Bad cracks!

This picture is of a 10A4213 head on our 5 Star pulling tractor. This seems like a weird crack. Especially since both heads are cracked the same, and both heads are cracked the same on both ends. Meaning two heads and 4 cracks. All very similar. My only thought is that this engine was put together by someone who didn't believe in torque patterns or torque wrenches. Which is believable since the center main bearing was spun and a wrist pin was eating a hole in a bore. Lesson learned about buying a pulling tractor off craigslist!! Haha oh well. So this bears the next question. The tractor was 4.8125x6. The crank is now 6.25. Do I find 4213 heads to replace these? Or is it time to upgrade to square port 30's or 32's? No matter what it will be expensive. I think these heads could be welded too if all else fails. Now for the next question, this tractor has a weird double valve spring set up with shims. This seems foolish to me on an engine running 1800 rpm in a hobby stock class. The valves should never float at that low of rpm, so why the extra spring? It just would be adding wear to the cam in my mind. Thanks in advance for the help guys.

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Im wondering if that was a weaker spot on some of the MM heads. I have two M5s that the heads both have
external cracks in the same places, and the same place I believe as yours, about 2 to 2 1/2" in from the spark
plug side on the bottom edge. If you have a spare head take a look and see if you can spot a crack on it in the
same place. Possibly too much "engine" caused it to split open. I think one of mine was a 4206 and the other a
4210. One of mine leaked anti-freeze and I used JB Weld to seal it. I would agree on the wear on the camshaft.
I dont think the original springs on some of the U-UB 5 Star engines were that strong of a spring in the first
place and they ran fine.

Alan, thanks for your input. I'm used to seeing cracks between the valves. I have some 4209 heads, but those don't crack very often. I'm tossing around the idea of seeing if these can be welded. I would think it would be an easy crack to fix. Looking at our local pull rules, heads are supposed to be "stock". So technically a 4230 or 4232 would be illegal. Although they are rather lenient, I do like to win fairly. Also good to know you agree on the valve springs. I may keep them because its now balanced- I want to see what this does at about 2150 RPM.

How did you get the 6.25 stroke?

Upon looking at your photo again, Im guessing it was highlighted with a black marker so it showed up where it was at? Im betting the crack was there and it went unnoticed. If I hadn't inspected mine on my M5 and it hadn't seeped some anti-freeze I wouldn't have really noticed it.

I agree with you in the sense that there are weak spots on some of the castings.

My long-time MM mechanic and friend that worked on them for a living for many years, told me about a failure he had found inside the old style 800 stationary engines where a crack could develop internally in the oil galley and dump oil back into the pan from inside the crankcase... Pretty hard to figure out why the oil pressure was going to heck with rare/obscure problems like that... But he thought the casting mold was just a bit thin in that area - and after a long term usage - it could crack in that spot...

Always having been around welding & metal repair on the farm - and being fascinated by casting in general - I thought that sort of thing was very interesting.

Improper torquing sure might not have helped any, but in general, heads cracking have always been a bit of a weak spot for the old MM engines.

A farming friend of mine had an irrigation MM engine he could not start unless the water was drained down below the heads. Fire it up, then fill it on up with water. Otherwise it would leak too much into the cylinders...

It sounds crazy, but I ran a 605 stationary on a well for 2 years that had cracks in the heads to the outside, so I kept a garden hose trickling just a bit of water into the reservoir.






Howard