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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 3 Jan 2007
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'88 Cranckshaft rebuild what to do?

Hi all,
I have a 1988 XT600 going through a complete rebuild, the top end is off to the machine shop for a big bore 11.5:1 along with head work. Now that I have gone through the process of splitting the crankcase, I am finding that the LH side (timing chain side) bearing is fitted to the crankshaft as opposed to the the crankcase, as is the case on the RH side. The timing chain gear also appears to be pressed on as well. As I carefully go over the procedure in the Clymer manual, I find that in one step the bearing and gear are on the shaft, in the next step the bearing and gear miraculously disappear. Nowhere in the book is the removal/installation of these items is covered. Much to my dismay Yamaha does not sell this bearing, it is listed as an integral part of the crankshaft LH side, i.e. you want the bearing, you must buy the crank half along with it @ $258.00 USD. Damn!! all the other bearings, seals and crankpin already cost me about $300.00 These are definitely two different bearings with different numbers. Has anyone got any ideas on how to avoid a new crank half, wihout doing a half-ass rebuild?

PS- the manual lists a SST to pull the crankshaft into the crankcase on assembly, they also show a homebuilt version of this tool, but very unclear instuctions on how either is used. Anyone have a hint?
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  #2  
Old 3 Jan 2007
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The bearings are not an integral part of the crankshaft assembly but are a tight press fit onto it. You normally will require a puller to get them off. The puller hooks onto the back of the bearing (or clamps to it if there is no room behind the bearing) and presses against the end of the crank as it's tightened. It's important to protect the end of the crank so the puller doesn't damage it. Heating the bearing will make it expand and so it'll be easier to pull off.

The bearings will have a number on them, this is not a manufacturer's part number but is a universal code which identifies the size. Only if you are real unlucky will Yamaha have used a special part made just for the bike. Go to bearing supplier (engineering or automotive) with the code, or preferably the old bearing and ask for a new one by a reputable manufacturer. It should only cost fraction of the Yamaha part.

Put the new bearing in an oven at about 150 (centigrade) to make it expand, and if you have one , put the crank into a freezer to make it shrink. With luck the hot bearing will just drop right onto the crank. If not use a tubular drift on the inner part of the bearing to tap into into place on the crankshaft. Try and do both sides while the bearings are hot.

The puller you describe is used to pull the crank and its bearings into the cases as it's important not to hammer the opposite end of the crank in order to drive the assembly home. However, it's worth trying to heat the cases first as aluminium (aluminum) expands much more than steel. Heat the cases slowly and evenly in an oven to about 100 centigrade (no more if you've left rubber seals in place) then try lowering the crankshaft assembly into the case making sure the bearing enters its housing square and parallel. If it doesnt go in, try tapping the cases gently with a rubber hammer. If it won't go at all, you'll need to figure out the puller which I assume pulls the end of the crank while pressing onto the casing and as you tighten it it draws the crankshaft bearing into the housing in the case.
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Old 3 Jan 2007
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Brilliant

I'm very impressed .......and you certainly know your way around the kitchen. and thats only utilizing an oven and fridge.

What would you use your conventional microwave oven for?.......know, really i'm impressed.

Good on you
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Old 3 Jan 2007
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I once had the head off my kawasaki 900R in the dishwasher to degrease it. It worked really well but left a tide-mark of oil all around the insides. Missus wasn't impressed and the food tasted of Castrol for weeks...
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  #5  
Old 3 Jan 2007
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Ok, I got most of that down already. I got all the other bearings out by way of heating, some needed a little persuasion, others just about fell out. I realize that the bearing is not integral to the crank half, just that Yamaha lists it that way. What concerns me is why Yamaha would choose to do this. Do they do this because rebuilding this in a conventional manner I run the risk of having the bearing fail? Or are they just trying to soak me for more money? Pretty much what I'm asking is: has anyone out there actually had this crank half rebuilt, and did you encounter any problems as a result? Also anyone have any pointers as to where to obtain such a bearing?
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Old 4 Jan 2007
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I've rebuilt a few single cylinder bikes including an XT500 which included replacing the main bearings. I've no reason to think that the 600 is any different and so the fact that they seem to ship a new crank with the main bearing attached is probably only because anyone replacing the crank would be crazy not to change the mains at the same time.

As I said in the first reply, the bearings should be available from any good bearing supply shop as long as you know the right code, or take the old bearing to be sure. Honda are particularly sneaky at using 'special' sizes in their bikes but Yamaha usually use standard sizes. Even if you do find it is an unusual size it's often possible to get a specialist supplier to grind the inside or outside diameter of the bearing to the correct size
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Old 4 Jan 2007
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Bearings

You can certainly only change the bearing on the L/H side. For the newer Tenere / XT models they are identical, left and right.
I did this and already did 30.000 happy km's.
You can certainly get these bearings from a specialised car part shop or something, they cost about 20 Euro's each.

Removing the gearwheel for the timing chain and the bearing, and putting them on again, is a 5 minute job for someone with a press and some experience.

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  #8  
Old 24 Jan 2007
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As it turns out the Clymer manual is full of baloney. I found the main bearing, and had the crankshaft rebuilt with new pin, bearings, etc. The crank slides right in with no pressure, heating, freezing blah blah. Did a test fit with the other crankcase half with the crank in place, nothing needs to be "pulled" together, just make sure all the mating surfaces are square with each other, the more I read the crank installation procedure, the less sense it made. The Yamaha shop confirmed this, the SST is for seperating only, if the crankcase halves, and the crankshaft don't slide all together easily, you messed up somewhere. I also noted in the manual that when the crankshaft service is covered, all of a sudden the procedures are shown with drawn illustrations insted of photographs, like the rest of the book. This suggests to me that the mechanics never rebuilt the crankshaft at all, and just gave a general description of inspection, runout and so forth. Always nice when things turn out easier than one expects . Thaks for all the input
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