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Discussion Starter #1
I have rebuilt my engine twice in the last three years, and continue to have a problem with sealing the rings. Both rebuilds have used the Motronic 10.1 pistons.

My machine shop has measured the piston to liner clearance as 5 thousandths inch. The specifications call for less than 2 thousandths. The machinist believes this is the problem. (The liners and pistons both show very little wear from new condition)

I thought I could resolve this with different piston sleeves. I gathered up approximately 30 used liners from local garages in the S.F. bay area to measure, they were all too large! I am beginning to believe that the pistons might be to small. They measure 3.3038 inch.

Has any one else had problem with oil consumption using the Motronic 10.1 piston and liner sets?

Thanks,

Larry
 

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Motronic pistons should be as follows (measured parallel to the wrist pin at the bottom of the skirt):
Class A, 3.3045"~3.3049"
Class B, 3.3049"~3.3053"
Class C, 3.3053"~3.3057"

So if your measurements are accurate and taken from that specified point, then yeah, yours are too small.
(perhaps as a result of someone skimming them to reduce weight?)

Ring gap can be custom dialed by going with a set of .010" oversize rings and grinding the gap.
Provided of course the pistons are correct and the bores are true.
 

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Discussion Starter #3
Pistons were not modified.
Still interested if anyone else has had problems with these. I called International Auto, and they had not had complaints, but a local shop said they did not have good success with them.

Larry
 

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I have the same problem. I think that it is due to the Federal Mogul rings that never bed in properly. I am going with Hastings rings next time. Also check out the recent thread regarding differences between European and US sourced pistons and rings.
 

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71 Berlina 74 GTV 17 Giulia Q4
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I also had problems with the stock rings, more specifically the one piece oil ring. I went with Total Seal rings with the 3 piece oil ring and no smoke now. As I understand it a lot of warrenty work was done for that same problem and the rings were replaced with pick your brand 3 or in the case of Deeves 4 piece oil control rings. You wouldn't think it should matter that much but apparently it does, is how you breakin the rings with the main thing being not to let off the gas and let the motor slow the car down and creating 0 vacuum on the intake side for the first 1000 miles. just my 02
 

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I did the first break in per Alfa - low revs and load for 1000 miles. I used the on and off full throttle method the second. Neither worked with the FM (Borgo) rings.

An interesting dilemna is when you have new rings and new cams in the same engine. The break in requirements are very different.
 

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Has any one else had problem with oil consumption using the Motronic 10.1 piston and liner sets?

Thanks,

Larry
YES. I have. I rebuilt my l-jet engine with the motronic pistons a few years ago and it has burned oil from the get go. At first I thought it was the head but I took that off and had it rechecked and it measured out perfectly. With the head back on the engine I did a leak down test and that showed it was the pistons. The eventual plan was to get a better set of rings like Deves or Hastings to replace the borgo rings that came with the pistons but if the clearance is 2 and a half times what it's supposed to be it might be best to replace the (almost new) piston/liner set.
I'm glad you posted this, I was kicking myself for botching the break in. (and that still might be the case) I'm curious to hear how you resolve this, be it better rings or some other solution.
 

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There seems to be a lot of focus on the break in, while that's good, don't lose sight of the fact that the piston to liner clearance is critical. I don't care how you break in the rings, if that clearance is double the allowable spec, it's going to burn oil.

Greg
 

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I've heard of pistons being sent out to be coated and gaining a couple of thou in size, the coating thickness can be specified within reason. It's a very popular solution with KLR 650 engines, many of which come from the factory with very loose pistons and an oil burning issue. The coating is a low friction type finish and is very reliable.
Oversize rings in undersize pistons don't tend to help too much (although individual cases may have worked for some), as undersize pistons tend to rock at top and bottom dead centre too much, momentarily destroying the ring seal and also wearing a wried finish onto the ring faces, plus wearing the ring lands much faster.
Could be worth looking in to as a reasonable solution.
 

