piston to wall clearance

Old January 28th, 2019, 04:31 AM
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piston to wall clearance

need some thought on piston to wall clearance .we've been discussing overheating at break-in on my" building a 455" thread .and im a little concerned it may be too tight clearance im using speed pro l2323f piston and i see in the machinist notes a(.0015/.002 piston to wall) does this seem too tight for a 9.6:1 street build motor ?and will things get looser after putting some time on the motor?
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Old January 28th, 2019, 07:02 AM
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No they wonít get looser unless they finally fail and collapse.
Iíd discuss this with your machinist and ask him why he used such tight clearances.
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Old January 28th, 2019, 07:07 AM
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He told me that all my pistons fall in this range and it is a common clearance. Mark do you think this is detrimental to my build ? Should I run it at all ? From what I read .003 is more like it
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Old January 28th, 2019, 07:43 AM
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.0015-.002 is typical for cast pistons. The L2323 requires .0045 or better, another reason I donít use those.
Your machinist is an idiot. I donít know of ANY forged piston thatís designed to run with less than .003.
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Old January 28th, 2019, 07:48 AM
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At this point what would my options be ? I don’t want to continue to move forward with this if the motor is going to fail down the road . I’m ready to cut my losses now if I have to.
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Old January 28th, 2019, 07:59 AM
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Originally Posted by cutlassefi View Post
.0015-.002 is typical for cast pistons. The L2323 requires .0045 or better, another reason I donít use those.
Your machinist is an idiot. I donít know of ANY forged piston thatís designed to run with less than .003.
Back in my stock eliminator days and stock cast pistons were required,we honed the block just enough to get the piston in the hole.
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Old January 28th, 2019, 08:14 AM
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in the years that the W30 was supposed to be "factory blueprinted" Olds used A pistons with a D bore for 0.0015" more clearance. I found out in the 1970s that TRW pistons would scuff in the bores at the TRW specified clearance, or even a little more like .0035" at the bottom of the skirt, and that .0045" or more was needed, as cutlass efi just said.
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Old January 28th, 2019, 08:23 AM
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Originally Posted by deadeyejedi View Post
At this point what would my options be ? I donít want to continue to move forward with this if the motor is going to fail down the road . Iím ready to cut my losses now if I have to.
Take it to someone else to fix the bores.
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Old January 28th, 2019, 10:32 PM
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I use those pistons and put the clearance at 0.005
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Old January 29th, 2019, 11:14 AM
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Originally Posted by rad View Post
I use those pistons and put the clearance at 0.005
Woof. Does it sound like a maraca?
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Old January 29th, 2019, 12:44 PM
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Originally Posted by oddball View Post
Woof. Does it sound like a maraca?
Now that was some funny sh%t right there spit coffee all over my desk
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Old January 29th, 2019, 05:53 PM
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The Speed Pro catalog I have at the shop says .0025" I looked in another old TRW cat this evening and it says .003. Although it does not state that in the catalog the specs are usually the minimum clearance. Depending on the application you may want more. In your case i would be happy with .003 to .0035

As far as finding another shop that might be taking it too far. As long as you feel that the guy does good machine work, take it back to him and explain that you found the correct specs for the pistons and ask him to take a little bit more out of the block. If it was me that made the mistake I would certainly not charge you. To be honest with you if the pistons were new the clearance should have been on the label on the box. If you still have the box you may even want to double check to be sure that Sealed Power hasnt changed them. It wont be the first time

Also, have you actually measured the clearance ? He might have put the wrong number on the build sheet out of habit. It is your responsibility to check everything if you are assembling the engine.
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Old January 29th, 2019, 06:06 PM
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Originally Posted by BillK View Post
It is your responsibility to check everything if you are assembling the engine.
Truer words have never been spoken. ^^^^^^^^^^^^^^^^^^^^^^^^^^
In reality it's the engine assembler who is responsible for double check. If you're building your own engine and can't verify,you're out of your league. I do not mean to be critical of anybody but it's the truth.
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Old January 29th, 2019, 06:34 PM
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I ran factory cast flat top pistons at .0055 well into the 6300 rpm range in my small block. It was fun and games until the skirts fell off. It didn't make any noise but I found out 3 of the skirts fell off because when I went to drain my oil it was not draining LOL this was after 2 season of racing too. those speed pro forged pistons really need .005 . I ran .005 in my last sbo with the speedpros.

x3 on the checking the machine shops work and knowing what your engine needs. Even some cheap bore gauges and mic sets will get you within a half thou +/- enough to make sure the machine shop did their work correctly or atleast in the ball park.

