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MG Midget and Sprite Technical - Bearing shells - confused

Its the big ends and try as I might I can't get the new bearings in and tightened up so the crank will turn. I haven't done anything else with any other bearings etc. at the bottom only removed the caps and the shells on the con rod big ends and one at a time so I can keep track.

So I thought, put the old shells back. Just done that on 3 and 4 but same effect when I tighten up. Now - the old bearings have just the last traces of white metal on them so definitely a few thou thinner than new ones. So I must be doing something wrong. But how? the caps are on the same rods and the old shells are on the same rods and the effect is the same for old shells and new. The tangs are correct.

Taking all the caps off and shells, keeping in order and putting one on at a time and seeing how it goes.

Really confused by this 'simple' job. Any thing I should be looking to do on reassembly apart from cleanliness and orderly ness?
Dave Squire (1500)

Did you find any identifying marks on the caps/rods?
Chris at Octarine Services

Sorry for silly question, but the crank is free to turn before you try to fit the shells, old or new,isn't it?
JB Anderson

Good points, took a rest so will totally take out caps and shells, keep in order, check for marks and check crank spinning and look for marks.

Thanks guys the red peril is setting in so just keep me on track.
Dave Squire (1500)

Are the shells reversed....

Im not sure how to explain that....but they are IIRC... handed, as there is a special little catch the shell fits into on the cap andthe rod

2nd thought...(((assembly grease)))...if your installing dry, that will certianly add some friction and instantly remove 10,000 miles on start up

Prop and the Blackhole Midget

When I say, assembly grease....I dont mean any old lube sitting on the shelf,

I mean its actually called assembly grease/lube by name at the auto parts store...behind the counter in most cases. and used for the purpose of rod and main bearings assembly
Prop and the Blackhole Midget

Right, crank now free of bearings and turning normally. No marks on any caps. Old bearings are std. New bearings are std. (I checked the part codes both at Sussex where I bought them and cross referenced them against MGOC shop, Rimmers, and a couple of triumph 1500 sites).

Quick coffee and will try cap # 1 with old shells first unless anyone has any more ideas / instructions. Then try turning engine before next one etc.
Dave Squire (1500)


Can you measure the bearing thickness to verify that it is actually a standard size bearing. While rare it's not unheard of for items to be made or marked incorrectly.
David Billington

Thats the way to do it Dave, one set at a time and check all is well before proceeding.
Lets hope all is well this time!
JB Anderson

The other simple check is to put some light oil on the bearing surface and then fit a pair of shells around a journal, holding them tight against the crank. The ends of the shells should just make contact at both sides. If you cannot squeeze them together then they may be oversized ones on a standard crank, but I thought you said you had std shells. Other possibility as I mentioned before, someone may have tried to grind a little off the bearing cap ends to compensate for crank wear.

I presume you realise that the pistons create a lot of drag? The crank should turn, but it will have a lot of resistance, especially by the time all 4 big ends are done up. It may need a lever like a hammer handle against the crankcase to get it to move. Put all 4 caps on, but with the bolts a couple of turns loose. Check the crank turns and feel the pistons dragging. Then tighten one cap at a time, turning the crank between each one. This will identify if any one is tight.
Guy W

Yes Prop, all tangs in correct position, well lubed etc.

Hi dave, I understand where you are coming from and no I don't have anything that accurate. Do you know the measurement off hand as I will get them measured in the week. (hopefully tomorrow). However now you mention it on closer inspection the new shells have a slight rub on the 'tang' end after being in the caps and rotated. There definitely was no rub when I put them in. All the old shells definitely say std on them so even if they are marked up wrong std new bearings should go in. The new bearings do need to be pushed in and 'jam in the caps, I assume this is normal until they have been worn in then tend to be loose? While I can see no obvious reasons for my problem there is concern as you say that the new ones are not the correct size.

BTW no marks on the caps at all.

In the mean time I am going to put the old ones back in #1 I think and just get my head around making that spin OK first. I am at the point where I have no faith in my method or workmanship and need confirmation that I am not going completely cuckoo over this relatively simple if grovelly job.

Oh and just wondering; I assume the shells are sacrificial and the crank is harder than the surface of the shells (the white metal bit).
Dave Squire (1500)

I like the two caps idea Guy, simples. Thanks, I was typing as you were last time. Tea finished so back under for an hour or so.
Dave Squire (1500)

Dave - I still reckon your problem is that someone has mixed up the caps at some time and that is why some shells were back to front.

Pull the rods down so that you can put the caps on (groove to groove) WITHOUT the shells and run your finger round the inside and feel the join line - there should be NO ridge.

If you find a ridge at the join then that cap DOES NOT belong to that rod - try it on other rods till you get no ridge.

