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MG Midget and Sprite Technical - A series re-bore in the North East

Hi all

Dad's finally got the sick mini in bits, dead head gasket between 2 and 3 and you can rock the pistons around in the bores. dry compression was 130 wet was 250.

So the Question is does anyone have any experience with or know anyone who might know of any decent reboring places / capable machine shops in the North East?

Going to try for the next one up (it's 1293 already) then if that doens't work then the 1380. If it still won't go (there's a suspicious groove/polished section on one of the bore walls and the others are pitted to an extent you can feel it with a fingernail) then we have a spare block.

Engine's totally in bits, so I guess you just turn up with the block and the people mill it out?
Rob Armstrong

1293 is +020
So you can try +040 +060 and 73mm before you go 73,5mm 1380.
Though there are some nice pistons cheaply available in 73 and 73,5.
Better choise than the normal oversizes...?
Onno Könemann

Cheers for the options Onno - dad's plan is to see how the block goes before buying pistons, where would you advise buying pistons from?

thanks :)
Rob Armstrong

As I understand it the machine shop will probably want your pistons so they can measure them before the rebore.
J White

I think mine is going the same way. It is reving really well (in my experience, a bad sign) and blowing a fair bit of blue smoke. I need to do some running tests before I strip it down to do any work on it so I know what the condition is like inside. Hoping it is not as bad as Rob's dad's mini!

Is it ever worth just fitting new rings without doing a full rebore and piston job?

When it was last rebuilt the machine shop did a really good job, and they supplied the pistons, shells etc for me to assemble
Guy

>>the machine shop will probably want your pistons<<

hum if that is the case then the capacity for unnecessary expense goes up somewhat. He's after the smallest re-bore possible, in order to keep the block alive for as long as possible.

Guy I reckon the simple compression test would show how bad it was, I don't know if these engines prefer to wear rings or bores or both. Dad's problem was that engine was left not running for about 17 years, the bores are worn because of rust we reckon.
Rob Armstrong

Guy, you asked,
"Is it ever worth just fitting new rings without doing a full rebore and piston job?"

A lot of people don't like them, but I have used Cords rings on a number of engines, including the one that is in my 1275 Sprite now.

As long as you don't have scoring, only wear, they are the biz for avoiding a rebore and new pistons. My engine is already 30+ and I didn't want to go any further or sleeve. The bores were good, -- no scores, so I whacked in the Cords.

Prior to the cords, it was a bit of a smokey lump with probably 90+ thou on the clock. Now it is a non smokey very good engine with an extra 40thou miles at least. I married them to a P burgess head.

I've used them for years, at least 35. An RR trained mechanic put me onto them, as a cheap and workable alt to a full job.

Check em out. They're still in business.
http://www.cordsduaflex.com/index.html
Lawrence Slater

Rob,
Yes I will be doing a wet/dry compression test. I have done these every few months and keep a record each time. The last one was beginning to show a dry compression drop that recovered well with the wet test. A fairly clear indication of piston ring seal failing.

But the question was how practical is it to just fit new rings and maybe do a quick whiz with a hone bore and expect that to work. That much I could do without removing the engine and sending it away for work so the concept is attractive, but may not be realistic!

Sorry to hijack your thread, but it is sort of the same topic! I could recommend an engineer in the NW (Lancaster) if that was any good to you!
Guy

Rob,

As I understand it, if the pitting/rust damage is minimal in the bores, cord rings will effectively cut a new surface, and once run in seal the bores. I've used them on some really crap engines and they work.

P.S. I have no financial or other interest in Cords. lol.
Lawrence Slater

You can let the machine shop have a look and ask for their advice.

Short highlines on what you want from a 1275 piston
-solid skirt
-3 rings
-holes behind the oil control ring not a slot!

Cast vs forged
Cast is more prone to breaking up due to detonation
Forged is a little less wear resistant
Cast is a hell of a lot cheaper and with care should not limit power in fast to very fast road engines

for std oversizes the MEGA pistons from minispares seem to be good (the 73 not so sure) Peter B uses them

Or just buy some omega cast pistons from Peter May slightly more expensive but it has the big name on the tin.

