512 stroker piston to wall clearance opinions

[Llamaback]

Hey guys, just looking for some feedback on an engine block I recently got back from the machine shop. I have been checking it over with a dial bore gauge and have noticed that it is looking like the piston to wall clearance is too tight. It is tight on the thrust faces of the walls though, I have two cylinders that measure as little as .0035'' clearance in the middle area of the cylinder. On all of the cylinders the middle area of the thrust faces seems to be the tightest (many cylinders are at .004'' clearance. Other than the tight thrust faces in the middle areas the bores in general are around .005'' clearance.

This block is at .055 overbore and using Icon forged 2618 T-6 aluminum pistons. The block was bored/honed with a torque plate, I even bolted on one of my old iron heads (I don't have my new aluminum heads yet) and re-measured and it looks like the bore is even a little tighter. Is there any possible reasons you know of why it would have been honed this way? Am I being too picky? Is it possible that when the engine is hot and up to operating temp that the thrust faces of the walls expand out further than the opposing faces?

I am kinda thinking I need to get it back to a machine shop and have it re-honed, the 440 source instructions call for a clearance right around .005''. Thanks for any feedback!

 

[pnora]

How accurate is your gauge?

 

[Llamaback]

How accurate is your gauge?

I think it is pretty accurate, but that is a good point. I mic'd off of a piston and zeroed the gauge to that and also measured the cylinder with the bore gauge and checked that with a micrometer as well. I also put a mark on the cylinder walls at the same depth on each side using a caliper to double check myself and the cylinder measured the same that way as well. I used the same gauge to measure my mains and my measurements agreed very well with plastigage.

 

[oldkimmer]

R u just checking 1 piston in one hole or all pistons in their respective holes? Or same piston in all holes? Kim

 

[dvw]

Are you saying the dial bore gauge reads .0015 tighter in the middle of the bore than at the top or bottom?
Doug

 

[Zeppelin264]

I'd call 440 Source and ask. We just went through this and are sitting at about .0045" and they said to run it but to not hang it at 8,000 rpm all day long.

I learned that machine shops usually under cut the bore by like .001 to make sure the piston to wall clearance is good. But in your case, it was not enough.

 

[RemCharger]

Put a ring in it and measure gaps down the cylinder

 

[Llamaback]

Are you saying the dial bore gauge reads .0015 tighter in the middle of the bore than at the top or bottom?
Doug

yes

 

[Llamaback]

R u just checking 1 piston in one hole or all pistons in their respective holes? Or same piston in all holes? Kim

I mic'd all the pistons and dial bore gauged all holes. I am looking at clearance with my smallest piston in the tightest hole

 

[RemCharger]

Back in the day they honed each cylinder for each piston. Is there a numbering?

 

[Llamaback]

Back in the day they honed each cylinder for each piston. Is there a numbering?

No the machine shop did not number any of the pistons. They are all within .0003 of each other

 

[oldkimmer]

Back in the day they honed each cylinder for each piston. Is there a numbering?

The Block Shop in Edmonton bored and torque plate honed a 440 block for a guy I know and all they did was measure 1 piston and bored all 8 holes from its measurement. And guess what what? All pistons were not all the same size like they said they were. Had to re hone some the bores bigger.

 

[Gunner1]

I would take it back to the shop. It is possible that depending on the hone used or clamping protocols used that the hone head overdwelled at the ends of its stroke. At least call them.

 

[Geoff 2]

Find out from the piston maker what the clearance should be.....& go from there. Do NOT rely on second hand info...

 

[icetech]

Put a ring in it and measure gaps down the cylinder

That's a good tip.. wouldn't have thought of that

 

[gkent]

Hey guys, just looking for some feedback on an engine block I recently got back from the machine shop. I have been checking it over with a dial bore gauge and have noticed that it is looking like the piston to wall clearance is too tight. It is tight on the thrust faces of the walls though, I have two cylinders that measure as little as .0035'' clearance in the middle area of the cylinder. On all of the cylinders the middle area of the thrust faces seems to be the tightest (many cylinders are at .004'' clearance. Other than the tight thrust faces in the middle areas the bores in general are around .005'' clearance.

