Shells or white metal

[Charles Levien]

Good evening all,

Can someone please tell me when shell bearings for big ends came in. My engine no is 
M278745 and I should like to know whether it’s a late enough engine to be fitted with shells.

Thanks,
Charles

[Colin Morgan]

According to the A7 Companion, shell bearings were fitted from engine no 268659 in March 1937.  

(However, my engine M289617 has non-original white metal bearings following an engine rebuild sometime in the distant past - so engine number may not reflect what is in there.)

Colin

[Charles Levien]

According to the A7 Companion, shell bearings were fitted from engine no 268659 in March 1937.  

(However, my engine M289617 has non-original white metal bearings following an engine rebuild sometime in the distant past - so engine number may not reflect what is in there.)

Colin

Thanks Colin, that’s helpful.

I will now drop the sump etc later this year and have a look see. I have a feeling that one of the big ends is trying to draw attention to itself. I normally take the engine out for any work but replacing shells from below shouldn’t be too difficult.
Ref the other thread on SU versus Zenith — I have a one inch SU fitted and reckon it’s a lot better than the original carb. ( D3 needle) Climbing the hills around here is easier ( ok they’re not proper hills) and getting to 50 mph and sustaining that is no problem.

Charles

[Colin Morgan]

Yes, I managed to take out and later refit a remetalled No 3 con rod without removing the engine.  However, I think I was lucky that the crank journal was serviceable - hardly marked and within the (couple of thou?) ovality limit.  (Getting a series of accurate micrometer measurements upsidedown in the confines of the crankcase took a bit of practice.)

Colin

[Charles Levien]

Yes, I managed to take out and later refit a remetalled No 3 con rod without removing the engine.  However, I think I was lucky that the crank journal was serviceable - hardly marked and within the (couple of thou?) ovality limit.  (Getting a series of accurate micrometer measurements upsidedown in the confines of the crankcase took a bit of practice.)

Colin

That’s a good point  — I’m rather hoping that the wear is taken by the shells rather than the journal, which I believe to be the case normally.

Charles

[Chris KC]

I've changed both big end and centre main shells from underneath, it's quite do-able so long as no damage on crankpins needs rectifying. Not much to lose though - in that case you still have to take the engine out but it's drained and the sump's off already.

[JonE]

Could I ask whether shell bearing conrods are any use for retrofitting on earlier 2 bearing 1 5/16" engines?

[Alan]

They aren’t really interchangeable. I’m not saying it’s never been done but 3brg rods are offset slightly to compensate for the different big end journal spacing. ( needed to get the centre bearing in)

[Robert Leigh]

According to the A7 Companion, shell bearings were fitted from engine no 268659 in March 1937.  

(However, my engine M289617 has non-original white metal bearings following an engine rebuild sometime in the distant past - so engine number may not reflect what is in there.)

Colin

Thanks Colin, that’s helpful.

I will now drop the sump etc later this year and have a look see. I have a feeling that one of the big ends is trying to draw attention to itself. I normally take the engine out for any work but replacing shells from below shouldn’t be too difficult.
Ref the other thread on SU versus Zenith — I have a one inch SU fitted and reckon it’s a lot better than the original carb. ( D3 needle) Climbing the hills around here is easier ( ok they’re not proper hills) and getting to 50 mph and sustaining that is no problem.

Charles

Yes, it's quite possible to change the shells from below. I did it once on the rally field at Beaulieu. I was camping so I drained the oil into the washing up bowl, and used the frying pan for all the nuts and bolts (none lost in the grass), checked what size shells I needed and found the right ones on a stall, then put it all together again, and drove back to Cambridge in the evening.