Engine Mechanical Topics Discussion for motor builds, cams, head work, stripped bolts and other engine related issues. The good and the bad. If it goes round and around or up and down, post it here.

How do I verify TDC on a cylinder?

Thread Tools
 
Search this Thread
 
Old May 26, 2025 | 09:33 PM
  #11  
LQQK_OUT's Avatar
LQQK_OUT
Thread Starter
|
Seasoned HDF Member
15 Year Member
Liked
Loved
Community Favorite
Joined: Nov 2006
Posts: 5,832
Likes: 1,870
From: East Coast, USA
Default

I have another question. When I align both timing marks on the crank and cam sprocket to get TDC on the rear cylinder, should both lifters for that cylinder be at their lowest point? When I looked inside the lifter cover, it looked like one lifter was slightly higher than the other one (which seemed to be at it's lowest point).
 
Reply
Old May 27, 2025 | 05:54 AM
  #12  
Schex's Avatar
Schex
Club Member
Joined: Apr 2011
Posts: 5,754
Likes: 7,777
From: SE Louisiana
Riders Club Member
Default

Yes they both should be on the base circles, can you push it down?
 
Reply
Old May 27, 2025 | 09:05 AM
  #13  
Fat11Lo's Avatar
Fat11Lo
Stellar HDF Member
10 Year Member
Liked
Loved
Community Favorite
Joined: Mar 2012
Posts: 2,008
Likes: 595
From: Columbus, OH
Default

Easiest way for me is to watch or feel intake lifter open then close turn a few more degrees and then install the pushrods, doesn't have to be exactly on TDC as stated before
 
Reply
Old May 27, 2025 | 11:05 AM
  #14  
LQQK_OUT's Avatar
LQQK_OUT
Thread Starter
|
Seasoned HDF Member
15 Year Member
Liked
Loved
Community Favorite
Joined: Nov 2006
Posts: 5,832
Likes: 1,870
From: East Coast, USA
Default

Originally Posted by Schex
Yes they both should be on the base circles, can you push it down?
Wow! A perfect example of Occam's razor.
Yes! I guess when I installed the lifter (I coated it with oil), it didn't fall all the way into the passageway. Now, with the timing marks on the crank and cam sprocket aligned, the lifters are at their lowest point and on the base circle of the cam. Thank you!

 
Reply
Old May 27, 2025 | 11:06 AM
  #15  
memphisharley's Avatar
memphisharley
Stellar HDF Member
Veteran: Marine Corps
5 Year Member
Liked
Community Favorite
Joined: Sep 2017
Posts: 2,117
Likes: 562
From: memphis
Default

this is how i do it:
remove the plugs
place in 6th gear
place a straw in the cylinder you are working on
turn the rear tire until straw shoots out of the cylinder
retrieve straw from the other side of the garage
insert straw into the cylinder and feel for the piston
rock rear wheel to bring the piston back to the top
repeat on other cylinder
 
Reply
Old May 27, 2025 | 02:05 PM
  #16  
98hotrodfatboy's Avatar
98hotrodfatboy
Seasoned HDF Member
15 Year Member
Liked
Loved
Top Answer: 5
Joined: Mar 2010
Posts: 20,850
Likes: 7,391
From: Poolville
Default

Whatever happened to just watching the rear cylinder intake and exhaust lifters going to overlap, which would be spin the motor over with the rear wheel in 6th gear watch the intake lifter come up and go down. continue spinning the rear wheel to watch the exhaust lifter go up an them start to go down.. as the exhaust lifter on the rear cylinder starts to go down you will see the intake lifter starting to come up at the same time, This would be the overlap.. stop spinning the rear wheels when the two lifters are even in the lifter bores stop turning the wheel and at this point you can install an adjust the front push rods to their desired preload any wears from 0.125" to 0.140".... To do the rear cylinder you would put the front cylinder in overlap the same way and then install an adjust the rear cylinder pushrods.. no guessing..
 
