Hole in Twin H manifold

JasonNC

While adjusting the carburetors on my Twin H engine, I noticed that I had developed a leak in the manifold.  It looks there are three small plugs in the lower part of the manifold and one of those plugs has developed a thumbnail size hole in it.  Can these plugs be replaced or will I need another method of repairing the hole?  I have attached a picture of the manifold looking from beneath the manifold.  Any help will be greatly appreciated.  

charles4d

Could get it welded or use jb weld a two part puddy when mixed become harder then steel and heat won't harm it

JasonNC

Thanks Ken,

I hope the O'Reilly Auto in my area has them.  Your stores in Texas seem to have more stuff than the store down the street....

Frankvintagefullflowcom

They are quite common so acquiring them shouldn't be a problem.......what is a problem is removing the remains of the existing plugs, cleaning the hole counterbores (the plugs seat against a shoulder) and driving the new ones home in an inaccessible area. Removal of the manifolds is the best way to accomplish that but adds to the project. Removal of the inner fender panel may work just as well. I have found that the thickness of the cast iron in the bottom of the counter-bore can be quite minimal, I suppose due to core shift when cast. It wouldn't be too hard to shear off the ledge in that case.

Frank

JasonNC

The plugs that the O'Reillys here in NC had in stock were slightly different than the ones that Ken recommended in that they don't have shoulders.  If they are not the right type, then I guess I'll have them order the right number plugs from another store.  Currently I'm in the process of removing the manifold.  Once again, it never fails to amaze me how the writer of the service manual makes this job sound so easy.  "Just simply remove the 14 nuts holding the manifold in place."  If I were a vengeful person, I think I'd go urinate on that guy's grave....

Glowplug

Jason- the plugs DO NOT have shoulders. The sides are smooth in the plugs. The shoulder is cast into the manifold in each hole.

Frankvintagefullflowcom

Correct. They are sometimes known as flat plugs but are actually somewhat convex from the outside.....uh, side. They are not a cupped plug. There isn't room for that type in those holes. The flat ones rely on the expansion of the plug when driven into place which is why I warned against shearing off of the floor of the counterbored hole. It takes a pretty good whack in the center to expand them. It should look like this:

.

The NAPA # is SEP 3811006 if you're near a NAPA store.

If you don't like what manuals say, just wait 'til you get to where it says "assembly is the reverse of dis-assembly". That's never quite true. It has become a bit of a joke around here.
F

JasonNC

Frank, Were you able to get the correct plug from NAPA? If so what is their part number?

JasonNC

Didn't see the line about the NAPA # on your last text because I was trying to read this from my iPad.  I'm back on the computer.  Thanks.  

JasonNC

I am thinking about having the manifolds sandblasted while I have them out. In light of the post about the cast iron of the counterbore being minimal, should I forego sandblasting or at least have it done before the old rotten plugs are removed.

Glowplug

Remove all the plugs. Once the plugs are out, use these openings to access the inside the manifold with long scraping tools that will allow you to remove built up carbon inside the manifold. Removal of the carbon is an essential part of restoring the manifold. Cleaning the manifold with a motor driven wire brush obtains a better outcome than sandblasting.

Frankvintagefullflowcom

Jason,

I didn't mean that the C/I is definately thin there, but that it should be taken into account before re-installing the plugs. Some may be, others not. By the time you get through cleaning the exhaust passages in the intake manifold, you'll have a good idea of that. Tedious job.

F

iceblade10

What is the technique for installing these plugs?  Whack 'em in the center with a large punch or something, so that they expand into the cast shoulders?

I just acquired a twin-h manifold that is missing EVERY plug... :-)

JasonNC

I just had the muffler shop install five new plugs in my manifold (one had been replaced with a bolt and we were afraid to take it out). Naturally on the last plug, the manifold broke when he tried to punch a hole in that plug,  We patched with JB Weld steel putty,  We'll see what happens. 

Frankvintagefullflowcom

Hmmmmmmmmmmmmmm.

JasonNC

Looks like I'll be doing an engine transplant soon....

JasonNC

The bolt that is mentioned in the comment above fell out, but the other plugs are holding up well.  The hole that needs a new plug, despite having a bolt JB Welded in it, looks to be in good shape.  At least the new plug I bought seems to almost fit perfectly.  This hole is located at the front of the manifold and is accessible, in my opinion, without necessarily taking the manifold off.  I’m thinking I can clean the hole out with a wire brush and taping the plug to the entrance of the hole to hold it in place long enough to give it a good whack from underneath.  If anyone thinks this is a bad idea, speak now or forever hold your peace.