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MG Midget and Sprite Technical - 1500 thrust washers

Hello again BBS,

Hopefully this is an issue which people know alot about and can tell me if I'm being stupid or not.

So, my crank is off at the grinders and in the meantime I'm putting together a shopping list and todo list. One of the major confusing bits for me is the thrush washers at main 3. I took out 2 semi circular washers either side of main 3 (ie front and back)... I was expecting 2 semi circular washers one top and one bottom - Am I crazy, am I missing 2 washers are there meant to be 4?

Is it just a case of buying new ones and replacing, or do I need to measure for wear and buy oversized ones, or shims?

Other questions I have on my mind are.

1. Big end bolts - even though they aren't TTY, i think i'll replace them, any suggestions of which ones and where to get them? I remember reading an article where Debs said go for ARP or Ford Sierra Cosworths?

2. Piston rings, any special ones - who/where to buy them?

3. Head gaskets - do people use any sort of jointing compound on it? I've seen people using wellseal, but I've always put mine on dry. (composite type)

Thanks in advance,
C L Carter

I thought there was a top and bottom one, giving a large bearing surface. It is in two halves so that you can get it round the crank.

That said, I don't actually know and have never taken a 1500 engine apart. But I will be eternally surprised if this is not the case.

Malcolm Le Chevalier

Malcolm -I'm also surprised - I can't understand it, I'm starting to think I dreamt it... but I'm certain that when is came apart there was one half either side just at the top not the bottom.
C L Carter

Yes, there are 4in total. You feed the top two in by getting the end started and then rotating the crank so that they feed in. Sometimes helps to use a worn one to push the new one round with. Then the second pair sit in recesses either side of the rear bearing cap. Check for endfloat by pushing the crank forwards and then rearwards as far as it will go and using a feeler gauge. Generally the wear should be to the washers rather than the crank, so you can expect to replace with standard ones.

Worth getting the crank balanced on these engines. And you might consider having the flywheel lightened a bit at the same time. It makes the engine feel a whole lot more lively!

Tbh guy, I haven't got the budget - I've found myself restoring a car that I wasn't planning to... one day I'll get myself a RWA but until then I'm reluctant to do any more than is necessary to this one.

So it would appear that my car has been running on only 2 of its 4 TWs... amazing... I can't believe that either... someone must have forgotten to put them back in one day.

What stops the bottom two just falling out into the sump when they are worn?
C L Carter

They are apparently known for dropping out when badly worn. Maybe that is where your other two went!


I am glad I checked the BB tonight - I was about to complete my bottom end rebuild this weekend and was only planning on two T washers - the top ones - as that was all was in the engine in the first place when I took it apart...!

I ended up ordering two 5 thou bigger washers ( come in pairs ) and with these and std ones I am pretty much at 1-2 thou float...
John Barber

Getting cold feet now, I hope I am giving the right advice! Its a long time since I sold my 1500!
Anyone else confirm?

I haven't done a 1500 bottom end, although I did do the bearings on my TR6 about 25+ years ago. I don't remember what thrusts were in there, although the diagrams on M*ss website only show top thrusts.

It should be fairly obvious by looking at the main bearing cap whether there is a groove for a thrust washer.
Dave O'Neill2

Triumph's better idea was that only half a TW was needed, so only 2 halves, on top, front and back. There's nothing on the cap to retain them, and damned little in the block.
Might explain why they wear out!

FR Millmore

Well my apologies if I have given duff information again! I replaced those thrust washers on my old 1500 more than once but have done quite a few other engines too so I have obviously remembered wrong! As I wasn't quite sure, I had checked the Moss catalogue drawing in which just one shown by way of illustration.
And on the Sussex Classic Cars site the photo of the thrust washers has 4 in it.

Don't feel bad, it is a pretty incomprehensible bit of accountant engineering. Every time I took one apart I sat and stared at it wondering where the "other half" had gone. I finally did get it firmly wedged in my noggin - yep, they really did that! Worse still, TR6 is the same.

