Big Bore Stroker DT Engine?

[HemiDusted]

I stumbled across someone (while searching google) on this forum doing a Blaster Crank Swap on a DT engine, and I've also heard from time to time that a few people have performed a Big Bore conversion on the DT125/DT175 engine that the 200 is based on (which makes sense, they share the same cylinder jug bolt pattern)

I have an early production '78 DT125E Motorcycle that I did the MX175 Top End Swap to years ago, as well as a full rebuild and custom colorshift paint job. It was my first motorcycle and I've had it for years. I have no intentions of getting rid of her to get a larger bike (I've got larger bikes, but I love the lightweight DT), yet I'm always searching for more power.

Does anyone know what all is involved in fitting a Blaster Stroker Crank in the DT125/175 Case? I would imagine some clearance work is needed, due to the longer stroke? I'm no stranger to that, having built a few stroker V8's for my cars. Are the bearings themselves the same size? Require different bearings?

I know I could fit a Big Bore Top End to her, with a Vito's Spacer to make up the difference in stroke between the Blaster and DT, but that would only net me about a 200cc engine. If I've got her torn down, I might as well aim for a 230-240cc build, meaning I'll need that longer stroke crank too. EDIT I actually have that backwards, the Big Bore Cylinder would have to be shaved/milled to take some off to make up the difference in stroke between the Blaster & DT Cranks if I kept the stock DT Crank

Seems like the perfect time to take on a project like this, with winter here I'm definitely not riding the lil DT to work any time soon. Before I go ordering any parts though, It'd be nice to hear from some folks who have done this before.

 

[best]

I had a DT200 and my son put a DT200 cylinder on one of his Blasters.
I also have a BBK and 3mm stroker in one of my Blasters.
The 3mm stroker is a no brainer. No case trenching, maybe a bit of rod clearance on the case.
The DT200 takes a different flywheel and clutch but I THINK the crank ends are the same.

There is no BBK for the DT200 that I know of. You could put an air cooled cylinder on it but you lose the powervalve and watercooling. There is no gain really. Port the DT200 cylinder and rechamber the head and you can make nearly 40hp with it.

The aircooled Blaster cylinder and head will not fit in a DT frame or work with a DT pipe due to clearance.

Steve

 

[HemiDusted]

I had a DT200 and my son put a DT200 cylinder on one of his Blasters.
I also have a BBK and 3mm stroker in one of my Blasters.
The 3mm stroker is a no brainer. No case trenching, maybe a bit of rod clearance on the case.
The DT200 takes a different flywheel and clutch but I THINK the crank ends are the same.

There is no BBK for the DT200 that I know of. You could put an air cooled cylinder on it but you lose the powervalve and watercooling. There is no gain really. Port the DT200 cylinder and rechamber the head and you can make nearly 40hp with it.

The aircooled Blaster cylinder and head will not fit in a DT frame or work with a DT pipe due to clearance.

Steve

Mine doesn't have a Power Valve or Water Cooling, it's a 40 year old DT125 with a 175 MX Top End. Basically it's the same engine as the Blaster, minus the different stroke.

40HP would be a massive increase from the 17hp it has now.

It was the Blaster BBK that I've heard of people fitting to the 125/175. It's the difference in stroke that seemed to be an issue. If the Blaster Crank uses the same ends as the DT that's great, that gives me the option of running a +3 Crank.

Flywheel I'm not sure on. The Clutch though I've heard swaps over, the basket from a Blaster is supposed to be a heavy duty upgrade when used in a DT125/175