Cylinder Head Cracks
I have a matching numbers, perfect XK120 SE OTS. The car had been overheated a long time ago, which is why the car only has 54 K miles on it. When I got the car prior to the restoration, the cylinder head had a small crack on number 2 cylinder between a water passage and the valve seat. The head was also warped about .025". I had a good machine shop see what they could do about it. The head was actually straightened in an oven at 840 deg F. They later drilled and tapped some plugs into the crack. The head was then rebuilt, and I was told pressure checked. I installed it on the car and it seems to work fine, but I loose antifreeze. About every time I fill the car with gas, (250 miles) the water level is dangerously low. I know this because there is a point where the temperature gauge gets erratic (The probe is in the radiator on these cars.) I recently put 20 psig of air pressure into #2 cylinder, and I will slowly get an air bubble out of the radiator. (not a good sign.). I know I spent several thousand dollars trying to save this head, but I really would like to replace it, especially now since I must remove it again. The options as I see it are: 1) I understand that at 1 time, Bill Tracy had unmarked cylinder heads (now where did he get these from?) He did say they had different core plugs than the originals (the screw in plugs between the spark plugs). maybe these could be changed with my originals? 2) I know that C type heads were available, and I do not think that they carried the same engine numbers, but I am not sure. This may also mean that I would need to change the 1.75" carbs and intake for a 2" set up. This would be quite costly, but may be worth it if I could find the C head and set up etc. I do not know if they supplied C heads with 1.75' carbs. 3) Find another SE head, but the numbers won't match, and this could be a great loss in value. Do you have any insight into this, or where I could go for help? - Hugh Leidlein
Hugh, I can help answer number 2. C type heads were run with either the 1.75 H6 and 2.00 H8 carbs. Was the crack too bad to be welded? I have seen entire chambers welded and ground back to orginial shape. - Cleo Bay Jr., 52 XK120 OTS, 56 XK140 OTS
Once, many years ago, I had occassion to repair a damaged cylinder head using high-temperature epoxy resin. I had dropped a valve and dented the hemispherical combustion chamber. A company (which is still in business) makes an epoxy product called Bi-Pax or BiPax, with various blends of epoxy distributed in appropriate sets of resin and hardner (search the web or an industrial supplier like W. W. Granger for sources). I plugged the dents with the stuff (which was red in color); two years later when I removed the head to install a gold head (this was on an XK-140), the epoxy was still in place! Another timeI used some to repair an intake manifold where I had bored 1 3/4" out to 2" (for larger carbs) and accidently punctured the water passage. Same stuff, same duration! In your case, I'd counter-grind the crack so the epoxy would be mechanically locked in place, were I to choose that solution approach. A better and more permanent solution would involve removing the valve seat, welding up the crack with either heli-arc or Lumiweld, reboring the valve seat area, and fitting a new valve seat (might have to do several; aluminum conducts heat throughout the area very well). Might have to retrue the head then, too; too much milling might necessitate the use of two or more head gaskets to reach a desired compression ratio. Were I you, I'd take the latter approach, but the former might also do, if you don't stress the engine too much afterward. Best of luck; this way you'll keep the consistant numbers! - Larry Schear, Twin Cam, Inc.
I don't know why they didn't do any welding (heliarc) or another aluminum repair. All the drilling and pins accomplish is to hopefully stop the crack. Unless it is in a place where it is impossible to weld, it should be fixable. If not, engines and heads occasionally show up in the Hemmings magazine. It is advisable to not use antifreeze, if you are leaking water, as it tends to carbonize and seize the rings. Good Luck - Larry J, 660636
I bought an unnumbered new XK head at an autojumble sale in the UK about 20 years ago. It seemed to be late 120, early 140, and Terry McGrath now has it (part exchange for a 150 DHC hood frame he had). So they are around. - Regards, John Elmgreen
Hugh, Should you choose to revisit the notion of weld-reparing your head, you might want to contact Randy Neil at Cast Welding Technologies, Tel 770-446-1999. I have seen their work and it is exquisite. Good luck - Klaus Nielsen
Cleo, At the time, J.C. told me that they were having problems with welding heads, and subsequent warping due to this operation. They took the hairline crack which went from the water jacket to under one of the valve seats, and put some 3/16" or 1/4" diameter threaded plugs along the crack. Then they ground them smooth on the combustion side. I do not know if these are mild or stainless steel plugs. To weld this up now would require a lot of aluminum to fill in the hole once the plugs are removed. - Hugh Leidlein
The discussion about the 120 cylinder head evokes familiar memories of a similar problem I had on a 150 head. An exhaust valve separated from the stem with the engine at idle. The valve head was hammered by the piston. The combustion chamber was savaged by the fragments and the piston was ruined. Fortunately, damaged was confined to one chamber. I found a machine shop which specialized in building high-performance NASCAR engines, especially aluminum alloy 350 c.i. Chevrolets. The owner routinely salvaged both cylinder heads and blocks which had been brutalized. Anyway, he showed me examples of undone work in the stock pile along with his operation. He noted that extensive welding would invariably lead to serious warping. His countermeasure was a home-made device which applied pressure, much like a press, to the head after welding. The device fit in a huge oven which cooked the head to return it to a near perfect mating surface ready for the block. He said this procedure resulted in virtually no machining of the head and if needed at all, a skim of one to two thousands of an inch corrected the surface. My 150 cylinder head did not need this extensive treatment and was welded without any machining needed for the mating surface. With the increase in the use of aluminum alloy engine components on many of today's cars, we Jag owners have a better chance of finding quality help for reworking our cylinder heads. But I'm still careful who I choose and am not interested in someone using my valuable parts as a training exercise. - Bob Oates
For the record, the product that is used to detect cracks in aluminum
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