M20 Rings, Rod Bearings, Valve Job

E28 technical advice asked and given! Troubleshooting, modifications and more.
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gump
Posts: 29
Joined: Mar 10, 2019 12:03 PM
Location: Los Angeles

M20 Rings, Rod Bearings, Valve Job

Post by gump »

I am thinking about a partial rebuild for my 528e (M20). The major elements would include rings, rods bearings and a valve job. Of course all of the associated gaskets, seals and the "while you are there" things like timing belt, water pump, etc.

Now, I think I can do this job without pulling the motor. I've had the oil pan off as you can with the M20 and that's primarily what leads me to believe I can do this with the motor in the car.

What am I missing? What else should I consider?
Mike W.
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Joined: Feb 12, 2006 1:00 PM
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Re: M20 Rings, Rod Bearings, Valve Job

Post by Mike W. »

While I've rebuilt many an engine, including BMWs, and I always include rings, I've come to a different thought now. Now I don't specifically know on M20s, but on M30s by the late 70s the rings just didn't seem to wear. I mean one time the end gap on the new rings was larger than on the originals. So unless there is more to the story, I might do the rod bearings, but I'd probably skip the rings.
gump
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Joined: Mar 10, 2019 12:03 PM
Location: Los Angeles

Re: M20 Rings, Rod Bearings, Valve Job

Post by gump »

That's good input. Thank you. I will do a leak-down test before I touch it for no other reason than to have a benchmark.

If I am not getting any leakage past the rings and the cylinders look good, I might just leave them.

Stand by for results of the leak down test.
tn535i
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Location: Middle Tennessee

Re: M20 Rings, Rod Bearings, Valve Job

Post by tn535i »

You don't say how many miles on the clock ? If under 200k it's really unlikely you need to touch the rings or bearings. If I wanted to swap to higher comp pistons then I would consider but otherwise not. Some benefit from a refresh of the head and cleaning up all the valves and if I were into that of course do the t-belt if any doubt about it. Also do sintered timing gears. But I would only go into it if over maybe 150k and the compression test shows some irregularities.

These older M20 and M30 motors if cared for properly easily run 300k.

Still have and M20 I acquired around 24k that is in it's second chassis that was last examined for compression and valve lash at about 160k and there was nothing wrong at all. It's our project e30 that when it does get driven is wrung out hard. New belt and sintered gears in that motor.

On the other end of the scale we had an M20 i car a few years back of unknown history (5w-30 cheap oil change stickers) that was not well cared for that still ran OK at 300k+. It had some noisy valves that could not be adjusted out and it finally broke a rocker about 312k ? I rebuilt the head and it ran as smooth as a new motor with excellent compression numbers.

My M30 is at about 300k and still strong with good compression numbers. I need to check the valves again I suppose, but it has never been opened up and runs so well I forget it needs that periodically. I've had it a long time but only put the second half of those miles on it.

Where you are in these scenarios should dictate how hard you go looking for things to work on.
craigb93
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Location: Cumming, GA

Re: M20 Rings, Rod Bearings, Valve Job

Post by craigb93 »

If you take the pistons out of the block DO NOT try to reassemble it in the car. It will need to be honed for new rings to have any chance of seating. The residue from any kind of beneficial honing cannot be adequately flushed out of the engine short of pulling the crank and then thoroughly cleaning everything with HOT soapy water. Honing residue is exactly the same as valve grinding compound except it is now applied to all internal bearing surfaces if left in the engine. Makes for a merry demise of any good engine.

Unless the compression/leak-down results are really off you are better served, as noted above, by leaving the whole bottom end intact and concentrating on renewing all cylinder head components. -Dick
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