Found the noise in my engine

[dmaxlover]

Not sure if you're being sarcastic, or just don't know about engines, but for those readers who really don't know:

Nope, being serious. The indentation look pretty deep in the pics, but it's hard to tell how deep they really are. I realize there is expansion in the pistons, and they rock pretty damn good in the bores, but the clearance must of been very close to start with.

Mick, from what you can tell, do you know what the piston protrusion is now, and how thick the head gaskets were while clamped.

 

[Vasbinder]

I have a dumb question what is Piston Protrusion?

 

[LBZ]

I have a dumb question what is Piston Protrusion?

In layman's terms it's how far the piston sticks out of the hole at TDC.

 

[Mike]

The problem is getting the piston square in the hole and guessing at how much piston material has been beat off. It may take a bit to get the answer.

 

[LBZ]

I usually just measure at the wristpin to get as accurate a number as I can. I don't know what GM's reccomended procedure is for checking this.

 

[Mike]

Right on Dale, Thanks. He's only got a caliper at the moment for measurements.

 

[LBZ]

Right on Dale, Thanks. He's only got a caliper at the moment for measurements.

Straightedge and feeler strips would probably work as well.

 

[Mike]

When Mick measured like this suggestion, the smallest measurement was .020" but, this was on the edge with the most head to piston damage the biggest was greater but by how much depended on pressure applied. The gasket measured after removal and uncompressed but previously installed of course was .03?" can't recall for sure and failed to write it down. Sorry for the vague info but more detail soon.

 

[LBZ]

When Mick measured like this suggestion, the smallest measurement was .020" but, this was on the edge with the most head to piston damage the biggest was greater but by how much depended on pressure applied. The gasket measured after removal and uncompressed but previously installed of course was .03?" can't recall for sure and failed to write it down. Sorry for the vague info but more detail soon.

The spec eludes me for stock protrusion, but I believe that .020" is WAY too much.

 

[Mike]

Here is why it's hard to get an accurate protrusion measurement. Granted skirt measurements should measure .035" more. Still I think the block is no longer usable unless a .090" piston is available.

Umm.. the blow by was horrible.

 

[McRat]

Going off memory,

I like to run flush, but I believe the factory spec is .010" above.

4.030" is the factory dia, but pistons should be measured at the bottom of the skirt, it's larger. A .010" overbore will actually cleanup quite a bit of damage. He'll have to bore the worst cylinder first to see what piston options he has.

 

[Mike]

Going off memory,

I like to run flush, but I believe the factory spec is .010" above.

4.030" is the factory dia, but pistons should be measured at the bottom of the skirt, it's larger. A .010" overbore will actually cleanup quite a bit of damage. He'll have to bore the worst cylinder first to see what piston options he has.

I see, most likely is. I was measuring one of Kevin's stock pistons and got the .035" difference in piston top to skirt difference. Again, he we was rough measuring, nothing in stone as you know.

 

[JoshH]

Going off memory, max protrusion for C grade gaskets is .0148" or something like that. There's an overbore/decked block head gasket that can be used if you have more protrusion, but I don't think it is rated for that much protrusion.

 

[Mike]

Pat are you saying a .060" piston may repair this depending on the largest hole? Really though, it would be best for us to provide better measurements with the proper mic.

 

[Stingpuller]

Pistons

I run mine out .026 with the decked/overboard gasket and it would just kiss the head shifting at 4800 rpm. I did change it when I changed the head gaskets and dropped the piston .010 when it went back together. Alot of things happen at rpm that wouldn't turning it over on the stand. I have allways found a motor to make more power the closer you run the piston to the head. Jeff

 

[Mike]

I run mine out .026 with the decked/overboard gasket and it would just kiss the head shifting at 4800 rpm. I did change it when I changed the head gaskets and dropped the piston .010 when it went back together. Alot of things happen at rpm that wouldn't turning it over on the stand. I have allways found a motor to make more power the closer you run the piston to the head. Jeff

What about skirt to cylinder wall clearance? .030 seems to be a big load on the rings not counting the obvious.

 

[Stingpuller]

Piston to wall

I run .010 on the pistons. I think(fwiw) that to many people try and run these motors to tight. With the power that most are trying to make you need some clearance on the bearings and some room for the piston's to grow. It doesn't really matter gas or diesel when the power goes up the clearance needs to follow suite. If anyone thinks there going to get 100k on a race motor there not being relistic. Big power is hard on parts. I'm not bragging but my motor has been very reliable and I think i'm making ok power. I race every weekend there is someplace to race and I never give it any slack. Jeff

 

[Trippin]

Mike/Mick,

Piston skirt to cylinder wall clearance should be around .006 on that Mahle forged piston when it went together.

 

[Mike]

Mike/Mick,

Piston skirt to cylinder wall clearance should be around .006 on that Mahle forged piston when it went together.

Thanks Guy.

I wonder about the " at a glance " clearance. Would this help explain why the exhaust side of the piston top hit the head and sorta rolled " if you will " into the other side top to head?

 

[Trippin]

Thanks Guy.

I wonder about the " at a glance " clearance. Would this help explain why the exhaust side of the piston top hit the head and sorta rolled " if you will " into the other side top to head?

Yes.