A question on Les Andrews's ring specs

700rpm

700rpm

Well-known member
UPDATE A question on Les Andrews's ring specs

Les specifies ring gaps as .012-.015 for top; .010-.012 for middle. .008-.010 for bottom.
Tbirdtbird specifies .022 top; .-016-.018 for middle.

I used Les's when I put my engine together. I didn't have Tbird's specs at that time. The engine seems pretty tight when it's warmed up. Now I'm wondering if I should tear it down and reset the gap.

These are significantly different. Can anyone explain that?

See 5/21/15 followup below.
 
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700rpm said:
Les specifies ring gaps as .012-.015 for top; .010-.012 for middle. .008-.010 for bottom.
Tbirdtbird specifies .022 top; .-016-.018 for middle.

I used Les's when I put my engine together. I didn't have Tbird's specs at that time. The engine seems pretty tight when it's warmed up. Now I'm wondering if I should tear it down and reset the gap.

These are significantly different. Can anyone explain that?
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I would go with Les's specs , General rule is .004 per inch of bore for top ring and less for the others.
4 in. bore =.016, model a is 3 7/8.
.022 is kind of excessive.
Bill
 
I don't know the specifics on B&S engines, but the end gap is dependent on many factors, including bore diameter. All else being equal, the larger the diameter the larger the ring gap needed for expansion.
 
A Briggs is not a Model A, especially considering the bore size. I'd recommend .004/1" of bore for first and second rings. If you were to tear it down, if only for a look-see, check the ends of the rings to see if they are shiny. That would be a sure sign they do not have enough end gap. An end gap too large is always much less of a problem than one too tight.
That Briggs manual also said .005 ring groove to ring clearance max. which is way over any reasonable amount.
 
Joe K said:
Briggs & Stratton air cooled engines (warmer cylinder) specify 0.007 to 0.017 range for all sizes.

Been like this for a long time.

You may be fine where you are.

Here's the B&S Service Bulletin from the 1950s.
Click to expand...


Not sure if this is an apples to apples comparison that will work for something like the Model A engine, but what a book!
Thanks for sharing that with us.
When asked I have always told folks the engine is like an old Briggs and Stratton, but I was just trying to give them a sense of how different the modern engine is compared to the one in my Model A.

I liked these engines but had no idea how well you could rebuild them.
 
Listen to Flathead. What did the instructions recommend that came with the rings? You probably used either Grant or Hastings rings, I imagine, and they come with instructions. Certainly before yanking and ripping the engine apart.........check it out. And by the way, I use Hastings rings using the Les Andrews recommended gaps and works fine. Of course that is with lowly Snyder's pistons, mind you....
 
Flathead and Greg are correct gaps and clearance are manufacturer specific
follow the instructions from the manufacture and it is hard to go wrong
I see guys here quoting clearances for 1 single part that they may use and applying it to everything model A
Wrong if I used those clearance say with my Ross forged pistons that engine would never have gotten pass the 1st 5 minutes
Happily I followed the manufactures instructions and all is well
 
Good idea from Greg, Flathead, and Colin. I checked the Hastings specs, which were the rings I used. Top ring and middle rings: .012-.022; oil ring: .010-.050. So using Les's recommendations, I'm pretty good, except the middle ring might be a little tight.

I went on an 80-mile tour today with no adverse affects. I'm going to let it settle in a little more and see what happens. I might try a scope on Monday if I can find one and it isn't too cold to get out to the garage.

An added note: the engine was sleeved back to standard at the same time the new pistons and rings were installed.
 
Ray, you are prolly OK, if it did not lock up by now

"My" specs do not come from me but as I have mentioned a close friend who builds motors including racing motors.

As for the gentleman who thinks .022 is "excessive" consider that is not even the width of a spark plug gap. He needs to explain what he thinks the consequences are gonna be. Remember, the top ring sees much hotter temps than the other rings. Be nice to it.

Re-read what Fordors said.
 
Tbird, it would lock up in the first 500-600 miles, but would be OK after a few minutes of cooldown. But I also had a weak battery, and that made it difficult to turn over. But after about 1000 miles and a new battery, it seemed be OK. Now, at 1500 miles or so, there is no lockup, but when I shut it off it stops immediately. So it's still pretty tight.

Like I said, I'll scope it, and if it looks alright inside I'll drive it for another 500 miles and see what happens.
 
5/21/15 Update: With now 1875 miles on the new engine, it still locks up when it gets driven up to operating temps. I pulled the head and dropped the pan. There is no scoring or scuffing or discoloration on the cylinder walls. I conclude from this that my original ring gaps were too tight, and am going to regap them. There is minor carbon buildup on about 2/3s of each piston on the valve side, and a carbon ring at the top of each cylinder. I would like to hear from you experts what you think a better gap might be, and also your opinions on the carbon buildup.

Thank you.
 
I think you will find that the gaps have increased by now. If the engine actually locks up when hot there should be some visual clues in there.
 
700rpm said:
5/21/15 Update: With now 1875 miles on the new engine, it still locks up when it gets driven up to operating temps. I pulled the head and dropped the pan. There is no scoring or scuffing or discoloration on the cylinder walls. I conclude from this that my original ring gaps were too tight, and am going to regap them. There is minor carbon buildup on about 2/3s of each piston on the valve side, and a carbon ring at the top of each cylinder. I would like to hear from you experts what you think a better gap might be, and also your opinions on the carbon buildup.

Thank you.
Click to expand...

What exactly do you mean by "it locks up"? Does it seize? Does the starter not turn it over? How about the hand crank (with OR without spark plugs)?

It sure doesn't sound like rings.
 
Marco Tahtaras said:

What exactly do you mean by "it locks up"? Does it seize? Does the starter not turn it over? How about the hand crank (with OR without spark plugs)?

It sure doesn't sound like rings.
Click to expand...

Marco, it seizes up, and cannot be turned with starter or hand cranking. After about a 15 minute cool down, it will turn over with the starter. It has been like this since I put it back together last year. I haven't tried it without plugs, but I've got it torn down now and can't do that. When cold it turns fine. Bill Barlow set the crank, and I installed the rods with .001-.0015 clearance. The piston specs were .003 and that is what my engine shop honed the cylinders to. Why not rings, and what else is a possible?
 
Can you post a picture of the cylinder walls and piston skirts?

Sure seems like there should be some scuff marks if the pistons were seizing.
 
The Andrews book does have some problems that have been noted here over time. The ring gap spec does not seem to be one of them. Even with your original listing last year no one else chined in with "I had the same problem". Could it be that everyone else that has installed rings followed the ring manufacturers recommendation, I don't know.

I'm glad you updated your post and be sure that the members here will work to see that the problem is found and solved.

Would pistons placed 180 out cause them to seize?
 
If it seizes up while running it should be toast by now. If you mean "it's stuck" when you try to restart it when hot there is something else going on. If it seizes there should be scoring.
 
From the number of miles stated I've guessed that it hasn't left you stranded on the side of the road waiting for it to cool just so you could go a few more miles for a repeat multiple times to reach your destination.

If it simply won't turn over for a warm restart it could be battery related (even if the battery is new), or a starter issue when warm. That is why the hand crank question.
 
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