Shimming 750 to cure end float

Hi Andrew,

I found the following paragraphs on this very site! The entire article is at http://www.nortonownersclub.org/support/technical-support-commando/commando-main-bearings-service-releases :

Main Bearings:- There are so far, only two types of bearingIwould recommend to anyone to usein a Norton twin (500 up anyway). These bearings are both Superblend roller bearings; oneis Ransome and Marles, Norton Part No. 063906, and one from F.A.G., Norton Part No. 064118. Either should be usedin 500 - 750 engines; the factory reckoned only to use the F.A.G. bearingsin the 850s.There will be some end float with thedouble roller bearing setup which previously was controlled by the ball bearingin the timing side. This should be between 10 and 30 thou., butdon't worryifit's not, as long as thereis some float. The outer rings of the bearings are gluedin at the factory by Loctite Bearing Fit, so there's no reason why you shouldn't useit too, as long as you make sure that the rings are hard home before the glue sets, not when you find you haven't got any end float! Only use bearings with one of the following numbers:- NJ306E (Eis veryimportant, NJ306is weaker) or 6 MRJA30. The 6 may be hand engraved on the bearing. The timing side bearing need not be a tight fit on thecrank. Againdon't use just any roller bearings, these ones are barrelled to allowcrankshaft whip. Another numberis NJ306E M1 (harder).

Skip Brolund

OOPS,

I forgot to mention, there are 2 types of shims, the factory ones that go between the crank & inner race & the "Old Britts" type that go between the outer race & the crankcase (see: http://www.oldbritts.com/11_067569.html ). I generally try to center the crank in the case, but feel that with the amount of movement between the small end of the con rod & the piston, I don't know that it matters. I hope someone can correct me if I am wrong on this, as Ihaven'tfound the exact answer in print. As per the NOC/ Mick Hemmings CD on Norton Heavyweight twin engine rebuilding, I grind a "bevel" on 2 sides of the inner bearing race backs, to make it easier to remove them later. This also helps if you go with the factory type shims & need to remove the inner races toinstallshims to get the proper end float.

This is a great topic, I hope we see much info on this !!!!!!!!!!!!!

Skip Brolund

Andrew Orr previously wrote on Friday Feb 24th 2012 at 21.42hrs:

With massively excessive end float (30thou) I need to shim out. With engine now stripped and spilt which end do I shim? The timing side bearing has a LOT of in/out play. Do I shim this side? If so which side of the bearing do I shim? Alternatively, do I shim the other side to push the crankshaft over to take up the play? Ideas?

Andy

Hello Andy,

This is an interesting topic which should raise a number of different opinions, along with the usual blowing-hard.

I think there is enough information available for you to decide on a course of action, but I would advise talking to as many experienced Commando specialists and owner-repairersas you can.

Like Skip, I am keen on the shimming of the crank to run central. I have also stocked up with shims to fit outboard of the main bearing outer races. That's just my preference.

I believe that the Mick Hemmings advice on carefully grinding bevels on the inner races to provide access for initially easing the races before fitting the puller is useful, but don't over do it.

There is a reasonably balanced debate over a couple of pages on the accessnorton forum. A very user-friendly site, but with just as many 'interesting' characters in residence as this one:

http://www.accessnorton.com/crankshaft-end-play-t8587.html

What type of main bearingshave been in your engine up to now?

Best of luck,

Paul

As Paul Wilson says "an interesting topic which should raise a number of different opinions", my opinion is that the "barrelled roller" claim is a myth. The NJ306E is a standard roller bearing albeit with an extra roller to carry higher loads and in FAG's case a brass cage. Barrelled rollers of this type do exist but have a recommened maximum speed of 5,000 rpm.

Previously wrote:

Hi Andrew,

I found the following paragraphs on this very site! The entire article is at http://www.nortonownersclub.org/support/technical-support-commando/commando-main-bearings-service-releases :

Main Bearings:- There are so far, only two types of bearingIwould recommend to anyone to usein a Norton twin (500 up anyway). These bearings are both Superblend roller bearings; oneis Ransome and Marles, Norton Part No. 063906, and one from F.A.G., Norton Part No. 064118. Either should be usedin 500 - 750 engines; the factory reckoned only to use the F.A.G. bearingsin the 850s.There will be some end float with thedouble roller bearing setup which previously was controlled by the ball bearingin the timing side. This should be between 10 and 30 thou., butdon't worryifit's not, as long as thereis some float. The outer rings of the bearings are gluedin at the factory by Loctite Bearing Fit, so there's no reason why you shouldn't useit too, as long as you make sure that the rings are hard home before the glue sets, not when you find you haven't got any end float! Only use bearings with one of the following numbers:- NJ306E (Eis veryimportant, NJ306is weaker) or 6 MRJA30. The 6 may be hand engraved on the bearing. The timing side bearing need not be a tight fit on thecrank. Againdon't use just any roller bearings, these ones are barrelled to allowcrankshaft whip. Another numberis NJ306E M1 (harder).

Skip Brolund

Hello R&M 6.MRJA30R is the race bearing if you can get them they cost £130 each Your AJD

It's interesting that on another thread there are photos of main bearing shims that have been spat out and ended up in the sump plug filter. I suspect that if the bearing can move on the crankshaft (more common than you think), the shims will just chew up and disintegrate. Another engine strip anyone?

'It's interesting that on another thread there are photos of main bearing shims that have been spat out and ended up in the sump plug filter. I suspect that if the bearing can move on the crankshaft (more common than you think), the shims will just chew up and disintegrate. Another engine strip anyone?'

A very good point. Back in '98 my bike came with very poor cases which included turning mains. I kept finding metal in the oil and started to open up filters which were full of aluminum. The previous owner, a super bodger for 13 years had used soft drink cans as shims and the oil pump had successfully macerated what was left of the aluminum pieces. I rebuilt with the correct crank shims but with the help of a pattern con rod bolt from you know who it eventually blew!