Vintage Thing No145 - Four cylinder Moto Rumi

Greater than the sum of its parts I would say

While looking for a photograph of something else the other day, I came across an old smudge of this. Continuing the search for whatever it was - whatever that was escapes me now as it escaped me then - I found another photograph of this motorcycle, which intrigued me sufficiently in the good old/bad old days of 135mm films and SLR cameras to expend four whole frames on it.

Horizontally inclined (as opposed to horizontally opposed) cylinders make a lot of sense to me. I am surprised there aren't more of them.

I can't remember where or when I came across this machine but think it might have been at the Blackwater traction engine rally in the early 90s.

The engine consists of two 125 Moto Rumi two-stroke twin engines. The result is a two stroke in line four with horizontal cylinders.

As UJMs (Universal Japanese Motorcycles) go, across the frame fours are almost unremarkable but no Japanese manufacturer ever made a two-stroke in line four.

Special builders had to do that for themselves.

I seem to remember that I had been talking to a friend about the Suzuki X14 shortly before I saw this bike. That was a Suzuki X7 with two engines, giving a 500cc two-stroke four driving through a single X7 gearbox.

Consequently, I was intrigued to the power of n (where n is a very large integer) when I discovered  this 250 two-stroke four.

I particularly like the look of this powerplant

Moto Rumi were famous for scooters as well as their lightweight motorcycles. Many had a 125 two-stroke twin with horizontal cylinders, a powerplant that dated back to 1949. Originally putting out 6 bhp, this state of the art engine went on to produce 9 bhp at 8000rpm by 1960 and had a bore and stroke of 42 x 45mm for a cubic capacity of 124.68cc. On that basis, this machine would have a capacity of 249.36cc and maybe 18bhp if a little tuning had been carried out. Compression ratio was usually 10.5:1 and the carbs were downdraught 18mm Dell Ortos. There was a wet multiplate clutch and a four speed gearbox.

The frame was a very lightweight tubular affair on the bikes and a pressed aluminium beam on the scooters. Sport versions could manage 80mph and tuned racing machines were even faster.

Trago Mills were selling books om Moto Rumi a few weeks ago so it's as if the universe is bringing them to my attention. Rumi displayed some four stroke 250 racing machines around 1960 but these were never fully developed and never ran in a big race and the two stroke twins remained a staple until the frim went out of business in 1962.

As for the two-stroke twins, there was even a 150 (46 x 45mm) and a 175 (46 x 52mm for 173.75cc) version so you could make a 332cc or 347.5cc version - if you could find the parts.....

The cycle parts look in period with a big front drum but I don't what the forks are. The frame appears to be from a lightweight Yamaha - possibly a TZR125.

Look at those spansions!

I wish I had taken a fifth snap of the info attached to the handlebar fairing but film was scarce back then so I didn't. I am just glad I took what photos I did.

Might need bigger brakes