TY B ( 493 ) crankshaft

[Guy53]

Does anybody kbows if a DT crankshaft fit a TY 250 model 493 B model here in Canada

Guy

[David Lahey]

Guy a DT400B crankshaft will fit in the TY250B bottom end and it has suitable ends to fit TY250BCDE primary gear and flywheel. However I don't know if the if the DT250B crankshaft also has the same ends as the DT400B/TY250BCDE.

[Kurt]

It has to be asked David:
Does the DT400B barrel have the same bolting pattern as the TY250?

A TY400 would be a dangerous weapon.

[David Lahey]

It has to be asked David:
Does the DT400B barrel have the same bolting pattern as the TY250?

A TY400 would be a dangerous weapon.

I don't know about DT400B cylinders but the RT3 (360) cylinder (same stroke as DT400B) needs the TY250 rear cylinder hold-down holes moved outwards. The fronts are OK. The 360cc TY250 I rebuilt which has an RT3 cylinder had been seriously calmed down for trials use. Lower compression, much bigger flywheel weight, 26 mm carby.

[Guy53]

David, the DT 400 B is listed with a 70mm stroke, if I want to replace the crank in a TY 250 B and keep it standard, what choise do I have ?
We have looked all over the place to find a replcement for that crank, but can't find anyting.
Guy

[David Lahey]

David, the DT 400 B is listed with a 70mm stroke, if I want to replace the crank in a TY 250 B and keep it standard, what choise do I have ?
We have looked all over the place to find a replcement for that crank, but can't find anyting.
Guy

I'm fairly sure the right hand (drive half) from a DT250B crankshaft will work in a TY250B.
It is quite likely that the left hand (magneto half) from a DT250B crankshaft will fit the TY flywheel taper but I cannot guarantee it.
Are you saying that you can't find a second-hand TY250B crankshaft for sale?

[David Lahey]

I just thought of another thing Guy.
If it's the left hand end of your TY250B crankshaft that is damaged you can use the left hand end of a TY250A crankshaft and the right hand end of your crankshaft. TY250A crankshafts are easily available but differ from the later TY250 motors in that the primary drive gear sits on a spline. The left end of a TY250A crankshaft is the same as the later TY250 motors.
If it's the right hand end of your crankshaft that is damaged you can use the right hand end of a DT250B crankshaft with the left hand end of your crankshaft.
If you are still stuck after those suggestions, I can sell you a TY250C/D crankshaft (which will fit your TY250B) but the postage cost to Canada would probably be enormous.

[Guy53]

I have a couple of A model crankshaft here so we will have a look at the drive side half to see if it is still usable. The bike aparently was droped in a streem and left to rested for a long time, it took a lot of persuation to finaly '' unseize '' and take it appart.
Thank you for the offer to sell me a crankshaft but as you mentionned, I think going to your place and pick it up myself would be cheaper than have it shipped from Australia to Canada. I remember a while back, someone was interested in buying a TY mono piston that I have and It was crasy expensive to ship it ( with cost covering insurance ). I will update the post when we will finaly find a solution.
Guy

P.S. There is a few TY 250 crankshaft on the market but they are all A model.

[JC1]

If I recall correctly, the DT250 cranks have smaller OD than the TY ones. Not an insurmountable problem but you'd lose some crankcase compression and flywheel inertia with a straight swap.

[Guy53]

JC1 as the DT piston did not have the bottom of the skirt '' besseld '' as the TY ones, you certainly are right about the early DT but I was thinking about a late ( 1979 here in Canada ) one. Since the crank in question is about 500 miles from our place and not being sure that the seller will give me the real measurement, I would rater ask before order.

Guy