Topic: XR engine in a small CB??

[garretcb750]

Hello again.... Its been awhile since my last post. I havn't been doing much work on my 750 latly, just driving it. I just got back from a bike event in Digby and I have a few thoughts for a new project.

Has anyone ever thought of putting an XR dirt bike engine in a CB350/360 type bike. The small twins just seem so slow to me. I have an XR250R from 86 that has a great running engine. I love the the sound of a XR with a nice pipe. I also just picked up a few 350 and 360's for nothing. Geared alittle higher it might work.  I checked the HP ratings on both bikes the CB350 had 34hp and the XR is around 21hp. The XR hauls.. maybe its just because most of its power is on the bottom end and the CB is mid range. what do you guys think of this potential project. Maybe I should be on the lookout for an XR500 or 600. Or maybe stick with the 350 or 360 engine. 

The Goal is to build alittle bike to bomb around town and take to shows that just sounds ruthless and mean...  CB360 roller, rear struts, molded fiberglass cafe style seat, front forks lowered/modifed for about 2inches between the trees and seals, flat tracker style bars with lots of pullback. and of course, that unmistakable sound of an XR single... any thoughts?? 

[masonryman]

The only XR dirt bike I have rode was a XR650R, about an 2002.

Thats the way I would go if you can find one you can get right. In dirt bike trim, on dirt roads, it was stupid fast on top end compaired to a 1990 YZ 250 and a 2000 yz 450. The top speed was near 100 MPH, if not more and it was pretty easy on gas also.

Mark

[Retro Rocket]

+1 on the 650, now in a 350 frame that would not only sound sweet, it would go like hell...

Mick

[garretcb750]

Yes... I agree, I just sold my 2000 XR 650R with a baja designs dual sport kit. It was a blast on the street. I want an air cooled motor to stay vintage looking, plus those rads just look silly. There is a 84 XR600 needing a timing chain, or so the add says. Hes asking 900.00CAD. seems steap to me.

[garretcb750]

I just found a nice looking flat tracker styled bike.... something like what i had in mind.

[masonryman]

They seem to bring good money there was one 80 somthing xr 600 down the road for $1200.00, I wanted it but it was to much, so I thought

[garretcb750]

Could anyone tell me that the XR250R motor would be more fun than the CB350 or a 360?  Is it just the way the bikes feel /geared that make the XR feel like a more powerful bike. Would gearing the XR with a slightly smaller rear sprocket/larger front sprocket  take away all the fun on the low end?

[masonryman]

I guessing it's a combo of less weight and more gear

[garretcb750]

another option is rebuilding a 350/360 engine and putting a larger sprocket on the back to wake it up off the line.

[ohiocaferacer]

Check this link out.....he is using CB350f and CB400f frames
http://thekneeslider.com/archives/2009/08/27/cb450r-cafe-racer-kits-convert-honda-crf450r-dirt-bike-to-street-legal-cafe-racer/

I have always wanted to do this with a modern 450 MX motor.....thing would be fun!!

[garretcb750]

WOW..... thats just excellant. Very nice. Thanks for that link.

[Ecosse]

gerhed plopped a 600 thumper in his 360 a while back and has threads mentioning it.

http://forums.sohc4.net/index.php?topic=49537.0

http://forums.sohc4.net/index.php?topic=50250.0

[Ecosse]

Hmmm...nice idea.  But I am wondering why you don't just buy an older XL250/350 and modify it.  The frame is lighter and has better lines then either a 350 or 360 twin. I built a nice cafed XL250 in 1975 out of a wrecked 72 XL250.  It was great fun to ride and was an excellent around town bike.  The fork tubes are the same diameter as a CB 450 and CB 750, so it's pretty easy to replace the forks and add a front disc brake. 
Now the CRF450 really gets my interest.  I happen to have a CB350F frame.
Regards,
Five Fiftyfive

this idea has really captured my imagination lately too cafe, bobber, tracker, i think it's a great idea! i suppose you wouldn't have a picture of your creation 555?

ya had to see that question coming. 

[deuce_454]

it would also be a handfull with a CR500 2 stroke ... 64 horses and less weight than a 400 4-stroke

[garretcb750]

I had thoughts about a 2 stroke..I would love to get my hands on an old triple or even an RD400. I ran into a guy in Digby NS. who said he had 12 RD's and other twins. I would deffinatly grab a CR 500 if I came across one. There seems to be alot more 4 strokes around these parts though.

[ohiocaferacer]

One of my customers in Seattle, WA took an SL350.....and put an Yamaha XT500(I think??) motor in it. Said the thing hauled and was a blast to ride. He looked into using a CR500 motor but there was some issue with finding a lighting coil.....but said the Yamaha motor already was set up to run lights and didnt require setting up an electrical system to run lights.

Notice the GT750 water buffalo front end and the 2 stroke pipe run upside down with the expansion chamber under the motor.

NICE BIKE!!

[scartail]

Speaking of 2-strokers, stuffing that TSS 500 motor in it would be awesome.

[deuce_454]

very nice engine... but it deserves a better chassis IMHO...