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Factory Race Engines
#800656 03/10/20 4:31 pm
Joined: Sep 2001
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i was looking through the BSOC Goldie magazines for info on the BB engines and came across an article in the Sept 2017 issue that included some info on the engine preparation for the 1954 Daytona race. A dyno chart for one of the spare BB34 GS engines shows it was putting out 43.6 hp at 7000 rpm. Not too bad for a BB engine. It might help to explain the Daytona successes.

It also puts into perspective the success of privateers in the TT races who had "borrowed" factory engines.

Gordo


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Re: Factory Race Engines
Gordo in Comox #800836 03/12/20 3:19 am
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Gordo
Did that dyno test list the motor number?


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Re: Factory Race Engines
Gordo in Comox #800890 03/12/20 2:56 pm
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Bit of a swerve from your original topic but still factory race engines. Have you encountered any reference to use of sand-cast engine cases for CB series motors ? A person with some credibility once told me the factory made 17 sets of these for Daytona. I have a CB engine with these cases but I do not think it was a race motor. I have also seen die-cast CB engines. I,m just curious what the real story is.


Laurence Luce
Re: Factory Race Engines
Gordo in Comox #800893 03/12/20 4:29 pm
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BT: No engine number. This info was in a long article written by someone who had worked at BSA in the 1950s. In the para about Daytona he states that the 500 twins (A7s I guess) had 47 hp and that the best single was a spare engine giving 43.6 hp with a 8:1 piston. The hp data is a chart, not the dyno sheet, and it starts with 33.3 hp at 5000 rpm and climbs in 50 rpm increments to the 43.6 at 7000 rpm.

All the dyno sheets I have seen do not go up to that kind of rpm so it really does tell you where the extra power comes from. There is no comment about reliability.

SL: As for sand casting the CB cases I have seen nothing about them in the literature. I suppose sand casting would be quicker for a few development cases. The known big change to die casting was for the change to separate rocker boxes with the last of the ZB32/34GS engines that in the next model year were called BB engines. This change to die casting allowed for wider and finer cylinder and head fins. The early sand casting ZB fins were very crude and not very wide.

Gordo


The roadside repairs make for the best post ride stories.
Re: Factory Race Engines
Gordo in Comox #800901 03/12/20 5:59 pm
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In the late 50's and onto the late 60's the competition shop used a lot of sand castings on the Unit Single engines developed for the Scrambles competitions. Even after the modifications they developed went into general production they still sand cast the crankcases as the extra metal made them stronger. I do not think that just started at that point and must have been used on the previous engines too.

Re: Factory Race Engines
Gordo in Comox #800912 03/12/20 7:25 pm
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Once dies are made, die casting is definitely a faster process. I've been told sand-casting produces a denser product and, of coarse, a "cruder" thicker section. The person who told me of the Daytona connection was named Dick Brown. He was proprietor of GRB Engineering in Costa Mesa CA but had previously been the machinist for a shop called Modern Cycle. That was the shop Al Gunter rode for and they got factory support and special parts.


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Re: Factory Race Engines
Gordo in Comox #800921 03/12/20 8:33 pm
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SL: Further reading into the article mentioned above (following month issue) it is mentioned that the 1954 big fin 500 race engines were getting 50 hp, Maybe for the 55 race? Were there two models of GS engines in any Daytona race?

Gordo


The roadside repairs make for the best post ride stories.
Re: Factory Race Engines
Gordo in Comox #801181 03/14/20 6:32 am
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As a sidebar, relating to sand-cast versus die-cast, in the two-stroke world of 4 cylinder Yamaha competition engines, most engines came from Yamaha with die-case crankcases, though in the late 70's there were sand-cast aftermarket versions available, made for/by Yamaha in the USA. These cases are better in practice (though of course have no engine/frame provenance), as they were easier to weld without warping the cases (required if a rod came through), were stronger and apparently had a little more crankcase volume (not that this is relevant in 4 stroke discussion).

Legend has it that the sand-case cases were actually copied from the works magnesium cases.

Were there mag-alloy Gold Star crankcases? I suspect so - there were mag timing covers, rocker boxes and gearbox cases.

KW


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