Measure Measure Measure!! Piston Woes!!

HackersDna

Test don't Guess
Joined
Aug 29, 2017
So I'm reaching out for someone to confirm Im screwed. Sent block to machine shop to get bored due to cracked pistons which were already .020 over. I ordered JE's which measure 3.8275 out of the box. Was pleasantly surprised to see all were exactly the same. Told machine shop what numbers I had and to be gentle and I would sneak up on my size with a hone. Got block back and all cylinders are right at 3.836 & 3.837. WTH!!! Now what do I do? I know I could have them coated but if I'm correct I think that usually accounts for .005. What would you guys do??
 
accounts for .005.
nope.. .0005
Back to the machine shop w/ that boat anchor. Either you get 6 sleeves, or a fresh block, done as you ordered.
In any case, send the pistons w/ the engine to be machined, along w/ clearance/finish specs you want.
 
Why wouldn't you just hone it in the first place?.
You need to give them the pistions with your block and this shouldn't happen.
 
Yeah Im not saying I did not screw up myself. I should have took measurements before I handed it over. If I had to guess I would bet the bores were prouder than .020 over in the first place and if thats the case I could of honed up to the ideal size. Which updating.. I went and got a better bore mic.. Im still over but its a little closer @ 3.832 & 3.833. The pistons are 3.8275 on the nose. So with those numbers Im thinking the machinist just gave it .010 and ran with it.
And Dank I did have the pistons before but I only gave him the numbers.. Which I know is yet another screw up. But trust me when I say I had my reasons. So Dank I know u know ur engines. With this being a street warrior.. Would u send it?
 
I know where your going with that Archie, and would be happy to do so when I hit it again tomorrow. But I will explain. Yes?
I have two bore mic's. One digital, One sweep. At first I was using a slide mic to pin out my bore gauges because thats what I had here at home. I know a bore mic does not actually measure, It tells the difference which is what I was using the slide for. After my initial post I thought it just had to be me screwing it up. Rules of Diagnostic is always check your equipment. So thats when I went to work and got my Starret outside mic along with a 3" check gauge. Thats how I lost a .004. Did I hit right at what you were thinking?
 
That's odd that your machinest stopped at such odd numbers. Also odd that he left a thou in difference between cylinders. I can see being 1/2 a thou tight on the bottom of the bore, but nowhere near a full thousandths in total bore size.

Basically you've got a .036 and .037 over block. To use the pistons you already have, you'll need another block. To use the block you have, I can make you a set of .037's or you'll need to have it honed again and get some shelf .040's.
 
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There are the mics I have been using Archie. Today is another day. I’m going to recheck everything now that I have calmed down. We all know that errors are usually found in the user.
 
I've always handed the pistons to the machinist and tell him the clearance I want and let him fit the pistons. Fortunately, I have a competent machinist and builder.
 
Swain Tech in New York can coat piston skirts with PC-9 and add up to .004 to the diameter. I have had it done, and the coating is very hard and wears well, but the exact diameter is not very well controlled. Better to put the coating charges toward another set of pistons and sell yours.
 
As a question do you have a bunch of $$ in the block? I know you just had it bored and honed but does it have steel main caps and or a girdle? If not I'd tell you to get another block. Give the piston to the machinist and discuss what side clearance you want prior to machining it.

Neal
 
Which updating.. I went and got a better bore mic.. Im still over but its a little closer @ 3.832 & 3.833. The pistons are 3.8275 on the nose. So with those numbers Im thinking the machinist just gave it .010 and ran with it.

Sooo.... .0045 - .0055 clearance? Or is there a typo?
 
.0045 positive side. Why would I hone it Archie? If it was below spec of the piston you hone up. Not my case. However like I said, I’m sending it. Talked to some veterans of these and they are telling me that .004 is actually a good thing but I better have a good catch can system.
 
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