A question on Les Andrews's ring specs

[bbrocksr]

Originally Posted by 700rpm

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.

How do you conclude that it is locking up from too tight of ring gaps when there is no sign of scuffing or scoring on the cylinder walls? If you do some research you will find that Les Andrews, The Motors Manuals The ring manufacturers and most of the experienced engine builders on this site agree on approximately .004 per inch of bore! A Model A has a 3 7/8 bore which would be just under .016 for the top ring and less for the rest of them.
At .022 you would have increased the recommended gap by 50%, gaining nothing but a little more leakage through the ring gap.
Bill

[Tom Wesenberg]

Originally Posted by 700rpm

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?

A fresh rebuild will seem tight. The engine will come to a stop quicker than a worn engine, and it likely won't rock back and forth on the final compression stroke when the key is turned off.

I'm wondering what you meant by "seems pretty tight"?

[stouchton]

Curious if minimum piston clearance has been exceeded since it is sleeved.

[700rpm]

Originally Posted by stouchton

Curious if minimum piston clearance has been exceeded since it is sleeved.

How might that happen?

[700rpm]

Originally Posted by Tom Wesenberg

A fresh rebuild will seem tight. The engine will come to a stop quicker than a worn engine, and it likely won't rock back and forth on the final compression stroke when the key is turned off.

I'm wondering what you meant by "seems pretty tight"?

Yes, Tom. That is what I expected and experienced. My trouble is that when it is stopped and turned off after a drive of, say, 30 minutes at 35 mph, if I try to start it immediately after shutoff, it frequently will just grunt, not turn over, and I can't turn it by hand. When cold it can be cranked by hand or starter like normal for a new rebuild with 1800 miles on it. Stiff, but not unduly so. I had hoped that since my initial breakin at 500 miles that it would hace loosened up and this problem would have gone away. It hasn't, so here I am. I will take some photos later and post them.

[stouchton]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by 700rpm

How might that happen?

Screw up in boring diameter (geometry) prior to sleeve insertion or improper final hone?

[700rpm]

Originally Posted by stouchton

Screw up in boring diameter (geometry) prior to sleeve insertion or improper final hone?

Unlikely. The shop that sleeved and honed the block has a high and long-established reputation.

[stouchton]

Originally Posted by 700rpm

Unlikely. The shop that sleeved and honed the block has a high and long-established reputation.

Were the pistons installed of a brand and alloy that they were used to working with? Keep in mind I know nothing of the shop, but have seen folks trip on the proper piston clearance. Some folks are paranoid of piston slap so they keep them tight - sometimes too tight for a given piston. Tends to not "wear in" like piston rings will. And has similar issues as to what you are experiencing. Piston, depending on alloy, will expand more than cylinder wall with heat. I believe the cast iron pistons are the worst for this - requiring a significant gap and creating some slap till up to temp. Gap them too tight and they will bind.

I am in no way a model A engine expert, so all of this might be for moot.

[700rpm]

Originally Posted by stouchton

Were the pistons installed of a brand and alloy that they were used to working with? Keep in mind I know nothing of the shop, but have seen folks trip on the proper piston clearance. Some folks are paranoid of piston slap so they keep them tight - sometimes too tight for a given piston. Tends to not "wear in" like piston rings will. And has similar issues as to what you are experiencing. Piston, depending on alloy, will expand more than cylinder wall with heat. I believe the cast iron pistons are the worst for this - requiring a significant gap and creating some slap till up to temp. Gap them too tight and they will bind.

I am in no way a model A engine expert, so all of this might be for moot.

Good thoughts. Anything is possible, and I'm open to suggestions. Thanks!

[BILL WILLIAMSON]

Originally Posted by 700rpm

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?

