Will soon be timing the CT1C. As the cylinder head has the 2 holes which are bored at a very slight angle, will this require me to remove head, or will the dial indicator’s arm still contact piston adequately to measure TDC and BTDC accurately ?

You’ll have to remove the head. On those early bikes that don’t have separate nuts to hold the cylinder down you’ll want to be sure and hold the cylinder firmly down while finding TDC. And again while setting the timing. I just went through this last weekend with my RT1. On the RT1 there is a timing tab on the stator plate that lines up with a mark on the flywheel for the timing location. If the CT has that then once you find your correct timing be sure those marks line up. Then next time you replace the points you can simply spin the flywheel to that location and set the points to begin to open. If you haven’t done this before on this bike to confirm the marks line up then you’ll have to go the route of removing the head and reading TDC. I had to make a holder for my gauge as it is made to screw into the spark plug hole of a head with a vertical plug. Other guys on here have made holders too.

Thank you. Good info. I do have a holder I used on my TY250A as my dial indicator was too tall ( mounted on head) and hindered by gas tank. Thus had to remove head.

Does anyone here use a dial indicator or a vertical mike to set the timing thru the spark plug hole? I measure the "slight angle" referenced by the OP, then use the COS of the angle to determine the actual vertical piston movement. Never found an early 1970's Yamaha Enduro I could not time with the head installed.

PS, measure the "slight angle" with a cheap plastic compass (measures angles in drafting, not the thing you take on a hiking trip).

The only problem I have found with this is that the piston needs to be past contact point on the pin or it will jam from the angle. I bring the piston to visual tdc and then install the indicator, if the piston is backed off past the pin and brought back up it will jam or bend. All good info sir except for those with poor math skills nowadays I just cheat with a Kool cell phone thingy...

Yup. Plunger can jam because has to slide across the piston... and pistons are domed...

Can it be done? Yes. Is it perfect? Not exactly. Close enough? Probably.

Central Tools does make a dial indicator kit that allows the indicator plunger to go straight in on most angled plug holes... you can find them on ebay sometimes for a good price.... I think I paid $40 for mine.

Ended up making a holder from bits we had. Tapped the plate to screw in the spark plug threaded dial indicator adapter piece. Works like a charm. Thanks guys.

Ended up making a dial indicator holder from bits we had. Works like a charm. Thanks for the pointers.

The challenge is not TDC. The problem is precisely measuring the distance of the piston BTDC.

If indicator plunger is not parallel to the bore axis you need to use trigonometry to convert the dial indicator reading to the actual distance the piston is BTDC.

The harder part is with the plunger at an angle to the bore, it will also need to slide across the piston crown... since the piston top is crowned, this will add another error to the measurement.