Crankshaft sprocket fit

[Phil C]

Hello all, I'm trying to fit a new engine sprocket on my 1965 B40F, but it's very tight. Ideally I'd have a kind of tubular drift (bit of alli round bar with a blind hole in it) to use for tapping it on, but the only person I know with a lathe to make me one was taken ill on Sunday so that might take a while. So I've been trying to tap it on just using a bit of alli as a drift, tapping with a nylon hammer and moving around the circumference of the boss (see photos.) But, although it's gone on a bit, it seems very tight. I've tried a little bit of heat from a hot air gun (maybe not enough.) How tight should it be? Is there a better way?   Thanks in advance for any advice.   Phil

[DAVE BRADY]

Hi Phil,

I do not think that it is supposed to be that tight.  I would have thought a snug sliding fit with perhaps a bit of a tap to help.  Apart from that if you are going to try and force it on with a drift you could put the alternator rotor on and then use a long socket to hit against.  The problem with it being so tight is that you may real trouble getting it off again if you need to shim it or replace the seal.

Dave.

[Phil C]

Wouldn't that damage the rotor?

[DAVE BRADY]

Hi,

As you will be hitting against the centre probably not but as I said it should not be that tight.  If you do not want to use the rotor try and find an old bearing that slides on or a large nut that fill fit over the spines and hit against that with the long socket.
If you have knocked it on a bit how easy was it to pull off again?

Dave.

[Phil C]

Tried the rotor and socket. Went on a bit further but not all the way. I can't believe it should be this tight. So I'm sending it back.  More waiting now. Very disappointing.    Phil

[courtney]

Can you put the sprocket in the oven for a bit? Maybe cool the shaft with compressed air too, if you've got a compressor. Of course, no good if it's in the post already.

[Phil C]

Well, it's in a jiffy bag ready to go. I don't think an oven etc should be necessary really. Thanks anyway Courtney. Phil

[DAVE BRADY]

Hi,

If it takes heating the sprocket and cooling the shaft it is too tight and may never come off without a lot of difficulty.  Consider that in the factory this had to be assembled quickly and basically by hand.  Sending it back is probably the best option.

Dave.

[Beesy]

The new rotor nut I bought was a really tight fit. Couldn't be bothered to send it back. I put some valve grinding paste on it and tightened it and loosened it for about 10 mins and its fine. Disappointing, but less faff than senging it back.

Didn't need to change the sprocket but I wouldn't be happy about heating it up to get it on.

[AdrianS]

When replacing mine, I found it to be a snug fit but not an interference fit! I would not be happy hitting it on to seat it as if it binds, you are just walloping the crankshaft.

[Phil C]

It's on its way back.

[Pete C]

I had the same problem. Tried fitting it in every position in case it was hanging up on a particular spline..no luck. Ended up relieving the sprocket using a file, not an optimal solution but it worked. If you have to hammer it on you are going to have a real Problem getting it off again.

Cheers
Pete

[Phil C]

I guess the dangers with that are taking off too much and/or taking it from the wrong place. Engineer's blue might help maybe. But anyway hopefully they'll send me a new one that fits. Phil 

[Pete C]

I tried fitting the sprocket to find in which position it went on furthest and used blue to note where it needed relieving. File a bit and repeat, always fitting the sprocket in the same position related to the splines. Eventually worked

Of course, getting one that fits straight off is preferable 

[Phil C]

Of course I might have the same problem with the next one. I wonder how much they vary in size when new.   Phil