E: Engine Main bearing outer race width

[Bill Thomas]

We Fitted Some mains for a friend a few years ago, To a Comet, Which are better than a Twin, More close together and lighter crank.
We had a hell of a job to get the old ones out, Somebody had ground Two huge bits out of the side of the outer track, And bashed the alloy into them, We got the cases very hot, But still had to use a lot of force to get them out.
I don't like the idea of screws, In case they come loose. Cheers Bill.

 

[Peter Holmes]

I guess the chroming solution works fine if the main bearing housings are in perfect alignment, I was told that mine were not and would require sleeving and boring back to alignment, that all made sense to me despite the fact that the crankcases were a matched pair, but had had a hard life, still don't know why the bearings walked again though, but we all know this is not an uncommon fault, I wonder if the Stuart Jenkinson bike suffered the same problem, were the die cast crankcases as susceptible to walking bearings.

 

[passenger0_0]

Could the long crankpin in a twin flex during operation and cause the inner main bearing sleeves to be pulled out? Rather than trying to retain the main bearing sleeves, why not stiffen the crankshaft?

 

[timetraveller]

Several things come to mind from various of the above. First Bill; the screws used were purpose made large, cheese headed screws with slot heads. After they were screwed in the ali was punched into the slots to stop the screws rotating and prevent any head that broke of its thread falling out.
Next; crank pins. I always used special crankpins for sprinting/racing. On these the large diameter of the crankpin is extended at each end so that it has to be pressed into the flywheels which have to have the holes for the crank pin bored out on each inner face. The hardened washers also have to be bored out. Castellated Manx Norton nuts were used on each end of the crank pin. This way the stiffness of the crank shaft assembly is massively increased. It no longer relies entirely on the relatively small diameter of the ends of the original crank pin and the normal nuts.
Finally, the complete answer to drive side bearings walking in is the modification that fits a special top had bush into the crank case opening for the drive side bearing. This opening has to be enlarged and the outer face relieved to take the thickness of the flange on the outer end of the top hat bush. The inside of the top hat bush has an inner smaller diameter ring inside and back to back taper roller bearings are fitted. The outer inner end of the top hat bush has a thread and into that is screwed a ring to take an oil seal. The whole assembly is pulled up tight when the ESA nut is tightened and the lay out of the bearings prevents any possible walk inwards of the bearings. I have hoped for years that someone would come up with a design for this and produce some to be fitted by engine repairers. It does require that the bearing housing is machined but if it is worn anyway then there is no loss there. The design was sketched out for me by Robert Watson and my understanding is that several of our Canadian members have this modification fitted and they have lasted for years.

 

[greg brillus]

Yes there are a couple of good designs used in the HD engines.......The drive side main bearings are strong and very long lasting, and the roller cam/follower's far better than a Vincent.

 

[Peter Holmes]

Better stop referring to them as Hardley Ablesoms then!

 

[vibrac]

Better stop referring to them as Hardley Ablesoms then!

I have an idea that there are a few other features that still relegate them to the ridicule room

 

[Cyborg]

Another option for increasing the OD of the outer race.

 

[bmetcalf]

Does the flange of it get in the way of anything?

 

[roy the mechanic]

The speedi sleeve is for shaft "repair" not housing "bodge". The back to back timken bearings, introduced by h-d in 1936 are still used . John Renwick swears by them in his hot rods.