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Millenium Technologies (Michigan) might be able to caot the pistons for you. They do lots of cylinder bores but I have never sent pistons to them.
 

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Discussion Starter #13
I checked out millennium.. there price was $195/ liner. Too expensive for me.
i have ordered new liners from Alfa Originals in London. If they will not work for me, i would be interested in selling them for my cost ($450) rather than shipping them back over the pond.) PM me. Larry
 

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motronic ring confusion

Hi Larry,

I just came across your thread while searching for something else - and i think you may have run into the same problem I did - buying Motronic pistons from europe but sourcing better rings in the USA - where the Motronic piston had a different sized center groove.

Everything I learned on the topic is in this thread
http://www.alfabb.com/bb/forums/engine-rebuilding/173187-rebuilt-2000-using-burning-oil-2.html

Good luck,

-Richard
 

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Chalk me up as yet another user of Motronic 10.1 pistons which never seemed to seat the rings properly. I bought a set of Hastings rings along with the P&L so that I would have the multi-piece oil rings. Of course, I installed all three Hastings rings - not just the oil rings - on the Motronic pistons.

It sounds like there are two problems with this setup:

- Excessive piston to liner clearance. Has anyone besides Larry measured .005" clearance in the 10.1 Motronic P&L's ?

- Narrow center ring in a wide center ring groove. I'm puzzled why an ill-fitting compression ring would cause excessive oil consumption. I might expect a lack of compression, but why would a problem with the compression ring cause the oil ring to not work?

I keep postponing pulling my engine, because it runs great otherwise. But I'm getting sick of polishing oil residue off my back bumper. I'm glad I saw this thread - I was going to just re-hone the liners, get a new set of Hastings rings, and reassemble it.

I went back to Centerline's website, and noted that they show three different part numbers for 2 liter Hastings piston ring sets. They have different sets for 9.1:1, 10.0:1, and 10.4:1 pistons (I assume that "10.0" is a typo, and that they meant "10.1").
 

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- Narrow center ring in a wide center ring groove. I'm puzzled why an ill-fitting compression ring would cause excessive oil consumption. I might expect a lack of compression, but why would a problem with the compression ring cause the oil ring to not work?
.
Jay,

I would think that the loose center ring is allowing blow by and vacuum is sucking the oil up past the oil scrapers. Sad to say but the rigs must fit right to be effective.
 

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I would think that the loose center ring is allowing blow by and vacuum is sucking the oil up past the oil scrapers. Sad to say but the rigs must fit right to be effective.
OK, thanks for the explanation.

Here's a follow-on question: If I also discover that I have excessive clearance between my piston and liner - i.e., the .005" that Larry reports in post #1 - will simply installing the correct thickness rings solve the problem? Has anyone been able to get a set of 10.1 Motronic's to work properly with piston-to-liner clearances that are 2.5 X the recommended spec.?
 

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Jay,

I'm not a real expert at piston clearances but here is my thinking. The oversized pistons will "rock" very slightly in the bore or remain square but pushed to one side, and this will keep the rings from remaining square in the bore. Is the just slide to one side, then I would be thinking that the rings are not supported properly on the opposite side and this again keeps them from sealing/seating.

If your going to break it down to replace the rings, then I would fix the complete poor fit problem.

Just my .002
 

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How did you clean the liners? I had the same problem and was using Deeves, then a set of Total Seal for the merican motronics. ring gap was in spec both times. The oil burners I built all had great compression of 190. The only thing that produced a no burn oil motor was the way I cleaned the liners and what I used on the pistons when assembled. WD-40 and washing the liners in the dishwasher. Specs aside, the assembly technique and the first 10 minutes of running a new motor seems to determine if it's going to be an oil burner or not. I had the exact same problem and the only thing I changed was the wd40 and the cleaning of the liners. Now I'm using about 1/4 of a quart every 1000 miles.
 
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