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denvoyager |
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denvoyager L Plate Warrior
Joined: 28 Jul 2015 Karma :
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Posted: 16:20 - 18 Apr 2019 Post subject: stiff crankshaft replacement |
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Hi,everyone,
I've just replaced a crankshaft on my Yamaha YP 250 Majesty 2001 4str.
It has gone back in ok, and I have fitted the two crank case halves back together. The oil/water pump shaft is rotating correctly, and is not jammed.
The problem is that the whole assembly seems a little stiff, I can only turn it with a spanner on the spline end - it goes 360, but it's stiff - any ideas,please , anyone, or is this normal, and will it turn on the starter, and 'bed' itself in do you think?
Cheers, Den, Swansea |
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MCN |
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MCN Super Spammer
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Robby |
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Robby Dirty Old Man
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Grubscrew |
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Grubscrew Scooby Slapper
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Riejufixing |
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Riejufixing World Chat Champion
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RhynoCZ |
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RhynoCZ Super Spammer
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Riejufixing |
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Riejufixing World Chat Champion
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MCN |
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MCN Super Spammer
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Pete. |
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Pete. Super Spammer
Joined: 22 Aug 2006 Karma :
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Posted: 18:43 - 18 Apr 2019 Post subject: |
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A common issue when fitting roller bearing cranks in vertically-split cases. The bearings are tight on the journals so pulling the halves together puts an axial pre-load through the bearing. If you try to run the engine the bearings will fail very quickly. If you check the manufacturer's assembly procedure you might find that the case or the bearing should be heated to make sure that you get no pre-load (as an example, Aprilia say heat the case to 80 degrees for the RS125 engine IIRC).
You need to put a shock through the bearing to release the pre-load. You have a couple of options, you could give the crank a crack on each end with a hammer to bump the bearing deeper into the seat, we're talking fractions of a mm here. Protect the end threads with a piece of soft metal like ally. Put the nut/bolt on the end if you can (but DON'T hit the nut). You want a sharp crack with no real weight and no follow-through. Bit hard to explain but easy enough to do. Or you could do the same with a tube spacer to give the case a crack over the bearing outer ring for the same effect. You should also put a snug fitting wedge in the gap between the crank webs opposite the big end to avoid putting a bending moment on the crank pin.
Neither of these things are what you'd call great practice and they do carry a bit of risk and best left to someone with a good bit of mechanical empathy but if you do nothing you're going to knock the new bearings out in no time flat. I've put together cases that needed nothing but a small tap to free up the rotation and the odd one that needed a bit more. ____________________ a.k.a 'Geri'
132.9mph off and walked away. Gear is good, gear is good, gear is very very good |
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Posted: 19:52 - 18 Apr 2019 Post subject: |
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OP IS turning the oil and water pumps too. This may have a bearing.
How did you fit the cases? Just drop them on and wind them up? Hot cases onto cold crank? Did you tighten them together using rhe crankcase bolts or pull the case onto the shaft with a spacer tube and the crank nut? ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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Pete. |
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Pete. Super Spammer
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Riejufixing |
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Riejufixing World Chat Champion
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Pete. |
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Pete. Super Spammer
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Riejufixing |
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Riejufixing World Chat Champion
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steve the grease |
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steve the grease Crazy Courier
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Pete. |
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Pete. Super Spammer
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Meatybeaty |
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Meatybeaty World Chat Champion
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Posted: 08:42 - 19 Apr 2019 Post subject: |
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denvoyager |
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denvoyager L Plate Warrior
Joined: 28 Jul 2015 Karma :
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Posted: 09:38 - 19 Apr 2019 Post subject: stiff replacement crank |
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Hi, and thanks everyone for the really helpful advice. The bolts are torqued to 10 newtons, as per the manual.
When I back them off slightly , the rotation is a LOT freer.
I think the (complete with bearings already on) unit is the correct one, and that it is almost certainly that the whole needs a bit more movement to bed the bearings in.
I 'froze' the unit , and it went in ok, seemed to mate/butt to the end of the bearing space.
With the second split casing, I pre-heated it, after putting sealant on the first casing, then tapped it down. Again it seemed to go in easily, especially after a 'wiggle' to align the slot of the oil/water pump axle.
I'm going to try backing off again, to see how free it really is. That'll confirm the 'spacing' issue. I'll keep you posted,
Cheers, and thanks again, Den, Swansea |
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stinkwheel |
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stinkwheel Bovine Proctologist
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denvoyager |
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denvoyager L Plate Warrior
Joined: 28 Jul 2015 Karma :
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Riejufixing |
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Riejufixing World Chat Champion
Joined: 24 Jun 2018 Karma :
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Pete. |
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Pete. Super Spammer
Joined: 22 Aug 2006 Karma :
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Posted: 13:24 - 19 Apr 2019 Post subject: |
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What's all that white powdery crap all over the assembly? I hope it's nothing more than frost. ____________________ a.k.a 'Geri'
132.9mph off and walked away. Gear is good, gear is good, gear is very very good |
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Old Thread Alert!
The last post was made 4 years, 345 days ago. Instead of replying here, would creating a new thread be more useful? |
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