2-71 Super M

This was my winter project. It's a '53 Super M with a 2-71 GM two stroke Diesel. It turned out to be a lot more work than I thought but I did a lot of different stuff to it also. I completely rebuilt and re-machined the brakes (I can drag a tire with my big toe), new seals all around, completely rebuilt the front end, all new steering, rebuilt shifter, tranny seems good and quiet because it was a loader tractor for many years, dual air filter set-up with K&N filters inside, electric radiator fan, new radiator.

The engine runs out at 2100 RPM max and should put out about 65 HP. I'll find out next weekend at a local tractor show. I machined up a custom billet rear cover for the engine and I machined about a 2 inch spacer between the crank and flywheel. This allows you to use the stock flywheel, clutch and starter location. Everything is balanced up also. 2-71's have counter balance shafts and the engine runs amazingly smooth for a two cylinder. I also made a custom oil filler, air intake and relocated the original oil filter and breather so I didn't have to cut the hood at all. Believe it or not it is not very loud either with a muffler and a good silenced air intake. I had a straight intake on it this spring and those 2-stroke blowers make as much noise as the exhaust! I've got K&N filters inside the original oil bath air cleaners and a lot of rubber inside them also so it silences it nearly completely.

Next I want to get some nice 16.9's on it since the rims are already widened 2 inches and eventually paint. For now though I'll just have to be happy playing with it at the shows the next few months and a tractor ride this weekend to re-familiarize myself with my family. I’ve been known as that “guy in the shop” for a too many months now!

I can answer any other questions. Fire away.

Mark

• SM 2-71 photos

Mark

I particularly like your dual air cleaner setup. The 2-71 requires prodigious amounts of air to run right - you've designed a slick way to provide it.

Very well done!!! ...Bob M

Why do you say they aren't the best on efficiency? A 2-71 in a genset will run forever on fuel. (rather detuned though) I don't know about the larger 71 series engines. A 2-71 is certainly better than a diesel tractor engine of the era for efficiency.

Mark

They're really are a lot more quality components in them than tractors of that vintage. Roller tappets, full pressure valve train, oil coolers more machined components etc. etc.

Thanks for the compliments!

Mark

Doesn't the governor on most 2-71 retrofits interfere with the hood?

I suppose it is too late now but I would like to see a picture of the replacement rear engine cover before assembly on engine. Are the stamped cam and balance shaft covers retained?

Are you sure about 65 hp? Seems like less than 60 might be more reasonable. Did GM make four valve 2-71s?. If it is a two valve engine, I would think 40 hp might be more likely.

Don't think that I have seen you on the GM 2-stroke Yahoo group.

Ya know you are going to need a contemporary IH hauler truck with a 4-53 or 4-71 engine. No, my 1947 4-53 KB-5 is not for sale.

-The rear cover is not stamped. It is cast and is a structural member of the engine. It is a rear cover/bell housing with the rear main seal and oil pan gasket attached to it.

-2-71's were rather detuned for generator applications. They ran either 1200 or 1800 rpm's depending on the generator used (2 or 3 pole) GM never made a four valve head for the 2-71. Again 4 valve heads were for the higher rpm engines. I never said I have stock injectors in it either! I've got the later style N70 (I think I'd have to look) injectors in it. That and higher rpm, free flowing intake and exhaust and I know it will be well over 60 HP. It is stronger than my 560 gas and about the same as my SWD9. Much different HP than the SWD9 though. It won't pull out as big of a stump as my SWD9!

-The GM 2-stroke group STINKS! I've never been in a group as wierd as that one. It seems like a good 'ol boys club to me. I've never gotten any help there. A bunch of sound clips and who put what in what bus? Your better off asking a 2-stroke question here on YTmag.

-Your truck is for sale! Everything is for sale! I just couldn't afford it. I'm sure it's a nice rig.

Mark

You call it a rear engine cover but most call it a flywheel housing. At the top of the casting are two openings about 6" in diameter. Access to the cam and balance shaft driving gears is there. Alot of accessories are driven from there. That would be air compressors, generators, tach drives, hydraulic pumps, etc. I was wondering whether you were planning to drive a live pump from either shaft. If not, there would be a stamped cover. Perhaps the 2-71 is set up differently than the larger 2 strokes.

There is currently alot of chatter on the Yahoo site about performance modifications. One guy is talking about a 375 hp 4-71 that GM built for marine applications. That would equate to about 187 hp for two cylinders. But you will never get it with a two valve head. I am not even sure that a two valve head can breathe adequately at 2100 rpm. I wouldn't know. I have nine Detroits rangeing from 4-53 to 12V71. They are all four valve.

As for selling, I have only sold two vehicles in the past 40 years. My KB-5 was my first purchase and it won't be sold, period. Now, if you want to buy the 12V71, we can talk. It would look bitchin in a Cub.

Yes a 2-71 is completely different than the other 71 series engines. There is no access to the camshaft or counter balance shaft from the rear other than removing the entire rear cover/bell housing what ever you want to call it. Even if there was it would be within the perimeter of the flywheel and would do you no good as far as driving a pump. A marine front cover would accomplish this but I'm just going to drive a pump directly of the front of the crank with a love joy coupling set up. I've got plenty of room in front.

Mark