'97 with big end bearing trouble. - K-Bikes.com - Excellence in Motion
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post #1 of 4 (permalink) Old Mar 9th, 2010, 6:23 am Thread Starter
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'97 with big end bearing trouble.

Hi Guys,

I am dipping my feet into the sea of road bikes again here. Managed to find a very very clean k1200rs that cosmetically was good and only had a seized engine. The description said it would not turn over.

The price was worth just getting it and parting it out if the damage was too much. So took it home and started tearing away at the usual suspects. Gearbox is good, bevel drive is good, clutch is good.

What I did find was that the drained sump oil looked like copper grease so off came the head and the crank cover. The cam shafts, the valves and the piston bores are all ok. The main bearings were also good.

However the bearing on the first conrod big end was fubar. It was all flaked out and had also galled itself to the crank. This obviously needs grinding to the stage 1 that BMW spec.

Question here is if anybody else has ever had to grind a k1200 series crank? Any experiences?

I have given the crank to a engine reconditioner who will grind the crank to the stage 1 as speced in the maintenance manual. It also calls for heat treatment of the journals once ground. does anybody have any ideas on this one?

Once the grinding is done I plan to purchase the 3 different colour stage 1 shells and find the best fitting using plastigauges. Again comments welcome.

The whole process will be marginally cheaper than getting a second hand crank btw

Pics of the failure to follow
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post #2 of 4 (permalink) Old Mar 9th, 2010, 11:11 am
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Well you are doing what I might have done some years ago. But oems don't seem to offer the piston and crank options they used to, almost as if the motor is built to last its life.

Personally, I would always Google around the boneyards first for a good motor in a crashed bike. New BMW parts are horrendously expensive. Just getting consumbles like gaskets and seals can cost quite a bit. You could get lucky and find a good motor low miles off a newer bike.

I've never done it, but if you can't get undersized shells - and you are normally talking 10-20 thou to clean up a journal, you can metal spray and grind down to a stock shell size. Actually, thinking about it, if you only have one journal duff, that makes more sense, because you wouldn't need to touch the other journals. Not sure if crank balance would change much, but these motors are tractorial so might not be a big issue. I don't know if the BMW shell codes are real undersizes or just a narrow range to cope with production machining tolerances.

In my experience, you can't easily estimate beforehand how much needs to be ground away to get a journal properly clean after a siezure. Another reason to consider metal spraying.

Don't forget to take a hard look at the oil pump and have a gauge on the sender port, just to check the pressure at first run.

Good Luck - Vox

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post #3 of 4 (permalink) Old Mar 9th, 2010, 11:32 am
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Well well....Hi again! I see you followed my lead and already got some good advice!


Benelli 50cc at 14
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post #4 of 4 (permalink) Old Mar 10th, 2010, 7:03 am Thread Starter
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Ended up stopping the machinist. have ordered a crank with matched conrods. Now all I need to do is match the mains and job done. Cant be bothered with all the faffing and 100 different shells
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