemed to be running to rich.
Mahle* 850 demon double pumper
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Old 05-08-2010, 10:26 PM
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Tod74
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Did the machine shop have all 8 pistons when they did the machine work?
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Old 05-09-2010, 04:52 AM
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kwkracing
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Metal sloshing in the oil pan gets on the pistons and cylinder walls and scratches them.

Inproperly filed rings also can scar up cylinders.

Inproper cyllinder clearance.

No lube on cylinders on assembly

???
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Old 05-09-2010, 07:05 AM
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zipper06
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Is this a hyperutectic piston or a forged piston, Mahle makes both. If you bought a rotating assy it's possible that they are hyperutetic's and if that's the case the ring end gap is way too little and could cause scoring of the cylinder walls. Also do you know how much piston to wall clearance you have?

Zip.
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Old 05-09-2010, 09:23 AM
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josh4ku
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Default Machine shop

Yes they had all 8 pistons at machine shop, and yes they had lube at assembly, I am pretty sure I have forged pistons but I am going to double check, And I will check what the pistons to cylinder clearance is and get back to you guys. Thanks.
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Old 05-09-2010, 10:59 AM
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josh4ku
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Default Pistons.

Originally Posted by josh4ku
Yes they had all 8 pistons at machine shop, and yes they had lube at assembly, I am pretty sure I have forged pistons but I am going to double check, And I will check what the pistons to cylinder clearance is and get back to you guys. Thanks.
Yes they are forged pistons.
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Old 05-09-2010, 11:01 AM
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josh4ku
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Default Running to rich.

Can running the engine to rich wash down the cylinder walls enought to cause scoring? The pistons seemed really wet when we pulled the head off.
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Old 05-10-2010, 06:38 AM
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hink
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Originally Posted by zipper06
Is this a hyperutectic piston or a forged piston, Mahle makes both. If you bought a rotating assy it's possible that they are hyperutetic's and if that's the case the ring end gap is way too little and could cause scoring of the cylinder walls. Also do you know how much piston to wall clearance you have?

Zip.
We buy alot of Mahle pistons and never new they had a hyper piston, they have a 2618 forging and 4032 forging.

What is their hyper piston P/N???
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Old 05-10-2010, 06:44 AM
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hink
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Default Re: 383 cylinder scoring? Anybody have any ideas?

Originally Posted by josh4ku
I am building a 383 stroker, ran for about 2 hours and started to hear a wierd noise, sounded like pistons slap so i pulled the motor back out and actually found the one of the pistons was dented in on the skirt, Found out somebody had knocked that piston off of the bench and didn't tell me about it, Anyway while I had that head off i noticed the cylinder walls seamed to be scored just a bit, But i had only ran the engine for a few hours all together. Just wondering if anyone would know why it would have scoring already. I have molly pistons. top end gap .018 and bottum end gap .021. 850 carburator, seemed to be running to rich.
Sounds like debris as we have used these Mahle pisotns in a few of our circle track builds and after a season of running the cylinders are not marked up at all, It pretty much looks like the pistons never have been up and down in the cylinders.

Was your block plate honed??
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