cast iron exhaust port fix?
Moderator: Team
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turboshelby
cast iron exhaust port fix?
hey folks,im a little new here,im hoping someone has a idea that will work for me.i have a cast iron head that was broken through about the size of a bb,heres what i have done so far,i took to a local dude and had him weld it(with nickel rods)and first time he did it,i pressure tested it and it still leaked,so i took it back and he rewelded it while i waited(i thought your supposed to heat it up and then weld the head)he said it he thought it wouldnt leak,so i stupidly said it was probalby ok,i took it to polydyn and had them coat the exhaust ports to keep heat away from the already thin exhaust ports,when i get it back it looks like the spot he welded on top of collapsed and i havnt tested it yet,but im willing to bet my left arm it leaks.can this be fixed?can i have the polydyn rewelded?i have heard epoxy is no good on the exhaust side,what do you guys think?
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bill jones
- Guru
- Posts: 2650
- Joined: Sun Sep 05, 2004 6:38 pm
- Location: salt lake city, ut
- Contact:
-From all the cast iron weld repairs I've seen and having brazed up heads myself and seen how easy it really is once you have the equipment, I would never waste any time on anything else.
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-The coatings I don't know about but I would grind the coating away all around the wound, and I'd grind away all the sh-t the other guy tried to put in there even if you have to open up a a dime sized hole to fill.
-I'd fabricate a tin foil tent oveer the head with a hole at the top to allow the heat to circulate and I'd make it so that you could open up a smnall door in the tent near the wound so that you can get the torch in there.
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-Then preheat the head in a barbeque grill for an hour or so until it's at 350 to 400 degrees F (check it with a tempil stick) then braze around the the hole and finish the weld in the center of the wound using 3/32" coated brazing rod.
--You don't just weld the entire hole in one shot, you need to run the torch around and about the wound to get heat spread out several inches and then you stop and daub a short amount of brass lift the torch and spread the heat again for a moment, then drop another daub etc.
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-I use a rear exhaust die grinder and grind away the excess brass and verify that the integrity of the weld doesn't have any pinholes.
-Then let it slow cool down for several hours or even until the next morning.
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-If you are doing it for the first time you need to practice on a similar repair and make sure it doesn't have bubbles in the brass.
-One of the problems is, if the location of the hole is on a side wall you'll need to stand the head up to do the best job, and that is a problem with a barbeque grill
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-The coatings I don't know about but I would grind the coating away all around the wound, and I'd grind away all the sh-t the other guy tried to put in there even if you have to open up a a dime sized hole to fill.
-I'd fabricate a tin foil tent oveer the head with a hole at the top to allow the heat to circulate and I'd make it so that you could open up a smnall door in the tent near the wound so that you can get the torch in there.
-------------------------------------------------------------------------------
-Then preheat the head in a barbeque grill for an hour or so until it's at 350 to 400 degrees F (check it with a tempil stick) then braze around the the hole and finish the weld in the center of the wound using 3/32" coated brazing rod.
--You don't just weld the entire hole in one shot, you need to run the torch around and about the wound to get heat spread out several inches and then you stop and daub a short amount of brass lift the torch and spread the heat again for a moment, then drop another daub etc.
---------------------------------------
-I use a rear exhaust die grinder and grind away the excess brass and verify that the integrity of the weld doesn't have any pinholes.
-Then let it slow cool down for several hours or even until the next morning.
-----------------------------------
-If you are doing it for the first time you need to practice on a similar repair and make sure it doesn't have bubbles in the brass.
-One of the problems is, if the location of the hole is on a side wall you'll need to stand the head up to do the best job, and that is a problem with a barbeque grill
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turboshelby
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bill jones
- Guru
- Posts: 2650
- Joined: Sun Sep 05, 2004 6:38 pm
- Location: salt lake city, ut
- Contact:
-The first head I ever brazed was a 391 ford truck head that someone had dropped the milling cutter and broached an ugly groove across the face of the head.
-That was a real bitch to get enough heat into it to without an oven so we used some firebrick and heat blanket and several torches to heat the head and another torch to do the actual brazing.
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-I was showing a guy how to port his SBF heads and he ported thru a side exhaust wall while I was out of town and when I got back he had brazed the head himself.
-I asked him what happened and how he did it and he said he just ground out the hole, warmed up the head standing it up on end on the bench and "I just brazed it up" like it was no big deal.
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-The hardest repair I ever did was on a BBC cast iron head where a rocker stud pedestal had broken off, and the problem with that was the total mass and surface area of the repair required a ton of heat to get the brass to flow.
