Crescent 500 specs

[OUTBOARDER]

I recall a C-Hydro race at St Joseph, MO (1966/67 ?) in which Bill Seebold was driving a Crescent. It sounded like it was having fuel problems, but about 1/2 way through the race it cleaned out and looked like it had 5 mph and a ton of acceleration on everyone. I don't recall where he finished or if he finished at all, but when it was running it was in a class by itself.

Here's what I recall about the alky Crescent:

1. Pure piston-port intake with no reeds.
2. Central combustion chamber.
3. Slightly domed pistons. One ring(?).
4. The compression was very high.
5. The bottom exhaust passage was angled upstream slightly.
6. The exhaust inside the housing was a straight pipe and short (6" or so) megaphone.
7. The entire engine assembly with housing and lower unit was very light.
8. The cylinder walls were chrome plated (I think).

Overall, I thought it was a very impressive engine, but then I've always been a fan of 3-cylinder engines. The only possible show stopper for me would be the chromed cylinders.

Frank

anyone know actual Port Specs ????

[Mark75H]

Nope, AFAIK there are no relationship between the SAAB and Crescent engine. I will speak to a couple of knowledgeable people and see what I come up with...

Per is correct, there is no direct relationship. In truth, they are radically different motors, only sharing the 3 cylinder inline, 2 stroke commonality

[Mark75H]

Here are the NOA specs of the Crescent Alky

If you are looking for a port map with the widths and contours, you will probably have to purchase a motor and disassemble it.

[Mark75H]

I recall a C-Hydro race at St Joseph, MO (1966/67 ?) in which Bill Seebold was driving a Crescent. It sounded like it was having fuel problems, but about 1/2 way through the race it cleaned out and looked like it had 5 mph and a ton of acceleration on everyone. I don't recall where he finished or if he finished at all, but when it was running it was in a class by itself.

Here's what I recall about the alky Crescent:

1. Pure piston-port intake with no reeds.
2. Central combustion chamber.
3. Slightly domed pistons. One ring(?).
4. The compression was very high.
5. The bottom exhaust passage was angled upstream slightly.
6. The exhaust inside the housing was a straight pipe and short (6" or so) megaphone.
7. The entire engine assembly with housing and lower unit was very light.
8. The cylinder walls were chrome plated (I think).

Overall, I thought it was a very impressive engine, but then I've always been a fan of 3-cylinder engines. The only possible show stopper for me would be the chromed cylinders.

Frank

Frank is correct, piston port intake with a rear wall transfer port complementing the side transfers. The cylinders were chrome directly on aluminum, so they were not repairable in that era.

There was no interchangeable tuner.

It was not related to the Archimedes Monark triples either.

The reason it was abandoned was the cylinder spacing was so tight there was no room to alter the porting or make any other changes to the design ... the power had been surpassed by the 1966/67 Konig VC design motor and was obsolete without a complete redesign from the ground up. The cylinders lay together slightly tilted so the port passages of the center cylinder interlay between those of the top and bottom cylinders. Tight, compact, light and - stuck as a design build.

[Mark75H]

Had to look thru a couple hundred pages of archives ... rpm range around 8,000

[OUTBOARDER]

Here are the NOA specs of the Crescent Alky

If you are looking for a port map with the widths and contours, you will probably have to purchase a motor and disassemble it.

these numbers make sense, exh opens at about 87 deg atdc and trans at about 114 deg atdc (like omc 49)
thx Sam

[BRIAN HENDRICK]

"The Crescent was built by Monarch Crescent, they also built bicycles and mopeds. Some of the same engineers may have been consulted. Most of the powerhead main components were made in Germany. M.C. was later purchased by Volvo Penta.
-Dick O'Dea"

No more to add to the info re: the 500cc o/b, but I did own a MONARK motorcycle for a time back in the late 50s.
It was a 350cc 2 cylinder, 2 cycle, 3rd port motor.
For that era, it was ahead of the Brit bikes.
Also this brochure on a MONARK 250cc twin . Note this motor is a JLO.
a well known German maker of 2 strokes.
All to say they were well capable of producing a 3 cyl o/b.

[champ20B]

Frank is correct, piston port intake with a rear wall transfer port complementing the side transfers. The cylinders were chrome directly on aluminum, so they were not repairable in that era.

There was no interchangeable tuner.

It was not related to the Archimedes Monark triples either.

The reason it was abandoned was the cylinder spacing was so tight there was no room to alter the porting or make any other changes to the design ... the power had been surpassed by the 1966/67 Konig VC design motor and was obsolete without a complete redesign from the ground up. The cylinders lay together slightly tilted so the port passages of the center cylinder interlay between those of the top and bottom cylinders. Tight, compact, light and - stuck as a design build.

Might better double check that info about the tuner.......It did have two different length internal pipes. One was for long run coarse and one for short. They were easily changed out according to historian and collector, Mark Suter. This engine was very similar to the Archimedes 45 hp and was actually close in horsepower output. The Cresent was likely the same as any other manufactured race outboard as to be derived from an existing domestic version engine with only few changes and castings. It is doubtful to me as a former machinist, that a production company would tool up just to make one special race engine totally separate from any other components they make for other use, in such little quantity. It is likely that with a little research, one could interchange some parts to build a Cresent engine from an Archimedes or Volvo the same as a Sweet 16 champion can be used to build a 6MMHR hotrod... or.....a Merc200-250 to make a 25SS. There's probably nothing outstanding to it at all. This engine could probably be built as a COPO. That could be a good idea to possibly consider, building a good historical race engine for anyone who would like to have one of these.

[Mark75H]

Doubtful or not they did. It is a unique project. Unlike OMC, Mercury and Champion, they did not build the C off of any of their production parts.

If you read Swedish and German there is a bounty of documentation of the development of the project. The tuner was not an option thing, like the super long nose cone on the record motor, it was a one off piece. Probably only 1 or 2 made, its not like you could order one - more like the factory made ONE for themselves to use. I don't consider that a regularly available part to say "They made this and that and the other." Do you follow me? Its like the Merc dual torpedo SuperSpeedmaster unit.

There is a guy in England building such a replica, but it is very different from a true Crescent C racer; essentially NO C racer parts are on his replica other than the orange paint.

No COPO here.

[BRIAN HENDRICK]

,,No COPO here.

OK, I will bite, what is a COPO ?