IMP 1402 Conversion

[nutsster]

I finally found some time to post a few photos of my 1402 IMP that has been totally rebuilt and modified. I purchased the machine to use for cabin access in the Uinta Mountains of Utah. I added the full cab right after I purchased the machine. It even required a engine cover. After running it for the first couple of winters, I decided to make things even better by adding torsion axles to the chassis. Someone re-engined it with a 2.0 liter engine from a 1972 pinto before I purchased it. I added a C4 tranny to it so my wife could drive it. It comes it at about .40 psi ground pressure now and will go anywhere in our soft Utah snow. A real sweet little machine!





What is a 1402? The 1402 used the same chassis as the 1404 but didn't have the front cab. It had just a windshield. It was to be used like a tractor to haul things. It originally had an Wisconsin engine and was sinfully underpowered. I talked to some original Thiokol empoyees about this machine and they where confused about the squared off forward lower chassis. They believe it could have been a prototype or special order. The simpler front end made it lighter than the 1404. It has a more modern look than the 1404 in some ways.

 

[Snowcat Operations]

I like it! Very nice work. Did you do all the work your self? You and member "Byoung" will have alot to talk about.

 

[Melensdad]

I noticed you change the track design from the original raised center ridge type tracks to a wider flat snow type track. Is that to help with floatation on the powder snow you get in Utah? I remember when I used to ski a lot, the bowls near Park City had much lighter snow than anything I'd encounter in Colorado.

Also, when you had the original tracks on your machine, did you find that they made it more suitable for non-snow/low-snow conditions?

Also, I noticed you now have fewer bogie wheels. Did that affect the ride? And how?


BTW . . . how about some interior photos!

 

[nutsster]

I really wanted to get away from the drop center grousers. So I studied several snow cats to see what worked well. The strait grouser gives the cat more ground clearance. I liked the design of the later model Imps and LMC tracks. The strait grousers on the Super Imps were designed to give it some height. The Sprite/LMC 1200 has a very good track, with the multi-belts to help shed snow.
My first test of the new tracks proved that they worked well. I found the machine to turn much better. It also works better in shallow snow conditions, since it didn't tear up my yard near as much as the old track.
The real test was climbing in deep powder where I saw an improvement in too. This I think was due to the taller grouser and many more paddles.
The bad part of it all was it took me nearly all summer to make the grousers and tire guides. Alot of man hours.
The torsion axles with larger wheels was a huge improvement on the ride. My friend who grooms Dear Valley Ski Area was shocked at the difference. He said it rides like a big cat now. It's logical, if you run a larger wheel over a grouser, the less impact it will have and a smoother ride.
With larger wheels, I was able to reduce the number of wheels that a IMP utilizes. I have also seen some Leitner cats in Europe that run with large gaps between the tires, mostly in the center section. So I felt that was not so critical.
It was worth all the work that I put into it. I only wish that I would have droped the forward idler wheels and just put the front axle further forward
to increase the length. Much like the LMC 1500.

 

[Doc]

Nice work. It looks awesome.

Did you fabricate the cab from scratch?

 

[nutsster]

The cab was fabricated from scratch. I studied several IMPs and sprites to see how Thiokol built their cabs. I used 3/4" square tube to frame up the structure then rivited aluminum sheeting to the frame work.



Here's a couple shots of the inside. They are a couple of years old and I have made some more changes to the interior.

 

[BigAl]

Very Nice work ! I tip my hat to you sir . I am very impressed with your cab construction . I am currently looking for ideas for my "full cab construction" I intend to do on my Kristi KT4 . Been leaning towards fiberglass ,but now maybe I will consider Aluminum .Thanks for sharing your pictures and welcome to the FF site .
Allen

 

[nutsster]

Here's a couple of photos of the cat from behind and with the old drop center tracks that where widened. The gas tanks where added to the rear of the machine to keep it out of the cab.

 

[Snowcat Operations]

How many passengers can you fit inside now?

 

[nutsster]

It will easily fit four adults in back and two up front. I've had many more kids in it.

 

[cooper]

Nice work Ive got a 1404 that I have been thinking about putting torsion bar suspension under also. How heavy of torsion bar axels did you use in your cat? Also what did you use for growsers for your new tracks?
thanks.

 

[nutsster]

I used three axles. They can be custom made to the width that you need. Next time I would remove the forward idler wheel and just run the front axle up front like the 1200 or 1500 LMC. That would give you more ground contact. Also, the IMP could do better to have the C-4 differential relocated a little more aft. You also need to lower the rear differential about 3 to 4 inches. I raised the whole chassis to get better ground and track to cab clearance. It takes alot of planning and calculating to get it right.
I made the grousers out of 1" square steel and a 1" strap welded to the side. They have worked out much better than I thought they would. I didn't bend any of them this winter. I didn't have a way of having them heat tempered like most steel grousers on production models. I would just weld the tire guides to the grouser, rather than bolt them on like I did.

