Upgrades - Diablo 500 (1967) to 502/3 (1968-69)

[Go Go Diablo]

When Bolens designed the first Diablo 500 in 1966 (for the 1967 production year), I presume they were learning on the fly. Although I have confidence the engineers and designers had significant experience, this was still a time when snowmobiles of every make were an ever-changing design and upgrades were inevitable.

From my experience, there were several upgrades done during the first production year. This is why some Diablo 500's have the long nose tin and 2-bracket bumpers and some have the shorter nose tin with the 4-bracket bumper. This along with changes to the suspension, dash and some other things changed during that very first year. This is a good topic for another time.

This post will focus more on what changed in 1967 with the 1968 Production of the Diablo 502 and 503. After these changes, Bolens must have figured they got it right because I am not aware of any changes during the two years they made the 502 and 503 models (quiet you Hus Ski guys!). Over the next month or so, I will attempt to detail the upgrades and promise it to be interesting reading to even the most knowledgable Diablo expert.

Information reported in this post will come from a technical document of unknown origin. Someone gave this document to me and it has no reference to Bolens nor is it written from a factory type of document. In fact, it is just a type written document. However, I believe it to be accurate and also believe it to be written by someone with Bolens Factory or Engineering ties as you will see. In each following post, I will quote the statement (quote will be in blue)from the document and may add some of my own comments and pictures.

If you are following this post and find the information useful or interesting, I'd appreciate you joining with your comments or observations as we cover each piece of upgraded Red Devil fun!

Bruce

[Go Go Diablo]

Deck Assembly and Frame

The frame in constructed of 1-1/4" square tubing of 12 gauge steel instead of 14. Front extension angle iron has been replaced by 11 gauge tubing for additional strength. Track adjuster bolts are constructed from Grade #5 high tensile steel and extra guide plates have been added to hold the bolt in a rigid position.

The steel for the construction of the deck has been increased to 19 gauge. The side of the deck has been formed to give added strength. Also inside of deck center channel, 14 gauge brackets have been installed to reinforce front end. Deck nose is 2" shorter and made of 18 gauge reinforcing braces. A rubber pad has been added at front of deck to prevent snow entry between deck and chaincase.

For those that have looked at a 500 chassis and a 502/3 chassis side by side, these upgrades are quite obvious and make for a much more robust chassis. The additional tubing supporting the front bogie stations help support the double bogie assembly through rouge terrain. The thicker steel throughout makes for a sturdier chassis less likely to crack at the weldments. The mention of "the deck has been formed" means the outer edges of the chassis near the tracks have been folded upwards to increase the rigidity of the side walls.

The 500 Chassis:

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The 502 Chassis:

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It was interesting to note the addition of the rubber pad. I wonder what engineer looked at that and said "where did all that snow come from?"

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[Go Go Diablo]

Several changes the document did not mention include the redesigned front post, the longer square tube under the tank, and changes to the tunnel and side brackets.

I refer to the post as the vertical tube up near the front of the chassis where the bottom motor mounts attach. The 500 model had a simple post design.

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The upgrade was to use heavier steel and attach the weldment to the tube below.

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The fuel tank sits on top of two square tubes and the tube that the tank strap goes through was short on the 500 model. The upgrade here was to lengthen the tube to match the width of the tank and add a pad under the tank to protect and cushion the tank.

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On the bottom side of the chassis near the snow flap, the tunnel tube was made of thicker steel and designed to be more square than the 500 model. The side support wing brackets originally made of a bar of flat steel were replaced with a round piece of steel and securely welded from the wings to the bogie rails.

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[Roy Teske]

Hi Bruce! Good post illustrated with pictures. I sent you that document way back in 2009. Boy, time flies when you're having fun. I got a package of diablo and hus-ski manuals, waranty flat rate time repair guides, parts price lists , service bulletins and a Bolens distributors order from Sept. 1967. The distributor was M.L Coffins Co. Inc. in Bangor Maine. When I saw your post, I pulled out the papers again to look at them. I see the bulletins signed by people whose names are now familiar to me and others. Maurice Cyr.... I've heard mentioned by Barrie. Gordon Peters.....Parts manager. A.A. Meyers ....Service manager. And to my surprise, G.E. Mackisoc..... Hus-Ski Ed.... Whom a lot of us met in Alliston last year.

