Well
A piston moves up, toggels, and goes down again, if not caught repeat
A piston moves up, toggels, and goes down again, if not caught repeat
TDC Tool
- Thread starter bmetcalf
- Start date
Nine turns of my spark plug stop gets me to 25 deg before TDC +- 3 degrees ,unscrew, turn over TDC, nine turns, bring back piston 25degrees after TDC +-3 degrees. Add together the two real measurments, divide by two, set degree plate to that number. presto a true accurate TDC
Example 23deg BTDC +27deg ATDC 23+27=50/2=25 move from 27 to 25 job done
Example 23deg BTDC +27deg ATDC 23+27=50/2=25 move from 27 to 25 job done
The problem is the dwell. 6 or 8 degrees of dwell at the top means the volume fails to change, thus the whistle or bubble cannot find TDC. The variation is probably fine for most situations, but repeatability is pretty poor.
Piston stops are the most accrurate, but you can damage the top of the piston with a rigid stop. Certainly, you could damage a ceramic coating.
David
Piston stops are the most accrurate, but you can damage the top of the piston with a rigid stop. Certainly, you could damage a ceramic coating.
David
That's what interests me in the soap bubble method. It would appear to be far more sensitive than the whistle with no risk of piston damage. Still, I have always used the piston stop method. I made one or two from old spark plugs but in the last few decades (can't believe that!) I've been using a nice commercially-made one.
I guess the main problem with the stop method arises when using the rear wheel/high gear method to spin the crank. It's hard to spin it gently, so as not to slam into the stop.
Gary,
Yes, that is true about the momentum of the rear wheel potentially causing problems. But, the soap bubble method will not work with any appreciable amount of dwell. The bubble will remain at the same volume over the span of the dwell, meaning that you will be guessing with a plus/minus of the number of degrees that the dwell spans. Again, I think it will not necessarily hut the bike, but most owners are fussy about ignition timing.
David
Yes, that is true about the momentum of the rear wheel potentially causing problems. But, the soap bubble method will not work with any appreciable amount of dwell. The bubble will remain at the same volume over the span of the dwell, meaning that you will be guessing with a plus/minus of the number of degrees that the dwell spans. Again, I think it will not necessarily hut the bike, but most owners are fussy about ignition timing.
David
Assuming the 39° value given in the owner's manual of my 1928 Ariel still should be 39.00° with modern gasoline, the timing stick I made for it is wrong because it is only able to get within ±~0.8° of that value when needed on the side of the road. However, despite the timing stick giving me the "wrong" value, it still happens to be quite useful.
Life would be frustrating indeed if wrong actually were the opposite of nearly right. Luckily, it's not. Stated differently, perfect is the enemy of good enough.
it would be nice if the VOC spares would do a samll center tool to fit a degree disc on, with an expanding collet to secure in the oil hole.
I made me one, yet again an other day gone... and then the exhaust was still on.... and made up one bit longer.....
show them here, we might get some drawing work done!!!!
I made me one, yet again an other day gone... and then the exhaust was still on.... and made up one bit longer.....
show them here, we might get some drawing work done!!!!
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I made mine more simply many years ago. I used a piece of solid copper rod, about one quarter of an inch diameter. The inner end was cut along the length of the rod with two cut at right angles to each other. These were then slightly bent so that the end is still the original diameter but the diameter is enlarged about one inch from the end. The outer end was threaded one quarter BSW or BSF, I'm not sure at the moment, and a couple of nuts and penny washers used to hold the degree disc. In use the big end quill is removed and the rod and disc tapped into the hole in. the main shaft. It might sound crude but it does not slip in use, can be carefully rotated to get TDC aligned with whatever pointer is used and in fifty years and timing many bikes it has never required re_bending or repairing in any other way. The copper of course cannot damage the drilling in the main shaft.