Piston ring gap clearance

[Tom Endy]

When installing new rings in a Model A engine how important is it to check the end gap clearance on a set of rings. What should the end gap clearance measure on a standard bore.

When you order a set of rings for a given bore size can you expect the end gap clearance to already be set?

It seems to me years ago a mechanic would place each ring down into the bore, measure the gap and grind the ends to achieve the desired gap.

Tom Endy

 

[Brentwood Bob]

I believe the rings all need to be gaped. Did that on a motor and remember there are rules of thumb. Will see if my notes on the rebuild.mention the rules for you. No promises I can find it. Bob

 

[Brentwood Bob]

try this:
www.aa1car.com/library/ring_end_gap.htm

bob

 

[Patrick L.]

What you say about how to measure the gap is correct and then to file them to what you want. The ring maker will have their specs, but, a general generic gap would be in the .010-.012" range. The professionals here will know exactly.

 

[pat in Santa Cruz]

ring gap is specified by the manufacturer and usually stated on the packaging. Its nominally .003-.004/inch of bore. Grant recommends .003, while Mahle recommends .004. I always check every ring. They usually need to be filed to fit, although I have had some packages of rings that were perfect out of the box. But I never trust that they are without verification. In the case of re ringing an engine that has been used, check the ring gap at the lowest point in the cylinder where it will be. The only time you should not check the gap is when you really want to tear the engine down a second time

heres a few tips from Mahle. In case you might be running nitro, you'll need a wider gap

http://underthehood.mahleclevite.com/?p=121

 

[Purdy Swoft]

I have used .008 to .010 for the lower ring. center ring gap .010 to.012 top ring .012 to .015. If the manufacturer recommends something different I would follow label instructions. Usually when reringing an engine that hasn't been rebored the new rings will have too much gap . I have used oversize rings and filed the ring gaps. As has been said you need to measure gaps at lowest point of travel.

 

[Chuck Sea/Tac]

I had a .100"over engine I was repairing, and the piston clearance was a little high, about .006" so the rings were about .024" gap. I bought 3 sets of rings (brands) and they were all the same. I called Hastings and talked to their tech, who told me that on a low compression engine it wouldn't matter. They had actually tested different end gaps , and that was their conclusion. So I put it together and it ran fine. It probably hasn't been started in 3 years now, but that's another story.

 

[Purdy Swoft]

My thought is if the ring gap is way too much, you won't have as much tension between the ring and the cylinder wall. Oversize rings that have been filed to fit the cylinder with correct gap will have more tension and will help overcome the wear in the cylinder wall. It doesn't matter what oversize the cylinders have been bored, the ring gap specs will remain the same. Oversize rings for modern engines are usually no problem to obtain at the local parts store. The model A vendors only offer ring sizes in .020 incriments. I have filed ring gaps on .020 oversizes rings and used them on NOS .005 oversize pistons. As long as you have the correct gap at the bottom of ring travel in the cylinder, the rings will have room for expansion as the heat increases. Its better to have too much gap than not enough. Back in the day, Ford made pistons and rings in oversizes like three, five, ten, and fifteen thousants oversizes. Ive seen pistons in sizes like .045 and .090 oversize. Rings and pistons are no longer made in odball oversizes for model A engines that I know of. I've had good luck finding rings in odball sizes for model A engines on eBay.