DO THE TON

Blood Sweat Tears and Grease => Engines => Topic started by: der_nanno on Oct 11, 2018, 03:10:39

Title: DT250 in RD250 frame and DT2-racing guide
Post by: der_nanno on Oct 11, 2018, 03:10:39
Guys,

due to a stroke of luck, I might end up being the proud owner of a DT250 engine.

Which brings me to two questions:

1) Has anybody ever fitted a DT250 into a RD250 (aircooled) frame? Not sure if the DT250 isn't too tall to go in there.
2) There used to be a DT2-racing guide - anybody got that one or if not, some good portmaps from a DT250/YZ250 of the same era. (I am well versed in RD250/350 tuning, combustion chamber reshaping, but I would like to start off with a port map that is known to work...)

As can be somewhat read out of the above, the bike will be used on the road or more precisely in short-track racing and judging by the kind of success MZ250ies can have in the class this hybrid would be eligible, I think this might be a very, very interesting package.

Cheers
Greg
Title: Re: DT250 in RD250 frame and DT2-racing guide
Post by: stroker crazy on Oct 11, 2018, 06:20:09
I can't help, but I'm fascinated by the possibility!

Crazy
Title: Re: DT250 in RD250 frame and DT2-racing guide
Post by: der_nanno on Oct 11, 2018, 06:30:24
Well, I expect quite a bit of fabrication work and on paper it doesn't make sense at first glance. But if I manage to squeeze out a genuine 30hp (should be doable, early stockers are 24hp and expansion chamber design and carburettors have come a long way since then) it mainly means, getting all the rest as light as possibe and I should be on to a very competitive bike for short and narrow tracks. Much like the 250 Bultaco road-racing bikes of the late 60ies and 70ies.

But actually with better brakes (disks) and suspension (Koni shocks) and a box-section swingarm. Strip everything off and it might go beneath 100kg with half a tank of gas...
Title: Re: DT250 in RD250 frame and DT2-racing guide
Post by: der_nanno on Oct 14, 2018, 04:36:39
Guess, nobody ever tried this... until now. For simplicity's sake I'll probably snag up an un-titled German DT250 as it'll give me all the electrical parts I need and make the whole project a tad easier.

Watch this space. (Or much rather the project's section...)  ;)
Title: Re: DT250 in RD250 frame and DT2-racing guide
Post by: stroker crazy on Oct 14, 2018, 05:06:22
Waiting ...

Crazy
Title: Re: DT250 in RD250 frame and DT2-racing guide
Post by: Pete12 on Oct 14, 2018, 19:40:00
I built a Maico with an MX250 motor years ago. I ported the cylinder, squished and cc'd the head, built a pipe, installed a yz250 close ratio gearbox and straight cut primary gears, used an RM250 piston, installed a bigger reed block and a 38mm Mikuni and used an internal rotor ignition with a YZ85 black box - it made a lot more horsepower than 30, that's for sure.
If you're getting a complete DT250 it may be just easier to use the frame on it, but if you, like everyone else on here, like a challenge then go for it - I'm interested to see how it turns out.

Title: Re: DT250 in RD250 frame and DT2-racing guide
Post by: TranceMachineVienna on Oct 15, 2018, 06:19:07
Canīt wait for the result!  :)
Title: Re: DT250 in RD250 frame and DT2-racing guide
Post by: der_nanno on Oct 15, 2018, 14:10:19
If you're getting a complete DT250 it may be just easier to use the frame on it, but if you, like everyone else on here, like a challenge then go for it - I'm interested to see how it turns out.

Rules of the racing series I want to take part in: no converted MX bikes. Additionally, I want to register the build for legal road use and as such it will be easier to stuff it in a frame with papers than the other way round.

As I said: genuine 30hp will do me just fine to be very competitive in my class, especially with a lightweight bike, if I can have a few extra hrspwrs, that'll be fine, but a broader powerband will be more useful over peak power every single day. But be forewarned: Your name is on my list to ask for cylinder wraps and some more detailed specs on which piston to use etc.

Oh and anybody wanna buy a seized DS7-engine?  ;)
Title: Re: DT250 in RD250 frame and DT2-racing guide
Post by: pidjones on Oct 15, 2018, 16:44:21
It's been ........ (gets out calculator)......... 44 years, but I seem to remember my RD250 was pretty poor handling with a mushy suspension. Don't know how much of that was components and how much was frame flex. I do remember the RD400 I traded it for was a night-and-day improvement.
Title: Re: DT250 in RD250 frame and DT2-racing guide
Post by: Pete12 on Oct 15, 2018, 17:11:04
But be forewarned: Your name is on my list to ask for cylinder wraps and some more detailed specs on which piston to use etc.
No problem at all.