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TR4/4A New TR3-TR4 RingTolerance Questions ????

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M

mallard

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Was going to put the engine together this weekend but just ran into this. The new 87MM piston and liner set that I got does not meet the rings gap specs from the manufacturer. I was suspect about these County piston and liner sets in the first place but they did come from one of the better parts houses.

The specs state that there should be .003--.004 gap per inch of cylinder diameter. Cylinder diameter is 3.45" That works out to .01035 to .0138

What I come up with when I measure is .016 .017 and .018 for all the rings. Very sloppy even with the .0138 tolerance.

Without spending a ton of money on pistons and liners is this what I should expect?

By the way the original factory tolerances were .003 .010

Has anybody else delt with this? I'm thinking of sending the whole lot back, but I've had them for 2 or 3 months.
 
I'd send them back! .010 is plenty if you aren't going racing; and new rings are typically slightly oversize so you can file them to fit.
 
Hi Keith, It might be better to ask the parts supplier to send you a suitable set of new piston rings, but only if the piston and cylinders spec out and look presentable. Good luck, Bill C. Mesa,Az
 
Even in racing you need to use the above stated .003 for every inch. Otherwise you will score the cylinder walls.
.016" would be a bit wide but may not be worth sedning them back or selling the kit.
 
<span style="font-weight: bold"><span style="text-decoration: underline">SEND THEM BACK</span></span> - what you received is not acceptable. If they offer to send you replacements, ask them to measure the pistons and rig gaps first, as to avoid a repeat performance! IMO, If they balk, I would trade with someone else!
 
Thanks guys, will call them tomorrow and see what happens. May have to break down and spend some more. I'm not looking at building a hot engine, just one that will last.
 
I got the new rings from BPNW and checked them today. Ring gap is at the low end of the tolerance specs. and the ring width and gap is just where it should be. The rings were made by Grant but they fit great with the County pistons. I did have to file a few of the rings to get them correct. Never just expect that the parts you buy will work, always check.
 
Thanks for the update Keith, and for the reminder.

Keep us posted on the engine rebuild, and some pictures if you get a chance would be great ;-)
 
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