MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - My Engine Rebuild - Questions


Hello Everyone,

Following an outbreak of real work, I've not got as far along on removing the engine as I would have liked, but at the weekend did manage to remove all of the ancillaries and stuff, and it will be coming out tomorrow.

Not having gone through this experience before, I will have loads of questions as i go along, but I already have one before we even start...the alternator has been a bit noisy for a while, and with it out, I can feel that the bearings are shot. is replacing the bearings a job i can undertake easily? does anyone have a step-by-step guide?

Thanks in advance, and when the true horror of what's gone on in the engine is revealed tomorrow, I'll be back for advice!

many thanks
Mark
MarkH1

Can't say it something I have come across personally - not sure how serviceable the bearings are Mark.. I would just dismantle it methodically and and assess what you find..
may be worth looking for a used one somewhere. Not sure what a used one would cost - but may not be too steep..
John Barber

Cost you less hassle and will be more reliable to get an exchange. I doubt the bearing will work out cost effective. If the bearing is shot, there's also the possibility other parts of the alternator are on the way too. I'd run it until it stops charging and then exchange it. Unless of course it's so noisy it sounds like it's going to have a hearT attack. :) In which case exchange now.
Lawrence Slater

Mark replacing bearings is not that difficult but takes a bit of skill and care. If the bearings are that stuffed, then as others have said it'll probably need a bit more than just the bearings. The other bits that wear are the brushes and the slipring. Slipring could be ok but brushes will defintely need replacing. Brushes can be done with just a soldering iron but if it does need a new slipring then it'll need skimming on a lathe after it's been installed. None of it is hard with a bit of guidance, but unless you've got the tools, fairly capable and are keen to learn how it's done it'd be easier to get an exchange unit.

Was it charging ok before you removed it? There are other bits in there than can fail but if it was working ok then the other bits should be ok. If it wasn't then defintely go exchange.

If you really want to have a go I can give you the steps.
Greg H

Well, I think I can see what the problem is...
MarkH1

Not used to using the site on my phone. Will try again.

Wont let me upload pics from the phone. But there's a chunk missing from the side of one of the pistons.
Will upload a pic tomorrow
MarkH1

Ouch!
Dave O'Neill2

Hi Mark ,sounds as though work is in progress, are you using cornwall engine co.


gordon
g c pugh


Here's the evidence.

Not pretty.

MarkH1

That's not so bad, you just need a set of pistons and a rebore I would imagine. Although I can't see from that pic, how badly the bore is scuffed/scored.

Doesn't appear to be much of a wear lip though, again as far as I can see from that pic.
Lawrence Slater

When you have cleaned up the block, check between each cylinder with a straight edge and a torch held behind it. That looks a bit like sooty deposits between 3 and 4 so it may have been blowing across the top of the block between the cylinders there. Between 2 and 3 is the most vulnerable on a 1275 engine.
Guy


I think it has been blowing slightly across 3 and 4. The others look OK, but I think I will get the block decked anyway both to clean it up and to up the CR. Is there a straightforward dimension I can check to see whether the block has previously been decked? It's been re-worked before, I can read +.020 on one of the pistons so I don't want to take anything for granted.

the bore is not too badly scuffed, and the wear lip is not chronic so i think the block will do again...I'm going to go for the minimum rebore I can given that it's already been rebored once.

Gordon, it's going to the Cornwall engine co I think - had a chat with them and they seemed to be on the ball. Going to get on with stripping it in the next few days and then hand it over to them to bore, assemble the bottom end and balance it. I could assemble it myself but then would have to take it back to them again for balancing, and that just seems like a waste.

Another question as I go along - the ring gear looks pretty battered...do I need a replacement or is this normal? Was considering lightening the flywheel while I have everything in bits but if the ring gear is OK and the crank doesn't need re-grinding I may just leave it...

Thanks everyone - hope to get an hour or two in the garage this afternoon, so will be back again I 'm sure!

Cheers,
Mark

MarkH1

Mark,
You seem to imply that they would balance the crank after fitting to the block? Is this what you meant, because I don't believe that is correct.

Might be worth getting the mains line-bored as well.

