Lotus Elan

TDC Tool (Prezoom)

PostPost by: holywood3645 » Mon May 04, 2015 11:29 pm

My good buddy Rob Walker made this, So simple yet brilliant, I though I would share, If any one has done cam on a LTC timing in or out of the body you will realize how difficult it is to secure a dial indicator and measure TDC. :D

Thanks Rob !!!
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PostPost by: john.p.clegg » Tue May 05, 2015 5:24 am

It's O.K. taking TDC from the piston movement through the plug hole ( very little movement over quite a few degrees) but much more accurate taking it from somewhere like halfway down the stroke ( equidistant BTDC,ATDC) with a timimg disc and finding the mean (TDC)...

John :wink:
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PostPost by: Craven » Tue May 05, 2015 10:57 am

Hi,
Used all the time in the motorcycle world, no access to end of crank. Timing given as a measurement BTDC, eg fully advanced 38 deg = 15/32? or 11.88mm.
Ron.
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PostPost by: john.p.clegg » Tue May 05, 2015 11:30 am

Sorry,I thought we were talking cam timing ( 26,66,66,26 etc)...

John :wink:
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PostPost by: CBUEB1771 » Tue May 05, 2015 1:25 pm

john.p.clegg wrote:very little movement over quite a few degrees) but much more accurate taking it from somewhere like halfway down the stroke ( equidistant BTDC,ATDC) with a timimg disc and finding the mean (TDC)...

John :wink:


There is no reason that this dial indicator with plug hole adapter can't be used in exactly the way you describe. You just need to find something like ).060" on either side of the approximate TDC and then set up your degree wheel accordingly.
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PostPost by: john.p.clegg » Tue May 05, 2015 1:43 pm

If I was better at Trig. I could tell you how many degrees movement there is in 120 thou. ( 60 thou. either side of TDC ) as compared to 120 thou. ( 60 thou passing through 90 degrees BTDC and ATDC )
Maybe someone could enlighten us?

John :wink:
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PostPost by: Chancer » Tue May 05, 2015 3:03 pm

D?pends on the stroke of the crank and the con rod length to give an accurate answer.
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PostPost by: prezoom » Tue May 05, 2015 3:46 pm

I actually made it as a quicky to find how far off the timing mark was on the crankshaft pulley. It turns out it was 11 degrees advanced. As the age goes upward, and the mind retention goes downward, I finally remembered that back in 2006 I first discovered this. But I forgot this when I went to check and set the timing. The result was a really crappy running car. It was raining pretty hard when I finished the timing routine, and I didn't road test the car. Rolling out of the driveway, early the next morning, to run up to the Queens-English car show, was a real eye opener. Performance and fuel mileage were swirling in the porcelain fixture.
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PostPost by: billwill » Tue May 05, 2015 10:22 pm

john.p.clegg wrote:If I was better at Trig. I could tell you how many degrees movement there is in 120 thou. ( 60 thou. either side of TDC ) as compared to 120 thou. ( 60 thou passing through 90 degrees BTDC and ATDC )
Maybe someone could enlighten us?

John :wink:



TDC is at the top of a sine wave with a magnitude equal to the stroke of the crankshaft.
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PostPost by: englishmaninwales » Wed May 06, 2015 7:17 am

This setup with an analogue dial gauge is accurate for locating TDC simply by measuring the needle dwell and splitting the difference.
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PostPost by: oldchieft » Wed May 06, 2015 8:32 am

billwill wrote:
john.p.clegg wrote:If I was better at Trig. I could tell you how many degrees movement there is in 120 thou. ( 60 thou. either side of TDC ) as compared to 120 thou. ( 60 thou passing through 90 degrees BTDC and ATDC )
Maybe someone could enlighten us?

John :wink:



TDC is at the top of a sine wave with a magnitude equal to the stroke of the crankshaft.


Only true for simple harmonic motion, connecting rod angle changes it.

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PostPost by: john.p.clegg » Wed May 06, 2015 8:55 am

"TDC is at the top of a sine wave with a magnitude equal to the stroke of the crankshaft."-Bill Williams

Yes,and we all know how flat the top of a sine wave is...no vertical movement...

"Only true for simple harmonic motion, connecting rod angle changes it."-Jon the Chief

Yes,the crankpin/conrod just makes taking accurate readings even worse...

John :wink:
Last edited by john.p.clegg on Wed May 06, 2015 9:29 am, edited 1 time in total.
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PostPost by: elan66 » Wed May 06, 2015 9:15 am

My heads spinning :?
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PostPost by: john.p.clegg » Wed May 06, 2015 9:28 am

My camshaft's spinning....

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PostPost by: holywood3645 » Thu May 07, 2015 12:52 am

It's a sine wave, not a square wave.
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