Front Bearing Puller.

[Chris KC]

In my humble opinion Tony's last two paragraphs hit the nail on the head. A slightly slack fit on the front is necessary and acceptable, a tighter fit on the rear is desirable (though I hasten to add, not one achieved by dot punching).

[Terrytuned]

When fitting front crank bearing I always polish out the bore of the bearings with an emery flap wheel so they are a sliding fit on the crank they
 are not going to move clamped by a timing gear and a 5/8 dog bolt, do not reduce the crank or you will have a loose fit timing gear.
The rear bearing needs to be a light press fit, anything less use loctite bearing fit, I don't use thrust front bearing instead I use a NMJ 1 1/8 next
 to the crank this is a double track self aligning bearing and a single track MJ 1 1/8 this gives you a triple ball set up with no preload but adequate thrust capability. I have been using this set up in engines with heavy clutch springs and running up to 7500rpm for the last 10yrs
with no problems just another alternative to thrust bearings.
Terry.

[Bob Culver]

Tony's post very appropriate, but the  the word fit may puzzle. It is a while since I pondered tolerance tables and it made me think. For others challenged and to whom it may not all be immediately obvious, a little expansion of the story may assist.
 
The makers tolerance of bearing bores and OD is self explanatory. (from NSK catalogue and Machinerys Handbook, both 1996, current tolerances slightly different)
 
The letter/numbers are from an established convention table and represent various tolerance ranges for shafts and for bores (capitals)
 
For particular applications bearing makers recommend particular fits, achieved by adopting shafts/bores in particular tolerance ranges to go with the bearings and their tolerances. Tony has given the tolerance ranges recommended  for our applications .
 
To obtain the actual fits, compare the bearings with the shaft/bore figures. If Seven cranks were finished as per the old 1929 drawing, rear 0 to +1/4 thou, it is evident why so many bearings were found loose.
 
A tight fit expands the inner ring almost directly. Assembly can then be difficult with close tolerance (or even standard) roller bearings. C3 races are used where a very tight fit required.

On a different tack, Seven bearings are very generous compared with very much more powerful motor cycles, and normal failure by fatigue seems rare if not unknown. Modern bearings due better steels are rated much higher than in the 1920s/30s. I suspect two basic ball races (maybe just one of new) would suffice in the front.

[Ritchie Wilson]

Really interesting stuff particularly Terry's description of opening out the bearings so they are a sliding fit. I imagine that at the Austin the cranks and bearings would be measured with go/no-go gauges and classified so that larger bearings were used on larger cranks and vice versa. Some bearings and cranks must have been discarded. The modern day equivalent would be to purchase a number of bearings and then use the one which fits the crank best or, more practically, as Terry does, modify the bearing if it is too tight. It is great to see a consensus (if I am following the discussion correctly) that tight front mains are not a good thing.
Interesting use of non-standard front mains also Terry. What do you mean by "Next to the crank"? Do you differ from the crowd in your rear mains also? How about the middle bearings in 3-bearing engines?
And, not to go too far off topic, would Bob and Robert agree that gauges would be much more accurate than micrometers, especially in less experienced hands?

[Bob Culver]

A gauge is only applicable to one size. For that size it would be more accurate, esp if the micrometer is used as a gauge.

Complete novices overlook the very significant effect of an oil film on the anvil of mics when used in normal manner.

Many mics have been very roughly used and the anvils, thread and nut are strained or worn and out of adj at least in some positions.

In some applications mechanics easing fits is a cause of trouble. On javelin cars the gearbox bearings have to be drawn from the  housing and shaft simultaneously; easing the latter hugely simplifies but it results in the shafts working free and moving endways with sad consequences.

[Terrytuned]

Photo of double track bearing next to crank single track bearing is in front of it, prefer brass cage roller at the rear will photo special rear bearing
 and front pair with bearing numbers under new post.   Terry.

[Ritchie Wilson]

Thanks for the reply Terry, I do see what you mean. That bottom end certainly looks the business.

[Charles P]

I like the filter arrangement Terry.
Any pointers towards a source or one of your excellent "How To...." guides?

Thanks

Charles

[Terrytuned]

Pickup filter is a hydraulic suction filter from MFH online  mfhydraulics. co.uk  part no. CV105-38  CV105-12  CV105-34 depending what size
  the last no. is the fitting size 3/8bsp 1/2bsp 3/4bsp a nylon connecting thread. the one in the photo is a 3/4 size but I remove the nylon
  connector and make a steel one so I can solder it to a 10mm 3/8 pickup pipe on a over bored splash pump or a 12mm pipe on pressure pump. The 3/8bsp you could fit directly to a pipe but the filter is a bit small, they are quite cheap to buy so you could buy all 3 sizes and decide which to use, the photo is a 3/4 on a 10mm pipe because that's what I had at the time.
Terry.

[Charles P]

Thanks Terry - fab as usual