Piston Clearance Question
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Mountain Pass
Joined: Feb 2002
Posts: 243
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From: Houston USA
Piston Clearance Question
Long story short. I bought a mild built 460 from an offroad only mud truck. It was pulled out, torn down to the short block to inspect. It had been bored .030 over and there is very slight ridge at the top of the cylinders. Measuring above the ridge shows the original bore was 4.394. Right below the ridge, it measures about 4.398. It has cast pistons and they seem a little loose to me. Feeler gauge from the bottom next to piston skirt, I measure .008 piston clearance, (with feeler gauge pretty tight against skirt) Question, I have is, do you think I’ll hear any piston slap when it’s cold with this engine if I run it the way it is?
Fleet Mechanic
Joined: Apr 2012
Posts: 1,275
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If it was bred 030, measuring above the ridge is the 030 bore after it was bored, measuring below the ridge tells you how much the cyl is worn now, they bore from the top of the cyl, not just under where the ring travel is.
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Mountain Pass
Joined: Feb 2002
Posts: 243
Likes: 1
From: Houston USA
Yep, I shouldn't have said "original bore", by that I meant that's what it was after they bored an honed it .030 over. Then after wear is what I measured right below the ridge. It appears to me whoever built this engine put it together originally on the loose side based on the measurements
Lead Driver
Joined: Mar 2004
Posts: 8,922
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On the street with a cast piston you will start to notice piston slap somewhere beyond .005 measured from the very bottom of the piston. What are you wanting to do with this motor, street or mud truck ? You need to get some real measurements with a set of mics and a bore gage. If it's looking bad and has a noticeable ridge. I'd bet those bores are way out of round and tapered pretty bad as well.
Tuned
Joined: Jan 2019
Posts: 364
Likes: 91
The question is what do you plan to do with it? If it's just for driving around,I would knock the ridge off with a ridge reamer,touch up the bore with a ball hone,stick a set of cast rings in it and let her rip. May or may not hear piston slap when cold but I doubt it.Last a long time,won't cost much.Make sure you know how to operate a ridge reamer!
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