Repeat for all the rods until you get a perfect fit.

Then try again with the shells.
Chris at Octarine Services

OK yous guys. Now you got me looking more closely there are differences between things and I see the detail. #2 old cap shell is a bit shorter than the others to fit #2 cap. Probably causing my earlier problem.

Thanks for the heads up on the grooves Chris.

I have #1 back together with the old shells, torqued up and its fine. So my workmanship checks out.

I need to call it a day as I need to take SWMBO to work tomorrow to borrow the modern for my workies if I need it tomorrow. (She starts at 4.45am so it will be beddy bies soon). As I will be at my desk early I may be able to squeeze some afternoon time under the car.

Plan to take old shells out of one and put in new ones tomorrow and see if they work the same or bind.

Thanks for your help today the support is much appreciated. Cheers all I will keep you informed as to progress tomorrow.

:-) Dave
Dave Squire (1500)

<< #2 old cap shell is a bit shorter than the others to fit #2 cap >>

It shouldn't be. Although the bearing caps are matched to their rods, the shells should still be identical - after all they have to go around the same sized crank pins! If you are certain that #2 cap is shorter, and the shell that goes into it is also shorter, then it implies that bearing cap has been ground down for some reason. Maybe some more careful inspection is needed.

Before you fit the shells tomorrow, follow Chris' advice about trial fitting the caps to the rods to be certain that you have them matched up properly. Don't skip this step - it will save you time in the long run. You need to be methodical, one stage at a time with constant checking. If it is done properly, the whole task, big ends and mains, from when you first start to remove the sump to when you restart the engine can be done within 2 hours.
Guy W

The #2 cap shell is definitely shorter than all the others. This also fits with the mangled shoulders observed on the bolts for Cap #2 (mentioned in last weeks thread). Some PO either did a get by or more likely a garage did. I will be until I have chance to refurb my other engine (which rotates lovely after at least 10 years lay up btw). Which is extremely rusty.

At least I feel better this morning after a week of trying to work out why I was so bad at a more or less simple job.

Have decided if I get the time today I will go over to Rimmers, take the bits, and get some new bolts and the shells checked so I definitely have the right ones. Man on the trade collections desk there knows 1500s very well.
Dave Squire (1500)

Dave, if you can get hold of a 2" micrometer, measure the diameter of #2 big end. Or at least test it with 2 new shells held together around the journal
Guy W

Looking at the new shells I put in and torqued up its a goner so looking to do as previous and shave the shells for now. (the torqued new up ones look slightly rippled at the ends. Could be from being squashed in a cap that was too small I think).

Have a new set of shells from Rimmers with two new bolts with good heads for #2.

If I was getting a 'cheap' micrometer Guy what size would you say is the all round performer on the Mide?

Can anyone on here tell me the difference between colour died and phosphate by looking at them? The man at Rimmers has no idea. As far as he is concerned they are all the same. The ones he gave me are steel coloured with a slight tarnish on the heads. The ones I have are black with the steel showing through on the shoulders of the bolt head where the wrench has rested against it.

Rather busy with work today / tomorrow so not made any more headway. On top of that its BNO (boys night out) tonight and I am going to be having flack viz my midget is not reliable!
Dave Squire (1500)

Dave, a thought - did you check the backs of ALL of the old shells to see if they are all the same. I have only ever heard of cranks being reground with all of the journals reduced to the same undersize, but I guess it could be that just one crank pin has been reground.

Standard shells will have either STD or nothing on the backs (other than a part number) Check they are all the marked same.
Guy W

They are all the same and the man at Rimmers says they are standard.

The #2 cap is ground off a bit though as all the old and new shells are a touch too long.

So plan standard bearings in and shorten one for #2 for now.

Off to workies so may have a go this afternoon but have a man on holiday so its see how I go for time before BNO.
Dave Squire (1500)

Well that is definitely odd! In theory, if you shorten the shells then they won't go fully around the crankpin. The ends of the shells won't touch, unless the crankpin is undersized as well.
Some PO has been playing silly games with it!
Guy W

There is a product here we call "plasi-gauge"

Its a strip of plastic you torque in place of the shells then you remove it, compare onba small paper gauge and that tells you the size and wear anount in the shells

Im betting you have similar over there...its been around here for about 30 years

Prop and the Blackhole Midget

Here is a link for the plasti-gage from summit racing

Prop and the Blackhole Midget


Can you post a pic of the ground off cap / shell ?

Very interested to see whats been carried out and why if the journals are not grooved etc.

richard boobier

Crap camera for that detail but looking at it the caps 'normal end' is 'black / dirty brown' and some of the ends have shiny grinding tool marks. Now thinking back to working in a machine shop making the engineered parts for Fork Lift Trucks in my school holidays when a lad I know they bespoke all sorts of parts to fit so these marks may be original, I don't know.

