LLY: Fingers pistons PTW and ring land clearance

[dirtymax36]

Does anyone here happen to know the PTW tolerance for a set of mahle cast oval bowls with .025 valve reliefs ?

Also, can anyone tell me the bore size of my pistons i have here just to verify..theres no specific number or bore size stamped on the piston is why i ask. The bore itself measures a 4.088 and the piston measures a 4.054. I believe this is stock bore but would like someone to verify. Thanks!

 

[PureHybrid]

Clearance is in the .003-.004 range I think. Those pistons are stock bore, your block is definitely not.

 

[Chevy1925]

Clearance is in the .003-.004 range I think. Those pistons are stock bore, your block is definitely not.

probably just a used high mileage block on stock bore.

EDIT: clearly need to look at the damn 0 zeros.

 

[DAVe3283]

His block is at least 20 over (close to 30 over?!?). The stock bore production value is 4.0551-4.0557 in.

I built my motor with 300k on the clock, and it was within service limits for the stock bore (spec is 4.0594" max). I can't imagine that block ran long enough to get 28 thousandths over the service max without beating the pistons to death and worse. I suspect it is either mis-measured, or some really whack machine work.

 

[PureHybrid]

The last engine I pulled apart that was wore +.020, it wouldn't even run. If his block is truly wore that bad, it would have a ridge (or a cliff!) so bad, I'd hope he'd be smart enough to NOT use it.

I'd say his block was set up for +.030"

 

[DetailsUnlimited]

John told me Cast PISTON PTW 0.0015"-0.0025" for my 20% overs

 

[Chevy1925]

His block is at least 20 over (close to 30 over?!?). The stock bore production value is 4.0551-4.0557 in.

I built my motor with 300k on the clock, and it was within service limits for the stock bore (spec is 4.0594" max). I can't imagine that block ran long enough to get 28 thousandths over the service max without beating the pistons to death and worse. I suspect it is either mis-measured, or some really whack machine work.

The last engine I pulled apart that was wore +.020, it wouldn't even run. If his block is truly wore that bad, it would have a ridge (or a cliff!) so bad, I'd hope he'd be smart enough to NOT use it.

I'd say his block was set up for +.030"

no no, you guys are right, my visual skills are subpar today.

 

[dirtymax36]

Update; I got another set of calipers to measure the bore. Here’s the most recent measurements
Bore; some cyls are 4.088, largest ran a 4.091
Piston; 4.052

Edit= engine did have blow by on higher rpm runs

 

[dirtymax36]

These pistons out of this engine fit in a stock bore block fine physically, and a stock lb7 piston measures a 4.016 on my calipers just in case my calipers are off.

If I take a stock piston back into the larger bore block, it’s extremely loose.

 

[PureHybrid]

Your measurements make no sense at all. Are you measuring both pistons around the skirt? Find a good mic, measure a piston skirt, lock the mic down and clamp in a vise, set up a dial bore gauge, set zero on the gauge inside the mic, take the differential measurement of the cylinder bore. That will give you PTW.

 

[S Phinney]

Stock pistons and bore run .0015 clearance. Mahle race cast run .0035 ptw clearance. Stock bore is 4.055. Clearance is built into the piston.


Sent from my iPhone using Tapatalk

 

[torqued2dmax]

These pistons out of this engine fit in a stock bore block fine physically, and a stock lb7 piston measures a 4.016 on my calipers just in case my calipers are off.

If I take a stock piston back into the larger bore block, it’s extremely loose.

Yes if you put a stock piston in a 30 over block , bad things will take place very fast ! Are you going to build this eng yourself ? If yes , keep us informed as to your progress !

 

[Fingers]

Does anyone here happen to know the PTW tolerance for a set of mahle cast oval bowls with .025 valve reliefs ?

Also, can anyone tell me the bore size of my pistons i have here just to verify..theres no specific number or bore size stamped on the piston is why i ask. The bore itself measures a 4.088 and the piston measures a 4.054. I believe this is stock bore but would like someone to verify. Thanks!

PTW should be 0.0015" to 0.0025". Expected bore should be one of 4.055", 4.075", or 4.095".

You're gonna need some block work and/or a different set of pistons.

I would have to go back through my records, but I haven't made 0.025 relief pistons in over 5 years. Do you have pictures?

 

[Fingers]

These pistons out of this engine fit in a stock bore block fine physically, and a stock lb7 piston measures a 4.016 on my calipers just in case my calipers are off.

If I take a stock piston back into the larger bore block, it’s extremely loose.

You are measuring in the wrong place. Measure just above the bottom of the skirt, perpendicular to the pin.

 

[Fingers]

I hope your not trying to measure the bore with a set of calipers. Epic fail. If your going to do this, either get the proper tools or borrow them. Get a bore gauge or at least a set of telescoping gauges like these https://www.mscdirect.com/product/details/86421013

There is a proper way to use them.

 

[dirtymax36]

The reliefs were cut by a different machine shop. Not factory.