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Re: [alfa] Dial Indicators for Finding TDC



Having use both the dial indicator method and the pulley pointer method, in
my opinion the differences are moot and not enough to affect 99 percent of
Alfa engines.  Not a waste of time but perhaps not time well spent.

Don

----- Original Message -----
From: Ed Lutz <[email protected]>
To: Paul Bayly <[email protected]>; alfa digest <[email protected]>
Sent: Saturday, October 25, 2003 9:27 PM
Subject: Re: [alfa] Dial Indicators for Finding TDC


> You may find a bit of error is possible in using this method. this is due
> to the slowing motion of the piston as it rocks over TDC, it can be
> difficult to decide just where in the cranks rotation true TDC is really
> at. The most accurate method of determining TDC is probably (in my
opinion)
> the use of a degree wheel and piston stop. Mount the degree wheel as you
> would in timing cams. Insert the piston stop in the spark plug hole and
> turn the crank one direction until the piston stops on the piston stop.
> Record the reading on the degree wheel. Rotate the engine in the opposite
> direction and record the reading where the piston is stopped. True TDC
will
> be in the exact middle of these two readings. This method removes the
> "slop" inherent in the dial indicator method.
>
> Ed
>
> At 11:40 AM 10/26/03 +0930, Paul Bayly wrote:
> >Albert,  Good idea on confirming TDC.
> >
> >Most dial indicators I work with have some means of being attached to a
> >sliding rod, which in turn is attached to a clamp or magnetic base.
> >
> >Now obviously the magnetic base won't be any use on the alloy head, but a
> >suitably shaped iron plate simply held down across three head nuts will
> >suffice.This method would need a second pair of hands to rotate the
crank.
> >By using three resting points instead of four there is no rocking of the
> >plate. There will be very little force applied to the indicator by the
> >piston so variations in readings shouldn't present any problems due to
> >distortion of the dial clamping device/attaching arm.
> >
> >Alternatively, you could build some form of attachment using an old spark
> >plug, suitably hollowed out to allow the point of the indictor to feed
thru
> >onto the piston crown.  You may require an instrument with a longer point
> >than standard.
> >
> >The absolute value/measurement of the height of the piston relative to
the
> >top of the block is irrelevant, so is it's relative 'squareness' to the
top
> >of the block You are only after an indication of when the piston has
reached
> >the top of its travel, and you will be measuring the rotation over only a
> >few degrees as you rock the crank.  Once confirmed as correct, you can go
> >back to using the pointer on the front of the engine.
> >
> >Beatle
> >Oz
> >--
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