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

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?

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
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
It sounds to me like a lack of communications on the radial width of your ring set for your pistons got mess up

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

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

Will back cutting these rings weaken there ability to seal the engine?
Brian

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

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

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

Brian

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.

Just need the correct radial sized top ring. They are made in various sizes to fit various manufacturers piston specs.

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

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

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

Your welcome. So all you need to fix this is a set of backcut rings

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..........

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

Total seal would have them as well as Diamond, if you gave Diamond your piston # they could make sure you get what you need

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

I run the napier back cut 2nd ring as well..........lower tensions, more power from reduced friction............

Ever since Diamond was aquired their shipping and QC has been off the mark.I'm sure it will level off.


http://www.performanceracing.com/news/ra...end-performance

I think they are doing like CP did with that odd radial depth--think it is a Diamond thing--why?? Who knows!! Total Seal is the go to for any rings and remember they sell Lots of rings not just gapless

All the Diamond piston packages with rings I've bought in the last ten years came with rings size and type I ordered in Total Seal boxes

Talked Kevin at Total Seal today, less than 3 mi he gave me a part # for the rings that I need, they come in a set. Told me that Diamond makes a lot of custom piston to fit their "advanced profile" ring sets.
Thanks for all your help, I learned something new! Will never make this mistake again.

Brian

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 [/quote]

4.600 bore engine I would have top ring gap over .030 for N/A and a little more if forced induction or nitrous. A little extra gap doesn't hurt anything, not enough could get ugly fast. Dan

DO NOT CUT THE RINGS... I'd simply contact Diamond and discuss the matter with them.

I'e been working for a major global piston ring manufacturer for past 12 years... interesting things I've learned!

[/quote]

4.600 bore engine I would have top ring gap over .030 for N/A and a little more if forced induction or nitrous. A little extra gap doesn't hurt anything, not enough could get ugly fast. Dan [/quote]

No, .016", just tight enough so the feeler gauge by itself is held in the gap.

Diamond doesn't build engines, or rings.

And yes, it makes a difference.