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MG Midget and Sprite Technical - Message for John Barber

Hi John,

I remember reading on one of your earlier posts (at least I think I do) that you needed 1 STD and 1 +5 thou Thrust washer for your 1500, and that you had to buy a pair of both. Does that mean you have one of each left over? It turns out I need the same sizes and thought we could do a deal that is if you don't want to keep them?

Christian
C L Carter

You are not far off the mark Christian. The fact is I got a pair of plus five thou and used one of the old ones ( cheap skate I know) as it looked fine.

So I do have a std and +5 thou - I can confirm measurements and you need to check its exactly what you need. The std one I have left does have some what I can only describe as some missing surface. Not sure why - but I can photo and let you judge if its what you want.
.
John Barber

Ah I see,

My thrust washers are the same. The missing surface is fatigue cracking, in theory they really should be replaced although as thrust bearers rather than load bearers(mains)then it matters much less.

I suppose its hardly worth the postage for the one, as I'll have to order another anyhow, but thanks for getting back to me so quickly.

Is your engine back in your car yet? I'd be interested to know what you plan to do in terms of "running it in"

Cheers
Christian
C L Carter

Christian Dimensions are

2.47mm copper ( plus 5 thou washer)
2.33mm white metal std brg

which by my rough calc is 5 thou between them.
pictures follow



John Barber

I have the engine assembled and on the bench ready to go back in. I haven't looked into run in process yet - I have glaze busted the bore and fitted new rings and a few new tappets - so I am not sure how much I need to coddle it. Probably bore/rings is the bit I need to treat with care..

You are welcome to the bearings - but in all honesty the one std one is not up to it I would say.

I got my new bits from MGB hive - copper based brg.(made in India it said on the bag) but look okay..

John Barber

Oh its copper? that is surprising.

Also weird, I rang the hive and they said they didn't stock +5s

I have some on order now with Greg and Sussex so I'll see what he comes up with.

I also have new rings in honed cylinders... they are pretty stiff in there so will need bedding in. But at the top and bottom stroke (where the pistons are stationary) it moves beautifully, so I'm not so worried.

I was contemplating taking the plugs out so there is no compression and running it on a spare starter motor and battery for a while... don't know much about electrics and what damage it can do though.
C L Carter

"The missing surface is fatigue cracking,"
Or corrosion.

"... in theory they really should be replaced although as thrust bearers rather than load bearers(mains)then it matters much less."
Still cost you an engine, or at least another R&R, when it fails, which will be quick when it happens. And the crap circulated does no good.

Cheapest bit in the engine, and the most overloaded, and already failing - don't be a idiot.

Do not try running it in on a starter. Starter only takes minutes to fry, and all you accomplish is to glaze the bores.

Get it up to temp, makes a dozen full throttle runs from 2000-4500, letting it slowdown on full closed throttle between. It takes gas pressure on the rings to seat them, and lubrication from the overrun (oil sucked up by vacuum) to keep them lubricated. I usually do this in third gear, then go out and drive briskly on country roads.
Best and quickest way to bed rings.

FRM
FR Millmore

Mine is definitely fatigue cracking, but I agree should be replaced.

Re the run in, full throttle - really? with brand new Big end and Main bearings... that sounds suicidal? Can you not just let it idle high at 1500...?
C L Carter

Bearings should not care. Not like old time hand fitted ones, where you had to let the high spots get beaten or worn down. Modern precision bearings with good oil pressure NEVER make metal to metal contact.

The idea with freshly honed bores is that they wear in with the rings against the rough and oil retaining surface. The longer it runs without the high pressures caused by gas behind the rings, the more likely it is to "smear" the peaks of the honing. This makes it much more difficult and slow to seat rings. When running and rings not seated, there is hot gas leakage past them, which gets them and the cylinder wall hot, which causes local lubrication failure, giving more wear and removing the break in coatings manufacturers apply. The result is cylinder wall glazing, and possible terminal ring failure.

The worst thing you can do is run at fairly high constant speeds at fairly light load = like 50 mph motorway. I keep them constantly changing speed and load for the first hundred miles, and pretty much for the first 500. Most dramatic example was my Cooper S spec 1275, which we push started and towed to the race track 7 miles away, while I sat in the car running the engine speed up and down. Retorqued the head, checked the valve clearance, and raced. Never used any oil, until I melted it by boiling all the water out due to circumstances beyond my control.

FRM
FR Millmore

I have some spare thrust washers too, but they don't look much better!

Just dropped my head and block off at the machine shop for a tidy up :-)

Cheers,
Malcolm
Malcolm Le Chevalier

Hi John,

I'm really struggling getting the +5 thou's so if you're offer is still open I'd like to buy your spare off you?

Give me shout, carter dot christian at gmail dot com

Best wishes,
Christian
C L Carter

This thread was discussed between 18/05/2012 and 22/05/2012

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