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MG Midget and Sprite Technical - 1500 Main Crank Bearing Replacement

Afternoon all,
Hope someone can offer me some advice on replacing my main crank bearings. Can this be done from underneath the car with the sump off, and the crank remaining in place?

My theory is that I could remove one bearing cap at a time, and tease the upper shell out in the direction of the tab, around the crank journal. Then slide the new shell in the same way. I am sure this can be done with the middle bearing, but I'm unsure if the same applies to the two end bearings.

Any advice from anyone who has tried this would be most welcome.

Many thanks,
Ben.

PS, Wasn't Spridget 50 brilliant! I did a 600 mile round trip to get there and the spectacle of a 1000+ midgets and Sprites in one place was worth the back ache.
Ben Whiteley

It is possible as I know people who've done it. Guy? Didn't you do this as a 20,000mile service interval on your 1500?

Nick

Ben --

I haven't done it, but someone on this board once posted the steps required. The tricky bit is the front main, as you have to remove an aluminium bridge piece to get to it. There are two (I think) timing cover bolts that run back into that bridge piece, and you need to remove those by reaching back under the radiator with a long extension.

But I'll let the more knowledgeable comment. I've read about it, but I haven't actually done it!

Oh, don't forget to renew the crank thrust washers as well.

Cheers,

-:G:-
Gryf Ketcherside

Gryf, Nick,
Thanks for the update. So long as I know it is possible I will have a go, and work out the details along the way. I just wanted to know it was actually possible before I committed myself to another dirty job laying on the garage floor.

Ben.
Ben

Ben,
Yes, it can be done. Your description of "teasing out the top shell in the direction of the tab" is correct. It also helps to gently rotate the crank at this stage. The centre and rear mains are straightforward.

The front one can only be reached with removal of the alloy cast "bridge" piece as Gryf describes. This is held by two bolts vertically into the block. But you also need to remove the bottom 2 (or is it 3 - cannot remember) pan-head bolts that fasten the timing cover. These are awkward but can be done with a bit of ingenuity. You may need to undo the front engine mounts and raise the engine a bit to give better access. Replace them with hex-headed bolts and it will be much easier.

The bridge piece is also sealed in place with two small wooden wedges (yes, Wood!!) There are other risk with this stage of the work. The bridge is fairly soft alloy and it is very easy to overtighten the two front sump bolts when compared to all the others which go into steel. Similarly, take care not to overtighten the bottom timing cover bolts. And of course you are likely to have damaged the exposed piece of the timing cover paper gasket in which case use a good application of a silicon gasket sealant when you re-assemble.

When you have the centre cap off replace the two "C" shaped thrust bearings at the same time. These are the ones that there are horror stories about them dropping out on 1500's, although strangely I have only ever seen these tales mentioned on USA -based message boards where it is common to see statements such as "it is essential to get the thrust washers pinned". I never did and although I have seen these tales they always seem to be second-hand, never actually experienced! Even so I put some bearing locktight on the backs when I replaced them - just to be safe!

After all this - the obvious shouldn't need stating, but if the crank surface has been damaged, is scratched or worn then putting new shells in will have only a very limited life - possibly only a few hundred miles at most, and is a complete waste of time unless you plan to con an unsuspecting buyer. Which I am sure you don't!

But if the crank is OK, then I think it is worth doing for a quiet engine. As Nick mentioned, I used to replace the mains and big-end shells on my 1500 every 20,000 miles or so, as a service item. I did them 3 times I think, or maybe 4.

Where in Cumbria are you?

Guy,
Guy Weller

I have successfully carried out this operation on a TR6.

With regard to the thrust washers, I had a friend with a Triumph Herald who was having difficulty disengaging his clutch. It transpired that the problem was caused by excessive crankshaft endfloat, due to the thrust washers being in the bottom of the sump!
Dave O'Neill 2

Thrust washers are normally at the bottom of a triumph's sump!
Nick

I've done the shell swap and it is just as Guy describes.

Nick - Only if you neglect 'em...

In all seriousness, those thrust washers have to get really badly worn before they're fine enough to drop out. When new the thrust washers go in they are about 0.25" thick and the gap they fall thru is about 0.10" thick. If you neglect the condition of your engine to that extent then you deserve all the consequences!

When i last checked my thrust washers they had only lost a couple of thou in 8000mls so I tend to think the problem has always been exaggerated.
Bob T

I dropped my sump a few years ago just for a look. The thrust washers actually looked pretty good, but since I didn't have any new ones on hand, I reversed their positions to place the relatively unworn rear washer in the front position, where it would receive loads from clutch disengagement. Of course I want to replace them eventually, but the need just isn't there at present.

Oh, if you do remove/replace the thrust washers, remember that the sides with the grooves need to face the bearing surfaces on the crankshaft; i.e., the slotted sides should not face the main bearing web. This is essential, to ensure that oil gets where it needs to be.

-:G:-
Gryf Ketcherside

Thanks again to everyone for your advice.

Guy - "Where exactly in Cumbria are you?".
I live at Egremont. What about you? Do you ever go to any of the Wigton Motor Club events?

Ben.


Ben Whiteley

I've done this with the Aseries centre main.

The trick is to:

- check the condition of the journal with the cap removed; excessive scoring will mean a crank regrind in the near future

- check the condition of the bearing in the cap you've removed; scoring and pitting are signs of unfiltered oil, lack of oil, or excess load/temperature in the bearing.

- you should place the new shell against the journal and rotate it round the journal to prise out the old 'top' shell.

- as above, some turning of the crank can help the process.

Consider new b/e shells at same time.

Have fun! Oil drips into the eyes are a particular joy during this process.

A
Anthony

Ben,
Kendal. Don't get up to Wigton much, and Egremont even less frequently!
Did the WMC Christmas Cracker run this year. Not much else but there are a couple of possibles coming up.

GUy
Guy Weller

>>> When you have the centre cap off replace the two "C" shaped thrust bearings at the same time. <<<

Minor correction here; the thrust bearings are located on either side of the REAR main on the 1500, not the center one.

>>> Thrust washers are normally at the bottom of a triumph's sump! <<<

Oh, have a heart, Nick! Things are hard enough as it is. ;-)

>>> Have fun! Oil drips into the eyes are a particular joy during this process. <<<

Or the mouth. It tastes foul. I know...

-:G:-
Gryf Ketcherside

This thread was discussed between 02/06/2008 and 06/06/2008

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