After more careful inspection of the old shells, and comparing the ends with new out of the box, some have tool marks on the ends and the new ones don't have any.

Anyway probably last attempts today before car in bin. (just a weary joke).

The old shells still fit and the engine rotates lovely with them. If I put just new shell in #1 it rotates fine with just a bit more drag like what you would expect. If I put new shells in any of the others as well it varies from not turning at all to very difficult. So treating each end and its shells as a bespoke. Nothing to loose as two sets of standard shells from two different suppliers give the same results in each end no matter what which ones. And if the crank had been ground these would be loose and the crank would turn easy they can't be to thick.

Right enough resties. Get out and get under the automobile.
Dave Squire (1500)

Right. Sorted.

1) always ignore the book.
2) expect PO to have done all sorts.
3) expect Friday night, Monday morning assembly.

ALWAYS disassemble and reassemble exactly the same, there is a reason for it, and testing bits here and there to 'get it right' is both confusing and demoralising. ALWAYS remind me of this in the future. GO WITH THE PO assembly no matter what the instructions and guide lines say.

For those of you following this thread.

Cap #1 on correct way around OK, caps #2, 3, 4, on the wrong way round otherwise seize up with new shells. Cap #2 shell needs a shave off the end as well. With old worn shells you can put the caps on how you like it makes no difference (presumably cos of the wear).

Crank now turns by hand with new shells in (yippee) sump on in a minute and going for it.

I agree with Guy, its a simple service item. 2 hours tops if done as above. (It certainly will be in the future).

PS cancelled skip, kissed car and made up. back to real driving soonest.
Dave Squire (1500)

Did you ever test the fit of the caps without shells?

That sort of fettling really is not right and whilst it may work OK is a bodge I would not be happy with!

Chris at Octarine Services

Putting the shells into the caps the wrong way around the slot for the tang will not match the tang on the shell, which will then be pinched / crushed inwards, distorting the shell and causing the crank to bind.

Earlier on you were saying that only one cap was reversed. Now that 3 were so presumably 1 was right, and 3 were wrong. Sounds like you have now got it sorted, although I am not sure if you have had to file or otherwise alter the shells to fit? You really shouldn't need to!

Not yet clear if you changed the mains bearing shells and thrust washers as well or not. The thrusts should most certainly be done!
Guy W

Guy - I think he put the shells in the caps correctly but the caps are on back to front on 3 rods ...
Chris at Octarine Services

Yes, that's what I thought. But then wondered if the binding was because of not getting the tang snug in the cap.

It just sounds like the engine has been messed about with by a PO!
Guy W

Congrats... im glad you got that sorted, that is just a scary situation

Ive been known to do some crazy things... but filing a rod cap is not one of them

But your correct, the caps go on only one way.

Any chance you damaged the (tang) little catch on the shell...if it got crushed id be fearful of the bearing spinning inside the rod.

Btw... my caps were marked 1-4 granted its hard to read

Good luck

Prop and the Blackhole Midget

Its as Chris says with #2 shell ground off a bit. All the tangs fit just fine.

It will teach me to think of putting it back together 'right'; should have known better and only thought of putting it back how it was. Thanks for 'bearing' :-) with me.

I wanted to make sure it would go OK before doing the thrusts and the mains so put it back together and started just fine. I now have an adapter for my battery drill for the sump bolts so does not take very long to take off. It sounds a lot better already but I can feel the mains now so will be looking to do the thrusts and mains tomorrow. It will be put back as is with new shells, not as the book, if there is any difference.

Should be a piece of cake LoL. Then car OK for running in a bit on Sunday. Can't wait after two weeks of faffing around.

As you say Guy, its not that difficult if reassembled as disassembled, and its worth doing regularly for how little it costs for the amateur repairer.

Advice very much appreciated; its kept me going. Thanks again all.
Dave Squire (1500)

I wouldnt put much stock into a drill being able to perform like an impact wrench

You can get both air and electric impacts for electric was like $50, andis a god send for doing this kind of work

Otherwise a nice long piece of pipe does wonders with a breaker bar slipped inside

Prop and the Blackhole Midget

%"^!^"! Prop for SUMP bolts????

No Dave the battery drill is just fine for whizzing up the sump bolts - I tend to use a speed handle - the cranked thing in the socket set 8-)
Chris at Octarine Services

All main, big end and thrust bearings done; its back together and it runs. Less rattle and shake and sounds smoother. First proper run some time today.

Thanks everyone.
Dave Squire (1500)

This thread was discussed between 18/08/2013 and 27/08/2013

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