Still trying to find rings that or close enough to file down. Local machine shop who will be decking the block and honeing it tried to find oversize file to fit rings from his suppliers for building stock car engines. No luck there. His suggestion was to use .060 over rings and file them to fit. Said he would like to try a .060 over ring in the bore and see how the curvature of the ring fit the bore. Anyone out there got a used .060 over 312 top ring laying around they could spare? Willing to pay postage and reasonable fee.

The gap was measured with a feeler gauge and the ring I just took out of the engine about 1" down the bore. Rings have probably 5,000 miles on them, more or less. Yes i know the gap is too large per specs but the engine ran prety well that way untill the valves or valve guides gave out. Leak down test showed a couple of exhaust valves leaking badly and also the head gaskes were leaking. Still trying to find out if .040 over rings with a large end gap or filing .060 over rings down to the proper gap is the lesser of the two evils unless someone can tell me where to find .050 over rings, which would be fairliy easy to file down to fit mhy 3.847 bore.

I dont think your calculations re the large gap is right, that to me is far too big a gap.

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

.040 over rings with .040 t0 .050 end gap will run and work but I am not too thrilled about it. Anyone have thoughts on how .060 over rings filed down to the proper end gap will work? I am concerened with the curvature of the rings sealing to the cylinder walls properly.

What follows is lifted from a Perfect Circle Doctor of Motors Service Manual, printed 9/1973, page 64... (you can tell it's old because it was printed in the U.S.A.!)



"It is important that all rings have at least the minimum gap which is necessary to provide for the difference in expansion which may occur between the piston ring and the cylinder."



Ring diameter 3 to 3-31/32 . . . . . .010



"However, maximum end clearance tolerance is not critical and may be several times the minimum without affecting engine performance. A conservative maximum end clearance is one which is .040" greater than the minimum."

_________________________________



Engines are being machined and assembled with much closer tolerances than they were 40 years ago. The ring gap you presently have is not ideal from a performance standpoint today.



As I 'effort' to put my latest engine together, I continually have to remind myself how I'm really going to use it so that I don't slip into 'overkill' and so that I don't sink so much into building it that I can't enjoy driving it when I get done...

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Since "This will probably be the last time I go through this engine so I want it as right as I can make it without going bankrupt and get as much performance out of it as I can and keep it streeatable," I'd bite the bullet and get the next oversize. It'll solve the ring issue, too.


Lawrenceville, GA

Finaly got an inside micromoter and measured the bore and the pistions. Near as I can tell the bore is 3.847 and the pistons are 3.8425. This gives me .0045 skirt to cylinder clearance which is on the loose side but I can live with that. The Ford shop manual shows .0045 as the piston to bore clearance-bottom of skirt wear limit.The problem is coming up with proper rings. Checked my records and used .040 over rings when I rebuilt it in 1980. Got no idea what I used in 1969. Checked the ring gap with the current .040 over rings and came up with close to .050 which is way too much. Not having any luck finding rings close to 3.847. Found 3.850 rings but they are metric and the ring thickness don't match up. My choices seem to be using 3.840 rings which worked last time but I am concerned with the ring gap. Or I could use 3.860 rings and file them to get the proper end gap. My concern is that if I do that will the curvature of the ring fit the bore properly and seal  since they are being squeezed down to fit the bore? This may or may not be a problem since the 3.840 rings in the 3.847 bore workd fairly well . Question is would I be better off using the 3.840 rings with a large end gap or use 3.860 rings and file them for the proper end gap?

Unless someone knows where I can get 3.847 rings? I am thinking bad things for my Ford dealer selling me these pistons in 1969!

Ted, checked my Ford Shop Manual and you are dead on. I got my numbers from the 1962 Hot Rod Performance Manual that I originaly got most of my build info from back in 1968 when I originaly built this engine. Not sure where they got those numbers. Re buit it in '80 after spinning a rod bearing in it when I missed a shift several years before. Put a spare engine in it and left the race motor set for some time. Also had a cracked skirt on one piston at that time. Put it back together and been driving it since then with no major problems other than performance gradualy dropped off. No piston noise or excessive oil use. Checking my records I put standard .040 over rings in it at that time. No idea what rings I used in '68. I am looking for the proper rings now. Grant offers something that should work and I will check other sources. I will have a retired mechanic friend who is much better with micromoters and decimal points that I am check out everything. I think with new proper sized rings and Mummert heads I should be fine. I may have the block decked just to make sure head gasket problem does not come back. I think I will have machine shop do the cylinder hone job while it is there and drill and tap the mains for Mummerts ARP main bolts. I will use ARP rod and head bolts also. This will probably be the last time I go through this engine so I want it as right as I can make it without going bankrupt and get as much performance out of it as I can and keep it streeatable.

By the book, the wear limit is 0.0045” for the original cast pistons.  When new, the oem piston to wall clearance was 0.0015-0.0025”.

Lorena, Texas (South of Waco)

Thats what I keep telling myself!