FlyCutting/PTV issues/questions

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Jun 22, 2006 | 02:54 PM

Mcduffys

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FlyCutting/PTV issues and questions. Insight Please.

I have a couple questions inregards to flycutting and ptv, due to a recent incedent that happened with my brothers car.

When flycutting are you suppose to make reliefs for both the intake and exhaust? Or does it depend on your heads and ptv clearance?

If you dont flycut enough and have pistons kissing valves, could this cause a rod bolt/bolts to stretch?

Last edited by Mcduffys; Jun 22, 2006 at 05:24 PM.

Jun 22, 2006 | 03:57 PM

Xtnct00WS6

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In my opinion you only need to make valve relief's when you have below recommended clearances. This could mean only making relief's on just the intake. Minimum clearance should be .080 on the intake and .100 on the exhaust. If you're below either of those, you should flycut to attain those clearances.

If the valves hit the pistons, you can say bye bye to your engine.

This is what will happen if you don't have the right clearances:
https://ls1tech.com/forums/generation-iii-internal-engine/515815-damage-engine-pics.html

Good info on the topic:
https://ls1tech.com/forums/showpost....64&postcount=6

Jun 22, 2006 | 05:22 PM

Mcduffys

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Quote:

Originally Posted by Xtnct00WS6

In my opinion you only need to make valve relief's when you have below recommended clearances. This could mean only making relief's on just the intake. Minimum clearance should be .080 on the intake and .100 on the exhaust. If you're below either of those, you should flycut to attain those clearances.

If the valves hit the pistons, you can say bye bye to your engine.

This is what will happen if you don't have the right clearances:
https://ls1tech.com/forums/showthread.php?t=515815

Good info on the topic:
https://ls1tech.com/forums/showpost....64&postcount=6

Ok his particular case, only the Intake valve was flycut when his head swap was done. Well roughly 800-1000miles later, he loses oil pressure and is down on power.

We tear it down and find that every piston but #4 has hit on the exhaust valve. Not enough to destroy a piston but enough to kiss each one and mark it to the point that they look as if they have been flycut(which was confirmed wasnt done by the shop). We also noticed on one of heads that the #7 piston hit quite a bit and more so than any other.

Next we tore down the bottom end to find that #7 rod bearing is toast. As well as the fact that is fused itself to #3. With further insepction ALL of the other bearings, rod bearings and main caps look almost brand new(very little sign of wear), considering the car has 65k on it.

Through out the whole motor we also found 2 different types of metal.
Aluminum and bearing metal(obviously from the toasted bearing.) We found the aluminum EVERYWHERE. the pan, the pick up tube, on the valves, etc.

The question in hand is what would of caused this?

Is it a PTV issue?
-Did the piston hit and caused pieces of aluminum to to destroy that bearing?
-Did pistions hit and cause the rod bolt on #7 to strech?

Is it Rod Bolt issue?
-Did the #7 rod bolt stretch under load, which inter caused the rest of the pistons to hit valves ?

Is it another issue?
-Did all the aluminum/metal that was found under the pick up tube casue it ?
-Is it another issue that is not being thought of?

Any help or insight would be appreciated. Thanks in Advance.

Jun 23, 2006 | 09:24 AM

Mcduffys

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bump.....

Jun 23, 2006 | 09:31 AM

Xtnct00WS6

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I'd be willing to be it was a PTV clearance problem. The valves are NEVER supposed to hit the pistons. If they hit on the exhaust side, and you have evidence of this, then that's probably it.

Those bits of metal from the pistons had to go somewhere, so to the pan they went.

Jun 23, 2006 | 09:48 AM

Mcduffys

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Quote:

Originally Posted by Xtnct00WS6

Exaclty what we were thinking. Since they didnt cut the exhaust side and all pistons had kissed valves except #4.

Im thinking since the pickup tube sits over #3 and #7 all the metal that was being drawn to that area is what took out #7.

Any thoughts on that ?

Jun 23, 2006 | 02:49 PM

Patrick G

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The .080"/.100" clearance is a textbook figure for P to V. With wide splits between intake and exhaust duration, you'd be surprized how often the exhaust valve is the one that hits.

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