This block is at .055 overbore and using Icon forged 2618 T-6 aluminum pistons. The block was bored/honed with a torque plate, I even bolted on one of my old iron heads (I don't have my new aluminum heads yet) and re-measured and it looks like the bore is even a little tighter. Is there any possible reasons you know of why it would have been honed this way? Am I being too picky? Is it possible that when the engine is hot and up to operating temp that the thrust faces of the walls expand out further than the opposing faces?

I am kinda thinking I need to get it back to a machine shop and have it re-honed, the 440 source instructions call for a clearance right around .005''. Thanks for any feedback!

Didn't you give the shop a piston to work with and the specs before they machined it ??

 

[Rebelrouser]

Hey guys, just looking for some feedback on an engine block I recently got back from the machine shop. I have been checking it over with a dial bore gauge and have noticed that it is looking like the piston to wall clearance is too tight. It is tight on the thrust faces of the walls though, I have two cylinders that measure as little as .0035'' clearance in the middle area of the cylinder. On all of the cylinders the middle area of the thrust faces seems to be the tightest (many cylinders are at .004'' clearance. Other than the tight thrust faces in the middle areas the bores in general are around .005'' clearance.

This block is at .055 overbore and using Icon forged 2618 T-6 aluminum pistons. The block was bored/honed with a torque plate, I even bolted on one of my old iron heads (I don't have my new aluminum heads yet) and re-measured and it looks like the bore is even a little tighter. Is there any possible reasons you know of why it would have been honed this way? Am I being too picky? Is it possible that when the engine is hot and up to operating temp that the thrust faces of the walls expand out further than the opposing faces?

I am kinda thinking I need to get it back to a machine shop and have it re-honed, the 440 source instructions call for a clearance right around .005''. Thanks for any feedback!

2618 pistons expand more when hot, .005 is a good clearance in my experience, if they are as tight as you measure it will scuff the skirts. On a racing engine I run them as loose as .007 to keep them from scuffing. Make sure when measuring the piston you do it in the right spot on the skirt. Should be directions with the piston. Many times I measure it the old dog way, lay a long feeler gauge in the cylinder and insert the piston, you should have a slight drag when removing the gauge.

4032 alloy forged pistons expand less and the clearance you have is more in line with that alloy piston.

 

[zyzzyx]

When honing a block, it should be easy to keep the bores straight from top to bottom within 0.0003.

 

[gkent]

The Block Shop in Edmonton bored and torque plate honed a 440 block for a guy I know and all they did was measure 1 piston and bored all 8 holes from its measurement. And guess what what? All pistons were not all the same size like they said they were. Had to re hone some the bores bigger.

That's a piston manufacturer problem - not a machine shop problem. Poor QC by the piston mfg.. Even if the shop had measured all the slugs, they likely would have suggested you send them back. Just imagine if they'd fitted each piston to your block and at some point you damage a piston and the new one doesn't fit because the piston manufacturing tolerances suck !!

 

[69Bee]

It is possible that they did not "Short Stroke" it enough in the middle of the cylinder to keep it straight, but I have a better question for you, what is the resolution of your bore gauge? If you bore gauge measures in 0.0001" increments, you can read the size accurately, but if your gauge only measures in 0.001" increments, you are only guessing down to the ten thousandth dimension. If a torque plate was used, the top would be smaller by about 0.0025" since the head bolts will pull it out when tightened. The bore clearance will be determined by your conditions. Street N/A will run on average 0.003"-0.0035" piston clearance, whereas any power adders will increase the clearance required. The piston spec sheet included with your pistons will detail this for you. As for your rings, the same applies and will be detailed on the spec sheet that came with the rings.