Front Bearing Puller.

[Robert Foreman]

There has been quite a lot said recently about using a puller for the front bearings. You shouldn't have to. Looking at an original blueprint of the crankshaft, the tolerance for the front bearing journal is 1.124-1.125"

   I know replacement crankshafts are up on size, so the easy remedy is to rub some off.

[Zetomagneto]

Not so much a puller, more of a pusher, gets them out nice and square with no hammering

[Bob Culver]

A 1929 Austin dwg on the old site gave tolerances as front  -1/4 thou, rear + 1/4.

Tight fits certainly complicate matters and can lead to all sorts of damage.  Many, "mechanics" included, inflict enough damage with standard fits. But tight fits reduce working clearance and every ten thou gained reduces the traditional Seven sound.

If new cranks are  finished significantly larger, it may explain why bearing tolerances and clearances now not a major topic.

Those applying generous unmounted preload to a.c bearings must beware that if a tight fit on shaft, the preload will significantly further increase.

Modern tolerances seem more tight than older bearings.

Despite the claimed accuracy of micrometers, really accurate measuremnt requires skill and is seldom certain.

[Damian GT]

"Despite the claimed accuracy of micrometers, really accurate measurement requires skill and is seldom certain."

Wise words I reckon..

[Charles P]

"Despite the claimed accuracy of micrometers, really accurate measurement requires skill and is seldom certain."

Wise words I reckon..

They offer precision, usually down to a thou. Accuracy, however, is not quite the same thing.

[Colin Reed]

HI All,
Getting accuracy with any measuring tool is down to having a lot of practice , this is one reason why the same person should do measurements   for fits ie  od on a shaft and id on the bearing this way if you need a specified clearance or interference that is what you will end up with because every bodys feel is slightly different .
and lots of practice , if having parts machined take all the parts a long and let them do the measurements .
and most people with little experience will take to long taking the measurement and end up not to sure if they are right,
but don't let it put you off just practice and you will gain confidence

Colin
NZ

[Bob Culver]

Claimed accuracy of new ext mics is often +- .0001 inch. When an internal mike also involved, tolerance is large cf the fits of rolling bearings.
Actual accuracy usually less. Those with mics just close without looking at scale. Record. Repeat several times. Release and repeat much later. Unlikley all readings within a range of .0002. Beyond zero inherent thread errors etc add.

[Robert Foreman]

Hello Bob,
you obviously don't have much experience of using a micrometer. If engineers can only measure to within 0.002" then how come so many Austin Sevens were made.
I regularly tie myself down to 10ths of a thou and yes using a micrometer. If you measure rubber or paper then you need to have sensitivity otherwise the materials will compress and give you a false reading.

[Colin Wilks]

To be fair to Bob, you're traducing him for an order of magnitude: .0002 vs .002.

[Tony Press]

This applies to both the 'Front Bearing Puller' and 'Rear Main Bearings' discussions.

Taken from a 60 year old SKF Catalogue-

The British Standard for both Ball and Roller Bearings-

Size Tolerances for bearings

Bore over 1"   - 0.0003" to + 0.0002"

Outside diameter 2" to 3"  - 0.0005" to - 0.0010"

Outside diameter 3" to 5"  - 0.0008" to - 0.0013"

The SKF Shaft Fit recommended for normal and heavy loads  such as internal combustion engines

Cylindrical Roller Bearings up to 1 1/2" shaft diameter - k5i

Ball Bearings up to 4" shaft diameter - k5i  

Tolerances k5i for 1 1/8" shaft diameter Ball and Roller Bearing  + 0.0002" to + 0.0005" 

Tolerances k5i for 1 1/4" shaft diameter Roller Bearing  + 0.0003 to + 0.0007"

The SKF Housing Fit recommended for normal and heavy loads  such as crankshaft main bearings, direction of loading indeterminate-

Ball and Cylindrical Roller Bearings K7i

Tolerances K7i for housing diameter 2 13/16"  - 0.0013" to - 0.0001"

Tolerances K7i for housing diameter 3 1/8"  - 0.0016" to - 0.0003"

The bore and housing sizes shown are for SKF Ball Bearing RMS 9, Angular Contact Ball Bearing AMS 9 and Roller Bearing CRM 9 fitted to the Light Shaft and later heavy shaft and CRM 10 from the heavy shaft.

Longbridge could have opted for a looser shaft fit for the front ball/roller and later angular contact bearings to aid assembly,  relying on the clamping force of the front crank handle dog to stop any rotation. Given that most shafts don't seem to have suffered from much inner ring 'creep' here this would have been acceptable. 

The rear bearing fit is possibly not heavy enough given the number of Light Shafts that had been knurled in the 60's (a very short lived solution)

Sorry for the long post.

Tony.