700,
Once bought a '26 Chev, that had been re-ringed, if run OVER 50 MPH, for only 1/2 mile, it would SEIZE & engine would STOP. I would coast in neutral, down to 10 MPH, kick it in gear to start it & it ran perfect if held to 50MPH!
I just drove it "easy" & in time, as the rings settled/wore in, and it became normal.
With any new engine/overhauled engine, just drive it EASY & with CARE, until everything settles in/laps in & you'll be set to go! AND, don't do some "WEIRD" procedure to "seat" in the rings, the rings WILL do what they are designed to DO!
As for ring gaps, do what the instructions say, for THAT PARTICULAR SET OF RINGS!----------Is READING a LOST ART?
Just like when your wallpaper hanging goes to CRAP, you probably DIDN'T read the instructions, for THAT PARTICULAR WALLPAPER!
Bill W.

[700rpm]

Here are some photos of my condition. The vertical lines may be scoring, but they are so slight I am not able to feel them with a fingernail. The cylinder walls are shiny, and what appears to be discoloration is merely the reflection of carbon on the piston heads.

[Tom Wesenberg]

With only 1500 miles I would have expected to see a nice crosshatch pattern yet.

The crosshatch was still visible on my dad's 1970 Pontiac 400 engine with over 100,000 miles, and the engine was spotless inside.

I would remove the pistons and fit the rings to the cylinders to check the gaps. Also measure the piston clearance.

Also make sure the water jacket is spotless clean. Rust and junk likes to build up in the rear by #3 and #4.

[700rpm]

A couple more photos.

[700rpm]

Originally Posted by BILL WILLIAMSON

700,
Once bought a '26 Chev, that had been re-ringed, if run OVER 50 MPH, for only 1/2 mile, it would SEIZE & engine would STOP. I would coast in neutral, down to 10 MPH, kick it in gear to start it & it ran perfect if held to 50MPH!
I just drove it "easy" & in time, as the rings settled/wore in, and it became normal.
With any new engine/overhauled engine, just drive it EASY & with CARE, until everything settles in/laps in & you'll be set to go! AND, don't do some "WEIRD" procedure to "seat" in the rings, the rings WILL do what they are designed to DO!
As for ring gaps, do what the instructions say, for THAT PARTICULAR SET OF RINGS!----------Is READING a LOST ART?
Just like when your wallpaper hanging goes to CRAP, you probably DIDN'T read the instructions, for THAT PARTICULAR WALLPAPER!
Bill W.

Bill, I didn't get any instructions about gaps with those rings. Or if I did, I didn't see them, and I'm pretty careful about stuff like that. That's why I relied on Les's book, which I have come to believe was/is incorrect, at least in my case.

[40 Deluxe]

Could be the piston clearance is just a tad bit on the tight side so when up to running temperature, the pistons have expanded just enough to be at or near zero clearance. Let's assume we still have an oil film on the cylinder walls for just enough lubrication to prevent scoring but at shut down, the pistons squeeze the oil off the cylinder walls. Now the pistons are tight against the cylinder walls without that oil film, so the engine won't turn until the pistons cool down and contract.
For this to happen, you must be right on the ragged edge of seizing the pistons in the bores!

[1931 flamingo]

As long as you're this far into it have you re-checked brg clearances?? I can't see how ring clrncs could cause your problem.
Paul in CT

[700rpm]

Paul, that is on the agenda. Thanks.

[BILL WILLIAMSON]

You say you can't feel them with your fingernails. From what I see, if they're IRON rings, this may be "normal" until the ring surfaces polish over & those marks "may" go away.
IF, the marks were from pistons too tight, you should see, almost like ALUJIMUM like deposits in the marks. I'd just drive it & DON'T WURRY! BUT, WHUT DO I KNOW--------------?????????????????????--(The Dorg's SMILIN')
Bill W.

[Kurt in NJ]

looks like it is passing some oil the way the carbon is washed away in some areas of the piston

can you rock the pistons any in the bore---left to right

[700rpm]

Originally Posted by Kurt in NJ

looks like it is passing some oil the way the carbon is washed away in some areas of the piston

can you rock the pistons any in the bore---left to right

Kurt, excellent suggestion, and I'll check that this weekend and let you know.

Even though I may have missed it on the packaging, I see that Snyders specifies that Hastings suggests that their top and middle rings be gapped at .012-.022. Since I gapped mine at .012-.014, I'm at the low end. More and more, with Barner suggestions and other data gathered, I'm settling on just increasing the ring gaps.