Service Bulletin: Flywheel Stop Pin Tool
Original Triumph Service Bulletin 4-8-1968
Hey fellow C.B.S. fans, customers, and readers. This Triumph service bulletin dated April 8, 1968, goes into detail about a top dead center (T.D.C.) crankshaft locating pin that was sent out to eastern dealers to be used on 1968 Triumph 500 and 650 twins to coupe with the narrow crankshaft locating slots.
"1968 was an odd year..."
1968 was an odd year for Triumph 650 twins in regards to the T.D.C. crankshaft locating hole. Most of us are aware that the T.D.C. hole on a Triumph 650 unit twin is usually behind the cylinder barrel near the back of the tappet block. Although that applies to most models, 1968 was a year that it did not apply to all during the beginning.
The 3 types of Triumph 650 T.D.C. locations for 1968
For 1968 Triumph 650 models there where 3 iterations of the T.D.C. locating hole that was used that model year. That means Triumph had to cast each case differently and the crankshafts to accommodate each change. 1st condition is the early variety that only featured 1 T.D.C. hole on the timing side in the front of the case. (Very similar to BSA unit twins). 2nd condition features 2 T.D.C. holes. 1 in the front (like the 1st condition) and 1 in the back. 3rd condition has 1 T.D.C. hole behind the cylinder barrel in its typical location like most 650 unit twins. Also known as MKI, MKII, and MKIII variety's.
So what does this have to do with this service bulletin?
Original, NOS Triumph T.D.C. pin tool for 1968 cranks (notice the tapered end)
Since Triumph was experimenting with T.D.C. holes, there had to be additional slots on the crankshaft. This pin has a more tapered angle to fit the narrow slots of the 1968 crankshafts. Some T.D.C. timing pins tools will not fit in 1968 cranks.
Technically you could make your own tool as stated in the service bulletin either with a lathe or by hand girding. If you choose to make your own pin, use this measurements as shown in this Triumph service bulletin.