clearance between piston and cylinder wall?

vikingpower

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Dec 6, 2004

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CWU Ellensburg, WA

Aug 29, 2005

#1

• Aug 29, 2005

• #1

So I pulled my old heads off this weekend and noticed a gap about 1/8 inch on all the pistons and was wondering if this is normal or if anyone else has seen this? I've got 89K miles on it, the engine uses about 1 1/2 quarts of oil between oil changes @3000 miles during normal driving... well, 'spirited driving' would be more accurate. I'm was hoping I get another year or two out of the shortblock.

 

vikingpower

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Dec 6, 2004

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CWU Ellensburg, WA

Aug 30, 2005

#2

• Aug 30, 2005

• #2

anybody?

 

2

2002BLGT

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Dec 18, 2003

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Bedford VA

Aug 30, 2005

#3

• Aug 30, 2005

• #3

1/8th is ALOT .....pull the motor and go .030 over with new pistons , rings , bearings etc........

 

garystocker

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New Jersey

Aug 30, 2005

#4

• Aug 30, 2005

• #4

I can't believe the thing runs at all!! Does it crank on start-up "quickly" like the plugs were out?

Do a compression check to determine the health of your rotating assembly before digging in.

I suspect this was an opical illusion

 

vristang

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Mar 31, 2005

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Aug 30, 2005

#5

• Aug 30, 2005

• #5

vikingpower said:

So I pulled my old heads off this weekend and noticed a gap about 1/8 inch on all the pistons and was wondering if this is normal or if anyone else has seen this? I've got 89K miles on it, the engine uses about 1 1/2 quarts of oil between oil changes @3000 miles during normal driving... well, 'spirited driving' would be more accurate. I'm was hoping I get another year or two out of the shortblock.

Click to expand...

Have you verified that the oil is not coming through the intake/pcv? I only ask because it is so common.

Some feeler gauge can help get a better idea of what the gap is, although it is not very accurate. Is this a stock short block? Forged pistons will have larger clearance. Are the bores worn more at the top than the bottom? Are there any score marks/gouges? Can you feel any ridges at the top of the cyl? Have you been getting blue smoke out of the exhaust? Does the motor seem lacking for power lately? What mods have you done?

 

garystocker

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Aug 30, 2005

#6

• Aug 30, 2005

• #6

good questions!

 

vikingpower

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Dec 6, 2004

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Aug 30, 2005

#7

• Aug 30, 2005

• #7

It seems that the gap is bigger at the bottom of the stroke than the top, but that could have been an illusion I suppose. In any case it was pretty darn big, there was no indication before hand other than the oil consumption. Runs like a champ and fires up right away everytime, and I've never seen any blue smoke coming out the tailpipes, even when I set the ignition timing and hold the engine at about 3000 RPMs for a minute or so. The original honing marks are still visible too, and the top rings are visible around the edge of the pistons as well, so I guess thats why the engine still runs so damn good. I guess since this piston wear is so abnormal I'll start saving for a new shortblock... Sucks cuz I was really anticipating being able to run the snot out of it with my new heads I'm putting on.

 

vikingpower

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Dec 6, 2004

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#8

• Aug 30, 2005

• #8

Oh, I also got oil in the intake manifold but havent been able to figure that one out yet.

 

vristang

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Mar 31, 2005

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Aug 30, 2005

#9

• Aug 30, 2005

• #9

Can yu get some feeler gauge in there? This will help you know rather than guessing. The old EYEcrometer is not known for accuracy.

If you can see the original hone marks, and the you cannot see any gouges, then it might be your eyes playing tricks on you. I know when I looked at my forged pistons in the fresh bores (while putting it together) I had to check it a couple of times to convince myself all was well.

The oil in the intake can be a couple of things. Did you remove the stock baffle in the valve cover for roller rockers? Oil has been known to blow into the intake here via the TB/VC hose.
Another common problem seems to occur most often with intake swaps. It seems that the increased airflow results in an increase in the volume of contaminated air being pulled from the crankcase via the pcv. The larger the volume being pulled from the crankcase the more oil you will see in the intake. An oil seperator can help as well as a restrictor on the TB/VC hose. In some cases (ie mine) this doesn't seem to work as well.
How much oil is there in the intake?

 

vikingpower

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Dec 6, 2004

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Aug 30, 2005

#10

• Aug 30, 2005

• #10

Maybe the gap wasnt as big as I thought it was, and I cant check it now (should have) because my heads are already torqued on, I'm just waiting for my pushrods to get here so I can finish putting everything back together... ugghhh. Anybody know how much the stock pistons expand when the engine heats up to normal operating temp? that would help a little. I've had a Typhoon intake manifold for about a year now, and its always had oil in it. I'm gonna modify that PCV thingy in the back of the manifold, either plug it or put a breather there or something. I havent modified the stock valve covers yet, I'm hoping I wont have too when I put them on my TFS heads and Comp rockers, the Comps are about the same size as the stock rockers except for the poly locks.

 

vikingpower

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Dec 6, 2004

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CWU Ellensburg, WA

Aug 30, 2005

#11

• Aug 30, 2005

• #11

vristang said:

If you can see the original hone marks, and the you cannot see any gouges, then it might be your eyes playing tricks on you. I know when I looked at my forged pistons in the fresh bores (while putting it together) I had to check it a couple of times to convince myself all was well.

Click to expand...

Do you remember how big the gap appeared to be? Could you see the top rings clearly when the pistons were installed?