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MG Midget and Sprite Technical - Miles on the clock versus Rebore

When is a rebore generally required on a 1275cc CE engine, mine has done an original 90k, just wondering if this mileage suggests that a rebore is imminent or not.
J Bond

had my 12CC 1275 bored out +30 thou at 109000 miles
David Cox

Do a compression test. Reasonably accurate testers are quite cheap and with proper use can tell you a lot about the engine condition.

90k is quite high for an original A series engine but a lot will depend on how those miles have been driven and how frequently the oil has been changed.
GuyW

Thanks, I will carry out a compression test, any recommendations for a suitable tester to use?
The oil level never seems to decrease and the exhaust doesn't exhale any blue smoke.
J Bond

If it ain't broke don't fix it springs to mind!

I wouldn't even bother with a compression test, if it goes ok, oil pressure is good, doesn't smoke or use oil then surely it must be fine? If you do a test and the figures say it's worn out are you really going to rip it apart when it sounds like it's running fine?

Just keep doing whatever good work has been done over the years to get it to 90k!
John Payne

Agree with JP. Change the oil and filter at whatever the book says, use quality oil, don't thrash it, check vv clearances and timing every 5000 or so, use decent fuel, change coolant at whatever book says.
Oggers

It's not using oil and it doesn't smoke from the exhaust, so I guess it runs well. LEAVE IT ALONE!

It's quite impossible to say that any type of engine will need a rebore at X thousand miles. How much the engine wears is dependent on so many things, like how it has been driven, how much maintenance it has received, whether it has done mostly short trips or long journeys, etc, etc.
Mike Howlett

Did my 1500 engine at 58000 miles. It ran well but I could see some scoring in the cylinders. The fellow who did the work was an MG factory trained mechanic and when it was apart, he did say it was pretty tired inside. He said these engines, 1500s maybe, weren't like today's engines and not expected to do 100,000 miles plus. With that being said, my daily driver is approaching the 200,000 mile mark soon!!

Clive from Canada
Clive from Canada

There don't seem to be any obvious signs of needing a rebore.

Our original Minor 948 engine from 1958 was rebored by the first owner to 0.030" at 30,000 miles in 1962 because of wear (oils then were nothing like they are today).

My family bought it in 1965, and I had it bored out to +0.060" in 1970 at ~50,000 miles, for reasons totally unrelated to bore wear.

The crankshaft was exchanged for a BMC unit in 1967, and the exchange unit had all standard journal sizes.

The engine was then well modified with a 12G 295 head, 2A 948 camshaft, HS4 SU, LCB exhaust etc. It was removed in 1992 at 99,000 miles, to be replaced with the current 1380, and there were no visible signs of bore or crankshaft wear at that time. I always used a top quality oil in it.

It sat in our garage until ~2012 and is now fitted into a Frogeye. The current owner says that oil consumption is minimal, and the oil pressure is excellent.

Unless there is something indicating a need to rebore - scoring etc., I would leave well alone!

Richard
Richard Wale

This thread was discussed between 20/05/2018 and 23/05/2018

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