Flathead V8 Welch Plugs

Bob Moseley (RIP) · #1 03-08-04, 01:07

Hi all
Whilst happily working on my flathead the other day I was talking to another restorer mate who expressed surprise when I mentioned the Welch plugs located under the sump cover in the block. He was not aware of these. Probably most of you readers would be but these plugs are a real trap for new players. When water is found in the sump and the owner can’t find any Welch plugs in the block, they often assume its one or both of the head gaskets or something more devastating. BIG TIP – if you have your motor out, remove the sump and check and replace with brass ones. Whilst you are there it is also a good opportunity to check the oil pump.
Bob

Bob Moseley (RIP) · #2 03-08-04, 01:09

I believe this is common to the Canadian flatheads but maybe not others. Educate me please.
Bob

Keith Webb · #3 03-08-04, 03:57

It's timely - I was thinking of making one myself, having heard from John Belfield about the engine in his LP4 and another restorer with the same problem. The symptom is water in the oil, which may of course be from other troubles, but Bob's is good advice.
Looks like after 60 or so years these plugs are finally reaching their use by date.
What wonderful motors these flatheads are!

Tony Smith · #4 03-08-04, 06:44

Some people can't afford the cost of welch plugs! I've pulled one motor apart to find the hole filled with RTV Silastic, no doubt relying on the sump pan gasket and the sump to complete the seal! Gad, some people

Perhaps this might have been a field fix that should have been fixed at a later time, but the repair kept working, so it was left.
Bob, as far as international variations go I've got 3 Canadian blitz motors, 1 English Generator motor and 1 US 1939 truck motor and ALL have these plug holes on the sump face. Interestingly, the American '39 motor had these holes threaded at some time in it's life and allen key plugs now seal the holes instead of welch plugs.
Below is a pic of the silastic block. After the Silastic was removed, there remains a plie of rusty crud in the bottom of the water jacket. This leads me to think that the threaded plugs are perhaps a good way to go, clean 'em out evey time!

Bob Moseley (RIP) · #5 27-12-08, 11:53

Hi Keefy - if I knew how to link this to your current enquiry I would. However this is the information I posted on these plugs back in 2004.

Bob

Bob Moseley (RIP) · #6 27-12-08, 12:19

Hi all - just some more information on the Welch Plug.

"A Welch Plug is a round hammer-in device that is tapped into the side of an Engine Block to fill a Casting Hole that was left there to allow air to escape during the casting process".

Brief History of the Welch Plug

by Nevin Hubbard of www.hubbardspring.com

A brief bit of totally obscure history that I am one of the few living persons who knows.

My family business, established in Pontiac, Michigan in 1905, is the original manufacturer of the "Welch" plug. The Welch brothers had a motor car company at the turn of the century that was later bought by General Motors - the Welch Motor Car company. They would run the cars around Pontiac to "break them in."

At that time core holes in the engine blocks were fitted with pipe plugs. During one of these run-ins a pipe plug backed out. In order to get back on the road one of the brothers drove a quarter or half dollar into the hole. From this they developed the Welch plug, some with the help of my Great Grandfather Martin Hubbard. They then patented the plug and the M.D. Hubbard Spring Company become the sole manufacturer of the Welch plug for the life of the patent. To this day we have the largest range of sizes available anywhere.

So the Welch plug in origin is an American innovation and name.

Best Regards,

Nevin Hubbard
M.D. Hubbard Spring Company
www.hubbardspring.com

Bob

Keith Webb · #7 27-12-08, 01:50

Recently I took the sump off a Mercury V8. Hidden by the sump gasket are four small (about 11/16" or 18mm) welsh plugs. The two towards the front of the engine weren't fitted so this seems not to be a serious problem to the previous rebuilder. The holes were full of gunk and quite deep and they seem to go into the water jacket.

Has anyone had any experience of this?

A source of supply for these dished plugs in Melbourne? Once you could get this sort of thing at Repco but no longer.

Alex Blair (RIP) · #8 27-12-08, 02:21

Quote:

Originally Posted by Keith Webb

Recently I took the sump off a Mercury V8. Hidden by the sump gasket are four small (about 11/16" or 18mm) welsh plugs. The two towards the front of the engine weren't fitted so this seems not to be a serious problem to the previous rebuilder. The holes were full of gunk and quite deep and they seem to go into the water jacket.

Has anyone had any experience of this?

A source of supply for these dished plugs in Melbourne? Once you could get this sort of thing at Repco but no longer.

Keith ..
I don't know what welsh plugs are but they look like frost plug holes to me///.If the block freezes ..they pop out instead of you block cracking..very common in Canada..Can pick them up at Canadian tire the next time you are by..
Merry Christmas..
Alex

T Creighton · #9 27-12-08, 07:47

The holes all go into the water jacket Keith. Try to get some brass replacement plugs Ford part no. 741135 B ($10 at our local V8 shop)
Cheers Terry

Lynn Eades · #10 28-12-08, 00:43

Welch plugs, Core plugs, Frost plugs (Mr Frost must have been Welsh)Get with it Alex!!!

sth65pac · #11 28-12-08, 10:51

Hi Keith,

Three options:

try http://www.flatattackracing.com/
They are an Australian Company. In Victor Harbour (South Aus). You might need to email him.

Autopro are always pretty good with the small stuff. As long as you have teh Outside diameter you are halfway there (You can use the MAC's website for a reference size from their parts.....)

Otherwise an engine re-conditioner should have the size you require.

If you have no joy with any of the above, PM me & I will look into it after mid January when everyone recommences work.

Ian

Tony Smith · #12 28-12-08, 15:53

Until a Moderator takes Bob's "Hint, hint" and links This thread to this current one, may I suggest using threaded Allen Plugs? 3/4"UNC ought to do the job fine (Or should that be Coarse?).

Also, I don't think these can be regarded as "Frost plugs" as once the sump pan is secured in place, these plugs would have nowhere to go IF the coolant in the waterjackets did freeze over.

sth65pac · #13 28-12-08, 22:27

Tony,

Questions/clarification

:

Are you saying you need to tap a thread into the hole and then fit a threaded plug? I presume you would have to use some red silicone sealant to provide a gas/watertight seal.

How long is the 3/4 UNC allen plug? 1/4"? Is it a standard length.

I have this task ahead of me in the next few weeks. My engine is 'resting' on the garage floor now.....

Ian

Keith Webb · #14 28-12-08, 23:13

...for all the suggestions and help. I measured 18mm but I think 3/4" would make sense. There is only a small lip in which to nest them which is why the originals are dished rather than cupped. It's interesting just the sump gasket managed to seal this in the past - but there was a lot of gunk built up in there.

Tony, have you tried the allen plugs? I would have thought they were too deep to fit.

Bob Moseley (RIP) · #15 28-12-08, 23:40

Thanks for your comment Tony. I cannot believe the lack of knowledge of such a basic engine componant, although I must admit I haven't heard of or seen an Allen Plug. Welch plugs are readily available but if possible try to obtain the brass ones as most originals were steel. They are simple to fit, merely place them in the hole in the block with the concave surface to the outside and then expand the plug using a hammer and a drift. A touch of gasket cement around the edge of the hole wouldn't go ammis either. In the meantime read my thread on these or get that thread linked.

Bob