Crankshaft wobble

["Slack Alice" Simon]

I took the engine out of my '34 tourer in order to sort out the horrendous oil leaks, and to check it because it came with the car with no history.

With the crank in its bearings in the crankcase, flywheel on, the was a very small but perceptible movement in the rear main.   What I would expect, I think.

On spinning the crank, there was a recurring noise on every revolution.  A heavy "click" or a light "clunk".

So I have pulled the rear main outer out.    There is no perceptible roughness or end float in the front mains.

On spinning the crank, the rear end has a pronounced wobble, which I guess was producing the noise inside the rear main, as the inner moved from side to side in the outer.

This must impose a bending movement on the crank.   It cannot be good, but is it normal?

Crank and case are marked 191580, it isn't the original engine, but isn't far off it, and is the correct rubber mounted high frame crankcase.

Any thoughts welcome.

Thanks

Simon

[Chris KC]

To be honest Simon I'm hesitant to venture a view as there are so many unknowns here. However if only to give following contributors something to snipe at...

You don't specify how far you have gone with stripping down - for example are the camshaft, oil pump, fuel pump still in place? Or is it simply a crank suspended between 2(?) main bearings?

What type of bearings do you have at each end? Sounds like a roller rear, but several configurations have been tried by various people over the years.

I don't think movement in the rear bearing should be perceptible. If it is you probably need a new rear bearing. But 'perceptible' is slightly open to interpretation...

Are you saying the crankshaft wobbles when spun when it's only supported by the front bearings? (i.e. with the rear main outer removed?) A certain amount of looseness is to be expected in the fronts if they've put in some service. How much? Well a lot of people would tell you to fit new ones regardless once you've stripped to this point, as it's so much work and inconvenience to strip it again later. There are ways to take up a touch of slack, which are covered in the A7 companion.

If we're talking about an original crank you might be well advised to get it checked for straightness and also for cracks. Might consider checking balance too. A competent specialist is the best call for these things, though there are DIY routes.

Sorry, I'm not sure how helpful the above is, and I don't want to teach you to suck eggs, at least we got the thread started!

btw if you don't already have the A7 companion I'd strongly recommend acquiring a copy

[Bob Culver]

I presume the timing gear is removed.  Even if the front of crank had been bent, would likely cause flywheel runout but unlikely to affect the smooth turning of rear main. The droop of the unsupported crank depends a lot on the type, tolerance and wear of the front bearings. New or shimmed ac front races can allow almost no droop. Whether or not this is a desirable condition is questionable.
At this delicate stage the top priority is not to break the front lip!

["Slack Alice" Simon]

I presume the timing gear is removed.  Even if the front of crank had been bent, would likely cause flywheel runout but unlikely to affect the smooth turning of rear main. The droop of the unsupported crank depends a lot on the type, tolerance and wear of the front bearings. New or shimmed ac front races can allow almost no droop. Whether or not this is a desirable condition is questionable.
At this delicate stage the top priority is not to break the front lip!

Thanks for the comments.

Its a standard set up, roller rear/ac fronts,  ten thou off the crank and plus 30 pistons, so hasn't done a lot of work.
The front bearing housing is the shorter version, and the assembled bearings projected a little from it.

I suppose I have never tried this particular action before, maybe they all do it.

Crank was just supported by the front ac bearings, which on removal appear to have little or no preload.
Camshaft removed.

How much pre-load should there be on the front angular contact bearings?   In the green book, Jack French says "from .002" to .008", with the higher figure "beneficial".

What is the current thinking?

Jack thought that .0013 clearance in the rear main "is quite acceptable".   This rear main is as good as, or better, than that.

Cannot find any cracks in the crank.

Front bearings are a push fit in the 'case, so it is going back together with Loctite and a bit of shim for pre-load and see how it goes.

Cheers

Simon

[Chris KC]

Just take care to use a grade of loctite which you'll be able to dismantle next time around...

[Bob Culver]

The experts will doubtless disagree but personally I would be very wary of preloaded ac races. I have done but car had an all steel housing inserted. Preload would seem to stress the lip. Bearing manuals for applications with bending, as gearbox mainshafts and semi floating hubs often recommend wide tolerance bearings.
It is difficult to establish working clearance of worn rollers. The housings are seldom truly circular. Whilst many other engines run rolling bearings the Seven seems especially sensitive to any clearance. In the 1940s/50s with “classic” oils of the time and short runs my meticulous father replaced the rear main every 2 or 3 years, 10,000 miles or less! He reckoned he could detect the difference between new one spot and two spot bearings!
Any cracks are unlikely to be obvious by eye. The last rear radius to flywheel is a major suspect. Any crank with evidence of heating there to build up is dubious. All radii should be uniform and unridged. If genuinely uncracked may be worth tidying the inner radii, even if means slight undercutting.
Loctite can hugely complicate disassembly. Brute force leads to broken lips. Thousands of Sevens went millions of miles reliably without it.

[Hedd_Jones]

Simon

Be carefull with the projection of the bearings at the front. You can easily pop the bearing lip off.

Having been brought up with Austin 7 engines being rebuilt on the kitchen table, and had a fair few built by others in pieces on my own, I would suggest that you have nothing to worry about overly.

I have noticed the ball and roller set up at the front is liable with very little running to give what most normal engine rebuilders would consider far too much end float, and the very nature of the bearings mean that the back of the crank wobbles round a good bit with no bearing in.

If you have no end float its a good un!.

["Slack Alice" Simon]

Simon

Be carefull with the projection of the bearings at the front. You can easily pop the bearing lip off.

Having been brought up with Austin 7 engines being rebuilt on the kitchen table, and had a fair few built by others in pieces on my own, I would suggest that you have nothing to worry about overly.

I have noticed the ball and roller set up at the front is liable with very little running to give what most normal engine rebuilders would consider far too much end float, and the very nature of the bearings mean that the back of the crank wobbles round a good bit with no bearing in.

If you have no end float its a good un!.

Thanks again.

I am of the "kitchen table rebuild" and "they will tolerate abuse" school too, Hedd.

Loctite 641 claims it will fit bearings, etc. but is removable with "normal tools", which is all I need.

The ac bearing housings were designed to let the bearings project 1/64" as I understand it, the front plate will probably bend enough to accomodate this without too much push back on the lip, I think.

I am incline to introduce a 2.5 thou shim, just to give a little preload - it is the only shimstock I have, anyway, and 5 thou feels too much.

I used a 2 part fine dye crack detector kit, Bob, which is far more than I have ever used before.

I do not really trust it, but have done three tests and still can see no cracks, and, as I say, the engine is relatively low mileage, and it hasn't been bodged - yet!

I was going to use an engine sold to me as "rebuilt".   It came with the bills for the work done.   On checking it - yes, the crank was ground and the rods re-metalled - but there is evidence of welding all round the rear roller bearing journal to the rear crank web - why would anyone regrind a welded crank?

Break over - back to the workbench.

Simon

[Chris KC]

I must say I'd aspire to 0.002 rather than 0.008, which is fearsome tight. I have a feeling there's also a bit in the companion to this effect, sorry don't have it to hand.

[Robert Leigh]

If you are going to shim the front bearings, BMC (NOT BMW) Mini track rod end shims are the right diameter, and used to be available in many thicknesses, and getting shims which are already the right size is so much nicer than cutting from shim stock sheet.
Robert Leigh