Front Pulley Issues

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swooshdave

swooshdave

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Front Pulley Issues


Front Pulley Issues




Well, I think I found the source of the clunking noise. I was hoping it was the clutch but it wasn't.

It's the front pulley. The crank had some gouges in it, I assume because someone had a loose chain pulley. I filed them smooth so my belt pulley would fit.

When I fit the pulley it didn't feel loose.

I think my choices are to pull the engine apart and get the shaft hard-chromed. Or just park it and look at it for the rest of my life.

Would a speedy sleeve work on a tapered shaft?
 
Dress the crank taper up in situ, bore out the front pulley taper and sleeve back to slightly undersize to match the crank taper .
Check with front pulley manufacturer as to what size the taper is in case its the pulley thats at fault.
No need to strip the motor either way IMHO
Regards Mike
 
Probably not a speedy sleeve but you might get by with a piece of .005 brass shim stock fit inside the pulley.
I did that once on a race motor with that problem.
 
I'm with Mike. You should check to see if your chain pulley is tight or slack as well to see if the belt pulley is at fault.
 
It’s not the pulley’s fault. It fit perfectly on the other crank.

I’m not sure if RGM has an oversized pulley.
 
Unless it’s miles out, you may well recover it by lapping in with fine grinding paste.

Only use the fine.

EDIT:

I posted before watching the video. I suspect if you were to grind it to the point where the taper was a good fit, you’d have serious clearance issues with the cases and even oil seal.

Sorry to say it, but I’m with Knut.

I know it’s painful. But you know everything inside is ok apart from the crank. And the process is still fresh in your head. You could have that crank out in a weekend. Spend a bit of time sorting it. Back together in another weekend.

If you stick it back of the shed now, it could languish there for years...
 
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I think your crankshaft has spun for the last time. Uneven wear and hand dressing seems to have damaged the crank taper. Wiggling of the pulley has taken a toll also. Get yourself a new crankshaft, or change the drive side at least (re-balancing will be required). Before assembly, ensure the shaft tapering is to factory spec.

-Knut
 
@swooshdave RGM have some pulleys that are not bored (supplied with just a pilot hole) - i suggest you give Roger a call or drop him an email and explain the problem.

You can then get a local machine shop to machine your taper for you - I have just done one myself for the 650ss and it's not a difficult job.

I think this will be your easiest solution, and involve the least amount of disassembly.
 
Your alternative is to start with a pulley for a single cylinder alternator model (which they have in stock)

The crankshaft is a smaller diameter on these engines, so the hole in the pulley is smaller.
Then just enlarge the taper until you’ve got the fit you’re looking for.

I have done exactly this with a Bob Newby kit, and it worked out great!
 
I d have to say the music is best faced in the shed not by the side of the road.
Have you dialed the crank to make sure it is true? If all is well then proceed
with a new pulley.
Tough break but its an old English bike...
 
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How much material did you remove when you dressed the crank taper? If you filed so much that the pulley is loose then I would very much suspect it's no longer round.
 
Have you tried the original triplex sprocket to see if it has the same problem? The pulley might fit on another crank (not fitted in crankcases) but be “bottoming out” against main bearing oil seal because it’s slightly oversize.
 
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Thanks for all the suggestions.

Here’s what I’m going to try:

1. New key
2. Shim stock per Jim
3. New pulley that can be machined to size.

Given that this bike will not be ridden much I’m not ready to replace the crank yet. And it’s certainly not going to get raced.
 
maylar said:
How much material did you remove when you dressed the crank taper? If you filed so much that the pulley is loose then I would very much suspect it's no longer round.
Click to expand...

Someone at some point had scored the crank trying to build up material to address the issue. I just knocked down those bits carefully.

So I didn’t make it any more undersized than it was.
 
I would try what Jim said, Maybe take a piece of paper and make a pattern of the taper and then cut it out of thin shim stock?
 
I'd chose door #3. If the shaft taper is still concentric, the custom machined undersized pulley taper solves all the problems best... IMO of course...
 
I vote the undersized pulley machined to suit idea too.

But I would still use the old pulley, or an old sprocket as a tool, and with fine grinding paste, work that crank taper. Then a very gentle lap, with the new pulley.

Tapers are brilliant things, when they fit. One raised spot, or a touch of ovality and they’re next to useless.

Theres no point in making up a custom pulley and fitting it to a crank with a raised or oval taper. It’ll do exactly what your current one does!

It really won’t take long to lap the taper in.

It’s not about race vs low use etc, unless the taper mates well, the keyway will give out one day, most likely at the least convenient opportunity !
 
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