Front bearings

[dannyteal1990]

I am in the process of rebuilding a 1935 crankcased engine and am struggling with the Front Bearings. I know this is something that has been discussed many times, I've searched through the forum and all the relevant books but can't seem to find an answer. I would appreciate some help to see if I can get this engine project moving.

A bit of background:
The bearing housing is "full width" and has the original lip. New AC bearings (from a cherished supplier) have been fitted Thrust to Thrust, tight up against the Lip. The crank is tight up against the inner race of the bearing and the outer bearing protudes from the housing by 14 thou.
The timing gear has been fitted and the starter nut tightened up.

The Problem:
When all fitted the crank is stiff to turn around and there is zero end float.

I thought there was something wrong with the bearing setup so I removed them again. Put them together in a vice with sockets pushing the centre races together (as they would be when fitted). The outer races do not turn smoothly, they appear to be pressed together.

It feels like I am missing something but not sure what....

If I fit a makeshift shim in between the inner races (cut up coke can) and then put back in the vice, things are a lot smoother and I can "just" turn the outer bearings individually.

A great reference for the vice trick was:
http://www.da7c.co.uk/technical_torque_a...t%204.html

The thing that concerns me is that in all the reference material I have looked at I havent seen any reference to anyone having to fit shims in between bearings? Any advice greatly appreciated 

Thanks

[John Cornforth]

Hi dannyteal

When I rebuilt my engine with new bearings (18 years ago) I was in ignorance about the niceties of paired bearings, preload etc.  I just fitted off the shelf bearings from a cherished supplier, but the crank was MIGHTY stiff to turn due to excessive preload, i.e. the bearing balls being squashed into their tracks.  I measured 1.5 lbs ft torque to turn the bare crank, the preload was probably about 10 thousandths of an inch, i.e. minus 10 thou of end float.

After some research and a steep learning curve, I took it all apart and fashioned a home made 7 thou spacer shim to go between the inner races. This reduced the preload to about 3 thou and the torque to about 0.5 lbs ft, which I felt was acceptable for a new engine.

I think part of the problem is that cherished suppliers have customers ranging all the way from those who do two engines a month to those who have never done one before.  There is maybe a bit of an assumption that the need for fettling new parts is understood. For those used to modern cars where everything is close tolerance and fits straight away, it can come as a bit of a surprise !

[bystander]

This why the original special bearings were a matched pair. Modern replacements, even of the best quality, are not. If they were to be selectively machined and matched in pairs prior to sale it would probably make the (already considerable) cost prohibitive.

[Parazine]

The Austin Motor Co. overcame this problem by producing a special pair of matched bearings with the outer races reduced in width to signify the change. They were initially fitted with shims on the outside face of the outer races to enable them to be used in the standard depth housing. Eventually, someone, somewhere woke up and had the housing machined to a reduced depth to allow the matched bearings to sit with the correct amount protruding without adjusting shims.

A random pair of bearings, especially if they are not "1st quality" (R&M, SKF etc) may need to be adjusted to get the preload correct at the time of fitment, using shims between either the inner or outer races.

[Robert Leigh]

It used to be that BMC offered a range of shims for adjusting clearance on early Mini track rod ends. These are ideal for fitting between the centre races of A7 front mains when packing is required. I don't know if any specialist supplier still offers these.

[Tony Betts]

Hi Danny,

Could I ask what manufacturer the bearing are you bought.

Thanks tony.

[dannyteal1990]

Thanks for all the great replies, I was under the impression that if I got a set no further fettling would be needed. 

Guess I need to have a look for some shims, the mini suggestion returns a few on Google so will look into that.

Tony- they were RHP MJT1.1/8M. They came 2 to a "set".
I've attached a picture of the box.

[Zetomagneto]

Robert, you mean the swivels on classic mini, not the TRE they are not adjustable

[Bob Culver]

despite 1935 I take it the bearings are full width. In the Seven application the reverse fitting would seem OK. This might avoid fiddling with shims. Whiist the bearings should not be loose seems to me preload endangers the frail lip.
I have an NSK manual whcih indicates that random bearings of standard tolerance would give slight clearance, and, unless preload is specifically required as for a machine tool spindle, this is recommended.

[Robert Leigh]

Yes, my brain is getting old; the swivels which perform the king pin function is what I meant. As far as I can see shim kits are still available, giving a choice of 3, 5 and 10 thou.