Head Repair Resource

Production K Models

Head Repair Resource

Postby MattInDillsburg » Fri Dec 08, 2017 9:37 pm

I have what seems to be a typical head crack across the spark plug hole. From reading various posts, this seems to be common and fixable. Does anyone have a good resource for fixing it?
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Crack in head
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Re: Head Repair Resource

Postby EKHKHK56 » Sat Dec 09, 2017 4:50 am

Hi. I just got my Mill and Lathes all restored. New motors, switches, wiring & 220v. Now I can repair cases, heads, etc again. Have a stack of heads I just started on. Some real butchered trade ins, etc. Looks like several cracks on this. The thing is to have factory heads to copy critical combustion chamber shapes and sizes after welding. You have to relieve deep into the cracks than stitch up. Preheat to 200 before welding. Slowly cool. I can do it but time and materials is all I'll venture for price. If it needs any clearancing above valves now's the time. Quick clay check will tell you. Erik K
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Re: Head Repair Resource

Postby MattInDillsburg » Sat Dec 09, 2017 12:08 pm

What about products like HTS-735 II, do they work for such repairs?
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Re: Head Repair Resource

Postby EKHKHK56 » Sat Dec 09, 2017 2:29 pm

I have an aircraft shop weld them up. They use TIG but i'm not sure of filler rod type. I do the machine finishing in the chambers.
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Re: Head Repair Resource

Postby Coolbreeze » Thu May 03, 2018 2:41 am

My big question is: "How long do these repairs last?" I have a few heads that I would love to get back into shape, but do not want to have a failure when I am hundreds of miles from home. I ride long miles and camp -- or at least plan on doing so. My goal is to make my '56 KHK the bike it should have been when it left the factory.
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Re: Head Repair Resource

Postby chuckthebeatertruck » Wed Jun 06, 2018 12:36 pm

Let's start this off right: I have NEVER repaired a K model head.

However, I have repaired a fair amount of alloy heads over the years.

When I did my first head about 25 years ago, I struggled to find a welder that didn't create a "hard spot" from the filler rod. Today, that's not as much of a challenge.

But, your question about length of service is a very, very good one.

In my case, I was flipping through an old book when I came across "cold stitching." This is a method of cylinder, water jacket, and head repair originally developed way back in the early 1800s for steam engines! It is still used today to repair engine blocks in some cases.

The concept is pretty simple. You start by fully identifying the crack. You then drill your first hole outboard of the crack terminus. Thread the hole you just drilled, and then thread in a rod of material that is the same or similar to the parent material. Cut it flush, peen it over. Then, you drill another hole, overlapping at least 50%, and repeat until you get to the other crack terminus. The end result is an overlapping set of circles -- all threaded into the parent material and locking each other in place. Strong as all get out and very low-tech.

I did a set of 914 heads like this in 1996. The crack ran right across the valve seats. I couldn't afford to pay a welder the $200 necessary to get it sorted and buying used heads were out of the question too. But, I had a machine shop at my disposal and lots of scrap aluminum. It took ages and reshaping the port and cutting the seats was a pain, but it was returned to service and I sold the car to an acquiantance. Last I heard, that motor was still going.

I would only do this method today if I couldn't get a really good welder to fix it . . . technology and techniques have really improved in the last 20 years.
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Re: Head Repair Resource

Postby 55panman » Thu Jun 07, 2018 10:08 am

Erik, Regarding your advise on welding alum. heads. You say you have to relieve deep into the crack. You HAVE to make sure the crack is completely gone. If you DON'T it WILL return later. Much of the time that means going 100% through to the other side. The crack may not look like it comes through to the other side but as you put heat to the metal the crack may propagate through to the other side and will, as I say return after you've put the part in service. I was a Boilermaker, Nuke certified high pressure steam welder by trade. One tool we used quite often is NDT (non destructive testing) Dye Penetrant, to check for cracks in a weldment. It's a 3 part, spray can, operation. Not real pricey, and you can get it at a welding supplier. One can is cleaner, you spray on let it sit per instruction. Then you spray 2nd can of penetrant, which is red in color. Let sit per instruct, then wipe off. Next is spray of developer, which is white in color. Any cracks remaining will show up as a fuzzy or distinct red line. We used on stainless and alloys that we couldn't mag particle test. But it works well on aluminum. Another trick I learned from a buddy who runs a sidecar Panhead at El Mirage and Bonneville, who was a aircraft mechanic. Heat your casting to 350 degrees in oven, I use an old gas grill, and hold it at that heat for 3-4 hours, then shut off grill and let cool. This works to stress relieve. Get temp sticks also from weld supplier. They are like a crayon, and they come in all degrees for checking temperature. As parts heat you rub the 350% stick on metal and when it gets to temp the stick will melt. Reduce heat and keep at that temp. I've found that Panhead cases that would keep cracking when I tried to weld using all know strategies, became weldable after this treatment. Also it really DOES help to go slow weld a little then stop and peen the weld with slag axe or whatever. I use an air chisel with a rounded pointed end to peen. I originally thought you just use peening on cast iron, but a guy who repair race car heads told me this. On weld wire I usually use 4043, but I've found if you're having hot short cracking problems, 4047 can help to stop cracking. This wire you may have to order and is more expensive, but I've also found it works. Hope you find this informative, and NO I do not take welding projects, I have 3 K's a KR, 2 XR750's, changes to my Bonneville Panhead, and 20 some other bikes of my own to get built. Ron L.
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Re: Head Repair Resource

Postby 55panman » Thu Jun 07, 2018 10:10 am

Oh, I have successfully repaired a number of K model heads.
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