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Old 10-08-2003, 05:29 AM
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File back rings.

My engine builder has given me a set of what he calls file back rings. Now I always thought these to benormal rings with an oversized top ring. What I actually have is a normal ring set for a bore size 005 bigger than mine. Ok so I have to file fit the top and second ring. But what about the oil control ring? Isn't it going to be made for the bigger bore size? You can't expect me to file fit this one as well! What end gap should be in the rails of the oil ring?


BTW Do you guys use a purpose built ring filler or just a smooth file in a vice? I have found the ring filler hard to use and the two tapered locating pins are damaging the edge of the ring.

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Old 10-08-2003, 09:10 AM
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Hand filing or machine filing doesn't matter. Both will get the job done. The machine filer will work the material faster. It should anyway. I would recommend not using the over bore rings. I see sealing problem by changing the tension they are designed to run at. Although .005 isn't alot, it can make a difference when searching for power gains. I say return those rings and use low tension rings from a reputable manufacturere and file fit them to your custom spec. You don't wanna file the oil control pack for the same reason above. It hard, time consuming, and isn't likely to work out the way you wanted.
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Old 10-08-2003, 11:47 AM
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Along with what is stated above, you may want to ask your machinest why he wants you to use those rings. Maybe he did a crappy job boring and honing and the bore ended up too big? If so, you'll have all kinds of piston rocking and slapping going on.

Also, if you are using a piston like the Keith Black hyperutectic, they need a much wider top ring gap due to the heat they reflect back into the combustion chamber. The piston top runs very hot compaired to most and require up to .027 for top gap. Second ring and oil rings are left alone but the top uses an extra big gap.
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Old 10-08-2003, 04:12 PM
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I think I might junk them and get a set of normal fit rings. I don't think he has made the bore too big, I think he just likes file fitting rings.

What high quality rings do you recommend? Pistons are SRP. Expect about 450hp plus a shot of NOS.
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Old 10-08-2003, 05:40 PM
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HQ,
File fit rings are generally designed with much closer gap tolerance, hence they are designated as being .005" oversize. Actually this is not necessarily the case, but they are given this designation to reduce the chance of mix-ups. For instance a 4.035 file-fit ring set is designed to be installed in a 4.030" bore after the rings have been filed. These rings are designed to be light-tight and have the proper tension in the final diameter. Only the compression rings are oversize in a file fit ring set. The oil ring assembly is designed to be installed with no filing. Do not use an oversize set, unless they are designed to be file-fit, otherwise you will not have the correct tension and the oil rings will not work correctly.
As far as which brand of ring to use, just about all of the major brands of rings are manufactured in the same factory.
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Old 10-09-2003, 02:44 AM
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Engineguy, thats what I'm saying, no where on the packaging does it say they are file back rings. It only shows that they are for a 4.065" bore. And I know you can get rings in 005" steps for people that wish to only hone a bore out slightly to clean it up. I really think they are for the bigger size.

I have started filling them and I really don't like it. Seriously considering ditching them. The only reason I haven't already done so is that I need an end gap of about 020". Most standard fit rings I have used have 016-018" which means I would have to file finish them anyway.
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Old 10-09-2003, 04:26 PM
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File fit rings will not overlap. .the're will still be a gap, just much tighter then a std set of rings. This allows for proper gap on each cylinder, pistons will vary a couple of thousands, ie: 4.028".

With a 450shot I wish you good luck. With NOS, you should use file fits to get proper gap. I'd run 24 on the top and 32 on the second.

Cstraub
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Old 10-09-2003, 07:37 PM
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HQ, file-fit rings are not identified as such on the packaging, in most cases. Pistons and rings are usually manufactured in popular oversizes such as .020", .030", .040" and .060". File fit rings are generally available in .025", .035", .045" and .065" oversizes. Custom piston manufacturers can build a piston in virtually any oversize and a corresponding ring may or may not be available.
In summary, the ring set you have sounds questionable. I would recommend ditching them and purchasing a good quality set for your net cylinder bore dimension.
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Old 10-10-2003, 05:51 AM
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Thanks guys. I bought a set of Speed Pro's today which are "slightly oversize to allow custom fitting". The gaps measured about .018" so I only had to do a little filling to open them up a bit. The process is much faster and I am much happier.

I really wanted the C&A Dura Moly's but they didn't have any in stock. Do you think the Speed Pro's will be ok? As far as I know no one has had any problems with them (including me, but I have never used them in such a severe application) and they were half the price anyway.
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Old 10-13-2003, 07:35 AM
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HQ,
I will let you in on a little secret here. The Speed Pro rings and the C & A DuraMoly are virtually the same ring, manufactured at the same plant. The C & A part may, or may not, have the paint stripe identification that is found on the Speed Pro's. The basic material (ductile iron) and the plasma spray procedure is exactly the same for both rings.
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