Corrosion on Drain Plug

[Capt. Rich]

Hello, I have a pair of Lehman SP275s. I noticed some weeping from the rear plug on the intercooler core. I went to wipe it off and noticed the bolt appeared loose. I put a wrench to it and it broke off leaving all the threads in the core. I removed the core and was able to back the thread portion of the bolt out using an easy out. I know salt water is one heck of an environment on machinery. There is no zinc anywhere on this assembly. The bolt was turned from the brass color to the pinkish electrolysis eaten color. I always thought the boat was well grounded-zinc saver installed, all thru hulls tied in, pressure brushes on shafts, etc. Any ideas on why this plug got eaten up.

[mike d.]

don't know, but see if you how much depth you have inside and if deep enough get a plug with internal threads so you can put a zinc on it and then periodically.

[Capt. Rich]

I have taken the bolt or plug to just about every marine supply and repair shop in the West Palm Beach, Fl. area. No luck in matching it. I talked with Brian at American Diesel and he did not carry any and was not sure on the threads. I know they are straight threads not pipe threads and Brian thought it was probably metric. Any thoughts on finding the right plug? If not, would there be any harm if I found a metric bolt in stainless that would fit?

[SKI]

Rich I don't know much about lehman but I did some research and they seem to have ties in the UK, maybe manufacturing? They may use a British standard parallel pipe thread British threads have rounded peaks and valleys where as National pipe(american) has flat spots on the peaks and in the valleys. If you can look at the threads closely maybe with a magnifying glass you may be able to tell. McMaster-carr has BPSS brass plugs.

[mike d.]

i believe Lehman is Ford so you could maybe check with a Ford tractor dealer
as i believe the Ford tractors used the same engines. see if a machine will be able to get thread for you. all they have to do is put the piece in a lathe and then set it to match the thread and it will tell them/you what thread it is, and probably cut you a new one

[Coachbolt61]

I have a ford lehmann 2712E and all the bolts out of mine so far have been UNC thread. Hope this helps.
Coachbolt.

[Capt. Rich]

Thanks all for the help. Great insight to what should be a simple problem. I have always said nothing to this boating stuff or just another 5 minute job, Ha Ha. But we love it. I am checking with some fastener specific companies in my area and will pass on this info and hopefully they can steer me to the correct plug.

[Capt. Rich]

Good news. I took a good plug over to a local machine shop. They machined 2 new ones for $35.00. I picked them up yesterday and they fit as well as the origional. Thanks for all the advice.