Finding True tdc the easy way

Go down

Finding True tdc the easy way

Post  bbf-falcon on July 17th 2015, 9:53 am

Found this neat little tool while surfing the interweb a while back. Say's it's for Chrysler Hemi engines only. Worked great on my ole swapmeet 466 build.w/flat tops. The plunger worked smoothly through the full cycle. Just need a dial indicator w/magnetic stand.Of course if you don't have the heads already installed ,you don't need it. Very Happy



bbf-falcon

Posts : 8992
Join date : 2008-12-03
Location : Jackson, Ohio

View user profile

Back to top Go down

Re: Finding True tdc the easy way

Post  kim on July 17th 2015, 10:12 pm

Because of an inherent dwell at TDC for several crank degrees, to find TRUE TDC, you need a degree wheel, an indicator, and a piston stop. You roll the motor over one way till it hits the stop, note number on degree wheel. Roll engine other direction till it hits the stop, note the number on the degree wheel. True Top dead center is dead middle between the two numbers.

kim

Posts : 700
Join date : 2009-06-27
Location : Tucson AZ

View user profile

Back to top Go down

Re: Finding True tdc the easy way

Post  10.0 on July 17th 2015, 10:24 pm

With the rockers removed, unless you want to bend a couple valves!

10.0

Posts : 44
Join date : 2011-04-23

View user profile

Back to top Go down

Re: Finding True tdc the easy way

Post  DFI429 on July 18th 2015, 1:54 am

"Warning Use Only On Hemi Engines"  Lol..  The rest must not be worthy Razz
avatar
DFI429

Posts : 452
Join date : 2009-08-17
Age : 40
Location : Westfield, MA

View user profile http://home.comcast.net/~dfi429/

Back to top Go down

Re: Finding True tdc the easy way

Post  bbf-falcon on July 18th 2015, 7:36 am

kim wrote:Because of an inherent dwell at TDC for several crank degrees, to find TRUE TDC, you need a degree wheel, an indicator, and a piston stop.  You roll the motor over one way till it hits the stop, note number on degree wheel.  Roll engine other direction till it hits the stop, note the number on the degree wheel.   True Top dead center is dead middle between the two numbers.

With the dial indicator,you know when the piston is at the top when the piston stops pushing the plunger and the needle on the Dial indicator stops,mark it,then spin it counter until it does the same ,mark it and between the 2 marks is tdc. Easy. This is a lot easier and safer for piston than a piston stop imo.

bbf-falcon

Posts : 8992
Join date : 2008-12-03
Location : Jackson, Ohio

View user profile

Back to top Go down

Re: Finding True tdc the easy way

Post  kim on July 18th 2015, 7:55 am

Similar principle, except dont target top or xero movement.  Target a value before top.  No dwell.  Hit the same .25 before TDC in the opposit direction and the difference on the degree wheel is TRUE TDC

kim

Posts : 700
Join date : 2009-06-27
Location : Tucson AZ

View user profile

Back to top Go down

Re: Finding True tdc the easy way

Post  DaveMcLain on July 18th 2015, 10:16 am

Finding TDC with the heads on the engine is always a pain.  I think your method will work ok if you're careful and you double check your results.  About the only real problem is that the piston isn't always consistent in how it rocks in the bore due to the skirt clearance as it is close to TDC.  

The method I've used if the piston doesn't have a dome is to get the engine into a position where both valves are closed and then insert a piece of 3/16 aluminum welding rod through the spark plug hole.  I stick it into the cylinder until it touches the cylinder wall on the opposite side as the spark plug.  Then I bar it over till it pinches the wire between the piston and the quench.  Mark the degree wheel or balancer and then go back the other direction, pinch, mark the wheel and the split the difference for TDC.  I've had this method be consistent when double checking a questionable timing pointer.

DaveMcLain

Posts : 360
Join date : 2009-09-15

View user profile

Back to top Go down

Re: Finding True tdc the easy way

Post  gmsmkr on July 18th 2015, 10:57 am

DaveMcLain wrote:Finding TDC with the heads on the engine is always a pain.  I think your method will work ok if you're careful and you double check your results.  About the only real problem is that the piston isn't always consistent in how it rocks in the bore due to the skirt clearance as it is close to TDC.  

The method I've used if the piston doesn't have a dome is to get the engine into a position where both valves are closed and then insert a piece of 3/16 aluminum welding rod through the spark plug hole.  I stick it into the cylinder until it touches the cylinder wall on the opposite side as the spark plug.  Then I bar it over till it pinches the wire between the piston and the quench.  Mark the degree wheel or balancer and then go back the other direction, pinch, mark the wheel and the split the difference for TDC.  I've had this method be consistent when double checking a questionable timing pointer.

I have never thought of this.... thanks Dave sounds like it works
avatar
gmsmkr

Posts : 1364
Join date : 2014-06-22
Location : alabama

View user profile

Back to top Go down

Re: Finding True tdc the easy way

Post  supervel45 on July 18th 2015, 2:51 pm

DFI429 wrote:"Warning Use Only On Hemi Engines"  Lol..  The rest must not be worthy Razz
Hemi's with flattop pistons. The tit on the end of the tool may be to long for popup pistons to clear.

supervel45

Posts : 3080
Join date : 2013-09-04

View user profile

Back to top Go down

Re: Finding True tdc the easy way

Post  cool40 on July 18th 2015, 7:20 pm

DaveMcLain wrote:Finding TDC with the heads on the engine is always a pain.  I think your method will work ok if you're careful and you double check your results.  About the only real problem is that the piston isn't always consistent in how it rocks in the bore due to the skirt clearance as it is close to TDC.  

The method I've used if the piston doesn't have a dome is to get the engine into a position where both valves are closed and then insert a piece of 3/16 aluminum welding rod through the spark plug hole.  I stick it into the cylinder until it touches the cylinder wall on the opposite side as the spark plug.  Then I bar it over till it pinches the wire between the piston and the quench.  Mark the degree wheel or balancer and then go back the other direction, pinch, mark the wheel and the split the difference for TDC.  I've had this method be consistent when double checking a questionable timing pointer.
i use a bump stop for tdc and silver solder through the plug hole to check quench and even valve to piston clearance sometimes. Very Happy
avatar
cool40
BBF CONTRIBUTOR
BBF CONTRIBUTOR

Posts : 7161
Join date : 2009-08-31
Age : 47
Location : on the 1/8 mile dyno

View user profile

Back to top Go down

Re: Finding True tdc the easy way

Post  Super Snake Steve on July 18th 2015, 9:39 pm

3/16" aluminum welding rod sounds a little more like round stock lol

Super Snake Steve

Posts : 141
Join date : 2012-07-18

View user profile

Back to top Go down

Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum