Bad crankshaft

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Unwound

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Mar 9, 2012
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Hello,

I have a 1988 Vmax with 19,000 miles on it. It had a horrible lower knock so I pulled the motor on it and dug into it. The knock was coming from a rod bearing that had spun on the left front cyl. and scored the crankshaft journal some. Does anyone know the limit that the journal can be ground down to? I'm just not finding it in the service manual. It shows smaller bearings that can be ordered but I can't find what size they are. Or is it smarter to try and replace the crankshaft?
*Also while I'm in there are there other areas prone to failure that I should be looking for?
The pistons and cylinders look great. Maybe have the valves ground?
Thanks for your help,
Gary
 
Awesome info. I'll need to inspect more. I have the rods out but the crank is still in. Thanks Mike.

I have never had any problem shifting, up or down, or popping out of 2nd. Is that something that would be wise to address while I have the motor out?
 
Unwound said:
Awesome info. I'll need to inspect more. I have the rods out but the crank is still in. Thanks Mike.

I have never had any problem shifting, up or down, or popping out of 2nd. Is that something that would be wise to address while I have the motor out?
Click to expand...
I don't think so. If that part ain't broke don't fix it. It IS one thing to look for if the motor is coming out though.
 
What should I be looking for? What are the signs of an upcoming 2nd gear failure?
 
All you can do is polish a crank for a Vmax. There are no under size bearings like on an automotive type crankshaft. There are a few different colors/sizes that correspond to the journal when it's new.This info is marked on the crankshaft. A bad journal can be welded up and then re cut. Then there's true and balancing. Usually it's cheaper to get a used crank. If you did two journals I think you'd approach the price of a brand new crank. I'd think Sean would be able to help you out. E-Bay has them sometimes too.
 
Unwound said:
Hello,

I have a 1988 Vmax with 19,000 miles on it. It had a horrible lower knock so I pulled the motor on it and dug into it. The knock was coming from a rod bearing that had spun on the left front cyl. and scored the crankshaft journal some. Does anyone know the limit that the journal can be ground down to? I'm just not finding it in the service manual. It shows smaller bearings that can be ordered but I can't find what size they are. Or is it smarter to try and replace the crankshaft?
*Also while I'm in there are there other areas prone to failure that I should be looking for?
The pistons and cylinders look great. Maybe have the valves ground?
Thanks for your help,
Gary
Click to expand...

Was there an orange o-ring bulging from the oil pump plumbing? Where it goes into the block channel? Early gen 1's are prone to this happening, you loose oil pressure and the knock follows. This can be addressed when reassembling with a better o-ring and oil pump upgrade and after market bracing. An oil pressure gauge is something I wouldn't want to go without. Valves at 19k are most likely in new condition. I'd
address that after you're done with the lower end.
 
Rats. That's why there are several different colored bearings available but no diameters listed? Maybe a short block from Sean would be the smartest way to go? Compression on the front 2 cylinders were low - 70 - 80 psi range. Valve job too?
 
I picked the O-ring out of the hole in the block after the T-shaped tubing came out. It seemed to look normal. I don't remember seeing it bulging out before the tubing came out, but then again I wasn't looking for it. Is that oil pump upgrade from Sean also?
 
We've got it all!
This is the blurry example of a blown out oring.
 

Attachments

  • O-ring blown out.jpg
    O-ring blown out.jpg
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Unwound said:
What should I be looking for? What are the signs of an upcoming 2nd gear failure?
Click to expand...

You need to look at the shifting lugs & the pockets they insert in. The leading edge should look like new on both. If they are shiny & rounded off they should be replaced.
 
Unwound said:
Rats. That's why there are several different colored bearings available but no diameters listed? Maybe a short block from Sean would be the smartest way to go? Compression on the front 2 cylinders were low - 70 - 80 psi range. Valve job too?
Click to expand...

I didn't explain that completely. The crank numbers correspond with markings on the case for each journal. Damon's video covers this completely. There really is not much you can do with this that makes $$ sense. Used motors are cheaper than the sum of the parts and machine work needed. 70-80 is 100 psi too low. I'm thinking $2k minimum to fix yourself. That's if the case is good,see Mikes post. Being an 85, you'd want to upgrade a couple of gears in the transmission too. And Sean's policy of standing behind his work is worth a lot.
Steve
 
Yep, a good used engine might be the way to go......although basically anything can be fixed with enough money.
 
Yes, a short block with an oil upgrade from Sean sounds like the smart and best way to go. I had a very nice conversation with him last night. What an immense wealth of knowledge he has. And he is so willing to share it after he paid for it all the hard way. It is quite obvious why he is so revered here.
*It looks like my bigger challenge now is not knowing how to fix it, but how to convince someone else that this is a better investment than a vacation or new couch set. I might even resort to parting it out (OUCH!) and saving up for another bike. We'll see. Thanks for all of the help/advice.
 
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