BSA A10 1960 Crank original size and main (Bush)

[Richard Hinton]

my crank is in for regrind on journals and oil feed side (Shaft). engineering firm wants to know what the original journal size is and for the oil feed side.

Crank had a grind in 1970-1 down to -10. oil feed side still original but has some score marks.

If any one has data sheet can you or show the sizes.

Regards Richard

[RDfella]

If you're grinding the timing side main bearing, worth considering grinding just enough to clean up and then making a new bush to suit rather than taking off more to suit an available bush - of questionable quality.

[Greybeard]

Leaving a chamfer/fillet at the edge of the journal is very important for the strength of the shaft.

[muskrat]

G'day RH.
Std size for the journal is 1.374", the radius is 0.085" to 0.090".
If the journal only needs 0.004" to clean up a -010 bush can be machined to fit.
Cheers

[RichardL]

Depending on if you have a small-journal or large-journal crank, the original O.D.'s would be 1.460" or 1.687" respectively, by adding 0.010" to the value shown in the attached picture of the grinding guidelines taken from one of my books.

Richard L.

If Julian S. chimes in, he would probably come up with the original BSA shop manual saying what grit grinding wheel they used.  (Don't wait for that info.)

[RichardL]

BTW, where the picture says, "Mark 0.010" here." That's just for the first grind, of course.

[Swarfcut]

 Crankshaft dimensions are fully detailed in Service Sheet 207,( find in the Literature Section) part of which is reproduced above, thanks to RichardL. Before it goes for grinding, remove the plugs and clear out the sludge trap. Replace after a good post grind wash out. On a late model with the big journal crank the central tube is removable to reveal more hidden crud. This is the single most important aspect of crankshaft renovation. Plenty to consider on previous Forum posts.

 In the case of the timing side journal it is better to grind to a dimension which cleans up the bearing journal, then line bore a one piece bronze timing bush to a running clearance. This gives the crank an extra lease of life, as they don't make them any more...

 Swarfy.

[RichardL]

...as they don't make them any more...

WHAT? OH MY GOD WHAT ARE WE GOING TO DO?

Richard L.

[Swarfcut]

 Sorry to spoil your day there Rich, it's true!!!!! But any Briggs and Stratton two cylinder  crank fits straight in, so no problem with finding a replacement*.

Swarfy.
* Urban Myth.

[groily]

One of these days someone will design and commission a batch of new ones I should think, at least the later LJ type.
 
I bet people at some of the household name traders and the Owners' Club - as well as on here - have thought about it, but it would probably need sign-up with £€$ deposits from interested parties unless it was a very wealthy supplier prepared to underwrite it.

I've got two new AMC twin ones that were done that way (well, one's done 20K miles now so is un-new!). Complicated jobs compared to a Beesa. There were rocks aplenty along the road as anyone involved in the project knows all too well, but the results are good. The 'overs' from the production run are a grand apiece (GBP) from the Owners' Club, initial subscribers got a much lower price. Just over 100 were made. So it can be done with serious commitment.

Just saying - so all those Briggs and Strattons don't get snaffled up to leave us without mowers!

[Richard Hinton]

Thanks all for your input, cant use -10 shells as the journey is egg shaped, so i hope the can recover with -20. but the firm wants to know the starting point as a reference (original size)
Not being a grinder this makes sense to me.

i have the sheet 207 but didn't see the original size indicated.

Getting bushes made think buying off the shelve is better at least you know what you have hopefully in size. The one place i could reply on the old man passed away and now seems hard to find good engineering shops who know what they are doing at least in the midlands.

So any info on the original size would be great. The Engine ref is DA10 10778 and i believe is large journal.

[RDfella]

I'm confused as to whether we're talking BE's or main bearing here. Conversation seems to jump between the two.
The sizes you ask for have been listed in the posts above, but Id still urge you to just clean up the main bearing and then either make a bronze bush to suit - or buy an undersize one and bore it out - which will probably have to be done anyway. This isn't like a car, where you just pop shells in and job's done.

[Swarfcut]

  From my Glacier Bearings Catalogue.... Alas these bearings are no longer made by the original manufacturer, but the reference numbers for the sets are still in use in the aftermarket. Grinders like to have the new shells to hand before starting the job. Not so cute here if the guy can't add 10 Thou to to a published undersize.

 Glacier  Big End Shells Code B 2046 M  These suit the big journal crank, standard big end journal size is 1.6865"/1.6870".

 The difference is an allowed half thou tolerance. The  journal dimensions should be within these parameters after grinding to the required undersize and final polishing. The face  radius is determined by the edge dressing on the grinding wheel.

 All cranks have the same size timing side journal 1.374"/1.3734" as standard according to the above service sheet.

 For journals in otherwise good condition a  wear limit of 2 Thou is specified, this applies to both big end and timing side main.

 Swarfy.