The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Hill Crest on 06.02. 2019 17:23

Title: Worn Crankshaft Splines
Post by: Hill Crest on 06.02. 2019 17:23
Hi guys,
I'm slowly getting on with my basket case A10 (1954 SA frame, 1962 SR/RGS casings) and have discovered what looks like a lot of wear on the drive splines on the crankshaft - see photo. Just how bad do they look?
The engine machine shops I have tried so far (Central Scotland) can't help me - my question is, does anyone know where/if I can get the splines repaired? Or is there another method I can pursue?

Any advice gratefully received.
Title: Re: Worn Crankshaft Splines
Post by: Bess on 06.02. 2019 17:42
    SRM Wales offer a service:

Best wishes...
Title: Re: Worn Crankshaft Splines
Post by: Swarfcut on 06.02. 2019 20:17
  Not the worst I have ever half the spline width worn away. Looks pretty good.
    In the short term, my cheapskate method is to use the stainless steel support strips taken from an old windscreen wiper blade, cut down to width and length, coated with Loctite and hammered into the gap between the crank splines and the drive sleeve inner splines. It may take a couple of strips to fill the wear gap on each spline.  Good material to work with, well up to the job.
 Requires a bit of trial and error, but will save a crank from an otherwise expensive repair.  Warm it up with a hot air gun if it ever needs to come apart. Obviously treat the motor with a bit of respect, so as not to apply sudden, heavy loads.

   The wear is caused by the big nut on the crank not being tight enough, allowing the drive sleeve to fret on the splines. When assembled correctly, two or three threads on the crank end should be within the end of the drive sleeve. This allows the big nut to bottom against the drive sleeve and push this down the crank to lock the sleeve and main bearing inner race against the crank cheek. The problem with a wear pattern like this is that the drive sleeve may snag on the worn spline, so must be rotated away from the worn crank spline side to make sure it can move down the crank splines as far as possible. Do the trial assembly without the cush drive.

  You could also have worn or missing circular crank shims and wear to the crank cheek bearing inner race location, but from the picture this area looks reasonable. There is also a witness mark where the crank cheek has rubbed against the main bearing outer race,  indicating loss of crank shims or incorrect initial set up, allowing the crank to move sideways and make contact.  Check for the correct location of this outer race, it should be a tight fit in the crankcase.

   Best to  get some new sludge trap plugs, yours look a bit butchered. They should not be screwed in more than the crank web face, to avoid blocking the oilway from  timing side journal.  Some pattern part plugs are made too long, and need shortening. Make sure that trap is nice and clean.  The design of the oilway and sludge trap differs depending on the crank. Early small journal or later big journal.

 The delights of shimming the crank end float await. When the float is correct, chain alignment sorted, add your strips just before the final tighten.

   Lots of information on this forum about the big nut, and its high torque requirement. Plus how to shim the crank end float.

Title: Re: Worn Crankshaft Splines
Post by: Triton Thrasher on 06.02. 2019 21:48
Swarfy isn’t mad.

You can get by with Loctite on worn splines, so long as it’s not the splines that the cush drive slides in and out on.
Title: Re: Worn Crankshaft Splines
Post by: Hill Crest on 07.02. 2019 11:12
Thanks guys for the great replies, Swarfy has given me a way forward. I'll get the big ends and timing side main bush and journal machined - the bush has been moving in the casing so I'll need an oversize OD bush, which I hope I can get from SRM.
Thanks again
Title: Re: Worn Crankshaft Splines
Post by: Swarfcut on 07.02. 2019 12:03
 Just a word of caution here.  Experience has shown that for the best results, where there is evidence of a fretting bush, the timing side case should be line bored concentric with the drive side bearing location. Then a custom made one piece bush inserted into the case and line bored again, to give the required running clearance between bush and crank. This means that only the minimum material needs to be removed from the crank, it is not necessary to grind to commonly available bush sizes.  You can just fit say a 40 thou u/s bush and have this line bored to suit the pre ground crank.  Lots of information on the forum. Case and bush joint must be oil tight to prevent oil and pressure loss.   SRM are not the only source for these bushes, so spread your net wide.

  This is a precision and somewhat difficult engineering challenge for many machinists, hopefully someone will be along soon with recommendations as to good value and timely completion.  It will be pricey.

  Good job interest rates are low.....arrange finance early, if you get my drift.


  Additional.  Thanks TT, Looks like I passed the sanity test. (Somehow)
Title: Re: Worn Crankshaft Splines
Post by: Hill Crest on 11.02. 2019 10:14
Swarfy, thanks again for your good advice.
I've been steered towards an engine machinist who is long on experience and will carry out the required line boring for me. No mention of price yet but fingers crossed  *contract* *doh*

I'll be back
Title: Re: Worn Crankshaft Splines
Post by: Swarfcut on 11.02. 2019 10:27
Hi, Hilly.  A good look on this forum and numerous YouTube Videos will show you what in involved. Thanks for the accolade.

Title: Re: Worn Crankshaft Splines
Post by: PDMiller on 11.02. 2019 18:17
Hi Hill Crest
I found my crankshaft splines to be in a similar condition to yours. The enclosed pic is a Mad Professor's contraption that I made up to remove the sludge plugs but hopefully you can see the splines in the background. The splines have been built up with some compound known only to the previous owner/ dismantler but I suspect its something like Q bond or JB Weld. The bike hadn't run since the repair so I've no idea if it will be successful till I try it . I think as previously mentioned the tightness of the nut is the major factor but if this doesn't work I'll certainly be trying Swarfy's windscreen wiper strip trick.
I lived in Fife for a number of years and there was a brilliant machine shop in Kirkcaldy that would tackle most things, I'm sure it was called Wm Anderson. Hopefully they're still there.
Good Luck
Title: Re: Worn Crankshaft Splines
Post by: Hill Crest on 12.02. 2019 12:17
Hi Pete
Thanks for the photo of the sludge trap plug remover - I've got that to look forward to  *smile*. Mine look as though they've been out a few times, even though from the history of the bike, it was only on the road for 20 odd years, it must've had a hard life!
I'm going to try to locate Wm Anderson's workshop - I'm not far from Kirkcaldy, all the best,
Title: Re: Worn Crankshaft Splines
Post by: Greybeard on 12.02. 2019 13:04
Title: Re: Worn Crankshaft Splines
Post by: Hill Crest on 12.02. 2019 14:18
Greybeard thanks for the link  *smiley4*
Title: Re: Worn Crankshaft Splines
Post by: PDMiller on 12.02. 2019 17:39
Nice to see that a good old fashioned machine shop has survived albeit at a new location. I used to visit them at the old place just to smell the cutting oil and look at all the bits of engines lying around. In the reception area they had a grease nipple location chart for an ancient Standard 12 on the wall which could be studied in great depth while waiting for my freshly ground crankshaft or skimmed head to be brought through.
No doubt the old blokes I dealt with are long gone but they always gave excellent service.

Ah the good old days *loveit*

nb I have no links or connections to Wm Anderson Engine Re builders Kirkcaldy.