For the bigger sizes (73/73.5)the Hypatec pistons from down under seem to be good and rather cheap (minisport.com.au)
The turbo mini guys give them a serious pounding and they seem to stand up

Dont be tempted by their normal sizes as these have a slot behind the oil control ring.....

In the end I think I'll go for a set of +020 cast omega's in my new build

Onno Könemann

Onno,
out of interest, - if slots behind the oil control ring are such a bad idea, why does anyone make them this way?
Guy

thanks for the info everyone - some things to think about there! Those Cord things sound clever, possibly not clever enough however but might be worth a shot... I wouldn't describe the bores as "good but worn", there's definite feel-able pitting in at least one of the walls.

presumably slots are cheaper to manufacture?
Rob Armstrong

Cheaper
And no problem for a std engine build

But if you fit a cam that goes to and over 7500rpm std and aim for a CR around the 11 to 1 region pistons that can keep up are not a bad idea.

And since they are not and ideotic amount more expensive they seem like good practice
Onno Könemann

Good point Onno - it'll be keeping the Piper 270 it's got in it at the moment, so makes sense to get decent pistons that match the rev range :)
Rob Armstrong

Rob, I can say from personal experience that cords are good, and they've been around long enough to be found out if they were crap.

Ring em up and have a chat, I'm sure they would be pleased to give you advice on cords suitability RE pitting in the bores.
Lawrence Slater

Rob, any good machine shop will bore the minimum needed to get a good finish and then hone to the final size. This being the case you should be able to get the piston size required and then get them to hone to these. It will mean the block is in the shop longer than if you pick the pistons first. Also, the machine shop will probably be happy to supply your chosen pistons, possibly at a slightly inflated price, which saves hassle.

I've not tried cords but have read many good things about their powers of recovery...

Keep us informed of progress and I really should get the 1380 sorted this winter!

MGmike
M McAndrew

Can't seem to find any dealers? Or do you order directly from the manufacturer?

I could use a set for my volvo and like to see what they got before I take out the engine.
Alex G Matla

Guy,

Who in Lancaster can you recommend for machining?
I live near Fleetwood and work in Preston, so thats not so far and a personal recommendation is always good. I have a set of 73mm Hypatec pitons from Oz waiting to go in a spare block. (Currently number 36 in the queue)

Mark
M Crossley

Hi Alex, I assume you are asking about cords.

Cords don't have dealers. Buy direct. They'll ship.

e-mail : info@cordsduaflex.com or Tel:+44 (0)1685 353240

Tell 'em your car make, engine, bore size etc.
Lawrence Slater

Thanks Lawrence!
Alex G Matla

Mark,
http://www.lancasterengines.co.uk/

Small, very "old school" engineering machine shop. Chaotic appearance of old machines and piles of engine parts they don't exactly give the appearance of the sort of high-tech specialists where you could eat your dinner off the floor! But they do know old engines, take an interest and are very reasonably priced. Reasonable turn-around time too if you say what you need. Not sure if they do assembly work, I always just get the machining done and then clean and assemble parts myself. Ask for Malcolm.
Guy

for future users and interested parties:

Dad's going to try Northern Rebores

http://www.northernrebore.co.uk/


They said best plan is if they look at the block they reckon they can tell if it's going to go out to +40 ok, he said the vast majority are fine to more than that but worth checking first, then he buys pistons, then it goes in with them and they bore and hone it to match the pistons.

Will report back, he's taking it in tomorrow :)
Rob Armstrong

And, for anyone who needs the same thing down south.

http://www.southern-rebore.co.uk/index.html
Lawrence Slater

Try Park Engineering in Malton, they do a lot of work with Keith Calver the Mini Guru (he's just across the road). You must specify exactly what you want though, so there are no misunderstandings..

Mark.
M T Boldry

This thread was discussed between 14/11/2011 and 26/11/2011

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