Engine rebore

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Flemming
Posts: 15
Joined: Fri Apr 06, 2007 2:11 pm
Location: Denmark

Engine rebore

Post by Flemming »

We are planning an overhaul of the engine of our 1934 SV 2-seater as the compression was quite poor, and it was being seriously outpaced by our Austin Seven (1936 Ruby Mk1), and as we all know that is not how it was supposed to be :( (the Austin engine had an overhaul a couple of years ago). I would be grateful for any advice/opinion on the following:

The engine is currently bored out to approximately 59mm, i.e. 2mm or 0.080” oversize. What are the chances that a rebore to 0.100” oversize will be possible? Should I expect that “sleeving” with liners will be necessary? (We had the Austin bored out to 0.080” and from what I learned then that was the maximum oversize that one can expect on the Seven engine, with a few percent failing (penetration of the cooling channels)).

An alternative of course would be to go for new rings only. Unfortunately we don’t have the proper tools to measure the inside diameter of the bore where it is worn, but there is a distinct edge where the piston turns at the top. Inserting one of the rings and measuring the difference in the gap in the ring when positioned above and just below the edge indicates a difference in circumference of about 0.4-0.5mm i.e. around 0.15mm (0.006”) wear on the diameter. Any opinions on how bad that is – would new rings be sufficient? (a contemporary Danish Morris 8 book says that any wear in excess of 0.07mm requires a rebore).

Are there any recommendable companies in UK which has experience with renovating Minor engines (rebore, new valve guides, etc.)? I’m sure I can find a company here in Denmark that is willing to do the job, but none with experience in the Minor engine, so combined with the current exchange rates it might be attractive to have it done in the UK. We had the Austin engine renovated in UK by John Barlow, and that was a very positive experience.
Ian Grace
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Re: Engine rebore

Post by Ian Grace »

Hello Flemming,

My personal opinion is that a sleeve back to standard with new pistons would be the way to go here. I doubt whether reboring to +100 thou would be a good idea, and I don't think pistons in this oversize are available. Re-ringing with that amount of wear might also be a waste of time and only put off the evil day by a thou or so anyway!

if you want to bring the engine over to the UK, I think that Sutton Rebore (in South London) would be a good option, and not too distant from the channel ports.

36 Lind Road, Sutton, SM1 4PN
(+44) 208 6425685
suttonrebore@btconnect.com

Your best bet would be to talk the options over with Sutton before hauling the engine out. If Sutton don't have the pistons or the liners, these are available from Mike Dowley at Sports & Vintage Motors (+44) 1939/210458 http://www.sportsandvintage.co.uk/ sales@sportsandvintage.co.uk

Good luck,

Ian
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