twin H manifold plugs

[Deleted User]

Has anyone ever had to replace the six plugs on the underside of a twin H manifold ?? They're about the size of a quarter or so, and look like mini frost plugs. What would the purpose of these be ?? Could they be casting aids, or maybe expansion reliefs ??



I bought an ebay twin H manifold a few months back, that turned out to have major cracks in it where you couldn't readily see them, as well as two of these plugs rotted right through in the centers. Since it cost me about six hundred bucks, I'm trying to salvage it by welding the cracks with special rod, and fixing these plug thingys. Would I dare pop out the old plugs and just weld these holes shut??



I'm a little spooked about cracking due to dissimilar metals expanding at different rates, etc.



Anyone care to offer some advice on this ??



silverone

Unknown

The plugs are the same as the freeze plugs in the block. Most engine rebuilders or stationary engine shops will have the plugs you need. removal is same as larger plugs... poke an awl throught the middle and pry out. Good Luck. I am no welding expert ... but I believe if the manifold is heated and the right cast iron rod is used the repairs can be done and are permanent. Once again best of luck with the repairs.

[Deleted User]

Thanks Ken, I'll pass this info on to the body shop doing the work for me. Hope they haven't screwed up yet and welded the holes shut or something.



silverone

hudsonguy

silverone wrote:

Has anyone ever had to replace the six plugs on the underside of a twin H manifold ?? They're about the size of a quarter or so, and look like mini frost plugs. What would the purpose of these be ?? Could they be casting aids, or maybe expansion reliefs ??



I bought an ebay twin H manifold a few months back, that turned out to have major cracks in it where you couldn't readily see them, as well as two of these plugs rotted right through in the centers. Since it cost me about six hundred bucks, I'm trying to salvage it by welding the cracks with special rod, and fixing these plug thingys. Would I dare pop out the old plugs and just weld these holes shut??



I'm a little spooked about cracking due to dissimilar metals expanding at different rates, etc.



Anyone care to offer some advice on this ??



silverone

These are simply 'core plugs'. They are necessary in the sand casting process used to make the manifold. The same goes for engine blocks. They're incorrectly called freeze plugs, or frost plugs, but they're really simply core plugs. I don't know how they got their freeze plug name, but have you ever seen one 'pop out' from freezing water inside?



You should be able to pick up replacements from your local auto parts store by measuring the diameter.



Good Luck,

Doug

nick s

silverone wrote:

Thanks Ken, I'll pass this info on to the body shop doing the work for me. Hope they haven't screwed up yet and welded the holes shut or something.



silverone

not to say your shop can't handle this, a "body shop" probably dosen't have the experience you need in making the repair. even welders who weld cast iron often will give a skeptical prognosis for such a repair. propper preparation, rod, pre-heat and post-heat are all critical if the repair is to hold up. done properly it should hold especially if your repairs are in the intake rather than the exhaust.



good luck with this

Park_W

hudsonguy wrote:

These are simply 'core plugs'. They are necessary in the sand casting process used to make the manifold. The same goes for engine blocks. They're incorrectly called freeze plugs, or frost plugs, but they're really simply core plugs. I don't know how they got their freeze plug name, but have you ever seen one 'pop out' from freezing water inside?



You should be able to pick up replacements from your local auto parts store by measuring the diameter.



Good Luck,

Doug

Yes, I HAVE seen "freeze plugs" pop out when water froze in the block! (Yeah, I know, why didn't I have anti-freeze in it. Duuuuhh!) LOL.

[Deleted User]

I rushed down to body shop this morning hoping they hadn't started "experimenting" with my manifolds, by trying to weld them, but no luck ---- they had them messed up big time !!! Their attitude was that if they couldn't fix them, they were junk anyway, so why not try

---

but I had other ideas and did not appreciate their efforts one bit !!



Sooo --- off I went with what was left of them to see an old time welder friend I've known for eons, and between him, me, and our friendly welding supply salesman, this is what we're going to try.



Firstly, the salesman told us not to do the usual procedure with cast material, which is to heat it up to high temperature before welding, as the temperature will fluctuate too much from end to end, due to the complex shapes of the thing, and we may wind up with some misalignment of the flanges after cooling.



Secondly, he says DO NOT GRIND OUT THE CRACK with a disc grinder, -- because you will be impregnating the surface area of the material with minute particles off the grinding wheel which will cause the weld to "bubble" as it mixes the metals, and become porous as it cools. Apparently the only way to prepare the crack is to use a special gouging rod, (the number of which I forget right now), that is specificlly for cast material, and performs in such a way that you actually have to "push" the molten material out of the way with the rod, rather than "blow" it away like you would with regular rod. Apparently this special rod also leaves some kind of film over the newly exposed surface as well, keeping it protected until you weld it.



Thirdly, he says to drill a small hole right at each end of the crack before welding, so that it will not continue to travel when you start welding.



Then, you use another special rod for the welding process. (made by arctec) and weld small areas at a time, keeping the surrounding material as cool as possible as you go, sort of like welding thin sheet metal in body work.



So this is what we're gonna try, and I'll keep everyone posted as to whether it works or not, as well as get the specific numbers of what rod we use.



Wish me luck, ---- if this works, there's a lot of old manifolds out there that will find new life once more.



silverone