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-Brazing the small holes in most port walls is fairly easy but the work is all in the preparation of the wound and having a dedicated "head barbequer" and then the experience of doing a couple of those repairs is nice to know.
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-The most significant brazed head I ever did was cracked thru the chamber, thru one side of the sparkplug hole, out and thru one head bolt hole towards the rear of the head, and across the exhaust shroud and out thru thru the rear of the water jacket to the outside of the rear of the head, where there was only about 1/4" of metal actually holding that entire corner of the head in place.
-This was something like 10" of total brazed length to salvage that head and the actual brazing time was only something less than 22 minutes.
-That head has run 4000 laps to date and I just brazed up the the cracked rear main cap on both sides to salvage the block.
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-Depending on where your hole is it could be pretty easy to fix.
-That was a real bitch to get enough heat into it to without an oven so we used some firebrick and heat blanket and several torches to heat the head and another torch to do the actual brazing.
--------------------------------------------
-I was showing a guy how to port his SBF heads and he ported thru a side exhaust wall while I was out of town and when I got back he had brazed the head himself.
-I asked him what happened and how he did it and he said he just ground out the hole, warmed up the head standing it up on end on the bench and "I just brazed it up" like it was no big deal.
--------------------------------------
-The hardest repair I ever did was on a BBC cast iron head where a rocker stud pedestal had broken off, and the problem with that was the total mass and surface area of the repair required a ton of heat to get the brass to flow.
------------------------------------
-Brazing the small holes in most port walls is fairly easy but the work is all in the preparation of the wound and having a dedicated "head barbequer" and then the experience of doing a couple of those repairs is nice to know.
----------------------------------
-The most significant brazed head I ever did was cracked thru the chamber, thru one side of the sparkplug hole, out and thru one head bolt hole towards the rear of the head, and across the exhaust shroud and out thru thru the rear of the water jacket to the outside of the rear of the head, where there was only about 1/4" of metal actually holding that entire corner of the head in place.
-This was something like 10" of total brazed length to salvage that head and the actual brazing time was only something less than 22 minutes.
-That head has run 4000 laps to date and I just brazed up the the cracked rear main cap on both sides to salvage the block.
-----------------------------------------
-Depending on where your hole is it could be pretty easy to fix.
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sheppard00
- Member
- Posts: 83
- Joined: Sun Jun 19, 2005 6:39 pm
- Location: Texas
here is another option since I have seen brazing melt through in the exhaust ports....
they sell a castiron welding rod for torch welding that requires a special flux.. you have to cheal the head throughly where the problem area is and remove all of the other material or contamination when it is cleaned you will want a hole or small gap 1/16 or so wide or the size of the bb like you said the problem is so that the weld pool can get full penitration... put the head in a grill for an hour or so like Bill said. when the head is between 400 and 500 deg pull it out and take the torch to the area to be welded till it turns red... then heat the cast iron rod till it is red and dip it in the flux powder. the flux will stick to the hot rod... return the torch to the head and heat the hole or weld area just untill it starts to look glossy then add the rod with the flux you can work the molten pool around with the torch so that you know that there wont be any holes.. somtime you have to clean it off and make more than one pass to get the metal built up like you want it... after the welding is done put the head back in the grill and put the heat on low.... let it cool in there untill the heat stops droping then put it on just one burner. after that just turn it off and leave the head in it so that it can cool as slow as possible
hope this helps
the cast iron welding rods are around $2.50 each but you should only need one for that small job
mark
they sell a castiron welding rod for torch welding that requires a special flux.. you have to cheal the head throughly where the problem area is and remove all of the other material or contamination when it is cleaned you will want a hole or small gap 1/16 or so wide or the size of the bb like you said the problem is so that the weld pool can get full penitration... put the head in a grill for an hour or so like Bill said. when the head is between 400 and 500 deg pull it out and take the torch to the area to be welded till it turns red... then heat the cast iron rod till it is red and dip it in the flux powder. the flux will stick to the hot rod... return the torch to the head and heat the hole or weld area just untill it starts to look glossy then add the rod with the flux you can work the molten pool around with the torch so that you know that there wont be any holes.. somtime you have to clean it off and make more than one pass to get the metal built up like you want it... after the welding is done put the head back in the grill and put the heat on low.... let it cool in there untill the heat stops droping then put it on just one burner. after that just turn it off and leave the head in it so that it can cool as slow as possible
hope this helps
the cast iron welding rods are around $2.50 each but you should only need one for that small job
mark
mark sheppard
I may not know, but I can find someone that does.
I may not know, but I can find someone that does.