Oudesluys coudesluijs at chello.nl
Sun Jun 13 08:34:54 MDT 2010

It is one of the most accurate methods I know, providing you have some 
heavy oil on the piston rings and valves for sealing. The nearer you 
initialy get to TDC and the smaller the bubble is you use, the more 
accurate the method. You will have to renew the soapy water when you are 
on TDC first time and then retry with a smaller bubble. You have to 
repeat once or twice but once you have a nearly flat `bubble`/membrane 
you can move your piston one thou and you will see a change in the soapy 
Allans method is only accurate if the crank and piston pin are in the 
same plane as the cilinder center lines, which is in most in line 
engines. If it is of center (as in some V engines) the arc on the pulley 
from left to TDC is not exactly the same as from right to TDC, although 
the difference is very slight.
Kees Oudesluijs

Eric Frenken wrote:
> Kees, I doubt that you'll come as close to the accuracy as Allen's method.  The piston moves near to nothing a few degrees BTDC and ATDC.
> Eric
> Clever idea.
> Another method is using a sparkplug core with a small diameter piece of 
> tube welded in. Bring the piston to TDC as best as you can, apply some 
> soapy water over the top of the tube and create by slowly cranking the 
> largest bubble possible, that is accurate TDC.
> Kees Oudesluijs
> NL
> allen c miller jr wrote:
>> My engine builder taught me a failsafe method for finding top dead center with
>> (literally) 'dead nutaccuracy'. I have posted a description and photos on the
>> Healey Forum maintained by team.net.
>> allen miller bn2/m

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