Piston position BTDC for Unit 650 timing

myron1950

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I’m sure this has been asked before but my search has not yielded results.

For a 1968 Triumph 650 what is the measurement from TDC to 38 degrees BTDC at the piston crown. My crankshaft has the TDC slot but no slot or hole for the 38 BTDC. I have used a degree wheel but would still like to know the piston position from TDC.

BTW is it as simple as (Stroke - (Cos 38 x Stroke))/2 = 8.69mm?
 

Esmerela

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I’m sure this has been asked before but my search has not yielded results.

For a 1968 Triumph 650 what is the measurement from TDC to 38 degrees BTDC at the piston crown. My crankshaft has the TDC slot but no slot or hole for the 38 BTDC. I have used a degree wheel but would still like to know the piston position from TDC.

BTW is it as simple as (Stroke - (Cos 38 x Stroke))/2 = 8.69mm?
If you know the length of your connecting rod centre to centre, this on line calculator will help.

http://www.torqsoft.net/piston-position.html
 

myron1950

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1. Alternator has marks. Unfortunately its a Wassel rotor and the marks align with nothing. However, I can make my own reference mark on rotor when crankshaft it locked at TDC and then using reference points on Primary cover move crank to 39 BTDC point. Thanks for suggestion Triton Thrasher.
2. Torqsoft program is pretty slick. Thank You Esmerela.
 

acadian

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I use one of these, easy enough to fabricate if you have a spare indicator lying around

dial gauge.JPG
 

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