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MG MGB Technical - max overbore on goldseal engine

Was is considered to be the max over bore on a sleeved goldseal engine please.

Mark
Mark Dollimore

good question!

theoretically a factory gold seal engine should be capable of taking any overbore available (or recommended) at the time. AFAIK that was +40.

Perhaps Mr Hunt, Burgess, or Gilmore know with some certainty. Gents?

Best of...
MGmike
M McAndrew

Goldseals were sleeved back to standard - they can be bored out to +20 on the original sleeves or you can bore the sleeves right out and go to +80 (1892cc) or +130 (1950cc)

You may need to sleeve the bigger overbores - it depends on the quality of the casting and whether the boring uncovers the mild steel straps between 1&2 or 3&4 cyls.
Chris at Octarine Services

Chris, interesting thought. What was the bore required to insert the sleeve? could I go to +60 as I have a nice set of rods and pistons this size?
M
Mark Dollimore

Hi Mark you cannot go to +60 on standard Goldseal liners. We understand not all Goldseal are linered blocks. When BL started using Qualcast in Leeds for the blocks in early 70s blocks were so poorly made with porsoities/inclusions in the bore area that to salvage the blocks liners had to be fitted. This means the Goldseal engine manufactured this way were new not recon! Because of the origin of a Goldseal with liners I would liner the block for whatever size you go to. Chris is on the button with +20 max. The chaplets Chris mentions were core supports and can show up on 1950s, I have seen engines run ok on these but not a good idea. All the above reasons plus the better quality of the spun cast iron liners is why we liner all our B blocks.

Peter
Peter Burgess Tuning

I dismantled, last year, what was documented as a gold seal engine. Certainly no liners, but I suspect the engine was just a minimum re-bore and sprayed gold. I understand this practice was rife as gold seals had a good reputation. So beware paint isn't everything!!!!
Allan Reeling

Mark - no you can't bore out a standard new liner to +60 - it would leave a liner thickness of only 22.5 thou.

1950cc liners are 41 thou to big an internal bore to start with and they need boring/honing out anyway.

If you really want to use the pistons you have then get your local machine shop to bore out one cylinder to +60 and see whether the bore cleans up - they should be able to advise whether they consider the block suitable to run without liners.

However unless the pistons are new it is false economy - they may look good but still be worn on the gudgeon pin and in the ring lands.

Chris at Octarine Services

Not conclusive as they can be faked, but the engine number on a correct Gold Seal has a different prefix - 48G in most cases, BHM in the last years.
Paul Hunt

Brilliant responses everyone many thanks
Mark
Mark Dollimore

This thread was discussed between 03/11/2013 and 04/11/2013

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