In my opinion take it all apart check whats already there and check it. I have had machine shops try to give me the run around and try to blame me . Then I tell them well...… lets measure it right now so I can see your claims are correct. Its that very reason I threw a crankshaft through that particular machine shops shop truck. I even left the call tag on it. I never heard from them

Last edited by coppercutlass; January 29th, 2019 at 06:39 PM.
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Old January 29th, 2019, 11:58 PM
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Originally Posted by oddball View Post
Woof. Does it sound like a maraca?
no it actually dont.
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Old January 30th, 2019, 07:24 AM
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Ok so . . . . . I had my warehouse pull a set of pistons off the shelf and take a picture of the label.

This is why you have to double check everything !!!!!!!!! Take a look at the clearance. Maybe the machine shop wasn't so much of an idiot after all ???
Personally I would have to call Sealed Power and check to be certain.


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Old January 30th, 2019, 09:12 AM
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Near 20 years ago I used the same pistons and told machinist that I always used, I'd like 0.0045 clearance. When I picked up the block he sarcastically said," you got your half." He was a good machinist, deceased now. I'd known him over 50 years. The engine is still in one of my cars, no problems.
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Old January 30th, 2019, 10:04 AM
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Speedpro decided China was too expensive, India is known for it's world class manufacturing. FM needs to correct this, specs are way too tight. Of course they are an ancient design anyways and they obviously don't give a dam.
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Old January 30th, 2019, 10:40 AM
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I thought the "F" in the L2323F meant they were forged pistons and forged pistons need more clearance. Either way, .001" clearance is not enough. A call to the manufacturer seems like a good idea. I would also look for the box (label) that the questionable pistons came in. I would think if the label was printed with the wrong minimum clearances, the "Manufacturer" owes you something more than an apology.
.......Just my two cents worth
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Old January 30th, 2019, 10:45 AM
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Originally Posted by olds 307 and 403 View Post
Speedpro decided China was too expensive, India is known for it's world class manufacturing. FM needs to correct this, specs are way too tight. Of course they are an ancient design anyways and they obviously don't give a dam.
For what it's worth. I checked with my buddy/engine builder and he says that SealedPower knows what they're talking about. He says piston design has changed drastically over the years. He said when he worked with a NASCAR Busch team with real racing pistons,.003-.0035 wall clearance was good.
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Old January 30th, 2019, 11:31 AM
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Originally Posted by 66-3X2 442 View Post
He says piston design has changed drastically over the years..
That was my point also. You cannot depend on 40 year old specifications for modern parts even if the part numbers are the same. There are some coated performance pistons that are actually set up with almost zero clearance. The coating is designed to wear away slightly.

What a lot of people do not seem to understand is that pistons expand differently depending on not only the material or the way they are made (cast or forged) but also the design of the skirts and the entire piston. You pretty much have to depend on the manufacturer to give you guidance on the clearances. I suppose you can guess if you want to or rely on old information but no decent machinist or engine builder will do that. Personally I do not try to "remember" or memorize anything when it comes to engine specifications. I look it up every time and if I am buying new parts I use the information from the manufacturer.


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Old January 30th, 2019, 11:32 AM
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Its a common knownthing. The specs speed pro suggest are too tight. Its nothing new.
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Old January 30th, 2019, 11:33 AM
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Originally Posted by OLDSter Ralph View Post
Either way, .001" clearance is not enough.
How can you state that ????
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Old January 30th, 2019, 12:07 PM
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Originally Posted by BillK View Post
How can you state that ????
I can state that because the "thermal coefficient of expansion" for aluminum is different than cast iron. Calling the manufacturer would be a good idea.
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Old January 30th, 2019, 12:14 PM
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Originally Posted by OLDSter Ralph View Post
I can state that because the "thermal coefficient of expansion" for aluminum is different than cast iron.
So ? Cast pistons are aluminum and they have always been run at very tight clearances.

