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Canadian Poncho Homepage -> Canadian Poncho -> 65-70 Full Size Power Train Tech Forum -> Timing verifying TDC with piston position and harmonic balance marks
Post Info TOPIC: Timing verifying TDC with piston position and harmonic balance marks
oshawacliff


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Timing verifying TDC with piston position and harmonic balance marks
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There has been questions as to whether the harmonic balancer has shifted and giving inaccurate readings.

Is there a technique or tool for checking TDC without removing the cylinder heads?

 

 



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Cliff

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rabbit64cs


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Use a piston stop similar to this .. Rotate forward .. Mark the damper .. Then reverse . Mark and spite the difference .. There is tdc.

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later...rog

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JC2+2


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Has anyone tried if a long reach spark plug would do the same thing? Like out of a LS or vortec engine.

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cdnpont


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I used one of those on my 350 Roger. And I promptly bent it. cry

Don't be too rough with them, they bend easy. Probably designed to.

 



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rabbit64cs


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A person can improvise .. Theory is to stop the piston gently evileye



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later...rog

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Mike Ward MB


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It's never occurred to me that the damper could slip and misalign with the timing marks. I'll definitely be checking that while assembling my engine this spring.



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4SPEED427


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Yes, make sure you do. It's very common on old GM dampers. Sometimes just a little but over the years I've seen some in the shop that had turned inches!

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Fake68


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Don't forget to back off the rocker arms before using a piston stop or you may up with a bent valve.

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rabbit64cs


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Carl Stevenson wrote:

Yes, make sure you do. It's very common on old GM dampers. Sometimes just a little but over the years I've seen some in the shop that had turned inches!

 Yes,move had 2 different ones that have walked .. Found them during the build.. So who knows for sure how Many? 



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Tin Injun


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Darn right they walk - had one walk clean off the crankshaft once !  Never did find it. no

Fred



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hawkeye5766


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No fancy tool. Have always used pencil in hole and racked back and forth with flexbar.

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Pontiacanada


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hawkeye5766 wrote:

No fancy tool. Have always used pencil in hole and racked back and forth with flexbar.

I was going to say. As long as you have a long enough pencil.blankstare 



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cdnpont


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hawkeye5766 wrote:

No fancy tool. Have always used pencil in hole and racked back and forth with flexbar.

 I've often thought of making a tube that you could thread in, then slip in a spring loaded pointer that would sense the piston, and transfer that moment to a fixed reference point on the end of the tube.



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oshawacliff


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Mark

I really like that idea.   I have a friend who has a full machine shop in his garage and has done a couple of items that I needed to be created that required machining.

He is "retired" and does odd jobs.  I am sure that he would like a challenge like that.   He calls his part time business "The Inventors Tool Box."

Very skilled workmanship from what I have seen .. 

 

Thanks for all of the other contributions.

Cliff 



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koolconvertible


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I broke the centre out of an old sparkplug and inserted a bolt then cut the head off. Worked a treat. Need to come around gently till piston touches, mark balancer, reverse rotaion gently until piston comes to stop. Mark and pointer should be dead centre of marks. If I can find it I'll post a pic.

I bought a degree wheel second hand off ebay and guage as well to check the camshaft dial in. Very handy. Was spot on to spec sheet.



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