12/4 Clutch Bearing Seals on 1926 Engine

Servicing, Repairs & Restoration for your Austins.
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Neil McL
Posts: 9
Joined: Thu Nov 17, 2016 2:55 pm

12/4 Clutch Bearing Seals on 1926 Engine

Post by Neil McL »

The clutch on my 12/4 short stroke engine has had problems with not always fully disengaging since I acquired the car almost four years ago. On dismantling it, it is apparent that the clutch bearing cover plate (AK25, see below) has rubbed against the bearing (AK24) which I assume has contributed to the clutch problem by causing drag on the input shaft to the gearbox.
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It looks like the cover plate has had a hard time over the past 94 years.
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I have pressed the cover plate back into the correct shape so that it now does not rub against the inner race of the bearing.

I've also bought a replacement clutch bearing with rubber seals on both sides - thinking that these could "only help" by retaining the grease and keeping any foreign material out of the bearing. However, I'm now wondering whether to remove one or both of the seals due to the friction they cause which appears to be similar to that due to the rubbing of the cover plate before I removed it.

So my questions are:
1) Is the friction due to the seals likely to reduce appreciably with the (little) "use" that the bearing will experience ?
2) What do you recommend with respect to removing the seals and why ?

Thanks in advance,
Neil
Martin27
Posts: 42
Joined: Thu May 26, 2016 9:38 pm

Re: 12/4 Clutch Bearing Seals on 1926 Engine

Post by Martin27 »

Hello Neil
Well now, I'm an Austin 20 man rather than 12/4 but the technology is much the same. First of all, if I understand you correctly I think you are looking at the problem from the wrong angle. Friction applied to the gearbox input shaft is going to help the clutch plate come to rest when you press the pedal.

This idea is often employed in the form of a "clutch stop" on large vehicles with heavy clutch components to assist with gear changing. Using the clutch stop slows the clutch plate & gearbox input shaft so you don't have to wait 30secs (!!!) in neutral before engaging the next gear.

The sealed for life bearings can be a good idea, but remember these are sealed for the life of the grease, not for the life of the bearing. Personally I would prise out the seal on one side, so that grease cannot escape into the clutch but the bearing can still receive fresh lubricant in the normal way. It's a matter of personal preference.

Your clutch not releasing problem is more likely due to incorrect adjustment of the release fingers. It is absolutely imperative that the fingers are all adjusted to exactly the same height above the flywheel.

Unfortunately this adjustment is not quite as straightforward as it may at first appear. Even if you have equal finger height above the flywheel, if you have uneven wear on the fingers and/or uneven wear on the release bearing carrier where the fingers bear you will still have the same problem.

Now this next bit may not be possible on the 12 - remember I'm a 20 man. With the gearbox on the car, there is just enough room to get a dial gauge probe onto the pressure plate close to one of the fingers. Press the clutch pedal fully and note the pressure plate travel. Repeat for the other two fingers. Are the three measurements equal? If not you have found your problem. In my case I had a 0.025" variation giving the same symptoms you are experiencing. Eventually I was able to reduce this to less than 0.0015" which fixed it. At last I was able to engage a gear silently from rest.

Best Regards
Martin
Neil McL
Posts: 9
Joined: Thu Nov 17, 2016 2:55 pm

Re: 12/4 Clutch Bearing Seals on 1926 Engine

Post by Neil McL »

Hello Martin,
Thanks for your input, that's very helpful and I'll investigate how to "setup/use" a dial indicator through the bell housing opening before refitting the gearbox since it's such a tight access/space.

On the bearing front, it's the "clutch" bearing (AK24) in the flywheel that I was referring to, hence the outer race is pressed into the flywheel, not a fixed casing, so the drag was/is against engine rotation rather than something stationary. I like the idea of having an active means to slow the input and lay shafts rapidly when changing up - maybe a future project to squeeze in some sort of electromagnetic brake?
Regards,
Neil
Martin27
Posts: 42
Joined: Thu May 26, 2016 9:38 pm

Re: 12/4 Clutch Bearing Seals on 1926 Engine

Post by Martin27 »

OK Neil, I misunderstood which bearing you were referring to. I don't have the 12/4 parts list so was making a guess. You are quite right, any drag on the clutch shaft spigot bearing in the flywheel will cause the problem.

Regards
Martin
Pottery50
Posts: 11
Joined: Tue Aug 08, 2017 12:52 pm

Re: 12/4 Clutch Bearing Seals on 1926 Engine

Post by Pottery50 »

Neil.
Think you are looking in the wrong place.
Check the centre plate is flat (not dished and grooved)and is sliding freely on the spline.
When depressing the clutch pedal(after 3/4 inch free play) the pressure should be even under your foot, if not the levers need adjusting.
Keep the oil level low in the gearbox,about a pint below the level tap, and use engine oil in it,straight 30.
The H12/4 is a slow gearchange (as is the twenty I believe).Start off in 2nd,straight change to third at 10 mph,run her up to 20-25 mph and then double de- clutch to top and keep her there until you stop !
Hope this helps.
Alec.
Neil McL
Posts: 9
Joined: Thu Nov 17, 2016 2:55 pm

Re: 12/4 Clutch Bearing Seals on 1926 Engine

Post by Neil McL »

Hi Alec,

Thanks for the info and advice - it all helps. My clutch plate is indeed dished and the linings are almost down to the rivets, so I've got a new clutch plate and linings ready on the bench (along with new springs, levers and pins etc). The splines aren't great - they are reasonably smooth but slightly "wavy".

I thought I'd see what the clutch action is like with the "wavy" splines once I've fitted the new parts and adjusted the new levers etc. Third gear is very noisy under full load and appears to be very worn - it's not smooth when spinning the output shaft "backwards" when in third gear - so I'm anticipating a gearbox rebuild this winter.

For now, I need to decide whether to remove the bearing seal(s) before starting the rebuild.

Regards,
Neil
Pottery50
Posts: 11
Joined: Tue Aug 08, 2017 12:52 pm

Re: 12/4 Clutch Bearing Seals on 1926 Engine

Post by Pottery50 »

Hi Neil,
If the spline on the first motion shaft is " Wavy" and there is corresponding wear in the female centre,together with the dished plate,it will be sticking in one place.
Keep your eye out for a replacement gearbox,rebuilding the one you have with worn gears and the input shaft would be a waste of time.
In the short term,get a good clutch centre plate AK 11 that is not worn on the spline.
The flywheel bearing,AK 24.I would leave the seals on if it don't foul the plate AK25,other than support the end of the first motion shaft,they don't rotate much,early cars used bronze bushes.
Good luck,
Alec.
Pottery50
Posts: 11
Joined: Tue Aug 08, 2017 12:52 pm

Re: 12/4 Clutch Bearing Seals on 1926 Engine

Post by Pottery50 »

Neil,
Have had a search and found some parts which may be of use to you.
Email, georgealecmcguire@hotmail.com Will forward images.
Regards
Alec.
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