fixing a hole in a cylinder head?

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monkey wrench

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hi

still a new guy.

i have a basket case 71 commando, with a hole forming in one of the intake ports. ill try and attach a photo. i believe its a result of over-boring the port. this happened back in the 70's when i was 5 so details are a bit fuzzy.

my question is, what would it take to weld or braze that hole up.? drill it out and braze in the hole? if so, what alloy would likely work?

fixing a hole in a cylinder head?
 
If the ports are to large it will spoil motors low an mid range so the easy option many be get another head instead of throwing time an money at that one.
 
Repairable, yes gas or tig welding. The big problem I see is the size of the port. What does it measure in at?

If it is a 71 head, it should be in the 28-30 mm range, which is good. Largest factory port was 32mm.

More than that and much is lost in performance and as you can see material available. In this case bigger is not better.

It looks huge, which is not a good thing. Others will add to this.
 
I've seen similar defects in ports repaired with a sleeve. If this one has been over bored the flow will not be the best and maybe a 1mm wall tube pressed in could suffice to make it usable, assuming the damage is not downstream of the valve guide.
 
Can be repaired by TIG or gas welding. This is how Steve Maney welds up that area for his Stage 3 heads. Your head shouldn't require that large a lump of weld to repair.

fixing a hole in a cylinder head?


Ken
 
thanks for the info.

the inside diameter of the port is 32.6 mm. maybe its an 850 head thats been messed with.

it sounds like finding a new head is my best option.
 
It's not unheard of to repair inlet ports with aluminium putty. (Devcon or similar).

If you can find someone to TIG weld it , it's a whole lot cheaper than a new head.
 
I's use JB weld or some other epoxy and forget about it! :) It's used all the time on auto intake runners and to repair carb casting plug problems.
 
Suggest either welding or alloy putty, then inserting a metal spacer that returns the ports to 30mm.
This is the cheapest option :idea: :?: :shock:
 
mike996 said:
I's use JB weld or some other epoxy and forget about it! :) It's used all the time on auto intake runners and to repair carb casting plug problems.
Click to expand...

Yeah, why not. That and some light honing..
 
A couple of products I see recommended are Z-Spar and Devcon. From what I see I would clean out the apparent daylight hole chemically and mechanically and simply go with a suitable epoxy.

I have a few race heads with epoxy (done by others) and they have stood up fine. Comnoz can elaborate on longevity. A friend used epoxy on a HD KR but heat got the better of the epoxy. The stuff pealed off and went through the engine but he was trying to resculpture the port and reduce the cross section. I suspect most of the epoxy applications are on water cooled engines so using epoxy on an air cooled vertical twin is probably pushing the limit. It looks like you want to stop up a hole so I suspect you will have good luck with it.

Pushing in and securing a sleeve to reduce port cross section is not a bad idea but will take some craftsmanship. Taking the port from 32.6mm down to say 30mm leaves a 1.3mm thick wall that should be feathered out towards the bowl of the port. You may be in a sweet position to raise the floor of the ports with aluminum inserts and epoxy and screws. Comnoz has done this in the past and it has some merit. You can get you port cross section down, velocity increased and increase the radius of the tight turn. Extend it all the way to the manifold and then mate the "D" shaped port at the flange with a "D" shaped carb adapter.
 
JBW is great for cold welding on stuff that stays cold or but only in low stress or pure shear stress parts if heated above 300'F with intake side of head could see and inhale. Ok on exhaust side experiment as blows out muffler. I'd be interested to try to modify the head with Devon level epoxy or the melt rods Muggy Welding and others sell that can be stronger that the base alloy. I'd leave the entry over size then tapper down below 30 mm and maybe incorporate some rigdes to trip up flow around the bend.

https://www.google.com/#q=muggyweld
 
i suppose if i were to jb weld or epoxy the hole and then use a sleeve that pressed far enough into the port that it would cover the hole i'd be set.

i'm contemplating trying to drill out the hole from the outside in hopes of removing any fracture lines that may be present. its difficult to see in the photo i posted but it appears like a larger flake of aluminum is getting ready to let loose.

i appreciate the input. thanks.
 
The best input I can send your way is to locate another head. This year's jumble I saw the same head, stock ,good exh.port threads for $125. Or spend like 3 grand after all said well and done delivered ,for the D-port new head. Yes it's time for money thoughts ,as always. But if you are poorer there's always JB weld.The worst it could do is let go after a while and spit out into exhaust pipe as Steve says. Had a chunk of carb slide do that once with no damage to motor whatsoever so that's the cheap option so try it ?
 
What would be a risk try the down-dirty recovery? Inhaled epoxy depending on size, if just flakes might chip or bend vale lip or mare seat as there is steel dust in the black part of JBW, if a big hunk taking some alloy with it then likely beat a piston hole or bend valves which stick into piston. Or more likely just bounce around till combustion heated to moosh and vented out the muffler. We really would like to know if good ole JBW is up to this or not. JBW held up in Peel's hard run head to fill in gas jet cuts out pistons into p-rod tunels with flamering gasket.
JBW should self adhere and stay attached if some mechanical texture or holes or posts to grab on to. It don't take much depth and even the cracks would help it stay on plus healing the cracks. JBW is magnet attacted so might be able to place magnets opposite wall to draw it in cracks and keep from flowing out of area or mold as much or at all. It would tend to insulate head from combustion heat so similar to cermic coat function in passages. How to actually do this would be educational to think out in public. Maybe a wax plug on the guide to take up most space, clay over the seat area and pour in and hand grind shape.

fixing a hole in a cylinder head?
 
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