[Go Go Diablo]

Thank you for your response Roy. Now we know how I got the document and it does not surprise me at all it came from you. I am still unclear of the original origin of the document, but it is a good one for sure.

More posts to follow.

[Go Go Diablo]

Idler Axel Assembly

To prevent axle bending, a stress-proof steel is used for the axle and the springs have been relocated closer to the sprockets.

Clamping plates with Grade #5 bolts are being used instead of "U" bolts to fasten spring to frame.

The idler shaft in the 500 versus the 502/3 is the same in regards to the dimensions. With the statement above, it's unknown to me if Bolens changed the material of the shaft or if this is a statement just stating what the shaft is made of. The comment about moving the springs closer refers to the location of the springs to the chassis and the shorter aluminum spacers used. The combination of the two move the springs closer to the sprockets.

It's difficult to tell in this picture of the 500 Idler Assembly, but you can see the "U" bolts that hold the springs to the chassis.

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In this picture, you can see the plates and bolts that hold the spring to the chassis.

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If someone has better pictures to share, please do.

[Go Go Diablo]

Power Train Assembly

The chain case casting has been redesigned to give more clearance for the chain. The all around thickness has been increased in the casting and ribs have been added for extra strength. Sprocket centers have been altered and an endless #50 North American Rex chain is being used for more dependability.

The 500 gearbox is on the left.

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The 500 chain assembly is on the left.

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To my knowledge, both gearboxes use the same size 50 chain. However, the length is different. The 500 gearbox uses 54 links and the 502/3 gearbox uses 56 links. The gear ratio is different also. The 500 has a 9 tooth drive sprocket and 26 tooth driven sprocket giving it a gear ratio of 2.88:1. The 502/3 has a 10 tooth drive sprocket and 28 tooth driven sprocket giving it a gear ratio of 2.8:1. All things being equal with engine RPM, clutch condition and belt wear, the 500 should have had slightly more power but less speed than the 502/503.

This is what happens if you do not adjust your track adjuster equally on each side.

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This pushes the gearbox sideways in the chassis and the driven sprocket will eventually wear through the case and wreck the seal cover.

[Go Go Diablo]

Power Train Assembly - Continued

The chain adjuster is an 11 teeth machine sprocket with oilite bearing revolving on a hardened and ground steel pin.

The clamp is welded to the pin for easy adjustment and better sealing of slot, to prevent snow from entering.

A filler plug has been added to top of chaincase for ease of adding oil. Keyways in all shafts are end milled for easier removal of rubber sprocket and clutch driven assembly.

The 500 idler sprocket is on the left. Quite a difference here. I thought is was funny to mention "to prevent snow from entering" when most of us care more about keeping the oil from getting out.

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And the filler plug on top, that was an awesome idea. If you have ever put oil in a 500 chaincase, you certainly know what I mean there!

[Go Go Diablo]

Bogie Stations

The entire suspension has been completely newly redesigned with two (2) front, ten (10) centers and two (2) rear bogie stations.

The front station shafts are constructed from a material with tensile strength of 180,000 lbs./in.

In the 502/503 Parts Catalog, ever wonder why the 10 center bogie stations have a different part number than the 2 rear bogie stations? I believe the only difference is where the rubber bumper is located. In the center stations, the bumper is located in the hole farthest from the pivot. In the rear stations, the bumper is in the hole closest to the pivot.

The 500 Bogie Station

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The 502/503 Bogie Station

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The comment about tensile strength is an interesting one. Makes me wonder why Bolens points this out for the front station only and if the other stations have a shaft of different material????????

[devil dog]

Right? It is usually the steel wheels that get bent, or the axle housing/ arm that fails at the weld or cracked at the bronze bushing. These front ones took such a licking and the others just rode over whatever was hit. Probobly the same axles on all. The arms on the 500's are pretty thin compared to the 502, a great improvement for sure.