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Diamond piston/ring problem **UPDATE** #2460715
03/04/18 02:15 AM
03/04/18 02:15 AM
Joined: Aug 2009
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Mooresburg, Tn
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'72CudaRacer Offline OP
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Mooresburg, Tn
Anyone one here ever run into this?? Diamond custom pistons, piston card calls for 1/16 x 1/16 x 3/32 rings, 4.600 bore. I got Mahle rings, correct size and fitted them to the bore. When I try to load the piston into the cylinder, the piston gets stuck in the ring compressor (tapered sleeve, correct size). After getting the piston assembly unstuck (without damaging anything!!), and doing a lot of investigating, I find that the top ring is bottoming out in the piston. Everything else is fine. I go retrieve the old rings that came off these pistons and find that width of the old ring is .169" (not top to bottom, but from the face of the ring to the inside diameter). The new top ring is .194", and the ring gap in the cyl bore is correct at .021", but when it is on the piston and "bottomed out", the gap is in excess of .030" and the diameter of the ring at that point is in excess of 4.602".
I have the actual work order from when the pistons were made and it list the rings as 4.600b 1/16ap x 1/16nap x 3/16std.
At this point I'm standing here going WTH?? Any suggestions other than calling Diamond on Monday?

Thanks, Brian

Last edited by '72CudaRacer; 03/05/18 09:29 PM.
Re: Diamond piston/ring problem [Re: '72CudaRacer] #2460721
03/04/18 02:41 AM
03/04/18 02:41 AM
Joined: Oct 2006
Posts: 732
New York, USA
Chargerfan68 Offline
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Chargerfan68  Offline
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New York, USA
The rings must be the wrong radial thickness. The proper rings have to give you the proper back clearance. Iff the old rings were .069” and it gives you correct back clearance or gap, the new rings radial thickness is incorrect. Did diamond supply the rings to you? Some ring manufacturers will back cut the rings to thinner dimensions. I had total seal back ut my rings for example. Maybe those can be corrected?


1.50 60Ft. , 10.75@ 127MPH Hauling 3900 LBS.
Re: Diamond piston/ring problem [Re: '72CudaRacer] #2460722
03/04/18 02:42 AM
03/04/18 02:42 AM
Joined: Aug 2003
Posts: 32,298
Bend,OR USA
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Cab_Burge Offline
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Bend,OR USA
If you have access to a good machinist with a lathe and the proper tool to hold that ring you can have them back cut down to the width you want them to have work scope
We use to do that in NHRA stocker motors a long time ago to reduce ring tension on both the stock top and second rings and use ring spacers behind the rings to get the proper .005 to .008 in and out play shruggy
It sounds to me like a lack of communications on the radial width of your ring set for your pistons got mess up shruggy work


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Diamond piston/ring problem [Re: Cab_Burge] #2460725
03/04/18 02:53 AM
03/04/18 02:53 AM
Joined: Aug 2009
Posts: 1,742
Mooresburg, Tn
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'72CudaRacer Offline OP
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I forgot to mention that this engine was running, just needed fixing. The pistons were bought and installed by the previous owner and it looks like the pistons and rings were bought from Diamond together. With the piston card not mentioning anything out of the ordinary for rings, I bought what I thought was correct...

Brian

Re: Diamond piston/ring problem [Re: Chargerfan68] #2460728
03/04/18 02:57 AM
03/04/18 02:57 AM
Joined: Aug 2009
Posts: 1,742
Mooresburg, Tn
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'72CudaRacer Offline OP
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Mooresburg, Tn
Originally Posted By Chargerfan68
Iff the old rings were .069” and it gives you correct back clearance or gap,


The old rings were gapped for nitrous use (but not used), top ring gap was over .030". This owner will not use nitrous, that was one of the reasons for me fixing the engine.

Brian

Re: Diamond piston/ring problem [Re: '72CudaRacer] #2460730
03/04/18 02:58 AM
03/04/18 02:58 AM
Joined: Aug 2009
Posts: 1,742
Mooresburg, Tn
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'72CudaRacer Offline OP
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Will back cutting these rings weaken there ability to seal the engine?
Brian

Re: Diamond piston/ring problem [Re: '72CudaRacer] #2460732
03/04/18 03:03 AM
03/04/18 03:03 AM
Joined: Aug 2003
Posts: 32,298
Bend,OR USA
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Cab_Burge Offline
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If this is a street or non serious race motor have the piston ring grooves cut to the proper depth for these rings and make sure and get the back spacing depth correct also scope


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Diamond piston/ring problem [Re: '72CudaRacer] #2460774
03/04/18 10:39 AM
03/04/18 10:39 AM
Joined: Mar 2006
Posts: 7,483
MI, usa
dvw Offline
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MI, usa
Call Total Seal and order the correct top rings. You can buy just the 8 you need.
Doug

Re: Diamond piston/ring problem [Re: dvw] #2460795
03/04/18 11:49 AM
03/04/18 11:49 AM
Joined: Aug 2009
Posts: 1,742
Mooresburg, Tn
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'72CudaRacer Offline OP
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Mooresburg, Tn
Originally Posted By dvw
Call Total Seal and order the correct top rings. You can buy just the 8 you need.
Doug

Well Doug, this has to be the best news that I've heard yet.

Thanks, Brian

Re: Diamond piston/ring problem [Re: Cab_Burge] #2460796
03/04/18 11:51 AM
03/04/18 11:51 AM
Joined: Aug 2009
Posts: 1,742
Mooresburg, Tn
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'72CudaRacer Offline OP
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Mooresburg, Tn
Originally Posted By Cab_Burge
If this is a street or non serious race motor have the piston ring grooves cut to the proper depth for these rings and make sure and get the back spacing depth correct also scope


This is a 622 ci, for sure not a street engine. But I thought it might be a option.

