Piston pin to rod clearance

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They will bush them then hone them to clearance.
 
First, you shouldn't 'drill' the rods for pin clearance, you hone them.

But why bother with a low rpm cast piston? Although those pistons accept circlips for floating pins, there is no benefit for a low rpm street engine.

Depending on the rod, bushing it might weaken it with the metal removed for the bush.

Expensive operation for no benefit. Probably cheaper to buy new rods that come bushed & with high quality bolts.
 
famous bob said:
I ran steel to steel on a 383 sbc , worked fine , you have to make sure they get oil !!!
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It might "work", but then you have no sacrificial metal. Wear occurs on either the rod or the pin. Or both. Something has to give, and you should prefer to have it be the inexpensive bushing that is easily replaced. If operating on a tight budget I'd look for a decent set of forged 340 rods. If not so much, buy new forged.
 
Captainkirk said:
It might "work", but then you have no sacrificial metal. Wear occurs on either the rod or the pin. Or both. Something has to give, and you should prefer to have it be the inexpensive bushing that is easily replaced. If operating on a tight budget I'd look for a decent set of forged 340 rods. If not so much, buy new forged.
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Wasn`t my first choice , but in expensive and the machinist gauranteed it would work , said he`d done it many times , it did !
 
famous bob said:
Wasn`t my first choice , but in expensive and the machinist gauranteed it would work , said he`d done it many times , it did !
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It’s done more than people think, especially before aftermarket rods got so cheap. It works. You just have to do it right.
 
On the subject of pin clearance, a 440 I am building came supplied with Ross pistons. Quite surprised how 'sloppy' the pin fit is, much looser than the pin in a factory piston.
 
Bewy said:
On the subject of pin clearance, a 440 I am building came supplied with Ross pistons. Quite surprised how 'sloppy' the pin fit is, much looser than the pin in a factory piston.
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How loose ''is em "" ?
 
Many top race engines run unbushed rods today. I have two sets of Pankl rods ($2400.00) from Hendrick's NASCAR team and those are unbushed.

The Crower rods for my 388" BM are unbushed.

My old friend used used to be a crankshaft specoalist for Rousch... they don't run bushed rods anymore, either.
Pankl rods.jpg
 
Krooser said:
Many top race engines run unbushed rods today. I have two sets of Pankl rods ($2400.00) from Hendrick's NASCAR team and those are unbushed.

The Crower rods for my 388" BM are unbushed.

My old friend used used to be a crankshaft specoalist for Rousch... they don't run bushed rods anymore, either.View attachment 1715720026
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How often are those engines torn down, though?
 
Captainkirk said:
How often are those engines torn down, though?
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My Crower rods were new in 1990... ran in a street strip car all those years. The Pankl rods ran 500 miles at 9,000 rpm. I would think that is pretty good evidence that unbushed rods work and these NASCAR engines run a dry sump without much oil flying around the sump.

I questioned this too... every machine shop and engine builder I spoke with said it's not an issue. New cars and most aftermarket rod today do not have squirt holes in the rods, either. A big nono for many years.
 
Krooser said:
My Crower rods were new in 1990... ran in a street strip car all those years. The Pankl rods ran 500 miles at 9,000 rpm. I would think that is pretty good evidence that unbushed rods work and these NASCAR engines run a dry sump without much oil flying around the sump.

I questioned this too... every machine shop and engine builder I spoke with said it's not an issue. New cars and most aftermarket rod today do not have squirt holes in the rods, either. A big non.o for many years.
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No doubt they work, and likely pretty well on a strip or circle track motor. But for a 50 year old street car that gets the oil changed every 5000 miles or so...and you hope to get 100k out of...I would still recommend bushed rods.
 
Captainkirk said:
No doubt they work, and likely pretty well on a strip or circle track motor. But for a 50 year old street car that gets the oil changed every 5000 miles or so...and you hope to get 100k out of...I would still recommend bushed rods.
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Well we can agree to disagree...
 
Bob,
Post #13. To answer your question, how loose? Do not have a measured amount; but definitely 'looser' & looser than the pin fit in other aftermarket pistons that I have used.
 
I agree with a lower compression street build, floating pins probably add no more than ease of assembly. But in higher compression builds, it's been seen on a dyno where they can free up a little HP by reducing friction.
 
Krooser said:
My Crower rods were new in 1990... ran in a street strip car all those years. The Pankl rods ran 500 miles at 9,000 rpm. I would think that is pretty good evidence that unbushed rods work and these NASCAR engines run a dry sump without much oil flying around the sump.

I questioned this too... every machine shop and engine builder I spoke with said it's not an issue. New cars and most aftermarket rod today do not have squirt holes in the rods, either. A big nono for many years.
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Most pistons have forced oiling from the oil ring now ---------------
 
Bewy said:
Bob,
Post #13. To answer your question, how loose? Do not have a measured amount; but definitely 'looser' & looser than the pin fit in other aftermarket pistons that I have used.
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I have always been under the impression that .001 was perfect , thats the reason I asked what u had.
 
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