 

[Melensdad]

I made the grousers out of 1" square steel and a 1" strap welded to the side. They have worked out much better than I thought they would. I didn't bend any of them this winter. I didn't have a way of having them heat tempered like most steel grousers on production models. I would just weld the tire guides to the grouser, rather than bolt them on like I did.

When you get some time, please take several close up photos of those and post them here for us

 

[pixie]

Lower the differential ?????

I'm considering an axle modification to gain ground clearance under the differential !!!!

Please explain your reasoning ?

 

[nutsster]

The torsion axles mounted under the chassis added nearly 4" to the chassis ground clearance. If you leave the differential where it is, the drive sprocket would end up about 4" to 5" off the ground. It is desireable to have the rear drive sprocket off the ground approx. 1.5 to 2" to give it a smooth ride. ( no suspension in the rear differential ) In the rear photo above, you can see the 3" aluminum spacer that was added. The differential was dropped with spacers in the front so that the drive shaft barely clears the belly support. It is then angled downward to the rear of the machine. To gain differential clearance Thiokol went to strait grouser in the C shape. The strait grouser gives the rearend an instant 1.5" of clearance as far the belt to differential over the drop center grouser. Adding the taller C grouser even added more lift. This comes right from one of the original engineers in Logan. I will follow up with a couple of photo's to show what I mean.

Of course some cat's don't intend on using the drive sprocket for floatation and place it high up in the rear to get ground clearance. A cat like the IMP that has the drive sprocket slightly off the ground will get floatation in soft snow yet additional ground pressure on hard packed snow. It will also help a lot in the turning abilities of the IMP to have it slightly elevated.

 

[nutsster]

Here's a photo of the later Thiokol Strait grouser. Compare it to the very first photo of my 1402 with the 24" tracks or even the modified asymmetrical track of my cat above. "The belting which gives the support on the snow is almost 2" inside the circumference of the tires." ( giving up clearance! )



Here's a photo showing the rear sprocket about 2" off the ground. "Some IMP's have leaf springs so worn out that the sprocket rides on the ground, giving the cat a rough ride on hardpack snow."
Look through the sprocket an see how much higher the differential is off the ground verses a drop center track.

 

[cooper]

I have been fallowing your suspension mod (very nice work) I have a couple of questions for you. You mensioned running a big axel , tire up front would you run a torsion bar axel there to or a solid mounted axel? also how heavey of torsion bar axels did you use in your cat? ( 500, 1000, 1500#)?

 

[nutsster]

Cooper,
Study a LMC 1500 or Thiokol/DMC/LMC 1200. They run a torsion axle up front turned in reverse with about a 45 degrees angle down. I went with 1000# axles and they work well for an IMP. I have a DMC 1200 and they run quite heavy axles for the overall weight of the machine. I think if you go too light it could get bouncy or rockin forward and aft. The 1500 and 1200 use grease cylinders to adjust the track tension. You could easily use a threaded shaft and nut set-up for an IMP with an anchor plate to hold the position. Similar to a snowmobile rear wheel adjustment.

 

[mtncrawler]

I am enjoying what I see is the ultimate powder project. Question about re-locating the C-4 aft. I did a powder climb comparsion with and without my plow on my Spryte and it did better with. Since your fuel tanks are in back now why do you want more rear weight?

 

[Snowcat Operations]

The Swedes did an in depth study on snowcats to see what the absolute best configuration. The found that the ideal situation was to more weight up front than back. A smooth bottom and high snow clearance. Those three things were the biggest assests a snowcat can have. As far as his OC-4 farther back doesnt make much of a diffrence. If it helps extend his tracks then that would only help. Now if he was building a cat from the scratch then I would say an oc-12. (Nutsster if you ever want to sell that OC-4 let me know) NICE work!

 

[nutsster]

My idea of moving the differential back is to lengthen the whole machine and add some track area. The Thiokol Imps to me look very short and stubby, but this does help it turn better. The 1500's and 1200's have more length and work well in deep snow because of it. The OC-12 is a much much more durable rear end. If you put too much power on a C-4 rear end you will tear it up because it is lighter duty. C-4's don't turn anything like a OC-12 and can not take near the abuse. With my wider tracks and higher horse power, I was advised by Peterson's Equipment to not push it by pulling a drag or adding a blade. I was told by their mechanics that the Sprites with the C-4 rear end don't hold up to blade use real well.
The old Sprites also have drop boxes and gear reduction to help it handle more load over an IMP.
I totally agree with the smooth bottom, good clearance and foreward CG for climbing and deep snow operation. Almost all of the new small cats have mid engines and higher ground pressure. They just don't perform well in deep snow and steep terrain. Peterson's had the new Piston Bully Canyon and were not impressed at all. It couldn't go in the deep and steep.
The new Lite Foot that Piston Bully bought-out in Salt Lake City is a nice machine however. Pretty much a copy of the LMC 1500. (Designed by a LMC engineer)

 

[pixie]

For a year now, I've been trying to think of a way to gain ground clearance on my Imp and also to add support at the rear of the machine.

