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Piston Ring Gap

P

pburchett

Member
I have pulled the sleeves on my Ford 640 and replaced them with new. I have fitted the new pistons to their respective cylinders. I now need to gap the rings. The manual calls for a 0.01 to 0.02 gap.

Persons on here suggest a 0.003 to 0.004 gap per inch. The bore is 3 7/16 or 3.4375 inch which correlates to a gap of 0.010 to 0.014

What gap should I aim for?
 
4 x the bore for the top ring. .005 for
the 2nd ring. Generally will be a
instruction booklet with the rings.
 
WOW! Obsessing over ring end gap with new sleeves???

You must fear you have substandard parts?

ENNYWHO, ring end gap is highly over rated as to the cause of blowby or oil burning.

Piston ring side clearance in worn ring grooves is a far bigger issue, but with new pistons (hopefully) it will not be a concern.

In reality, the biggest concern with ring end gap (especially with a tapered bore) would be to have too little.


For a treatise on this subject, check out he site linked below.
Fit that ring
 
I never considered end gap if installing rings, pistons, and sleeves as a kit. Should be right, but Murphy's gremlins could be hiding under the workbench.
 
Using the specs you gave, You need to be .010 or as near to and above that as possible. .020 is probably the limit where you need to think
about replacing the rings.

I do check the rings: Most are o.k. right out of the box. BUT over the years I have found two that would have been under the minimum spec.
I was sure glad I checked them. If you ever saw the mess rings make of a piston when they have too little end clearance, you would
understand why.
 
I've rebuilt a few engines and always have measured the ring gap. Never yet found one that was not to spec. Despite that, I'll still measure on the next rebuild I do. The small amount of time it takes is nothing compared to the large amount of time and money it would take to fix the damage a a bad one would do should it happen. The same for bearings, pistons, and so on.
 
just as the manual says... its giving the min. and max. the fear is not too much its not enough that counts!
 
Checking ring gap in new sleeves with new rings is a very good idea. I bought a new kit from NAPA years ago with all the rings in one box. One pack of rings in the box of four would over lap by a couple thousands. When I took it back the counter guy said it happens sometimes!
 
It is good to check them. But I don't think I've had any that needed any fitting.
I have to admit I am guilty of not checking ALL of the rings. I today's poor quality control world of parts might be wise to take the extra time and check ALL of the rings.
 
Place a fine file in the vise and hold the ring on each side of the file pulling down gently filing the ring. No expensive tool needed. Ring gap has become of less concern in recent engine building thought. Better too much than not enough.
 
I gave each ring a good healthy 0.014 gap. Clamped the dremel in the vise and used a cut off disk. Just had to squeeze the ring together on the cut off disk to remove the excess. It worked great.
 
(quoted from post at 21:21:07 03/26/19) Place a fine file in the vise and hold the ring on each side of the file pulling down gently filing the ring. No expensive tool needed. Ring gap has become of less concern in recent engine building thought. Better too much than not enough.
Click to expand...

That not enough will get you a re-do every time :(
 
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