Thanks John, good suggestions there. Inserting piston into barrel would certainly have been more straightforward, then support barrel to insert wrist pin as you suggest. Must remember that if the job ever comes up again!
A friend here was recently attempting to fit his just rebored Tr*d*nt barrel when the center piston cocked so he lifted up barrel only to have it slip from his hands and hit the floor. No broken fins but one sleeve was pushed in slightly so piston wouldn’t go in!
He’s now looking for another sleeve or set of barrels, hen’s teeth both.
Keep shiny side up.
These are my principles, if you don’t like them, I have others. (Groucho Marx)
Here’s a thing I didn’t expect to come across when setting ignition timing. Using a dti on piston crown and gauge block of a little over 7/16” thickness, there’s nowhere near enough adjustment in the points plate to have the points opening at that position. After much head scratching, came to the conclusion that the new club shop sourced piston is longer from small end to crown. The cut outs for valve clearance are certainly deeper.
Is this the right deduction and have others found the same thing happening? At the moment, there’s only one mod I can think of to be able to set timing correctly.
Thanks for any and all comments in advance. (Pun intended)
Keep shiny side up.
These are my principles, if you don’t like them, I have others. (Groucho Marx)
Shouldn't matter what piston is in there for the purpose of finding TDC or any position before or after, as the 'stroke is the stroke' and will be same whether you're at 6:1 or 10:1, dished or lumpy. It's the crankshaft & con rod position that matters.
This is an alternator and coil ignition 1960 bike, yes?
Is the points cam, part 465939, detachable - on a taper? I simply don't know on those But if it is and is in the wrong spot, then you may not have enough movement on the backplate as you say. (That happens often enough on SR1 mags, whose cams are detachable, if people have played with them.)
Or, can the points backplate be fitted '180° about' maybe, to alter the position at which the cam opens the heel of the point? I don't know that either as I haven't got an alternator single to play with.
Whatever it is that's causing the problem, I don't think it's anything to do with the piston though!
I am assuming the points were in the right place before you changed the piston and that they were not moved during the work and that the gap is still correct. Because tdc is unaffected by the shape of the piston there seems to me to be two possible explanations. Sounds like your method of checking tdc is much more technical than mine normally is, which leaves me wondering if you were trying to set the points after tdc rather than before. A mistake I have made in the past and perhaps easier to make with the head off than with an old spoke down the plug hole.
Thanks for the prompt responses chaps. Okay, what seems to be going on is not so much finding TDC, or 7/16” BTDC but that when that piston position is established, the crank hasn’t turned the points cam far enough, so that even at maximum adjustment of the points plate, the points aren’t opening, even with with the ATD wedged open.
Nothing concerning ignition timing has been altered or slipped since last riding, so I was thinking the piston must be taller above the wrist pin and that the ATD and cam assembly needs to be pulled off the drive taper on the crank and refitted in a more anti clockwise position.
Does that make sense?
Keep shiny side up.
These are my principles, if you don’t like them, I have others. (Groucho Marx)
Head isn’t on and engine is on firing stroke confirmed by the timing/breaker setting as when last running is nearly there, not 180 deg off.
In normal course of maintenance, always used spoke down plug ‘ole method of checking, without problem.
Keep shiny side up.
These are my principles, if you don’t like them, I have others. (Groucho Marx)
