Rear Main Bearings

[Ruairidh Dunford]

Great news!

[David Stepney]

Thank you Ruairidh. I shall use it over the next week or so and see how it runs. I shall need to press it into service as my 'daily for a couple of weeks as soon as the lighter nights are with us so that I can get the engine out of my Mk2 Polo (which is the 'daily') and get to grips with all the oil leaks.

But I have had enough playing for tonight. I'm tired, hungry and want a bath. Also my bottle of The Ardmore beckons. The garage looks as if I have had a visitation by a suicide bomber but it can wait 'till tomorrow.

[Ruairidh Dunford]

Sounds like a pretty normal Sunday night to me - the similarities are uncanny.

Enjoy the Ardmore - yum!

[Chris KC]

Glad to hear you've got her running David!

If you think your garage is a mess you should take a look at mine - just cleared all the remaining odds and ends from Dad's garage and have nowhere to put them! Time to get on eBay...

[Bob Culver]

The traditional hashness of 2 bearing Seven engines is hugely influenced by clearance of main bearings (even the smallest) and by spark advance. A box saloon will be blessed with manual advance. This must not be more than necessary for performance, and a litle of that is best traded for long crank life. With new bearings and less harshness have to be careful to moderate advance.

Any observations of the replaced bearing would be of interest. Precisely on track, what thicknes of shim or paper can be freely rolled over? Can you asses the depth of the worn track in the outer ring?

Tracks and rollers should be shiny bright; often matt grey. Track should be close to centre of ring.

The recent threads Front Bearing Puller and Engine Strip Down relate. (Also Alternative Crank Bearings)

[David Stepney]

"If you think your garage is a mess you should take a look at mine - just cleared all the remaining odds and ends from Dad's garage and have nowhere to put them! Time to get on eBay... "

Yes, Chris, I know the feeling well. My garage seems to fill with the detritus of the years. having a good 'turn out' is one of the many jobs that i keep promising myself to do, but never seem to get around to. Today's job will be to find all the tools  and sweep the floor and that's going to take most of the afternoon.

Regarding Bob's comment, the old bearing is rough to turn. I suspect that it has become brinelled over the years. A friend of mine, who is an agricultural engineer, tells me that caged bearings behave a bit like epicyclic gear trains in service, which means that any recurring loads tend to take place at certain defined positions of the bearing Hence the brinelling.

I have set the maximum advance to 1 9/16" BTDC which is slightly less that 20 degrees advance, but find that the engine runs at its best (and quietest) at about haft to three quarters advance. I am also using a good quality 10w/40 semi-synthetic motor oil, which I am hoping will improve the longevity of the engine internals. I it is, after all a standard box saloon engine so I am after reliability more than performance. I much prefer driving the car rather than having it in bits! 

The next job however, will be to 'de-growl' the rear axle but that's a job for next winter and quite possibly another thread......

[Hedd_Jones]

when you've managed to de-growl the back axle, ill send TH4219 back your way for the same treatment!.

[Bob Culver]

Thanks David

It is great to have observant feedback. many enquiries just die. Presumably either someone fixes the problem and the enquirer does not know quite how,or it was something so obvious they are not game to reveal!

For a non sport, non racer your advance findings correspond with others very experienced. Manual advance is a great toy to pass the time when climbing hills!

The bearing roughness is unusual unless damaged during removal. Can you glimpse the inner track at all?

Rear axles have been well covered but it could be a mission tracing all the related posts.

[Ken Morton]

I recall seeing an article about 750 racing ~ 60 years ago where the "fast boys" did not fit rev counters as they knew when to change up when they could hear the middle two pistons hitting the cylinder head. We do know that original Austin cranks do flex when abused, so with that in mind the main reason for rear bearing "rumble" was probably a little crank flex and the parallel  rollers in a new bearing would be overloaded at the ends if the engine was over revved in neutral. This could also be one of the reasons that most original Austin cranks fail at the rear web. I believe there has been some experimentation with using ball bearings at the rear.

[David Stepney]

"when you've managed to de-growl the back axle, ill send TH4219 back your way for the same treatment!."

I would have hoped, Hedd, that the axle on TH 4219 would have been rebuilt by now. If not, it's been growling for 50 years!
FG's back axle is quiet when spun up with no load so I presume that the bearings are in good order, but there is a lot of backlash between the pinion and crownwheel and it has a darker growl on driving and a lighter one on the overrun. I have costed all the bits including one of David Cochrane's crownwheel and pinion sets and the bill will be about £800.00 so I'm going to have to do some serious saving up! However, if what I have surmised about TH 4219's axle is true, then it's not exactly urgent.

I would quite like to meet TH 4219 again. if you are agreeable, Hedd, perhaps you would like to give me a ring sometime: 01678 520284.

Bob, I note what you say, but since the bearing came off the crank with virtually no effort and went back on with only a couple of light taps, I can't see how it got damaged during dismantling. I can't see the inner track without digging the rollers out and there is no discernible rock in the bearing itself. But it was dreadfully noisy in the motor. I thought it had collapsed! The new bearing is much quieter although it has only done about 20 miles so far. I have to go to Llanfyllin on Wednesday evening which is about 25 miles distant from Bala over the mountains. This involves plenty of second and third gear work, so should give the new bearing a good test.

As I said in my previous post, I think is has become brinelled. when you rotate it, it feels sometim.es smooth and other times rather rough.It is clearly (as we say in Wales) 'wedi gorffen' (FUBARed) and is now in the scrap bucket.

Again, as I have said in a previous post, I am going to have to press the FG into service as my 'daily' whilst the Polo receives some much needed TLC so I shall report back on how it behaves. If the uncaged rear main continues to be satisfactory in service, this may reassure others.

Once again, thanks to everyone who has contributed to this thread. It has been most educational!