Originally Posted by OLDSter Ralph;1151516[b
Calling the manufacturer would be a good idea.[/b]
You are absolutely correct. But you also obviously do not work on any modern engines where .001 piston to wall clearance is pretty much normal. Main and rod bearing clearances less than .001 Etc Etc How do you know that Sealed Power has not redesigned their piston to a more modern design that will work just fine with that clearance ? Fact is none of us know. Except for the guy that actually designed the latest version of the part.

You cannot simply state that .001 is not enough clearance without knowing the design parameters of the piston, period.
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Old January 30th, 2019, 12:38 PM
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Originally Posted by BillK View Post
So ? Cast pistons are aluminum and they have always been run at very tight clearances.
Whats "very tight".

You are absolutely correct. But you also obviously do not work on any modern engines where .001 piston to wall clearance is pretty much normal. Main and rod bearing clearances less than .001 Etc Etc
No, I don't work on "modern engines" and could careless about them. The OP has an older Oldsmobile engine.

How do you know that Sealed Power has not redesigned their piston to a more modern design that will work just fine with that clearance ? Fact is none of us know. Except for the guy that actually designed the latest version of the part.
If you scroll back to post #1, you'll see that the engine is not a "modern engine". He is using some "modern parts" in an old engine. Without a doubt, things have changed. The OP was having a problem with overheating and piston clearance was something that was brought up.

You cannot simply state that .001 is not enough clearance without knowing the design parameters of the piston, period.
I certainly can state that and I did. You can disagree, and that's your choice.

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Old January 30th, 2019, 02:57 PM
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Originally Posted by BillK View Post
That was my point also. You cannot depend on 40 year old specifications for modern parts even if the part numbers are the same. There are some coated performance pistons that are actually set up with almost zero clearance. The coating is designed to wear away slightly.

What a lot of people do not seem to understand is that pistons expand differently depending on not only the material or the way they are made (cast or forged) but also the design of the skirts and the entire piston. You pretty much have to depend on the manufacturer to give you guidance on the clearances. I suppose you can guess if you want to or rely on old information but no decent machinist or engine builder will do that. Personally I do not try to "remember" or memorize anything when it comes to engine specifications. I look it up every time and if I am buying new parts I use the information from the manufacturer.
That was another one of my guys points. Coated pistons if they go in the hole are good. Let all of these other guys who know more than the piston manufacturer do it their way. I guess they still use 5/64 rings where .043 or narrower are the standard today on production engines. It always amazes me that instructions are meant to be thrown in the garbage.
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Old January 30th, 2019, 04:51 PM
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Originally Posted by 66-3x2 442 View Post
it always amazes me that instructions are meant to be thrown in the garbage.
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Old January 31st, 2019, 02:57 PM
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i spoke with a rep from sealed power today. he looked up my pistons and told me minimum clearance was .001 ,suggested was .0015 to .002 and .0025 was acceptable
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Old January 31st, 2019, 03:11 PM
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Good information and more complete than a box label.
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Old January 31st, 2019, 03:24 PM
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Originally Posted by deadeyejedi View Post
i spoke with a rep from sealed power today. he looked up my pistons and told me minimum clearance was .001 ,suggested was .0015 to .002 and .0025 was acceptable
Is he an experienced machinist or engineer? Cuz if heís just a rep then heís just reading from their own instructions, the same as everyone else. That doesnít necessarily make it right. Just saying.
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Old February 1st, 2019, 02:01 PM
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Originally Posted by cutlassefi View Post

Is he an experienced machinist or engineer? Cuz if heís just a rep then heís just reading from their own instructions, the same as everyone else. That doesnít necessarily make it right. Just saying.
there have been enough people over the years that have learned the hard way with these pistons that its pretty much common knowledge to run about 0.004 - 0.005 clearance with these pistons.
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