What a difference a few degrees makes
Discussion
... and I'm not talking about how nice it was today, though it was lovely, and I even raised a smile from an MS-5 owner when I gave him the thumbs-up for having his roof down too.
No! I'm talking about a few more degrees advance on my dizzy... seems to be very sensitive. I now know what my next job is - to calibrate TDC. It seems that I can use piston number 6 as a surrogate. I'm going to make an electronic piston stop out of an old spark plug with a needle welded to the centre core - when it makes contact it'll close the circuit and buzz a buzzer. Should be much more sensitive than a mechanical stop.
No! I'm talking about a few more degrees advance on my dizzy... seems to be very sensitive. I now know what my next job is - to calibrate TDC. It seems that I can use piston number 6 as a surrogate. I'm going to make an electronic piston stop out of an old spark plug with a needle welded to the centre core - when it makes contact it'll close the circuit and buzz a buzzer. Should be much more sensitive than a mechanical stop.
I thank you (takes a bow).... ;^)
Actually I just thought of an improvement - I have some spring-loaded contacts from an in-circuit tester (they get changed out when the fixture gets old) and they are good for a few microns repeatably being pushed in and out. So if I solder one of these onto the plug there'll be no issues with the piston coming up too high, it'll just spring in a bit.
The only issue would be if there's crud on top of the piston crown preventing a contact from being made, but the needles on the contacts are quite sharp, so should go through.
Actually I just thought of an improvement - I have some spring-loaded contacts from an in-circuit tester (they get changed out when the fixture gets old) and they are good for a few microns repeatably being pushed in and out. So if I solder one of these onto the plug there'll be no issues with the piston coming up too high, it'll just spring in a bit.
The only issue would be if there's crud on top of the piston crown preventing a contact from being made, but the needles on the contacts are quite sharp, so should go through.
Edited by adam quantrill on Tuesday 5th March 20:32
Adam,
As there is very little piston movement around TDC; The most accurate way to find TDC is as follows:-
1.
Turn engine until piston is a few mm BEFORE TDC (measure the distance or use your "indicator plug").
Mark crankshaft pulley in this position - in alignment with pointer (or some other suitable alignment point).
2.
Turn engine until piston is the SAME mm AFTER TDC.
Similarly mark crankshaft pulley in this position.
3.
TDC is midway between the two marks you have made on the pulley.
My engine has a pointer for the timing mark on the crankshaft pulley - but it is adjustable and has to be removed if you are dismantling parts in that area, so do not trust that it is correct until you have checked TDC.
Rgds
Hamish
As there is very little piston movement around TDC; The most accurate way to find TDC is as follows:-
1.
Turn engine until piston is a few mm BEFORE TDC (measure the distance or use your "indicator plug").
Mark crankshaft pulley in this position - in alignment with pointer (or some other suitable alignment point).
2.
Turn engine until piston is the SAME mm AFTER TDC.
Similarly mark crankshaft pulley in this position.
3.
TDC is midway between the two marks you have made on the pulley.
My engine has a pointer for the timing mark on the crankshaft pulley - but it is adjustable and has to be removed if you are dismantling parts in that area, so do not trust that it is correct until you have checked TDC.
Rgds
Hamish
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