ELSINORE BIG BORE

[maicomc490t]

That seems simple enough, a clever toolmaker / firey thinks !

A de-comp a la Maico etc would go a long way to keeping the kickstart in one piece. Had to laugh at their solution - no kickstart spindle !

So who is going to do one? And what a great way to recycle an old dunger. I'll go and warm up my milling M/C

Dave Mac 

[JohnnyO]

That's a cool bike. Would it still be pre '78 legal if you were to forward mount the shocks like that bike?

[JC]

Very interesting. I often wondered if that supposed 450 in 73 was an oversize 250 nowhere near 450 in actual capacity.

Gary Jones raced it too - for a few laps at the 73USGP until it broke a frame. Did he get sacked before he moved on to Maico? My recollection is that, having sampled the honda 'big-bore' & knowing 1st hand how uncompetitive it was, he went & bought a Maico to ride the open class Trans-ama in 73 - sort of 'in yr face Honda, since you can't provide me a competitive big-bore'. Then Honda sacked him.

There were aftermarket kits available in US in early 70's to take the elsie out to 324cc using an 80mm Yam piston & new liner. (Also available for the Yam & Suz)

According to Motorcyclist Retro & Terry Goode, the 1st Elsie prototypes were 335s, but it's unclear whether that was their actual capapcity or just a code-name. Does anybody know? Interestingly 78x70mm makes 335cc.

[JohnnyO]

JC i tend to agree with you about gary jones riding the maico then leaving honda. Does anyone have a pic of a '73 450 honda? I'll check thru some old mxa mags and see what i can find.

[Maicojames]

Actually, Gary was already in hot water with Honda prior to the open national. While he had ridden the big bore, one was not provided for him. The frames had broken earlier in the year-Don Jones Racing actually modifed production bikes with the works parts they wanted for the 250s.
Gary was in danger of not honoring his contract to ride all the nationals, so Don bought a 400 Maico -and Gary raced it-honoring his contract. There was some $$ on the line.

[JC]

Hmm, I just had a look at a pic of Gary Jones' 73 USGP 450 in an old MXA. Motor is definitely not std CR250 bottom end. It's only a small pic but it looks more akin to Karsmakers' RC400 in 74/75.

[albrid-3]

what is the limit you go to on a standard bore with these honda cr 250, would one need to resleeve it, or could a change of barrel, like a barrel off another make be addapted. for example suzuki ts 400 barrel. or a later model cr barrel

[Lozza]

Anything can be done with enough time and money,increasing the stroke is a better option.

[bazza]

Tried to get hold of our mechanic from 70s but think he moved to Auz for better sheep. we had a 74 CR bored to aprox 400cc with a triumph sports car piston,that bike won Beach racing national titles.

[JC]

Dave,

You'd need 72.25 bore (=264cc w 64.4 stroke) to get into Open class. Wiseco made up to 2mm o/s (ie 72mm) for most 250's of the era. You'd have to decide if 72 was the limit or if you could go slightly more. Thats if you can find a 72.25mm piston to suit. But would a 264 Elsie be competitive in the open class?

I have an MT crankcase in the shed & the spigot opening is 82.6mm dia. Wiseco/Serco listed blank flanged sleeve (from LA Sleeve) that is 82.5 OD & 76 ID which would slip in the cases & could be ported to match CR cylinder. If CR cases are the same that would give 292cc w'out machining the cases.

RM370 piston is 77mm = 300cc. Don't know what is 76mm - perhaps a  watercraft/jetski.

Early 250 Canams (pre78) are 74mm so P8 Wiseco would be 76mm if you could find one. Deck ht & skirt length are close to CR/MT.

You'd need to enlarge the ports to compensate for more capacity of course or you may end up w a grunty slug. Remember Loz's comment above in reply #3.

Typically, when you big-bore a 2 stroke you lose height on the Ex & Trans ports & lose depth on the inlet - which is hardly ideal.

And you still have the gearbox/selector limitations to deal with.

[albrid-3]

JC, THANK YOU SO MUCH FOR THAT INFORMATION, l WILL PRINT IT OFF. I WOULD LIKE TO MAKE THE CR LARGER, BUT IT WOULD NEED TO BE DONE BY AN ENGINEER.
CHEERS

[motomaniac]

according the MOTOXFOX guide for CR's Chaplins 73 bike was a prototype.
the RC 125 only bared resemblance to a CR, up pipe ,centre port , split cradle??