One idea was to add a small tire or pair of tires behind and below the sprocket and at the same time replace the original tires and axles with something very much like Nutsster's new axles but spaced to be lower. However, this would mean the sprocket only contacts the track for 1/3 of it's circumfrence instead of over half as it does now.

Have any of you thought about this or do you have any ideas how I can gain ground clearance under the differential which is the low point ?

They must not have rocks in Utah or whereever they thought that an Imp could be used on non-snow covered ground !!! ???

 

[Snowcat Operations]

NUTSSTER,
I can attest to the weak OC-4 Clark transmission. The guy that delivered my Thiokol swamp Spryte broke something in the transmission and now I have a thiokol that is permanetly in 2 gear (shifter on transaxle just flops in the breeze). Do you know anyone who can rebuild this transmission or at least work on them? I have been trying to find someone and so have had NO luck. Hell I would even swap in an OC12 if I can find one.

 

[mtncrawler]

Snowop- your OC-4 is really two boxes, one is the transmission and the other is the steering differential. On the front right side of the transmission is a cover plate that will allow access to the shifting forks. If my shifter was just flopping around I would start there.

 

[Snowcat Operations]

Thanks! I didnt mean to steal this post.

​

 

[nutsster]

It is my opinion that you could easily add too much track to the Clark 4 differential. Working it like you do "grooming" would be pushing your luck with a lot more track. I think the wide, strait grouser track would be your best option. If you want to go through the work of adding torsion axles, then drop the front idler and go with three or four torsion axles, depending on wheel size. If the drive sprocket is not at the end, I believe you would get tons of slipping.
I know from operating the track you have, that it doesn't give you much traction. The track I made has so much more bit and performance over the drop center design.

 

[nutsster]

Pixie,
You have a nice looking IMP 1404.
Does it groom or push snow well?
I think you said that you made the blade and compactor for it.

I'm going to build a drag for my DMC 1200 this fall to groom some roads in the Uinta's. I plan on coping the mogul master and a couple others I have seen.

First, I need to get the 1981 DMC completely restored to like new.
nutsster

 

[pixie]

Thanks, Nutsster. It does push snow well. The green thing on the back is for winching and skidding logs. We didn't have much snow here last winter so I haven't gotten to use it much. It came with the front blade.

I will probably be too busy in the next year or so to do anything about the tracks. I have other ways to move logs in the non-snow months , so I'll just hope we have a real winter next year

 

[Teeoster]

Hi Everyone, I am Pretty new to the site and am very excited to learn and share some stuff with everyone. I'm from Michigan and it looks like I am the only one on this site from here. Nuttster, very impressive machine! You're engineering skills show in every picture. I have a similar Cat I am restoring right now and have already gotten some good ideas from you. I really like the cab and torsion suspension. I too bought a 2 man cab and am converting it over to a full cab.

I have the good fortune of living in the Motor City and have a very extensive network of friends with shops to help with the project. My shop is called Quality Metal Craft and we build prototype sheetmetal components and are also extensivly involed in the automotive aftermarket business. If you have a chance check out these links.

This is a bike we just build for Chip Foose and sold at the Barret Jackson Auction last month:
http://www.uniqueperformance.com/FooseBike.aspx

My Shop:
http://www.qualitymetalcraft.com/

I was really intriged with the torsion suspension and did a little home work over the last few days, let me know what you think about attaching 2 opposing torsion ends to the existing suspension support tubes?
I was able to locate surplus 1300lb torsion axles for $60 a piece. They are only about 3ft wide but as you know the torsion "guts" only extend a foot or so into the axle tube. Extending them with 2 1/2" stock or cutting them off and attaching as is failry simple. Whats your thoughts on this approach??

If anyone is interested, the place I found has about 80 of these surplus torsion axles in stock.....only about $60 a piece.

John

 

[64Thiokol1201]

Nutster,
I noticed in your original post that you said you added a C4 so your wife could drive it. I presume this reference is to the Ford C4 Automatic transmission. If yes, I need to make the same conversion to a 1964 Thiokol 1201. Is the Pinto motor Ford in line 6, either a 170 c.i. or 200 c.i.? I am having trouble sourcing a transmission from the early 1970s that is a pan fill that will have the proper bell housing to bolt up to my Ford Industrial 200 c.i. In Line 6 cylinder. Do you have any photos of your configuration? Any ideas on locating a transmission? Any info would be very helpful. I would also like to do the full cab enclosure.
Thanks
64Thiokol1201