Replacing a crankshaft: any pointers?!!!!

[hools100RS]

Setting up a crankshaft: any pointers??
by hools100RS » Mon Feb 21, 2011 7:50 pm

G'day everyone it's been a while since I last posted but thought that the topic deserved some considered and meaningful contributions. On removing the crankshaft from my '81 100 RS I've discovered major damage and have decided to replace the unit with one that is in known good standard condition.
Yep, a high speed oil starvation drama appears to be the cause, as on blowing out the oilways and galleries with an air hose I discovered a black flaky material that I reckon may have blocked the odd hole or two!(the bike is new to me and it's history unknown........... looked good on the outside but......!!!!!)
Any way.... setting up a crank...... main bearings and thrust washers......different colours........ its intimidating but I'm prepared to give it my best shot!!!!!
The cases have been cleaned and all is in readiness for the replacement..........
Can someone start me off?..........Help,,,,,,,,,,,Jeff or GSPD are you out there???!!!!!!!!!!!!hools100RS

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Joined: Thu Aug 19, 2010 6:43 pm
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[ME 109]

Gidday hools, You can go to a lot of bother finding the perfect thrust washer sizes or, as GSPD advised, if you can spin the crank by hand with the guide ring torqued up, it'll be ok.
It worked ok for me.
Get the crank measured professionally and you'll know which size to get. Or, start with the standard red, and then try the next undersize. Trouble with that is you need to buy two lots of bearings.

I'd be looking further for the exact cause of the oil starvation.
You want to fix the cause as well as the symptom.
How did you know the crank was damaged? Have you check the oil filter bypass spring?
If the main bearings were blocked by crud, I'd expect to see some evidence in the bearing slots when the crank was removed.

Have you got a close up picture of the damaged crank?

[mattcfish]

Pull the jugs and remove the con rods with the crank still in the bike. If the crank is damaged by oil starvation you will certainly see it there. My friend's R90 lost oil pressure when the oil pump sump pick-up came unscrewed and fell off. Lots of metal in the pan. The Conrod bearings spun and chewed up the crank. However....the main bearing surfaces were not damaged.
Very few owners regrind these cranks. Ususally the red (standard) bearings are what you need. If you buy a good used crank ask if you can have the old bearings and thrust washers with it. The # size of the bearing will be stamped on the back of each one.
As far as the thrust bearings go...put the thickest one you have on the inside. You can buy new ones for the outside or just get one medium size used one and sand it down with fine paper until you get the desired end play.

Make sure you get an R100 crank. Other cranks from earlier model may have the same stroke , but the flywheel bolts may be too small and the counterweighting may be different.

[hools100RS]

Thanks Jeff and mattcfish!! Jeff your bypass spring and detent was the first thing I checked!!! Seems OK!!! The clanking rod definately chewed up the right hand side big end and the crank journal is deeply scored.The rear main bearing is really scored too, two even shiny tracks that suggest a high mileage machine!!! To lend weight to this idea, both gudgeon pins were grooved, that suggests that the motor was tired prior to the starvation issue. How's this...... the rocker covers had been painted inside and out and the paint on the inside was coming away in hard crusty chunks!!!! Looked suspiciosly like the stuff on the bottom of the oil pan, stuck in the oil pickup strainer and on the outside of the filter!!!!! I'd had both covers off to do the tappets but didn't pay any attention!!!!@#%$#@!! Any way a good crank and camshaft are on their way from the States and work should start soon. Jeff what do you mean when you say ........."with the guide ring torqued up"
The crank I bought doesn't come with bearing and spacers so i'll be starting from scratch!! Thank you both for your input. Watch this space and I'll keep you informed and squeeze you for more advice!! Cheers. Hools.

[ME 109]

Jeff what do you mean when you say ........."with the guide ring torqued up"

The guide ring is what the clutch carrier bolts to. The guide ring is what runs in the rear main seal.
With the thrust washers and crank in place, bolt the guide ring to the crank and torque it up.
You can then measure crank end play, or confirm that the crank can be spun by hand.

If your starting from scratch (bad pun) with thrust washers, the adjustments (thicker or thinner washers) can be made at the rear (outside) washer. As far as I know...

If the black paint hasn't caused the blockage, keep looking!

[dougie]

the rocker covers had been painted inside and out and the paint on the inside was coming away in hard crusty chunks!!!!

Any chance that paint is powder coating?
That stuff is quite hard.

[barndeadr80]

The amount of black paint from the factory that ended up on the inside of the valve covers on my '85 as overspray was rediculous. Bake and flake.

[hools100RS]

Not sure if it's factory spray but I dont think so!! But I have a stong suspicion that that 's what the big flakes of crud in the motor are and that they could easily have contributed to an oil starve at around 90 MPH! A few lads around here think that given the likelihood that I''ve bought a high miler, that the big end letting go was somehow inevitable. No way ! I've had enough to do with BM's to know that without some sort of warning, these things don't happen for no reason!!! Besides the other journal and big end was fine. ......and by the look at the gunk in the motor I can't rule out a blockage from some of that flakey crap!!!
Jeff, I'll also replace that bypass spring and ball as on closer inspection, even though the ball appears to be seating OK, I reckon the spring seems a bit weak on it!!!Do motobins carry them? Also in cleaning the block, I've decided to open up the oil galleries by taking out those blanking studs in the crankcase and giving everything a good blast. Are they put in with a type of loctight? Any other suggestions out there? I don't want to overlook anything if can help it!!

Not Happy Jan!

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[Duane Ausherman]

Why fix it? You can get a good used lower end for cheap/nothing.

[Major Softie]

Why fix it? You can get a good used lower end for cheap/nothing.

That's the most economically practical solution, but some people really care about maintaining "matching numbers." For them, replacing the whole lower end is an absolute last resort.