ICL vs. .050” Cam Degreeing Methods

General engine tech -- Drag Racing to Circle Track

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BobbyB
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Re: ICL vs. .050” Cam Degreeing Methods

Post by BobbyB »

How can you set TDC accurately when reversing crankshaft rotation if there is backlash in the system?
Your TDC setting will be off by half the backlash amount wont it?
Do you measure the backlash and account for it?
The slack (backlash) will always be in the same direction on a running engine as I understand it. Correct me if I am wrong in my understanding.
Warp Speed
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Re: ICL vs. .050” Cam Degreeing Methods

Post by Warp Speed »

BobbyB wrote: Fri Jul 13, 2018 11:05 am How can you set TDC accurately when reversing crankshaft rotation if there is backlash in the system?
Your TDC setting will be off by half the backlash amount wont it?
Do you measure the backlash and account for it?
The slack (backlash) will always be in the same direction on a running engine as I understand it. Correct me if I am wrong in my understanding.
I might not be understanding your question, but what system backlash are you talking about?
You referred to the timing chain earlier, are you talking about the backlash in the cam drive system (belt/chain ect)?
If so, it makes no difference, as you can set tdc on the degree wheel without the cam even being in there, because you are just setting the degree wheel in reference to piston position.
gmrocket
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Re: ICL vs. .050” Cam Degreeing Methods

Post by gmrocket »

BobbyB wrote: Fri Jul 13, 2018 11:05 am How can you set TDC accurately when reversing crankshaft rotation if there is backlash in the system?
Your TDC setting will be off by half the backlash amount wont it?
Do you measure the backlash and account for it?
The slack (backlash) will always be in the same direction on a running engine as I understand it. Correct me if I am wrong in my understanding.
That's why reversing it is the best and most accurate way...against a solid stop to take up the clearances in bearing and pin. If just rolling in the same direction when using a dial indicator, the clearance in bearing and pin are now making the piston crown distance to crank pin longer on the down stroke....so in that instance , your tdc is not the true tdc

And if you also take into account piston rock..the dial indicator method is really a poor way to get TDC
BobbyB
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Re: ICL vs. .050” Cam Degreeing Methods

Post by BobbyB »

Thanks Warp, I was talking about the backlash in the chain/belt. I see my error in thinking now.

But, how much difference could there be if you position an indicator near the center of the piston to minimize piston rock induced error versus a piston stop? ...Maybe .1 crank degrees?

Ultimately, like others have said, TDC is really just being used as a reference point. As long as we can reliably get back to the same reference point it works out OK.
user-23911

Re: ICL vs. .050” Cam Degreeing Methods

Post by user-23911 »

I found some of my old pics.
Degree wheel.....lol

http://www.iforce.co.nz/View.aspx?i=xyiccydd.vhg.jpg

Had to make a solid tensioner to keep the belt tight as possible during degreeing

http://www.iforce.co.nz/View.aspx?i=fpkn5ox1.u2t.jpg
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