Gas Start Diesel Heads

Why do these heads crack? Is it all because of improper warm up and cool down time? I am in the process of having my new to me SMD overhauled and lucked out in that my head wasn't cracked. So how do I keep it this way? I thought a coolant heater might be a good idea. I also heard it is important to not rev up the tractor too much when switching over to diesel. Unfortunately, mine revs up pretty bad when first switching over, at least before we tore it down it did.

Thanks for any insight,
Dan

had a gas/start diesel short period of time, i let it warm up on gas side, so when changing over to diesel, it wouldn't hit hard, made a smooth change over. as for the fast rev when changing over, my did it also for the diesel to ignite better..a heater couldn't hurt, saves on gas...i sure others have more experience with that engine...

Iv had a Super MD for about 4 years now went though the engine etc. They have a tendency to crack heads when they are shut down hot and not allowed to cool and equealize after they have been worked hard. If i for instance am using it for plowing, or bush hogging, i will park it in the shade and leave it just above an idle for ten or so mins. Make sure you leave it in the diesel postion when you have it off to allow the sarting valves to cool on their seats and not warp. As far as the sudden rev up, it shouldnt really be doing that, the manual says to have the speed control lever 'throttle' to about the 1/3 to 1/2 way position when switching to diesel. However mine will swithch lower then that. I think the main thing you have to worry about with the reving at a start would be to blow a head gasket, however this is true with all engines in general at a cold start. I personal dont see the need for a block heater that is why they start on gas, and where popular in cold climate areas where other diesels at the time would have had a much harder time starting.

Andrew

As Andy said--cool-down is critical on these gas start Diesels. Dad had 2 heads crack on the 450 from either adding cool water to the radiator while plowing in hot weather, or---broken radiator hose while discing. He would let the engine idle at minimum throttle --which shook the daylights out of the radiator & contributed to leaks. Then would take buckets of water out to the headland to add while working.
We haven't had any problems since with the head.

Casting tech used on the heads wasn't good enough for the design. There was several head changes on some of the head numbers trying for better sevice. Some heads had 7 or more changes for the same head #. For some reason some heads lasted, so if you have one not cracked thats saw a lot of use there's a good chance its a better casting or took care of. Back in the day a local construction dealer would get new machines with cracked heads when unloading or before leaving the lot.
Lot of good ways posted to help the heads last. Make sure there's gas and a good starting system to restart tractor if engine is killed when hot. Don't overload and keep the cooling system in top shape.

My reproduction manual says to switch on the fuel pump at the same time I pull back on the decompression lever. That is how I was doing it. I can even pull back the decompression lever a second before turning on the injection pump and it will still rev way up. Maybe it won"t do this after the rebuild. I had just had the entire injection system redone at DIS too, so I think that is working well.

Thanks,
Dan

(quoted from post at 13:42:34 12/02/11) My reproduction manual says to switch on the fuel pump at the same time I pull back on the decompression lever. That is how I was doing it. I can even pull back the decompression lever a second before turning on the injection pump and it will still rev way up. Maybe it won"t do this after the rebuild. I had just had the entire injection system redone at DIS too, so I think that is working well.

Thanks,
Dan

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Sounds like you have a lot of slop in the linkages.
There is no throttle control on the carb.

(quoted from post at 10:42:34 12/02/11) My reproduction manual says to switch on the fuel pump at the same time I pull back on the decompression lever. That is how I was doing it. I can even pull back the decompression lever a second before turning on the injection pump and it will still rev way up. Maybe it won"t do this after the rebuild. I had just had the entire injection system redone at DIS too, so I think that is working well.

Thanks,
Dan

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I don't read the manual quite like that. My interpretation is when going back to gas it says to do both at the same time, but to go to diesel it says to do the decompression lever first by a hair. I quote the good book (not that one, but close enough :lol: )

CHANGING TO DIESEL OPERATION

1. Push the compression release lever all the way forward, Illusst. 3.

2. Immediately advance the engine speed control lever up far enough to keep the engine from stalling.
...

STOPPING THE ENGINE

1. Be sure that the gasoline supply is turned on.

2. Retard the engine speed control lever and, at the same time, pull the compression release lever all the way back (to gasoline position).

3. Shut off the gasoline supply at the tank, Illust. 9, and allow the engine to use up the gasoline in the carburetor.

4. After the engine stops on gasoline, push the compression release lever to the Diesel position to premit the starting valves to cool on their seats.

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