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MG Midget and Sprite Technical - Running in with one replaced piston

I've read the archives about running in new and rebuilt engines and understand the options and how to do this. However, what about my engine where I have three nicely worn in pistons and one brand new one?
Do I treat it as a rebuilt engine or not.
My intention is fill with thinner oil and set timing on Saturday then do the London bridges run on Sunday) Lots of stop start with no high speed long cruising. The problem is that thje following weekend I intend to drive it from London to Donington and back, which will all be motorway speeds.
Suggestions please.
G Lazarus

I was always told to run it in how you are going to use it . In your case give it a good thrash .
Not sure about your comment about using a thin oil , use a cheap oil yes and change oil and filter after 500 miles.
Roy
R Mcknight

surprised you would only change one piston and not the lot, but I would have thought you would need to run it in, did you hone the bore, or just put the new piston in ?
P Bentley

I didn't fit it but I believe that the bore was honed. Alan Anstead, who sometimes posts here, put the piston in for me.
G Lazarus

I'd use normal grade oil but maybe a cheaper brand, drive it at 85% for 250 miles, change oil & filter to normal brand, carry on as normal.
David Smith

Gary,
Although its a new piston (and rings) its in an old bore (albeit honed). So although it will likely be tighter than the other 3, it shouldn't be excessively tight and all that needs doing is for the new rings to bed in a little - hence Alan has honed the bore to break any glazing and give the correct surface to encourage the rings to bed in (i.e. wear down a little) to create a good seal.

Lots of changing engine speed coupled with short bursts at higher revs (the traffic light starts!) on the Bridges Run would be ideal bedding in process. After this a longish high speed run the following weekend should be fine. Just keep an eye on the temperature and change the oil and filter after about 500 miles to get rid of any debris.

I wouldn't use a thinner oil - the other three pistons are doing what they always do and the oil thickness really relates to mains and big end bearing lubrication, which is also unchanged, so stick with the normal viscosity.
Guy W

Ta for the replies.
Gary
G Lazarus

What Guy said

Should be good to go in a short time

And yes I mean GO as YOU do
Bill1

I replaced 1 piston in mine a few years back, the bores were fairly new so not worn at all. I just gave it a light hone and was gentle with it for a few miles, building up the the revs, not letting it labour etc. Probably only did a hundred miles or so then it was straight to Peter B's for a tune. It's since been stripped and checked with no signs of problems.
john payne

Just wondering. Do people advise the use of a cheap oil because it's a waste of money to use good oil for such a short period, or because the cheap oil has some benifit to using good quality oil in this situation?
G Lazarus

X3 what guy said

Gary,

The main benefit of cheap oil for a new engine is the oil will most likely have no additives, like your better oils

You want the new engine to wear and seat its self with alot of vigor in a short period of time ...under 500 miles, if that fails, then you have alot of issues ...namely if the rings dont get bed in quickly and the oil dosnt break down then the clys devolop a slick glaze and the rings never bed in and you get lots of blow by, lost compression, and oil leaks....the only way to fix it, tear the engine apart and hone the cly and new rings

Thats why you dont baby a new engine, but treat it like a $3 crack whore in order to get everything to bed into each other.

Worst thing you can give a new engine is oil that has additives that gives it longer life or is formulated to preserving life in an old high milage engine...all you want is minimal lubercation, nothing else, otherwise the engine will not break its self in

Prop

Prop and the Blackhole Midget

Both; due to short intended use you don't need the detergents and long-life additives of more expensive oils.
David Smith

Just drive it as normal, If it's been fitted correctly, you have absolutely nothing to worry about.
HALL JOHN

John....

Just drive it as normal....hmmm

What if gary car jacked someone for his midget.....

So drive it like you stole it ???

Haha

Prop
Prop and the Blackhole Midget

That is the way I drive it Prop
G Lazarus

Rock on down to B and Q. "Daytona" brand 20w 50 multi grade oil is only 11 quid for 5L.

Malcolm.
M Le Chevalier

I bought some cheap 20/50 from a supermarket once for this purpose. Opened it...smelt and looked at it and refused to put it anywhere near the engine (!). Brown, and very "chemically".

Give me nice green Duckhams/Halfords 20/50 all the time. (Especially when with an oil cooler its impossible to change it all at once - without huge amounts of faff.)

Ridiculous really.
Dean Smith ('73 RWA)

Using cheap oil hopefully has less detergents and friction modifiers allowing the bed in/break in process to take place. Best is to use straight 30w oil with no additives. Give the engine some abuse then change the oil for good stuff.

Peter
Peter Burgess Tuning

Yes it's running (nicely) and all put together again. More details later, as I've got to get into the shower then cook dinner. Thanks for everyone's help
G Lazarus

Im glad you posted this...I always wanted to mix old and new parts to make the engine a survivor...but once its apart I talk myself to going the rest of the way. Goodluck with it!
Steven Devine

In for a penny, in for a pound...being im here and its apart I might as well do this, and that

Augh

Prop

Prop and the Blackhole Midget

Steven, this is no more "mixing old and new parts" than it is when changing one damaged tyre!
Guy W

This thread was discussed between 25/04/2014 and 27/04/2014

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