Ring gear usually wears at two points diagonally opposite - where the engine normally comes to rest. Yours doesn't look too bad where visible but may be worse further round? I replaced my ring gear and although worried that something would go badly wrong it was surprisingly easy - quite a satisfying job even!

Good to see that you are doing the work on the comfort of your living room carpet. Do you not have a SWIMBO at home at the moment?
Guy

Sorry to hi jack....but

How did you upload pics to this site from yiur phone... I have to email the photos to myself and get them off my g mail, then resize then store in a folder then transfer to the bbs.... Its a hassle

I got android

Prop
and and the Blackhole Midget

Piston is what happens when it is run hard while out of water, although the final cause might be detonation due to overheat. You will likely find that #4 is pretty close; the speckles on top are melted aluminum. I have a pair that matches, but mine's worser! Mine melted the gudgeon pin as if you had hit it with a cutting torch. I was trying to finish a race; didn't make it but let it be known who was fastest.

Your ring gear is scrap - worn halfway across the teeth. You will want a new one on there before they balance it - you'd be unhappy if you broke the gear and had to take it all apart and rebalance later because of bad teeth.

Don't know of any good way to reference what has been done to the top of the block; normally you determine piston to deck in a trial build before decking.

I always stamp the block (or other parts) that have been machined with the info. Block might be B+.020 D-.012 etc. I also stamp all the engine info on a plate that attaches securely somewhere. Of course, I've not had the pleasure of finding that anyone else does this!

FRM
FR Millmore


Took the sump off yesterday. Lots of bits of piston ring in there. There was plenty of water in radiator, Fletcher, but there was very little (1/2 ltr) very black oil in the sump when i drained it. Oil pressure dropped just before failure.

One very obvious thing I spotted yesterday is that the oil strainer bracket was put on the wrong way around and has been rubbing on the crankshaft. The PO told me the engine had been professionally rebuilt, he didn't do much to the car himself. don't know who did it, there are no markings to indicate any details.

Guy - my life would be over if I tried to take the engine indoors! bit of old carpet in the garage makes rolling around on the floor a bit more bearable, though.

and Prop - I didn't manage to upload photos direct from my phone, tried but couldn't make it work.

I will get a new ring gear - unhappy would be an understatement if I needed to take the engine out again.

Thanks for the help and support everyone - I will be back with more questions soon, I'm sure!

Cheers
Mark

MarkH1

Mark,
When I did my ring gear I was worried that it would all go pear-shaped (literally and metaphorically!) Visions of it going on crooked and then cooling and shrinking in that position, never to move again! In practice it was very straightforward, Flywheel went in the freezer overnight. Ring gear went in the oven at 200 C for 40 minutes. I set up a couple of bricks on a sheet of ply beside the oven door so I didn't have to move hot and cold bits too far.

Then flywheel out of fridge and set onto the bricks, Open oven door, grab ring gear with a couple of pairs of pliers (long- handled water pump pliers were good for this) and lower the hot ring gear onto the cold flywheel. It went on very easily with plenty of clearance and time to check that I had put it on the right way round, and then to go round the edge with a hammer to tap it down to ensure it was straight. Job done! Quite fun really!
Guy

Mark-
What's the history of this? I had the impression that this was a spare or recently acquired engine. Might have been overheated earlier, or possible that it was only detonation. No oil makes sense if it was run after the piston/s melted.
My race car was still running like a scalded rat when I shut it off because it had totally obscured the track (county fair) with blue smoke, and I did not want to destroy the crank and block and gearbox. It was an Austin 1300 junkyard special to more or less Cooper S specs, and I was trouncing a 2L+ Datsun and Volvo, both full race and running Webers and alcohol. Started fine the next day, but a bit lumpy running.

FRM
FR Millmore

Midland Sports & Classics have the flywheel ring gear on offer @ £14.13

http://www.mgpartsuk.co.uk/prods/3608.html
Dave O'Neill2

This thread was discussed between 05/03/2012 and 10/03/2012

MG Midget and Sprite Technical index

This thread is from the archives. Join the live MG Midget and Sprite Technical BBS now