TY175B DT175B DT175E motors - mainly for Subanator

[David Lahey]

Today I had to take the cylinder off a DT175E motor and compared a few dimensions on it with TY175B and DT175B

The DT175 E is the late type DT motor with some significantly different design features compared with the ABCD DT175 motors, but retaining the same bore x stroke and piston dimensions.

The port tops and bottoms on the DT175B and DT175E are the same. The DT175E exhaust port has smaller radius corners than the DT175B.

The DT175E and the DT175B heads are the same volume (21ml) and the TY175B is 23ml.

The combustion recess in the TY175B and DT175B heads is central while the DT175E recess is offset to the rear

The reed cages of the DT175B and DT175E are the same size and are also the same size as the TY250 twinshock reed cage. The TY175 reed cage is quite a bit smaller than the others.

[Tee-Why]

Thanks David, would have expected more changes to the later DT, as it performed better. Put that down to the elec ignition and exhaust design and higher compression I suppose.
With the reed block size difference, the inlet port is the same size to the TY? Transfer ports the same too?
Also is there a difference in the port window size in the piston between the DT's?

[David Lahey]

I've recently being doing more experiments with the TY175 that has the DT175E motor in it. When previously reported on, it had TY175 exhaust, TY175 ignition, TY175 flywheel and TY175 airbox and an AG175 carby (26mm Mikuni). The bike was loaned out for a while and when it came back I decided that it was time to get the jetting working better, and in the mean time a DT175G basket case had turned up in the shed, so I thought I would see what could be done with the carby off it. Sad to say that carby has a bent needle and a partially squashed slide. Next step was to check a very weathered TY175JC that I bought from Hagsta years ago - bingo it had a carby on it that was complete and original. After a good cleanout, I tried it with the standard TY175 JC jetting and it was a fair way off being right. Next step was to try the jetting I use on my 205cc TY175 motor and bingo it ran like a dream. With the jetting finally right can say that the DT175 motor set up with the TY175 carby and the rest of the Ty175 gear is so similar to a TY175 motor in performance I can't split them. Where the TY motor is better though is in the gear ratios. I have geared the DT175 motor TY175 so that first gear is about the same overall ratio as a TY175 with a 13T front sprocket. Unfortunately this means that the DT motor second gear is about the same as the TY175 third gear, so if there was a section that would suit second gear on the TY175, the DT motor bike would be at a disadvantage.
The other thing I found was that having the smaller (22mm) carby on the DT motor TY175 has dulled the top end surge the bike used to have when it had the 26mm carby.