Summer 2002 Bike Project
Part one, two
Home / Features / ALMA 4
 Alma 4 Project, part three
By Mads H. Johnsen

Always wanting an Indian 4, but never having been in that income bracket, left me dreaming for years. A remedy for the last ten years has been my 1946 Nimbus 750 inline 4. A good workhorse, it has taking me anywhere. So rich in character that the lack of power didn't really make itself felt. Millions of cars must have passed me, but so did the years and one day I just had it. A bigger engine for the Nimbus was the obvious solution and the project started. Pretty soon I realized that with the amount of time spent I might as well go for the big one and build my dream. The Indian Four. Or rather sort of a replica.

My private parts

This part of the saga will primarily handle the the different aspects of transforming a sixties car lump into a twenties motorcycle heart. As stated, albeit poetically, in the last article one need guidelines - ("A brief and colorful thesis regarding design dynamics"). At least I do - and the sooner these are established the better. I'm still hindered by some wrong moves, made unknowingly in the startup process of this project a couple of years ago. Too difficult to correct I just leave them be, sore only to MY eyes - hopefully. Feel free to point them out if you think you spotted them! And to those of you ready to mail in about the obvious wrongness of the project - don't.

I've described the NSU-engine before, so I'll just state that we're dealing with an air-cooled 996 ccm (61") OHC inline four with aluminium block and cast iron cylinders.The original sump is a non stressed, pressed steel item. I don't know the total of engines produced from the NSU factory but it's a lot! I bought mine complete and in very good working order, basically ready to chop, for US$350. The going rate for complete engines with unknown mileage is one "dog" per cylinder. A "dog" being one "hund"rede (100) Danish Krones - approximately $US8.50 -So for less than fifty bucks you can get started! And yes! - NSU did make inline twins as well, for you cheapos.

Ahh! - that was the easy part. Now I just needed a new sump, a clutch/flywheel housing and an appropriate gearbox for my "Po'boy Four" (and basically a complete Four running chassis). I soon found out that dreaming up stuff that didn't exist in the first place was a very time consuming process. But in the end I reckon that's what people call zen. It is a rather special feeling designing your own private parts.

Thus: Things are created, they are inherently subject to decay, and then finally they are dissolved again.
 The sump(s)

The first sketches were done in 1998 and in '99 the first prototype sump was cast. I build a simple measuring tool to mike it with. That oil sump could have been for a Sherman tank! A serious diet was called for. The second and corrected (slimmed) casting was fine. It would work OK in an Indian frame but not really meant for it, I didn't find it optimal. So, swallowing hard, I went back to the drawing board. Actually the first sump never really made it to there, but was designed and constructed more in a "tongue in cheek" way. This time I would do it the proper way, especially as I'd learned a thing or two in the process. I would build the mould as the finished item plus shrinkage percentage, and not like the first time where I did a male-half and a female-half. This (if you're a raw amateur like me) allows you to control the thickness throughout in the part before heading down to the foundry. It proved harder to do than first thought, as I was doing it in MDF, a compressed wood-chippings material not really made for fine tolerances. 

"If you gotta go - go in style!"

Enough tech, let's have a bit of styling. One fine trait of the great inliners is the long cooling fins and I wanted a lot. Being unencumbered at the front, thanks to the original OHC design, I decided to let the fins sweep downwards starting from vertical and spreading over a hemisphere on each corner. To make the "corners" I had to turn a complete wood bowl, cut it in quarters, then 9mm lengths to fit it in between the fins. Slip-angles were a bit critical around these areas, and as it turned out later, I might've been a bit too bold. Next step were the sides, which were pretty straight forward, and the "wings". The "wings" being the four bearing points resting on the frame. I made these longer than necessary, as I didn't knew the exact width of my frame-to-be. That way I could adjust it later and be on the safe side. Aside from the fins, I wanted a sighting glass at the front with a straight look into the oil pump gear. Oil drainage was supposed to be from the side according to my drawings, but when I did the mould it just looked better positioned at the rear. After that it was just a matter of gluing the whole thing together, sand it, paint it and polish it. 80 hours in total...

I had a bad feeling when I handed the finished mould over to the foundry -the air just didn't smell right. And of course disaster struck. A bad combination of really small slip-angles and a workman with a bad day, (oh! why didn't his wife comply the night before?) turned a simple job into a mould wrecking experience. The boss of the foundry fortunately intervened, and saved most of it. The only problem was the extra couple of weeks work filing (no room for power tools) out material between the cooling fins, but finally I had my sump.