Reply
Old May 30, 2025 | 08:00 AM
  #17  
LQQK_OUT's Avatar
LQQK_OUT
Thread Starter
|
Seasoned HDF Member
15 Year Member
Liked
Loved
Community Favorite
Joined: Nov 2006
Posts: 5,832
Likes: 1,870
From: East Coast, USA
Default

Originally Posted by memphisharley
this is how i do it:
remove the plugs
place in 6th gear
place a straw in the cylinder you are working on
turn the rear tire until straw shoots out of the cylinder
retrieve straw from the other side of the garage
insert straw into the cylinder and feel for the piston
rock rear wheel to bring the piston back to the top
repeat on other cylinder
@memphisharley
I'm not understanding how this above procedure ensures that TDC is on the compression stroke.

Originally Posted by 98hotrodfatboy
Whatever happened to just watching the rear cylinder intake and exhaust lifters going to overlap, which would be spin the motor over with the rear wheel in 6th gear watch the intake lifter come up and go down. continue spinning the rear wheel to watch the exhaust lifter go up an them start to go down.. as the exhaust lifter on the rear cylinder starts to go down you will see the intake lifter starting to come up at the same time, This would be the overlap.. stop spinning the rear wheels when the two lifters are even in the lifter bores stop turning the wheel and at this point you can install an adjust the front push rods to their desired preload any wears from 0.125" to 0.140".... To do the rear cylinder you would put the front cylinder in overlap the same way and then install an adjust the rear cylinder pushrods.. no guessing..
It's just a lack of confidence on my ability since I have very little experience in this area. The fear of adjusting the pushrods while the piston isn't at TDC on the compression stroke is rather large. Also, working with the bike on a motorcycle jack, I'm on the floor, trying to spin the rear wheel and place my fingers inside the lifters is a job for a contortionist. If I had a helper, this would be much easier.
Anyways, I got it done.

I'd like to thank everyone for their help!
 
Reply
Old May 30, 2025 | 08:29 AM
  #18  
98hotrodfatboy's Avatar
98hotrodfatboy
Seasoned HDF Member
15 Year Member
Liked
Loved
Top Answer: 5
Joined: Mar 2010
Posts: 20,850
Likes: 7,391
From: Poolville
Default

Originally Posted by LQQK_OUT
@memphisharley
I'm not understanding how this above procedure ensures that TDC is on the compression stroke.



It's just a lack of confidence on my ability since I have very little experience in this area. The fear of adjusting the pushrods while the piston isn't at TDC on the compression stroke is rather large. Also, working with the bike on a motorcycle jack, I'm on the floor, trying to spin the rear wheel and place my fingers inside the lifters is a job for a contortionist. If I had a helper, this would be much easier.
Anyways, I got it done.

I'd like to thank everyone for their help!
When I do go by the TDC method I use a straw in the cylinder to verify the piston is up.. just make sure you also watch the intake lifter go up the down, once down and the straw full up and mostly out of the spark plug hole you know you're very close.. It doesn't have to be exact.. After putting the preload on the lifter make sure you wait till you can freely spin the pushrod. After tht you can move on to the other cylinder without worry.. .125" of preload works very well.
 
Reply
Old May 30, 2025 | 10:34 AM
  #19  
memphisharley's Avatar
memphisharley
Stellar HDF Member
Veteran: Marine Corps
5 Year Member
Liked
Community Favorite
Joined: Sep 2017
Posts: 2,117
Likes: 562
From: memphis
Default

Originally Posted by LQQK_OUT
@memphisharley
I'm not understanding how this above procedure ensures that TDC is on the compression stroke.
the compression is what throws the straw out of the spark plug hole to the other side of the garage.
 
Reply
Old May 30, 2025 | 12:21 PM
  #20  
Rounders's Avatar
Rounders
Seasoned HDF Member
Community Builder
Liked
Loved
Community Favorite
Joined: Mar 2021
Posts: 17,561
Likes: 3,445
From: backwoods
Default

Originally Posted by memphisharley
the compression is what throws the straw out of the spark plug hole to the other side of the garage.
What are you running a diesel?

When tearing an engine down i stick my finger in hole to feel pressure. Also do straw. I then feel pushrods spin freely with no tension

They use to make something that would screw in spark plug hole and rise and fall . Waste of money to some. But would be cool gizmo

 
Reply



All times are GMT -5. The time now is 12:59 AM.