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Old 09-09-2015, 09:50 AM   #1
1955cj5
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Default Piston movement...

I bought a core engine and am getting it ready to send to the machinist...

Happened to notice that there is quite a bit of side-to-side movement in the pistons..

I'm able to get an .030 feeler gauge in the gap no problem..

I don't have any way to measure the bore except at the top rim..it's about 3.909 to 3.914..

I'm thinking those .030 over pistons have been in there a very long time...there are piston expanders in the skirts...
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Old 09-09-2015, 09:56 AM   #2
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Default Re: Piston movement...

Depends on where you are measuring. The top of the piston is normally a smaller diameter at the top by the ring lands than the diameter of the skirt. Sticking a feeler gauge in at the top will not tell you what the piston clearance is.
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Old 09-09-2015, 10:11 AM   #3
Patrick L.
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Default Re: Piston movement...

Piston to wall clearance is measured from the piston skirt [90 to the pin] and the bore. The ring land area is smaller.
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Old 09-09-2015, 10:22 AM   #4
1955cj5
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Default Re: Piston movement...

OK I can measure that at the skirt....I'll let you know...Will the expanders need to come off? I'm not sure how they attach...there is an angled slit in the skirt and the expanders are in that slit
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Old 09-09-2015, 11:05 AM   #5
Tom Wesenberg
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Default Re: Piston movement...

If you are doing an engine rebuild, then I'd buy the next oversize and have the cylinders bored to fit.
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Old 09-09-2015, 11:08 AM   #6
George Miller
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Default Re: Piston movement...

Quote:
Originally Posted by Tom Wesenberg View Post
If you are doing an engine rebuild, then I'd buy the next oversize and have the cylinders bored to fit.
Plus 1
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Old 09-09-2015, 11:59 AM   #7
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Default Re: Piston movement...

There was a shop in L. A. Cal. Lou's Garage advertised overhauls with new rings and expanded pistons, adjust valves, new gaskets & Etc. A real bare bones job done very cheap. I went there with a friend to pick up his car and noticed the dirt parking area was well oiled! I thought of this when I saw your expanders
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Old 09-09-2015, 01:01 PM   #8
1955cj5
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Default Re: Piston movement...

Quote:
Originally Posted by Tom Wesenberg View Post
If you are doing an engine rebuild, then I'd buy the next oversize and have the cylinders bored to fit.
Well that was one of my questions...would you buy pistons first and then bore to fit, or see how far it needs to be bored and then buy pistons? Or is the .010 size increase generally enough to take care of out of roundness or other issues? There are a few small corrosion pits in the walls of #3..

I'm sure I'm dreaming but I was sort of thinking I could buy .010 over babbitt rods(the rod journals measure .009 under...all within .0005) from Bert's, and a set of .040 pistons and rings and after it's bored I could do the assembly myself....
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Old 09-09-2015, 01:33 PM   #9
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Default Re: Piston movement...

Have the machinist mike everything, then you can buy what is recommended and assemble it yourself. If the shop assembles it you may benefit from any implied warrantee.
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Old 09-09-2015, 02:18 PM   #10
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Default Re: Piston movement...

Interesting. I don't see any ridge, or did you remove such ?
I would have machinist / engine builder measure engine and IF it is in good sound basic condition...bore/fit pistons to his recommendations.
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Old 09-09-2015, 02:21 PM   #11
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Default Re: Piston movement...

Quote:
Originally Posted by 1955cj5 View Post
Well that was one of my questions...would you buy pistons first and then bore to fit, or see how far it needs to be bored and then buy pistons? Or is the .010 size increase generally enough to take care of out of roundness or other issues? There are a few small corrosion pits in the walls of #3..

I'm sure I'm dreaming but I was sort of thinking I could buy .010 over babbitt rods(the rod journals measure .009 under...all within .0005) from Bert's, and a set of .040 pistons and rings and after it's bored I could do the assembly myself....
You would have to purchase the pistons after the machine work because it may take more than .010 to get the cylinders cleaned up.
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Old 09-09-2015, 02:26 PM   #12
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Default Re: Piston movement...

A well oiled parking area is fine, as long as the dirt stays outside. I know a tractor mechanic that works with his hands full of dirt and grease, even while installing valves and pistons. He won't be doing any engine work for me. I also stopped at Harkin in Watertown, S.D. to see his babbit operation. He wouldn't let me see it buy pointed to the building it was in. It appeared to be an old chicken coup. My friend had his engine babbit done by him, and the block was full of dirt and sludge when he got it back. We had to take it apart and clean it up. Another guy had the same complaint from work done by him. I think he's no longer in business.
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Old 09-09-2015, 02:30 PM   #13
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Default Re: Piston movement...

Quote:
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You would have to purchase the pistons after the machine work because it may take more than .010 to get the cylinders cleaned up.
Actually the norm is to measure and inspect, then buy the pistons and bore and hone to fit the new pistons. A lot of shops will jump the bore by .030" just to be sure, but I'd rather go just enough to get past any out of round or taper.
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Old 09-09-2015, 02:48 PM   #14
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Default Re: Piston movement...

Cylinders wear more on one side than the other. Most of the time you need to double what the wear is. If it checks .010 over size at the top of cylinder, it probably is going to take .020 to clean up.
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Old 09-09-2015, 02:59 PM   #15
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Default Re: Piston movement...

Quote:
Originally Posted by Tom Wesenberg View Post
Actually the norm is to measure and inspect, then buy the pistons and bore and hone to fit the new pistons. A lot of shops will jump the bore by .030" just to be sure, but I'd rather go just enough to get past any out of round or taper.
You learn something new everyday! I thought it made sense to bore .010 over and see if that cleaned it up enough and if not then machine another .010 off and if that did the trick, then purchase pistons based on how much the machinist had to go over stock measurements. Then when pistons came in, hone the cylinders so the pistons had an adequate amount of clearance.
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Old 09-09-2015, 03:33 PM   #16
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Default Re: Piston movement...

I measure the bores with a bore gage to find the maximum taper and out of round. Take that measurement and divide it by .7, that usually gives you an approximation of the minimum oversize that you need. Example, .023 difference from top to bottom divided by .7= .0329, so you would need at least .040 larger than it is now. You will have to go to the next largest piston available, unless you want to spring for some custom made ones. $$$$$
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Old 09-09-2015, 07:57 PM   #17
1955cj5
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Default Re: Piston movement...

I'd say #2 had some "issues"..
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Old 09-09-2015, 08:01 PM   #18
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Default Re: Piston movement...

Quote:
Originally Posted by 1955cj5 View Post
I'd say #2 had some "issues"..
Just a few
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Old 09-10-2015, 12:42 PM   #19
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Default Re: Piston movement...

Cj5 do you have a photo of the entire top of the block where you posted the top of the piston? Just curious.
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Old 09-10-2015, 02:16 PM   #20
1955cj5
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Default Re: Piston movement...

I can sure take a picture...the pistons are all out but the valves are still there....are you looking for something specific?

Here's one...
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