SOHC.co.uk Forums > CB500/550
Crank not rotating
alexdecker:
Damn it.
Ok, assuming the crankshaft is bent and I need a new one. In that case, I don't need to measure anything, I can just pair the case markings with the crankshaft markings, and then get new bearings based off the result?
But what about the rod bearings? I assume I can't reuse the old ones, and would have to get new ones as well for the rods?
Oddjob:
So long as the rods aren't bent as well you can transfer them over. However, like you say the shells will need to match, you have a chance of that happening but I wouldn't count on it.
Have you checked the crank bearings, sometimes you can still see the colour on the side edge of them. Worth having a look.
I'd remove all the shell bearings one at a time, inspect them closely. It's possible you may have damaged one very slightly and that's why it's grabbing the crank.
I don't think the crank is bent, never heard of one ever.
Which journal is the iffy one?
alexdecker:
Ok, so gave it another go on the experimental part, and started moving bearings around a little more aggressively. I found it that not even did the problem follow a specific bearing, but it all came down the the specific screw on the specific bearing being tightened, and then the thing seized up (see picture).
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So I closely inspected it, and lo and behold, didn't even have to inspect it that closely. This is obviously a case of not being able to see the forest for the trees, but this bearing has a spot on it. Now, it's very small, and I can HARDLY see any bulge in the metal with my naked eye - but there is a tiny slight one. It seems much larger in the picture, but trust me, there is almost nothing. Basically nothing. It seems weird to me that such a minuscule spot can seize the entire crankshaft like that. But the problem followed wherever I put that bearing, and that is the only fault I can find in the bearings, so can't think it can be anything else.
What do you guys think?
Also - I can see the colours off most of the bearings, and they are green, brown or black. The offending bearing is green. What would be the best way to go about this issue? Plastigauge all of it, or just buy a new green bearing? Also, I find it really weird that it didn't lock the engine up before taking it apart. All bolts were pretty tight when taking it apart, so it was obviously torqued down alright. Wonder what that is about.
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Laverda Dave:
Good that you have found the potential problem. That shell is toast, no way would I try to use it again, you are talking microns of clearance on these bearings so not worth the potential problems of trying to rescue it.
If it were mine I would plastigauge all the bearings so at least you know what you have got to start with and especially now you have been swapping them around. I would use that as a starting point and buy new bearings to suit.
I still can't see how the bolt caused the bearing to spot in the way it has though, did you inspect every bearing shell during the engine strip and was the spot there before? To my eye it appears as though there was something on the crank journel when you initially torqued the cases and this caused the bearing damage and prevented the crank from turning. I would inspect the case very carefully in case there is a bit of grit floating around in there, same with the crank, give them both a good clean. A piece of grit may have become dislodged when you were hammering the rotor to remove it?
At least you have a way forward now and not a bent crank!
And best to check the crank journel of the damaged bearing for a score mark in the same location as the bearing spot.
Oddjob:
Looks to me to be a rust spot. When the bearing was removed it allowed the rusted area to expand (which it couldn't do before due to the crank stopping it) this then bloomed out to look like it is now.
Check all the others for similar damage, you're probably lucky as it's extremely rare for this to happen in my experience. You could just replace this bearing with another green but I'd strongly advise buying a pair of green bearings to replace those on that journal. Don't order new ones until you've checked the others very carefully.
Your lucky, green is about the only colours it's still easy to find. Yellows and blacks are rare and browns are starting to go the same way.
If your stuck finding new bearings contact me as I have quite a few NOS ones. I started to collect them many years ago and it's coming to the point where I'll sell them all and cash in. As soon as I've finished building the engine on my last restoration I'll be selling a lot of stuff.
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