ELSINORE BIG BORE

[albrid-3]

Why hasn`t this been done, has anybody made or turned a honda 73 - 74 250 Elsinore into a big bore. 300cc or 360 cc could it be possible to do.

[Mick22]

It possible because Honda was racing them in the US in 74 as a RC450. I've got some photos of the bike at home, it was basically a CR250M with a HUGE barrell and head on it.

But apart from making it as a garage queen it would not be a worthwhile project in my opinion. The 250's gearbox can bearly handle standard HP let alone the torque a big bore would put out.

[JohnnyO]

I doubt that honda used a CR250m bottom end for their factory 450. They made totally new works bikes every year and hardly anything on them resembled production stuff. A 250 bottom end would need a massive piston to take it to 450cc and it wouldn't be very nice to ride with such a short stroke. It might be possible to bore a 250m to 300cc using the piston from something else.

[Lozza]

Over a certain point, usually about the 285cc mark transfer duct entry starts to get compromised, then only a new cylinder with more efficient ports can take advantage of the bigger bore.

[albrid-3]

COULD YOU BORE IT TO 263 WITH OUT A PROBLEM, THEN THAT WOULD LEGAL FOR THE BIG BORE CLASS.

[Mick22]

I doubt that honda used a CR250m bottom end for their factory 450. They made totally new works bikes every year and hardly anything on them resembled production stuff. A 250 bottom end would need a massive piston to take it to 450cc and it wouldn't be very nice to ride with such a short stroke. It might be possible to bore a 250m to 300cc using the piston from something else.

All of the factory bikes in 73 were identical to and based on the standard CR250M. The only specials they ran in 73 were at Daytona which  "Honda had put a little more capacity into than the AMA would have liked" as per Gary Chaplin. For the rest of the season the factory team ran stockers.

 The RC-450-73 obviously had a longer stroke and different Barrell but the bottom end was all CR250M. Even in 74 the "Trick" RC-74 250 was just a tarted up proddie bike which is probably why they were so far behind the other brands in 74. they didn't start making the full factory specials full of unobtainium until 75 with the RC-250-75 and the RC-400-75 (the RC125 was still similar to the proddie bike)

[albrid-3]

has anybody got any photo`s of the 73 - 74 model big bores

[JohnnyO]

A crank with a long enough stroke to make 450cc's wouldn't fit into 250m cases, the crank wheels would be too big. I don't think honda had a 450 in '73, isn't that why gary jones rode a maico in the trans ama series?

[Mick22]

Gary Jones rode the Maico because he got sacked along with Don & Dewayne by Honda prior to the Trans-AMA series.

Gary Chaplin rode the RC-450-73 in the 73 Trans-AMA, didn't do anything special though, probably because it was just a converted 250 not a ground up open class bike like the other brands.

Even though it was called a 450 no one really knew what capacity it was, may have only been a 280 or 300 etc. Just as with the later RC-400-75 wasn't a 400, during the season it was raced as a 360,380,400,420,460,480. Honda did some weird stuff back then as they were finding their feet with 2 strokes

Dave I've got some photos of the RC-450-73 and most of the factory Hondas up to 1980 (including my favorite, the RC380-79 VLRS)  but they don't scan very well, I'll try the scanner at work. They are classic photos, lots of porno mo's & body shirts in the pits back then If not i will bring them along to Campbelltown so you can have a look

[albrid-3]

Thanks mick, would be happy to see them. dav

[DR]

way back when Ray Ryan and another WA guy who's name I can't place built what I think was a CR360 based on the 250M. I had an article that went into detail somewhere but typically I can't find it when I want it

[firko]

Why hasn`t this been done, has anybody made or turned a honda 73 - 74 250 Elsinore into a big bore. 300cc or 360 cc could it be possible to do.

Dave..The factory actually tested a 360 (or maybe it was a 320, I can't remember based on a bored and stroked 250 but the gearbox had enough trouble putting up with 250cc, making a big 'un was out of the question without a major gearbox revamp or switch to 4 speed which was knocked back by the bean counters at head office.

[DR]

ok, got my facts wrong as usual. Ray Ryan did the report and the bike was built by Rick Gill



Full size here
http://nvr0jq.bay.livefilestore.com/y1pi5c7NfXQnnUP12oDYpAHRi8k_cLlVW1DS9AClkVZXASaked9H4PxGOHB0j4kri9hawvQxj3naQvghsNUz7xZ2aIHgp_JBQuT/Honda%20CR360M.jpg

[GD66]

Nice job ! Rick is still about, and still has a Honda shop at the same address...although these days, he races....grimace.... a car...

[albrid-3]

Thanks guys, you are a wealth of information, in that documant does it explain in detail the dimensions of the bike.