Dr Joe Ehrlich - Motobecane Record Breaking 50cc Two Stroke

Published on 29 August 2023 at 10:58
Dr Joseph Ehrlich's Motobecane d52 moped as found

My Mrs was less than impressed when she found out what I had paid for this old moped. I am still recovering from it too.

Sr Joseh Ehrlich's 50cc engine with boost port technology

The boost port engine has a much larger cylinder and head to accommodate the chambers, it is over twice as wide as the standard item. 

motobecane d52 with 617 miles on the speedo

Although the bike had been registered for the road the little speedo is only showing 617 miles, many of those would have  been development miles and from the 1 hour endurance record.

Dr Joe Ehrlich Motobecane d52 left hand side

It doesn't look any better from this side, you can see the dry air cooled clutch, the exhaust has seen better days, I wouldn't mind having a play with expansion chambers some day .


Amal 22mm carb fitted to Dr Joe Ehrlich's motobecane d52

The letter from Ted Snook says they got the best results with this  Amal carb

Motobecane 50cc cylinder with boost port technoology by Dr Joe Ehrlich

Perhaps the most interesting piece of the whole story, the head with adjustable boost port chambers, used to determine the ideal size. Sadly one adjuster is broken but as the other is intact I can easily replicate it. This needs to be in a museum really.

My history teacher once described me as a lazy loathsome idiot with a good brain but no interest whatsoever in the subject. On reflection I find it hard to argue with any of that, history has never really been of much interest to me unless it is something that directly affected me. I was pretty obnoxious as a kid too, the devil readily found work for my idle hands and blowing things up and smashing things was way more interesting and fulfilling than knowing what Oliver Cromwell may have been up to in the early 1600's

Anyway, my interest in one aspect of history was severely stirred recently when I came across a motorcycle and a box load of parts that were closely associated with somebody that many believe to be the father of modern two stroke technology - one Dr. Joseph Ehrlich. 

Dr Joe was an Austrian who had a remarkable career, much of which was spent developing two stroke engine technology, he had a few major innovations and did a lot of development based on other people's experience. He had his own motorcycle manufacturing company for a while - EMC or Ehrlich Motor Cycles, he produced a very fast 350 cc single split cylinder machine that had some success, he went on to develop engines for Mercury and Johnson the outboard engine makers and ended up on formula 3 car production.

For me, though the most interesting thing was a moped engine he developed for the French manufacturer Motobecane. You won't find out much about this because it never went in to production and the development work was done in secret. The Motobecane engineers weren't best chuffed that Dr Joe had been brought in to succeed where they had failed. Motobecane had sent Dr Joe a brand new D52 moped to get his hands on, the development that intrigued them the most was his boost port technology. The idea was that the cylinder head would have two chambers that could contain pressurised mixture that could be released by the piston to increase the amount of charge in the combustion chamber from that stored in the crankcase. It worked - the peak power was increased and the power band became wider, it still remains an issue on 2 stroke engines that their maximum power is only produced over a very narrow rev range - much smaller than that on a 4 stroke engine.


My story as far as this is concerned started when I purchases the 1951 Bianchi, which has been the subject of a number of other blog entries. I had spotted a badly decaying moped hanging on the wall of the guy's garage and was intrigued to notice that it had a much larger than usual cylinder and head, at first I thought it was the result of a motor change but the owner soon filled me in on the details.

This was the very bike that Motobecane had sent Dr Joe and the engine in it was the very one that had been in the bike when Joe's rider - Rex Avery had broken the moped 1 hour endurance record before the Italian Grand Prix in Monza. The information regarding speeds etc had been lost following a flood at Rex's home some time in the 1980's but the bike came with a letter from Rex that recounted some of his memories. It also came with a 5 page letter from a guy called Ted Snook, who was one of Ehrlich's development engineers. With the bike was a box of parts - mainly spares for the engine and a couple of tools. Perhaps the most interesting thing was a cylinder head with adjustable boost ports so that tests could be run with chambers of differing capacities. It is described in Snook's letter. There is also a 75cc piston and barrel, this is all one off unique stuff. I have found articles about his 350cc bikes and his work with puch and MZ but this is much less known about. He got some proper power out of this thing, about 7 horse power, which was remarkable for a 50 back in the 60's. It was enough to take the record, although it didn't stand for all that long, it was an official record.

The bike is in a terrible state, it does not run, the engine is locked up. With all the parts there I am not too bothered about that, it still has the  22mm Amal carb that Ted Snook says gave the best results - far better than the Gurtner GCV16 carb that Motobecane had fitted as standard. The wheels are beyond redemption but new spokes and rims should be easy enough to come by, as will new tyres. Nothing is rusted through, the bike was stripped a fair bit to lighten it, some of the removed parts are still with it.

I can trace the history and ownership all the way back, once Ehrlich had finished with it the bike was registered for the road, it does have a registration number, which has been helpful in verifying the story and provenance. Sadly DVLA do not seem to have a record of the registration number so it may prove difficult to retain the number it currently has. I do have a number of magazine articles though so if I can find somebody at DVLA that is a bit of an enthusiast it might be ok. They may force me to register it as a new bike and with the holes in it's registration record things may get difficult. My first job though is to try and get the engine in to a workable state and with so little technical detail available that could be my biggest challenge. I have been able to open a cd that came with the bike - that cd contains the original parts manual for the D52 so I am not worried about the bike itself. The manual is in incredible detail - for example the clutch push rod is missing. The manual tells me it is 2 pushrods, each of 5mm diameter and each 75.5mm in length with a 5mm diameter ball bearing between the ends of the two rods. Without that information getting the arrangement right would have been a nightmare, with that information it's a few minutes work and I can be sure it will function as intended.

The engine is soaking in penetrating fluid at the moment and will remain like that until it has learnt a lesson in humility and unlocked itself. The gearbox is also seized on it's output shaft, there is lots of naughtiness going on in there I reckon but you do very occasionally see them come up for sale, if I can't fix it it's unlikely to be the end of the world.

I will get cracking on it soon, It's going to be very challenging but incredibly worthwhile. This is an important piece of motorcycling history, I am delighted to be the one to be saving it.


Add comment


There are no comments yet.