FR Millmore

Yes, I do remember thinking the bright idea halves the thrust area and doubles the load. I suspect that wear rate more than doubles, its probably logarithmic!!


Thanks guys, good to know.

John, what bearings have you bought and where from? And where did you get your thrustwashers?
Oh and are you replacing the wooden wedges?
C L Carter

I am amazed! Crazy

John, hows progress?

Malcolm Le Chevalier

This is a known weakness in these engines, I've read of people having the big end caps machined to accept the extra thrust washer but that might be a bit overkill. I'd just replace with new ones and keep your foot off the clutch at traffic lights.

R.A Davis

I had read that tip somewhere too. Started doing it in my modern car in practice. Have my girlfriend doing it too. It is probably good practice in any car, but more so in BL trump powered machines

Malcolm Le Chevalier

Right, there are only two half-washers.

When you install the new ones, make sure the side with the oil groove bears against the crankshaft.

Gryf Ketcherside

"It is probably good practice in any car, but more so in BL trump powered machines"
Imperative in A series or any car with graphite release bearings, unless you really like pulling engines and buying clutches. It is possible to destroy the clutch in 3000 miles of city driving and foot resting.

FR Millmore

Since I posted that reply I gave it some more thought - would having thrust washers in the main cap be a good idea necessarily..?

Not sure if the side thrust exerted on the end main cap might cause the main bearing to be affected ( stressed in some adverse manner)

I got two +5 thou from the hive as the MGOC only do std and +10 thou steps. I had 8 thou endfloat with old bearings at std thickness (I checked the widths with a micrometer)

Washers I took out measured at 0.092 ( 92 thousandths of an inch) or 2.32mm avg.

I had 8 thou endfloat with old bearings in..

I purchased a pair at +5 thou - which came in at around 0.098 thou or 2.49mm.

Christian - I haven't replaced the wooden wedges - they seemed okay - I used some blue hylomar on them also. Mains and Big ends came from MGOC .. Thrusts from the Hive.

Malcolm - slow progress I am afraid.. however I hope to gett he engine back together this weekend..
What about your progress?
John Barber

A couple of links on thrusts that I have found useful.

John Barber

Sorry to raise this again, but I've just re-confused myself... if there are only supposed to be 2, why does the kit from sussex cars (see link below) contain 4?
C L Carter

That is why I (wrongly) initially advised you that there were 4! I had checked the SCC site and saw their photo of 4. I think they have wrongly used the same photo for both the 1500 and the A series engines. Someone should tell Greg!

That's a pretty strange listing. No place for what size do you want?? They come in various oversizes. Perhaps they are supplying two std and two .005, which is what I usually get, but there are thicker OS available, as John said (and more). If the crank had wear or scores in the thrust faces and was ground on those faces, then you could need something different; best to not buy these until you get the crank in and can measure the clearances. Set the clearance at book minimum.

Side thrust on main caps is not an issue in any of the engines which use full thrusts. This is inexcusable crappy accountant engineering.

FR Millmore


1. Big end bolts - I used Cosworth. Cheaper than std and probably much stronger! They do take the stress very much deeper into the metal of the rod. Get them off the shelf from Burton

2. Piston rings - I just used some std ones from Sussex Classics that seem great. Made by County Pistons IIRC. I have heard stories about people using mk1 VW Polo pistons and rings as an upgrade but never researched it further.

3. Head gaskets - Shouldn't need any jointing, the composite gasket will seal perfectly if torqued correctly. Just make sure the torque wrench is dead-on accurate!

Hope this helps.

Bob T

I have used ARP bolts on my A series which is mildly tweaked, they give the feeling that they will never fail (famous last words) but they also look the part aswell (have them on the head too)however they were pricey, but i have the do it once, and where possible over engineer hat on occasionally when it comes to my midget !
p bentley

Thanks for the tips Bob. I was thinking about the cosworth ones too
C L Carter

This thread was discussed between 26/04/2012 and 06/05/2012

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