crankshaft end float

[Danny.Lee]

If the bearings are an interference fit in the crankcase, and a press fit on the shafts, where does the movement come from in crankshaft end float?
I only ask as I will be putting my VB crank back in this week.
Dan

[brenton.roy]

Hi Dan,
The main bearings are a sliding fit over the mainshafts.
There's a a good diagram of the measuring setup in 'tuning for speed'
Regards, Brenton

[pete.collings]

The ball bearing mains fitted on a VB are an interference fit in the crankcases (heat crankcases and chill new bearings in freezer to fit bearings), but the mainshafts should be a tight sliding fit in the bearing inner races, hence allowing end float movement.
It is only the roller bearings fitted to VH models that are a press fit on the mainshafts. The lipped timing side outer race restricts endfloat, if buying new rollers make sure the TS bearing is the lipped type. I have also heard of lipped DS roller mains, although it is preferable to have a plain outer DS roller, to allow the two bearings to be pulled together by the SA spring.

In practice, most mainshafts (especially drive side) will have some wear, making them an easy sliding fit into ball races, and a slack fit for roller inner races.
When rebuilding using roller races, I would sort out the endfloat shimming needed to centralise the crank with the rollers as a loose fit on the mainshafts, then fit the roller races (and shims) one at a time, and use some retaining compound (eg, loctite bearing fit) on the cleaned surfaces. I would then stand the crankcase half on a suitable container (I used an ordinary rigid waste paper basket) with the weight of the crankshaft holding the bearing in place whilst the compond cured overnight), and once set do the same for the other roller bearing.

This method worked well for me, with ball races there is no need for retaining compound unless the new bearing is a loose fit in the crankcases when both are cold.

For both ball and roller bearings, the shock absorber spring on the engine sprocket will pull the crank tight against the drive side bearings. I never bothered too much about setting the 12thou endfloat for the singles precisely, as availability of enough different thickness hardened shims can be a problem, I just made sure there was a bit of movements possible.
With the Huntmaster, I spent much more time on setting minimal end float (one to two thou), as endfloat always increased with mileage.

[brenton.roy]

That's what I meant to say.. Honest

[Danny.Lee]

Thanks guys
Im fitting new ball mains on chromed and ground spindles so I sort of assumed the inners would be tight on the shafts. Ive used bearinggrade Loctite on two of the three bearings because of clear evidence of past rotation. Interference cold only measured just over one thou...
Dan

[nevhunter]

There is nothing to stop the drive side inner bearing outer sleeve from coming out of the case when really hot and it will only be stopped by contact with the flywheel. Fitting a lipped roller or a quality (high duty) ball race will correct this) Only the VH's have a roller there. The timing side main is usually the first to fail, and most races die because of corrosion these days as we don't use the bikes regularly and get them really hot. A ball race will do the job most times unless you are racing on alcohol, and a lot cheaper. Nev

[pete.collings]

Nev makes a valid point about drive side roller outers coming loose and moving inwards, I have encountered one motor where this happened, the crankpin nut had a wear ridge in it where the outer race had been rubbing.
However, it is only the one motor I have seen this in, although I have seen crankcases with centre pops around the outer ring to prevent it moving outwards. If the outer is a loose fit when cold, then bearing loctite should hold it in place.
Careful inspection of the contact surface of the outer ring in the crankcase may indicate if it has moved (if this is not obvious on stripdown, or there is no outer in place).

My concern with a lipped drive side roller is whether the shock absorber spring pulls the roller inner into close contact with the lip of the outer, how dependable are roller mains to constant side thrust? Adjusting the position of the endfloat shims could ensure that the roller inner is moved inboard a little, to prevent any side thrust problems.

[nevhunter]

You have the same situation with a ball bearing Pete. You have to have the correct spacer. The ball is better suited to taking end thrust although some bearings better than others. The lipped rollers are not designed to take much end load but there is not much there is not much in a normal situation in a main bearing. If it had a clutch set up like a Douglas I wouldn't use it. Nev

[Bob.Murphy]

I believe Velocette singles have taper-roller mains to handle side thrust - though they are assembled with a couple of thou' pre-load which is intended to reduce to zero at full operating temp.

Bob.

[John.Cheetham]

One way to retain main bearings against moving towards the flywheels and also rotating in the crankcase is to drill and tap the crankcase and use a countersunk headed screw which fits into the drilled countersink in the crankcase and into a suitable notch ground freehand into the periphery of the outer race.

Not sure about Pete's comment about sliding fit ball races and loose fit roller races - I always thought that the bore of a bearing (irrespective of being a ball or roller bearing) had an upper and lower limit to give an interference fit, not a loose running fit.

The 500 single configuration of bearings is the only one that makes any engineering sense from the point of view of all three inner raceways being able to remain secure on the main shafts.

The NH & VB configuration of using three ball races is flawed and is in my view done to keep prices down at the time of manufacture.

I have read comments stating that roller races are overkill on anything other than the 500 OHV singles. Back in the 1970's my NH suffered a timing side bearing failure which removed the oil feed quill and invariably damaged the teeth on the timing gears.
I reconfigured it to a similar arrangement to the 500's using a ball and roller bearing on the drive side and a roller on the timing side, using shims and spacers to ensure no thrust was taken on the ends of the rollers as they are not intended for that purpose. In fact a lot of roller bearing rollers are not finely ground on their ends. It was quite time consuming but working in the Tool Room of the largest engineering company in the town obviously helped. I cannot recall the lip arrangements of the roller bearings after all these years but still have the bike in the shed (sadly unused for 35 years), although retirement will hopefully permit me the time to reacquaint myself with the bike.

Danny's comment of just over a thou' of interference when measured cold sounds fine to me. A bearing catalogue normally shows all the tolerances required for various shafts and housings. This info should be available from any reputable bearing supplier. You certainly don't need to thrash the bearings into place with a drift and 2lb hammer. Also bearings which are an easy sliding fit are going to rotate and ultimately wear the shafts.

Hope this helps.

regards: John