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M30 Crankshaft float

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randall977
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M30 Crankshaft float

Post by randall977 » Sun Mar 18, 2018 7:03 pm

There's more float in the crankshaft than there should be so I'm guessing that the thrust bearing is worn... I'm going to replace all the bottom end bearings and hope I can do this in situ by removing the sub-frame and dropping the sump? Anyone done this job? Do I need to replace any bolts? Thanks

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randall977
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Re: M30 Crankshaft float

Post by randall977 » Wed Apr 18, 2018 8:37 pm

Got into the bottom end today to find out why the excessive float. Turns out the thrust bearing has worn a groove on the flywheel side of the crankshaft. I called a local engineering firm to ask about my options - he immediately knew what side the wear was on and all about this problem (so obviously not rare). He said adding metal back in is not easy on these crankshafts due to the heat produced in doing so.

So replacement crankshaft and bottom end rebuild it is - fab!

Cranky.jpg
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Brucey
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Re: M30 Crankshaft float

Post by Brucey » Wed Apr 18, 2018 10:31 pm

the largest thrust appears on the crank whenever the clutch pedal is depressed. That wear looks pretty bad (unusual for an M30 I would say, it may indicate that the clutch went weird (high load) and may also have helped cause the gearbox to go bang...?).

Hmm just looked and both sides of the thrust bearing are formed into the shells for one of the main bearings.

http://2009.bmwfans.info/parts/catalog/ ... ng_shells/

Red and blue are for tiny variations in journal diameter. No conventional adjustment of crank end float possible. :shock:

Suggestion; before you buy a new crank, just make sure that new shells alone wont bring the end float back in spec.

Q; I wonder if aftermarket bearing manufacturers offer a shell bearing set that is oversized so that a worn crank can be accommodated with allowable end float?

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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randall977
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Re: M30 Crankshaft float

Post by randall977 » Thu Apr 19, 2018 8:34 am

Thanks for the reply and info Brucey. I haven't thoroughly investigated this but I'm told the oversizing tends not to be on the thrust ends - just a bit for cleaning.

I think a new standard bearing might reduce the float to around 0.5mm, still to much - it might interfere with the clutch operation etc.

An oversized bearing (oversized in the right place) would mean taking the crank out and regrinding it. Getting another good crank is probably still my best option...

I will keep you updated on progress 😵

janusz200
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Re: M30 Crankshaft float

Post by janusz200 » Thu Sep 13, 2018 5:36 pm

I've also noticed crankshaft axial play about 1 mm or more in my M90 engine. Have You already fixed your problem?

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Re: M30 Crankshaft float

Post by bpoliakoff » Fri Sep 14, 2018 1:32 am

There should be plenty of good cranks around reasonably priced. I would get one, have the sludge trap plugs removed and the traps cleaned out and the journals polished, new main and rod bearings, seals and off you go for another ungodly amount of miles. If you pull the motor, you may as well do rings, depending on cylinder wear and at the least a valve grind if needed and a total reseal. Odds are the guides are good but new valve seals as well.
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

janusz200
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Re: M30 Crankshaft float

Post by janusz200 » Fri Sep 14, 2018 2:52 pm

Thanks for information. At the moment I can't examinate the crankshaft again so I don't know exactly what's the reason of play. 25.000 km ago I've changed the shells, piston rings and maintained the cylinder head. Now engine takes too much oil - about 0,3 l/1000 km and is smoky from exhaust. There's also deposit on piston tops visible by endoscope camera and compression is very high (12,5-13 bar against 10-11 by factory manual) due to oil in chambers I'm afraid. Car pulls like hell by the way. I hope that the valve sealing is the problem. So I have to check different things and take the decision what to do. Anyway I’ll keep in mind You have a crank.

By the way I’ll appreciate advises what to check and how before I pull the motor off what will not be necessary I hope very much.

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Re: M30 Crankshaft float

Post by bpoliakoff » Sat Sep 15, 2018 2:53 am

If the rings have properly seated, it has to be valve guides or seals. Seals should be able to be done with everything in place, IIRC, by sliding the rockers to the side
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

janusz200
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Re: M30 Crankshaft float

Post by janusz200 » Sat Sep 15, 2018 9:32 am

Seals replacement without head dismounting is very good news especially that the gasket mating surface was machined already of 0,1 mm.

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Re: M30 Crankshaft float

Post by bpoliakoff » Wed Sep 19, 2018 1:11 am

Randall

This on thee MyE28 forum. Should give you an idea on prices. At least stateside.
The crankshaft in front is an m30b35 crank that is the lighter weight version (or so I have been told). $125 plus shipping

The other crankshaft is from an S38B35 (M5/6) not sure what to price that at - offers???

Both are in excellent condition just clean and polish and ready for service!!!
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

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