Just wondering if anyone knows if there is such a thing as a -.050" rod bearing for a commando crank? My crank is at .040" under, and one pin is worn oval. So it needs fixing, I could maybe get it welded and re-ground std, I'm waiting on a price on that but am guessing it may be expensive. Another option is to just grind the dodgey pin till it cleans up, maybe to -.045" and get shells made, unless someone does a -.050".
Yes it will be expensive....no need to worry on that one!!First saw it being done to a 8 inch dia grinding mill motor plain bearing shaft what must be 50 years ago.It certainly wasnt cheap having an A65 gearbox mainshaft built up so it could be splined forthe Norton clutch centre.. that stoped the bloody thing coming loose on the 800+cc A65 scrambles motor. STUPID silly taper. Shells. NON that I know off but I havent investigated for well over 20 years since the gent at Vandervell found all the minus 40 sheels in dealers for me but at that time ,IF memory serves correctly, the 1275 Layland/BMC mini big end shells were the same apart from being 0.001 inch bigger on the O.D. Cannot understand why shells stopped at minus 40 when people use these cranks and machine down the big ends for long stroke Triumph motors.....Apart from the inbuilt stress raiser inside the DS half of course which would lead to even quicker big bang failure!!. Just asked a friend...His memory banks threw up 6 cylinder Daimler big end shells but he is nearly as olde as me so.......certainly more grey haired!! NO SPELL OR GRAMMER CHECKS.
Re: Undersize Commando rod bearings?#72083 11/16/0711:20 pm11/16/0711:20 pm
Thanks for the info beltdriveman I've only seen the BMC bearings down to minus .040 so far, but maybe I'll yet find some a little smaller. The man did not recommend welding the crank because they often distort. If it comes down to it I'll just put it back together with new shells, my BSA manual gives rod clearences at .001-.0025" with advice to regrind if wear exceeds .002" Does that means .004" clearance is usable? I know from plastigauging (hard to do keeping the rod from moving)the worn pin has only about .002 clearence though the pin mikes 3-4thou under 1.710", and isn't perfectly round. I'm guessing the aftermarket alloy rods may put more crush on the bearing.
Re: Undersize Commando rod bearings?#72084 11/17/0712:43 am11/17/0712:43 am
Remembering it was many decades ago since I investigated things and all my olde catalogues have been borrowed but not returned...... Memory says that in those days the 1275 shells went to 80 under. I suspect I gave up investigating when a friendly Gent in Sheffield had all the Vandervell 40 under shells he could find in the dealership network returned so I could have them.Glacier shells only went to 30 under in those days. Cannot remember which way round it was but there was a difference of either a thou or half a thou in the fit on the big ends between Vandervell and Glacier shells...according to the shell drawings. Have just found the notes......they state that Norton always sourced Vandervell bearings because they were reported to be better. Certainly when Norton closed there were LOTS of vandervell shells around and I would not be suprised if Motor Cycle Shop in London dont still have fifty or so minus 30 Vandervell sets still in the bins. Ah hah.... found the note written on the shell drawing...'Most rods1.8950".... thus V.P. shells give 0,0009 clearence and Glacier shells give 0.0000 -0.0005 inch interference. Last time I had big ends ground by a company down Southampton way I had to supply the rods and shells to be used so they could grind the cranks to suit the IDs they measured within the shells with the rods fully torqued up. For years I could never work out why if I had cranks simply ground to correct size sometimes the rods would be a tighter fit than at other times... guess it must of been down to which shells I was using....
Re: Undersize Commando rod bearings?#72085 11/17/0712:52 pm11/17/0712:52 pm
This is the comparison of the 1275 BMC shells to the Norton; Rod ID; Norton 1.895"-1.8955" Mini 1.8955"-1.896" I wouldn't think that would be a problem. Width; Norton; 20mm Mini ; 21.59mm Would need to carefully linish that off, good thing they come in packs of 8. The tags may still be in the right spot, but in my motor it wouldn't matter as the aftermarket rods locate bearings with a pin, and I could remove tags alltogether if necessary. So all I need now is some in a .050" undersize, that are good quality.
Re: Undersize Commando rod bearings?#72086 11/17/073:23 pm11/17/073:23 pm
Best of luck finding some of good quality...... Of course I did once se a british bike so called mechanic use a bit of fag packet silver foil between the rods and shells on a customers motor.....HONEST.
Re: Undersize Commando rod bearings?#72087 11/20/077:00 am11/20/077:00 am
Looks like I don't need the silver foil I should have .050 undersize bearings from ACL in a couple of days, so quality shouldn't be a problem. It will just be a matter of a little width adjustment, and getting the crank ground.
Re: Undersize Commando rod bearings?#72088 11/20/079:50 am11/20/079:50 am
Originally posted by Mark Parker: Looks like I don't need the silver foil I should have .050 undersize bearings from ACL in a couple of days, so quality shouldn't be a problem. It will just be a matter of a little width adjustment, and getting the crank ground.
ACL are good folks, they have gasket factories here in Melb and also Brisbane, took them under 2 weeks to make me a top end kit for an obsolete Dorman engine for $100.00, the only OEM supplier I could find [ex UK] wanted $1200.00 for the headgasket alone !!!
1969 TR6R 7.62 x 51 is not a maths puzzle.
Re: Undersize Commando rod bearings?#72089 11/23/071:10 pm11/23/071:10 pm
ACL bearings for Mini compared to VP Norton bearings.
If there was a demand for smaller Norton rod bearings, like My crank needed, -.050" perhaps ACL would make some. However if one doesn't mind modifying rod bearings the Mini cooper ones are very close:
The main difference being the width, which in itself is not a problem because theres plenty of room in the rod and on the crank for the extra 1.6mm, the complication is with the tag (in a std rod) if its filed away on the outer side till the tag is the same width as the Norton bearing it will clip into the rod but a little off centre so when rod and cap are put together the shells are staggered to each other, if the shells are linished to remove the extra 1.6mm so they are the same width as the Norton shells they would be in line. As it is The ridgecrest rods I use retain the bearings with a central pin, so I have them centred keeping the extra width.