I'm getting ready to file fit my .005 over plasma moly rings. Ihave a speed pro .020 set. I'm getting different answers to what the correct ring gap should be so I figure I get the consensus of the motor heads here.
Some spec's first:

Speed Pro/ Sealed power/Fed Mogul hyper H345np pistons +.020
Speed Pro R-9343-25 rings
street 350 2 bolt, std deck, 67 cc heads, .040 gasket,etc,etc,etc shouldn't see more then a 5500 rpm shift with TH400 and 3.08's.

I was told 3 FM tech's to set the top ring gap at .016", then to .018", then as high as .020".

The 2nd ring was .020" from 2 different FM techs so I guess that's ok.

What do you guys set file fits for?

Thanks,
Gary

PS are file fits that much better then pre-gapped rings? What are pre-gapped set to?

 

I've been told 0.004" per inch of bore so a 4" bore would be 0.016". The confusion may come from that if you have a forced induction setup you need larger gaps. Forced induction creates more heat and the rings can butt up which will break the ring land between first & second ring. Common problem when people put superchargers on stock engines in 4th gen F-bodys (LT1).

 

A minimum of .0035" per inch of bore size is to be used, so a 4" bore would be .014 at least. Pre gapped sets are set pretty wide, don't be surprised if they are gapped well above .020, which results in blow by and poorer oil control

 

I think I would go by the piston manufacturers specs...
...redvetracr

 

hypers need .020- they run HOT.
forged, i do .012 they run cool.
if u know the lean cyl's u could custom gap the rich ones smaller
Note, next time buy pre gapped rings w/hypers as u may still have to file them a little, like maybe .004, so much less work. for me i'd run the stock .016 on the rich, .020 lean

 

says.....

Compression ring gap .010 to .020
Oil ring gap to .065

These specs are for a "stock" engine and components

Chris B

 

Thanks guys, the confusion came from calling Federal Mogul a few times on questions and asking the question to all of the tech service guys that answered. I was aware of the .004 per inch rule too but didn't know how much of a window I have to work in.

Gary

 

and what is the hyper window?

 

Hypereutectic pistons tend to reatin heat better than forged pistons. I would run a minimum of 0.020 top end gap and if you plan on racing the Vette at a road course on a "track days" session, I would go 0.022 top with a 0.20 2nd end gap. I wouldn't run N2O in a "cast piston" motor but if you do plan on it, I would go anothe 0.002 for a total of 0.024" top end gap. You should have recieved instructions with the pistons on end gap settings, if you are a little to wide it is OK, to narrow=cylinder wall damage when the ring ends "butt" together, you don't want to run the risk of that. The B.S. about 0% leakdown motors is just that, a BUNCH of B.S.! I hope you bought "ductile iron" piston rings and not "cast" rings, thay are twice a much $$$ but well worth it. I used to stick my file in a vise and file my piston rings, then I bought a rotating ring filer, now I get to use my buddies electrical filer with a venier guage and get my end gaps PERFECT every time. Remeber to put the rings at least 1.25-1.5" down in the bore when checking the end gaps if you were using a "stress plate" in the honing process because the top of the bore is distorted until the head bolts are torqued.

 

To follow up, I called back Fed mogul and asked about the gaps again and the heat associated with Hyper's. I was told again those rings are for those pistons and the .016-.018" gap is ok a larger gap wouldn't be a problem~.020" I set the top to that .016-.018 and the 2nd to .020-.021.

New question: I found one top ring groove was snug on the ring. It wasn't binding but it wasn't as loose as the other pistons/rings either. I looked over the groove for any high spot but didn't see anything. I took another ring and tried it and had the same thing. I rolled a ring around the groove but didn;t feel anything. Would you replace the piston or run it? I'm going to look at it real close under a microscope to see if the groove is nicked anywhere. I'll also check the ring to land clearence to see where that falls compared to the book or other pistons.

Gary

 

Rings need to rotate in the grooves to live! You should be sure that the fit is "free" or there will be some big problems! in ring and bore wear.

 

I also do a sanity check by setting the rings at the bottom of the swept area... to see if taper is closing up the gap. Every once in a while I catch one.

I use a piston upside down with an old ring in the 2nd groove to square the rings for measuring on the top end. Insert the new ring in the bore and then press it down square with the piston & ring.

I use a 6" machinists t-square to set the rings at about 3.2 to 3.4 (SBC) to square the rings in the bottom of the swept area.

FYI

Also... I am currently assembling a 305 +.030 with .030 pre-gapped rings. They are coming in at .018 to .020 with no filing, and with taper of .0005(/2) or less, there is no noticeable gap loss at the bottom.

This is using Craftsman feeler gages though because my good set got ruined by being stored in a moist storage unit last year. The Craftsman are off by about .0001 to .0004 to begin with.

So mic your feeler gages too.

 

Thanks guys, I wasn't able to get back to them yet to double check the ring fit. It was the end of the day when I got to that piston and so I was tired. It was enough to get my attention though. I may just have to return the piston for another one then get it balanced as I'm sure it will not be the same weight.

Tom - good point on the feeler gages I didn't check them with my mike. I used the piston/ring method to set the ring gap too but I didn't go deeper then that. I suppose I could use my machinist square to drop them in a little deeper. I'd have to remove the rings from the pistons though. Maybe I use my dial gage to check the lower bores again. They were pretty close as I remember.


Gary

 

Well I had a few minutes to get back to the piston/ring in question and found the piston groove was ok. I put another ring in there and it felt good. I tried a 3rd rign and that was snug too. The inner corner of the ring gap was dragging in the groove. Here is a picture of the ring.



Here is a picture of the good ring gap.



Now I'm short a couple of rings

Gary

 

is that a fresh rebore/hone job or a finish hone job to remove the glaze? If it's the last, it's better to measure the gap at the lower unworn part to make sure you don't have any cylinder taper that will give you too tight gaps at the bottom.

 

TT- it's a fresh .020" over bore & hone with plate.

 

Ok, I thought I saw a slight ridge still at the top of the bore, that's why I asked it it was just a refinishing job.

 

Tom I'm surprised the factory gapped rings are only .002" over the recommended fit gap~.016-.018".
Is this common, does the .002 tighter gap make that much difference? Next time I'll be better off buying the factory set then?

Thanks,
Gary

 

file fit w/hyper?
total waste of time

 

Well Matt I guess it's not the first time I was told that in my life,but I'll still do it anyway. At least you seemed to have enjoyed it.