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Rings size for 98mm Mahle

I recently aquired a used set of mahle 98mm P&C.

In measuring the ring grooves I seem to get an odd measurement. I've spoken with Peter Sanchez at Andial and I have a call in to EBS.

Here's what I'm measuring:

top compression groove: 1.21-1.22 mm (good for 1.2mm ring)

bottom compression groove: 1.20 mm

oil groove: 2.9mm


I can't see how a 3mm oil ring will work in a 2.9mm groove. Also the bottom compression groove would be tight for 1.20 rings. I've taken many measurements across all the pistons and I get basically the same results.

Do these measurements seem normal? Peter suggested that the pistons could have been damaged from running lean.

-Rob
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Old 09-06-2005, 01:22 PM
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Pistons that have been damaged due to detonation can have "collapsed ring grooves". The grooves usually collapse the most above the piston pins. The oil rings often have to be pried out.
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Old 09-06-2005, 08:51 PM
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The pistons that you have are the "Max Moritz" Mahle pistons. The correct piston ring thickness is 1.2 & 1.2 & 3.0 mm. I got my last set from our host, but they were available from Andial as well.

The reason that you are possibly getting odd sizes is that there may be carbon in the ring grooves. Clean the grooves with the end of the old piston ring, making sure not to damage the groove, and then measure it again.
Old 09-06-2005, 10:52 PM
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That's what I was told also, but after through cleaning the only way to get the correct ring groove height would have been to file them open. I had to replace mine.

Is there any way to re-cut a ring groove? Even if you could re-cut it, would anyone feel safe using a piston like this? In alphie's case you would have to remove .11 mm from the oil ring groove.
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Old 09-07-2005, 05:21 AM
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Quote:
Originally posted by vichang4
That's what I was told also, but after through cleaning the only way to get the correct ring groove height would have been to file them open. I had to replace mine.

Is there any way to re-cut a ring groove? Even if you could re-cut it, would anyone feel safe using a piston like this? In alphie's case you would have to remove .11 mm from the oil ring groove.
A friend of mine had piston ring grooves recut. I think Mahle might have done it for him.
-Chris
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Old 09-07-2005, 06:47 AM
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I am the person Chris mentioned above. I did have detonation issues (two times) on the Mahle 10.3 pistons. I had top rings shatter due to detonation. This made the top groove wider (sloppy fit for the std ring width. I had a local machinist regrove the top groove to 1.5 mm and I purchased rings from Total Seal (they make these rings all the time for just this application). The rings worked just fine (engine finally expired due to bearing failure, or I should say, my failure to find every spec of metal in the oil coolers etc, after my ring failures). I feel that re-groving the top ring to 1.5 is a great solution to fix the damged pistons.
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Old 09-07-2005, 07:05 AM
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What I find weird is that the ring groove sizes are the same across all pistons and at all points of the pistons. I would have thought that damaged pistons would have yielded more inconsistent measurements.

The pistons have no carbon build up in the grooves or anywhere else on them.

I've ordered the rings and I'm hoping for the best. If they don't fit then I'm looking at replacing them or getting the ring grooves cut, correct???

-Rob
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Old 09-07-2005, 11:33 AM
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Rob

I too was surprised how "consistent" the damage was on my pistolas as well. I believe I found a spec somewhere (maybe the small spec book) that gave a wear limit for the groove. In my case the wear/damage was above the limit. You should look for that and carefully measure your grooves. I know how most people feel about Motor Meister, but they have been "successfully" re-machining the groove. You might call them just to ask questions. You should also call Total Seal, they were very helpful and told me that they sold lots of the wider rings to Motor Meister.
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Old 09-11-2005, 04:39 PM
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Thanks Jerry,

Does anyone know where I can find the wear limit of the grooves of Mahle Max Moritz 98mm pistons???

-Rob
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Old 09-12-2005, 10:51 AM
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