80's model DT100 or MX100 - Help wanted

[subanator]

Anyone got a 80's model DT100 or MX100?
I need someone to measure the crank taper and shaft length to the flywheel etc.
I can explain in detail if you are able to help.
Cheers, Roger

[ChrisACT]

Anyone got a 80's model DT100 or MX100?
I need someone to measure the crank taper and shaft length to the flywheel etc.
I can explain in detail if you are able to help.
Cheers, Roger

I have a bunch of 70's DT100 cranks.  Are they different?

My 1977 DT100 crank has a YZ80J ignition rotor on it.  So you could bet that they're the same taper as the YZ80J.

[ChrisACT]

Just checked the microfiche.

DT100C ('76) thru to DT100K ('83) all had the same crankshaft (same part number).

So, what do you want me to measure?

[subanator]

Chris, your help will be appreciated. I have a photo with measurements, but my login for my web photo hosting is not letting me in.
So I will try and describe what I have:

Measured (as best as I could with plastic verniers!) with stator backing plate in place, from the backing plate Shaft dia 21mm, end of taper 15mm, length of taper 35mm (taper has key in it), length of thread 30mm, total length est. 71mm from backing plate I measured, but doesnt add up so 75/76mm may be it?

Stator backing plate mounting holes 102mm apart, dia of backing plate 120mm.

Interested to what you have said as per YZ80J, but rotor type not suitable, I need flywheel type and tying to upgrade from points/condenser to CDI.
So a smaller flywheel and source coils to adapt ok, as long as the backing plate and shaft taper is the same.

[Nathan S]

What engine do you have, and what CDI do you want to fit to it?

In my experience, the tapers and lengths of all the old school Yamaha 100, 125 and 175 dirt bike cranks is the same, with the exception of the 79 and later YZ125 (which have a smaller taper). (Hmmm... 1980+ IT175 may also be the smaller size, I'm not sure on that one).

The CDI from the previously mentioned AG100 is destined for my DT100A, several of my YZs have late DT175 ignitions, etc.

[ChrisACT]

OK, measurements from my '77 DT100D (1T9).

Shaft diameter is 20mm.
End of Taper diameter is 15mm
Length of taper is 26mm
Length of thread is 21mm
Backing plate to crank tip is 54mm

So, by my calculations the crank taper is 11 degrees.  Mind you, my measurements would only have to be .2mm out and it would be 12 degrees (which I think is what it actually is).

It might help if you were a little more specific about what you call the backing plate.  My DT has the YZ80J ignition on it so it has two plates.

The picture would be good.

[ChrisACT]

Just confirmed the same measurements from my '81 DT100H (1X1).

[subanator]

Thanks for the feedback Chris and time taken to measure, seems like this is a very close. Yes details - TY175 to adapt later model DT100 0r MX100 ignition coils and CDI.
Pics of my bike measured:
http://i45.photobucket.com/albums/f95/subanator/Bikes/Flywheelshaftmms.jpg

Here is a pic of a YZ125C found on the net, note similar taper and engine family, changed after this model I think, not DT100 as this was he same to '83 or '84. But AG100 then and current model is of earlier series from CT1 family is different Nathan, not sure of possible matching between engine families:
http://i45.photobucket.com/albums/f95/subanator/Bikes/YZ12580casing.jpg

Aim to get this DT100 flywheel and coils(source, pickup and lighting) with backing plate, and CDI. I may have to add a flywheel weight as per TY175 (sorry no pic)

I have a DT175C, taper is like YZ with keyway on a flat section , not along the taper as TY. This has a mechanical advance in the flywheel (inertia) to change the timing to points lobe to advance. I want to also change this to CDI too later on, possibly the later model DT175 may suit here also.

TY is all back together after pics taken, may need to reconfirm measurements. If DT100 flywheel taper angle the same, but length shorter, it may sit off the TY175 taper too much (keyway?) and would have to space out the coil backing plate to suit. There is a lot of room under the TY flywheel cover ompared to other models. Diameter of flywheel from the DT100 would be good too, also the backing plate dimensions if you have them too as described above.

[vandy010]

just to help with a bit more info.
i ran a monoshock DT175 stator,flywheel, cdi set~up on my little MX125a for a while and it bolted straight on, no mods needed. i don't know what model DT it came from as i picked it up from Ebay some time ago.
mixing and matching is easier than you think with them smaller motors.

[ChrisACT]

'81 DT100 flywheel is 112mm external diameter and 82mm internal diameter.

Bear in mind that this model had points ignition, not CDI.

[subanator]

Thanks Chris, you have given me enough info to go on.
Yeah Vandy010, looks are deceiving, as the DT175 was similar/different to the same year TY. I havent checked out the next series DT175 family engine properly yet either.

I will resign myself to the fact I will have to get around some wreckers next week, just is that I am not local to metro area and need the trip to be hopefully worthwhile. I think it will be possible to adapt one of the DT source/pickup coil backing plates, flywheel and CDI. Having a think today all i may need is an adapter made between the taper of my crank and another flywheel, as the taper to the DT100 is wider to the TY, so there is room to play with.

[lms6201]

i,ve looked at ty175  conversion before , when i,ve had later model 175 bits on hand , it isn,t worth the hassle , run the points , stick the (six cylinder holden) condenser up under the tank with the coil  ,keeps kool and dry , as most wetness failures occur wiith it ,  stick a spare in there two so on trail rides if one shits itself u just change leads over , and points can be fixed