Brian

Re: Diamond piston/ring problem [Re: dvw] #2460816
03/04/18 12:20 PM
03/04/18 12:20 PM
Joined: Jan 2005
Posts: 4,137
Charlotte, North Carolina
sgcuda Offline
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sgcuda  Offline
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Charlotte, North Carolina
Originally Posted By dvw
Call Total Seal and order the correct top rings. You can buy just the 8 you need.
Doug


I agree. I wouldn't be machining pistons or rings. I would get the proper rings for the piston application. Modifying parts would only complicate matters down the road on the next freshen up.

Re: Diamond piston/ring problem [Re: '72CudaRacer] #2460819
03/04/18 12:25 PM
03/04/18 12:25 PM
Joined: Jan 2003
Posts: 17,036
Las Vegas
Al_Alguire Offline
I Live Here
Al_Alguire  Offline
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Las Vegas
Just need the correct radial sized top ring. They are made in various sizes to fit various manufacturers piston specs.

Re: Diamond piston/ring problem [Re: '72CudaRacer] #2460831
03/04/18 12:35 PM
03/04/18 12:35 PM
Joined: Jan 2003
Posts: 961
Farmington Hills, Mich
Chuck@Best_Machine Offline
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Farmington Hills, Mich
Are you sure the radial on the old ring is .069 ? A normal backcut 1/6th ring is .170 and a normal non back cut is around.200 If you really needed a 1/16th (.062) backcut to .069 it would almost be square. If this is the case you have a piston problem

Re: Diamond piston/ring problem [Re: Cab_Burge] #2460887
03/04/18 02:10 PM
03/04/18 02:10 PM
Joined: Apr 2005
Posts: 1,454
TN
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SCATPACK 1 Offline
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TN
Originally Posted By Cab_Burge
If this is a street or non serious race motor have the piston ring grooves cut to the proper depth for these rings and make sure and get the back spacing depth correct also scope

iagree this.
It should give you more ring control and less ring roll over or flutter at high RPM


Old Geezer Racing
Re: Diamond piston/ring problem [Re: Chuck@Best_Machine] #2460905
03/04/18 02:31 PM
03/04/18 02:31 PM
Joined: Aug 2009
Posts: 1,742
Mooresburg, Tn
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'72CudaRacer Offline OP
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Originally Posted By Chuck@Best_Machine
Are you sure the radial on the old ring is .069 ? A normal backcut 1/6th ring is .170 and a normal non back cut is around.200 If you really needed a 1/16th (.062) backcut to .069 it would almost be square. If this is the case you have a piston problem


I believe that you are correct, Sir. My mistake (I corrected my original post). A good reason why mechanics shouldn't try to be machinist when its late and they are tired and annoyed. Thank you.

Brian

Re: Diamond piston/ring problem [Re: '72CudaRacer] #2460912
03/04/18 02:59 PM
03/04/18 02:59 PM
Joined: Jan 2003
Posts: 961
Farmington Hills, Mich
Chuck@Best_Machine Offline
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Farmington Hills, Mich
Your welcome. So all you need to fix this is a set of backcut rings

Last edited by Chuck@Best_Machine; 03/04/18 03:00 PM.
Re: Diamond piston/ring problem [Re: Cab_Burge] #2460916
03/04/18 03:04 PM
03/04/18 03:04 PM
Joined: Jul 2004
Posts: 18,980
State of confusion
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Thumperdart Offline
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State of confusion
Originally Posted By Cab_Burge
If you have access to a good machinist with a lathe and the proper tool to hold that ring you can have them back cut down to the width you want them to have work scope
We use to do that in NHRA stocker motors a long time ago to reduce ring tension on both the stock top and second rings and use ring spacers behind the rings to get the proper .005 to .008 in and out play shruggy
It sounds to me like a lack of communications on the radial width of your ring set for your pistons got mess up shruggy work



I'm running 1/16 back cut top n bottom rings in my 470 and use the rail spacer wrap to get the proper clearance.......... beer


72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
Re: Diamond piston/ring problem [Re: Chuck@Best_Machine] #2460955
03/04/18 04:17 PM
03/04/18 04:17 PM
Joined: Aug 2009
Posts: 1,742
Mooresburg, Tn
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'72CudaRacer Offline OP
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Mooresburg, Tn
Originally Posted By Chuck@Best_Machine
Your welcome. So all you need to fix this is a set of backcut rings


Is a item that would be on the shelf or is it a custom thing? Doug suggested Total Seal, sounds like he has experience.

Brian

Re: Diamond piston/ring problem [Re: '72CudaRacer] #2460958
03/04/18 04:22 PM
03/04/18 04:22 PM
Joined: Jan 2003
Posts: 961
Farmington Hills, Mich
Chuck@Best_Machine Offline
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Farmington Hills, Mich
Total seal would have them as well as Diamond, if you gave Diamond your piston # they could make sure you get what you need

Re: Diamond piston/ring problem [Re: Chuck@Best_Machine] #2460968
03/04/18 04:52 PM
03/04/18 04:52 PM
Joined: Aug 2009
Posts: 1,742
Mooresburg, Tn
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'72CudaRacer Offline OP
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Mooresburg, Tn
A little more research shows that the "1/16ap" is "advanced profile" and the "1/16nap" is a "napier" 2nd ring. Maybe?
This engine did have a napier style 2nd ring.

Thanks, Brian

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