Finding TDC

[MoparLeo]

The pictures allow us to see what you were working with and it looked like your stop was too short for this application.
I always thought that in order to verify true tdc you had to go with the stop inserted, clockwise until it stopped and then counterclockwise until it stopped again. And then split the difference in the 2 marks to find true tdc. ??

 

[33 IMP]

The pictures allow us to see what you were working with and it looked like your stop was too short for this application.
I always thought that in order to verify true tdc you had to go with the stop inserted, clockwise until it stopped and then counterclockwise until it stopped again. And then split the difference in the 2 marks to find true tdc. ??

Yep.

 

[Mike67]

Do you have a bore scope? I think you can buy a cheap on at HF for $30. It should fit in the plug hole and allow you to get pretty close.

 

[ksurfer2]

When I tries to find tdc using just the whistle, tdc marks werent in a place that made sense. I need to verify with a more exact method. I will try a longer piston stop and maybe putting a nyloc nut on the end to get a little more depth into the cylinder. If that doesnt work, I'll pick up a bore scope.

 

[451Mopar]

I was trying to find a link to the piston stop I use, bought in the 1980's, and looks like nobody sells them anymore.
It is a single brass rod that is threaded almost the entire length with the spark plug hole threads. This makes the stop about the diameter of the spark plug hole,
I'll have to get a photo after work.
Anyhow, the spark plug location and angle are pretty shallow on the big block Mopar, so the larger diameter and longer reach really helps (that what she said.. could'n help myself.)

 

[Mike67]

When I tries to find tdc using just the whistle, tdc marks werent in a place that made sense. I need to verify with a more exact method. I will try a longer piston stop and maybe putting a nyloc nut on the end to get a little more depth into the cylinder. If that doesnt work, I'll pick up a bore scope.

If you do end up going with a scope, take a plug with you to compare the head size, some are pretty big.
You may even be able to borrow one from AutoZone or other parts house.

 

[beanhead]

Yeah it takes up some extra length just getting through those heads. Your stop is probably only protruding in about an inch. And! If it was me I would remove the rocker shaft on that side, for safety's sake....as noted earlier because of the plug's angle and position in the chamber on those heads you may need to go pretty far across, and you don't want a valve to hit the stop.

 

[ksurfer2]

It took a scope, but I got it figured out. Thanks for the assistance.

 

[MCODECUDA]

When I tries to find tdc using just the whistle, tdc marks werent in a place that made sense. I need to verify with a more exact method. I will try a longer piston stop and maybe putting a nyloc nut on the end to get a little more depth into the cylinder. If that doesnt work, I'll pick up a bore scope.

It could be that the outer ring spun so now the timing mark won’t line up with true TDC. It would be a pain but you could pull off the damper, water pump and timing cover, line up the dots then temporarily reinstall the cover and damper to see where you are.

 

[Warhorse]

I'd like to purchase a TDC whistle tool. What is the spark plug hole size? Want to make sure I get the correct size threads.

 

[451Mopar]

I use the Old Crane Cams 14mm brass piston stop like this one on E-Bay:
https://www.ebay.com/itm/203596609774?chn=ps&mkevt=1&mkcid=28

 

[toolmanmike]

No need for anything fancy, use your finger or screw a compression tester hose in there. (with your thumb over the end)

 

[khryslerkid]

No need for anything fancy, use your finger or screw a compression tester hose in there. (with your thumb over the end)

That will tell you you're on the compression stroke but you need something more mechanical to check the actual top of the stroke with the mark on your balancer.

Made myself a Piston Stop for finding TDC with the heads on. Things you will need:

Long reach spark plug

3/8 x 16 x 2 1/4 bolt

Hack saw

5/16 drill bit

3/8 x 16 tap

Cut the shoulder that's holding the porcelain all the way around. Don't saw straight through. Turn the plug as you go, stopping when you hit the porcelain. Tap around the hex on the plug to release the glue that's holding it in. Cut off the ground strap and tap the electrode and porcelain out. Also remove the sealing ring on the threads.

Useing a 5/16 drill bit, drill through the center. The inside diameter is already 5/16 but there is a shoulder halfway down. Follow up with a 3/8 x 16 thread tap.
Use a 2 1/4 bolt with at least 1 1/4 of thread.

That's all there is to it

To use the stop:

Remove all the spark plugs in the engine.

Find the piston top, by turning the crank by hand, useing a wire, or what I like to use, a plastic wire tie, in the #1 plug hole. Try to find the TDC by hand first before inserting the tool. Then back if off just a little. Then insert the tool with the bolt backed off. Run the bolt in until you feel it just touch the piston. Make a mark on the damper.

Now rotate the crank in the opposite direction until you feel it touch the stop. Go slow and let the compression bleed off. When the piston contacts the stop, make a mark on the damper.

Half the distance between the marks is your TDC.

Fine tuning where you set the bolt, can narrow the distance between your marks. A little practice and patience will get you good results. Great for checking your dampner's accuracy.

Or you can buy one. You just need to know your plug size...
https://www.summitracing.com/parts/pro-67581/

 

[ToddMcF2002]

I just ran into this. My Piston stop is too short. I got it close just letting it blow my finger off the hole on the compression stroke but I need it accurate because my "mark" at "0" says I'm idling with 30 BTC. I trust the mark but not the so called "0" indicator.

 

[Geoff 2]

Make sure you back off the valves on the cyl you are using....or....

 

[ToddMcF2002]

Never felt any resistance at all so I don't think the stop hit anything. I'm going to use an endoscope I have to try to find exact TDC

 

[33 IMP]

Never felt any resistance at all so I don't think the stop hit anything. I'm going to use an endoscope I have to try to find exact TDC

Nothing wrong with trying the scope, but it's hard to visually see TDC, even without the heads on. Do what it takes to make your piston stop work, go at the stop from both directions, it will be more accurate.
(and yes I realize "visually see" is redundantdant).

 

[ToddMcF2002]

Well tried a long bolt and that was a fail. The 440 is so big I never felt it and the piston went right past it and bent the bolt.

 

[ToddMcF2002]

I just tried my Depstech endoscope on a random cylinder and I can see the piston reach TDC clear as day. Pretty cool. I'll try it with #1 tomorrow - just need to pump it onto the compression stroke. I try to post a video since Depstech has a record mode.

 

[BB BELLA]

even though you can see the piston stop moving "up" the crank has many degrees of rotation where you won't see the piston moving! to be accurate with ignition timing you need to do the both direction stop and mark spots on the damper! find the middle of the marks and thats tdc! a degree wheel makes it simple!
I like the dial indicator method when building, if you know your crank throw you can calculate your exact number of degrees rotation by piston drop to mark your initial and max.