Posted: Tue Oct 21, 2014 6:59pm

From Zoot-C The op mentions "core plugs" I have a leak from a core plug behind the alternator (no 65 on page a4 of the available service manual pdf) How do you repair a core plug leak? does it need replacing? If so how?- or can you temporarily use some sort sealant to stop the drip until a proper service by a proper mechanic - if so what's a good product for a temp repair? Thanks

Posted: Tue Oct 21, 2014 7:08pm

The poster added this to a question that has nothing to do with core plugs so I have reposted here to keep things on topic. If your BMC is running without a pressure cap on the cooling system then pushing some silicon or some such over the leak may hold it. However if there is a pressure cap then the coolant pressure is likely to blow the sealant off. You could try something like Radweld or Barssleak actually in the cooling system. Your plug might be a core plug (slightly dished) or a Welch plug ( a shallow cup. Both are dealt with in a similar way. The old plug is punched or drilled through, a bar inserted into the hole and then levered so the plug twists out. If its a Welch plug spread some gasket sealer around the edge and gently tap into the hole in the block. If its a core plug do the same with the sealer but the plug is just placed in the hole tight against the lip with the plug dish outward. Then use a drift to slightly flatten the dish. This will expand the plug and make a tight fit.

Posted: Wed Oct 22, 2014 12:54pm

Many thanks for the reply and moving the post to a new thread. The core plug in question is hidden behind the altenator (no 65 in the image from the workshop manual.) so a bit of a pain to get to to repair what at the moment is a very slight leak. The core plug is a flat disk slightly recessed into the engine block, and painted with the same metalic blue paint as the rest of the engine - which is a 1980's vintage - marinised by a firm in Nottingham The water system is pressurised. So I'll go for the readweld solution and see how it goes Thanks again for your prompt reply very much appreciated.

Posted: Wed Oct 22, 2014 5:14pm

The alternator will have to be taken off to gain access to that core plug. Its turn the master switches off,three bolts, lift the alternator clear and lay down still with cable connected (or note where the cables attach and move the whole things away). The trouble is that both core plugs and Welch plugs rust through with a pin hole but the whole area around the pinhole is likely to be very thin. Also if one plug has failed the rest may well be in a similar state but still waterproof. There have been so many different BMC marinisers and re-builders over the years it is very hard to be sure exactly what you have. it sounds like a core plug but may not be. For other readers. Please do not post pictures on the forum, They get reduced so much it is useless. It is better to email me directly (Tony@TB-Training.co.uk).