My ALMA dream

Wannabe Sherman-tank oil sump

"I'm getting there". My oil sump collection

New and final oil sump blueprint

In the glue..

The finished mould (NO, it dosn't glow red in the dark!)


Clutch housing blueprint

Mould + castings

In the clutches...

The other part that I needed and really looked forward to, was the clutch housing. The crankshaft lies pretty high in the block, and that combined with my deep oil-sump gives the engine a very tall broad side. Think "Velocette inline four"! I imagined the clutch-housing being able to visually stretch the lump, to balance it and make it a whole. So, knowing what I wanted, I went straight to the drawing board. The combined clutch/flywheel house was going to be mated to the '48 Nimbus gearbox that I'd acquired earlier. The main problem of using this gearbox is the kick-start. Not integrated in the 'box, it must be housed with the clutch. A lot of measuring was needed, and a lot of thinking, but finally I had a drawing. In need of a workshop (again), I trekked (again) to mainland Denmark, to a "communal house" Yes, I know it means whorehouse in Turkish but this place offers, as a communal service, very run-down metal work-shop facilities. The spirit is as high as the tolerance on their lathe, and I've learned a lot there. In time of need, the best place to go. Having done it all before it didn't take me that long, and all the aforementioned steps were taken Fast-Forward. Straight to the foundry which this time did what they were supposed to do.

Cashing in on some old friendship, the Royal Danish Academy of fine Arts (unknowingly) did all the machining (thanks Torben!). All needed now was a piece of billet aluminium to form the other end of the clutch house. This part holds the oil seal for the special adapter cone that mates the NSU crankshaft to the Nimbus fly-wheel. Out of money as usual, I found a piece at the scrap yard. 

Rearwiev-mirrorly-speaking, I should have bought a proper piece from the beginning, the alloy feels kind of strange, but after shaping it with hand files for a couple of weeks, there's really no turning back. In the mean-time Allan, a good friend from the Danish Nimbus Club, machined the sump flush with the block, and things started to look promising. A test assembly of the casings went real good, the only remaining problem being the line-up of the clutch and kick-starter ratchet. My blueprint tells me that it should be OK, but it looks like a really tight fit. Ah well, "Amateurs night" anyway! On the home front my girlfriend is getting ridiculous big. At the time of writing we're T minus two weeks. I slightly wonder how my focus will change. Oh yeah - it's going to be a girl, by the way! 

Adapter plate - before

-and after

Rites of passage

I like the Nimbus gearbox because it's strong, cheap and looks good. But yet another (...) problem surfaced. The oil. Originally lubricated by circulating engine oil, my problem was getting the oil from the high pressurized NSU gallery to the 'box without: A. Blowing it apart by pure overdose. B. Lowering the general pressure, especially at the mains. C. The whole 'box friction-welding itself solid from lack of oil. On top of all this, to actually get the oil there some really tricky routing was called for.

So what I needed to know was the original pressure of the oil when entering the gearbox. I put the question forth, in the Nimbus Club magazine "Technical page", and the wizard there answered: "Sufficient". Gee thanks! I borrowed an original factory prototype from the fifties. They put in oil seals where possible but it didn't really look convincing. Is this starting to bore you? Well - I got bored, so I found a family in Jutland that apparently has a tradition of running "closed circuit" 'boxes on their Nimbi. And with the words of the late Douglas Adams, it became "Somebody else's problem". So there you have it! Slow, but steady, progress.

Not alone in the universe!

As a piece of curio, check out G. Briggs Weavers' blueprint suggestion for a shaft-driven Four. It's from the summer of 1941 and shows a '38 type four. It's traditionally styled, and nowhere near the ugly "BMW" framed prototype that were conceived a couple of years later. Kind of makes you think...

And to those of you being uptight about my project - check this out! Built in South Dakota in the late 30's this bike incorporates a '28 Chevy in-line four with a mish-mash of Ford T parts. 

Next Issue: DOLUS EVENTUALIS or deliberate stupidity. And why I took all my savings and went to the former Rep. of Czechoslovakia with a bunch of grandmas with blue-dyed hair. Weaver blueprint courtesy of C. Lecach. 

"Weaver is my man!"

Sorry, no big version of this pic
Unknown hero

Home  -  Features  -  Archives  -  Back Issues  -  VI Mailing List  -  Contact VI