Piston/Bore Clearance
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TECH Junkie
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From: Port Neches, TX
Piston/Bore Clearance I posted this in external the other day by mistake. Asked a mod to move it and it didn't happen, so I'm posting it again (here)
How close can I get with feeler gauges? I AM gonna buy a 4-5 mic before assembling, just asking. I set each piston in it's bore with the crown flush to the deck and stuck the feeler in at least an inch while loading it to the opposite side. I get 0.002" perpendicular and 0.020" parallel to the crank. I know the pistons are barrel-shaped, but do these numbers sound right? These are forged Wiseco 4.070" slugs...
How close can I get with feeler gauges? I AM gonna buy a 4-5 mic before assembling, just asking. I set each piston in it's bore with the crown flush to the deck and stuck the feeler in at least an inch while loading it to the opposite side. I get 0.002" perpendicular and 0.020" parallel to the crank. I know the pistons are barrel-shaped, but do these numbers sound right? These are forged Wiseco 4.070" slugs...
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From: North Bay, CA
You're only going to be in the ballpark checking it that way, without the block being torqued up and using a properly set bore gauge it's going to be very hard to figure out the actual clearance.
Did you have a shop hone the block for those pistons and now you're just trying to double check their work?
Did you have a shop hone the block for those pistons and now you're just trying to double check their work?
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TECH Junkie
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Yup, just double checking things. Already had one ugly surprise and had to send the pistons back for a rework. Just missed out on a Starrett 4-5 mic, will prolly end up with a no-name special...
piston to Bore clearance... Your feeler gauge is flat and you cylinder bore round so you will not get an accurate reading, you need a bore gauge with a dial indicator wish will also read tenth of thousands so you can accurately satisfy your curiosity.
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True, it will....but part of the issue and why I say you're only going to get a ballpark number is that with how pistons are machined, and intended to be measured, the very bottom of the skirt which will be the tightest point with your feeler gauge is not the proper place to measure the diameter of the piston.
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TECH Junkie
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From: Port Neches, TX
OK, got my mic in yesterday and had a solid check. All pistons are 4.066" and I have only 0.003" clearance. I'm about to look it up on Wiseco's site, but doesn't this seem a little tight, even for coated pistons?
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Yeah, Wiseco usually recommends .0035" minimum so that would be a little tight.
Where are you measuring? If the cylinder was honed with a torque plate, you may see a variation when you measure without a torque plate. It almost certainly won't be as straight and round as it was with it.
Where are you measuring? If the cylinder was honed with a torque plate, you may see a variation when you measure without a torque plate. It almost certainly won't be as straight and round as it was with it.
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TECH Junkie
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From: Port Neches, TX
I measured perpendicular to the pin centerline, at various spots between just under the ring pack and the base of the skirt. Measurements were all identical at these locations. Ah, found my spec sheet, Wiseco recommends 0.004". Block was supposed to have been torque-plate honed. Sent an e-mail to the shop to get their take...
Are you measuring the pistons about an inch up from the bottom of the skirts ??
The shop may have meticulously honed the bores to the nominal bore size, and the pistons do usually gain a thou from the coating so that seems normal. Most of the shops I use will add between .0005" and .001" to the nominal bore size just to give a bit of safety clearance.
Even cast or hyper **** can use just a smidge of extra size as well....
The shop may have meticulously honed the bores to the nominal bore size, and the pistons do usually gain a thou from the coating so that seems normal. Most of the shops I use will add between .0005" and .001" to the nominal bore size just to give a bit of safety clearance.
Even cast or hyper **** can use just a smidge of extra size as well....
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TECH Junkie
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Wiseco sheet says to measure 1.3" down from the crown. Didn't matter though, from just under the ring pack to the end of the skirt was all the same. Shop says they hone for a 0.003" fit on n/a non-nitrous builds, so I'm good!
Thanks!
Thanks!
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TECH Junkie
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Another Q... Are there any 4.080" bore head gaskets around 0.040" thick? I have factory GM gaskets that are (supposed to be) 0.051" compressed. My piston "rock" measurements put me (avg) at + 0.0025" out of the hole, which makes my quench around 0.049" or so. Would love to chop that down a bit and raise my compression back up to 11.4 where I spec'ed it...
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TECH Junkie
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From: Port Neches, TX
!!!!!