another TDC question - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 03-06-2008, 07:21 AM
johnnyblaze's Avatar
Registered User
 
Join Date: Feb 2008
Location: edmonton,alberta,canada
Posts: 32
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
another TDC question

is a positive stop tool more accurate than the fingerin the hole method?
and when just using your finger,is it when you first feel pressure against your finger,or is it when you feel pressure,then keep turning till the pressure stops,
is TDC????to me it seems it would be the latter,as the piston would be pushing pressure till it was at the top,is this correct??as many details on this would be appreciated,thx in advance
P.S.THIS IS THE FORUM OF FORUMS,SIMPLY THE BEST!!!!!!!!!!!!

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 03-06-2008, 08:49 AM
inquiring_mind2's Avatar
a shade tree mechanic
 
Last photo:
Join Date: Jul 2004
Location: Illinois
Age: 43
Posts: 481
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I have used a wooden dowl rod I turned the motor over till I feel the pressure on my finger then I will stick a wooden dowl rod in the hole and watch it go up and when it starts to go down then I will rotate it back till it appears it is on tdc
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 03-06-2008, 09:11 AM
Registered User
 
Join Date: Mar 2007
Location: Iowa
Posts: 134
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Assuming you are doing the positive stop method correctly, it is absolutely the most accurate as it accounts for TDC dwell time and gets the crank exactly at the TDC point. Even if you don't use a degree wheel it is very accurate.

The correct positive stop method:
Make a stop that will stop the piston at somewhere around 1/2" before TDC. Install the stop, roll the piston up against it.
If using a degree wheel take note of the number of degrees before or after TDC. If using the factory balancer, mark it where the pointer is located.
Roll the engine in the opposite direction till it comes back against the stop, take note of the degree wheel location or mark the balancer again.

TDC is exactly at the mid point of the two end points you marked.......
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 03-06-2008, 10:28 AM
johnnyblaze's Avatar
Registered User
 
Join Date: Feb 2008
Location: edmonton,alberta,canada
Posts: 32
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
thx to the both of you,can anyone be just as accurate for the finger pressure method,or should i stay away from this for accuracy reasons?is a stop tool something you can buy,or do you have to make them?how wide in comprison to the plug hole is best,or does it matter?
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 03-06-2008, 10:39 AM
inquiring_mind2's Avatar
a shade tree mechanic
 
Last photo:
Join Date: Jul 2004
Location: Illinois
Age: 43
Posts: 481
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
it can be done pretty accurate with the finger method. If you decide to buy the tool. the tool is designed to be used with the head off. so it depends on what stage you are at building the motor. If its already put together then the finger method is good to use. I would still check it when you feel the preesure against your finger. LIke I said earlier I use a wooden dowl. I just stick it the hole and rotate the motor over watching the rod when it goes up and just starts to come down then you know you are on TDC.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 03-06-2008, 10:40 AM
Jmark's Avatar
Registered User
 
Last photo:
Join Date: Sep 2003
Location: phoenix
Age: 61
Posts: 4,925
Wiki Edits: 0

Thanks: 13
Thanked 47 Times in 36 Posts
The method you use depends on what you are trying to accomplish. If you are degreeing the cam or verifying the timing tab/balancer numbers, the finger method is NOT accurate. The main purpose of doing it this way is so you can "get close" to TDC and then slowly rotate the crank/balancer until the timing marks line up at zero.

If you are looking for exact TDC, accuracy is paramount. If the head is off, use a dial indicator on the piston top and a degree wheel on the crank.

I think you can buy an insert that screws into the plug hole that acts as a piston stop.

Mark

Last edited by Jmark; 03-06-2008 at 11:01 AM.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 03-06-2008, 10:53 AM
johnnyblaze's Avatar
Registered User
 
Join Date: Feb 2008
Location: edmonton,alberta,canada
Posts: 32
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
i could be wrong,but a positive stop tool is for when the head is installed,isnt it inquiring mind2??a dial indicator is for when the head is off...can anyone else comment on this wooden dowl,or whatever else you decide to use,good,no good,accurate,not accurate??
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 03-06-2008, 11:00 AM
Jmark's Avatar
Registered User
 
Last photo:
Join Date: Sep 2003
Location: phoenix
Age: 61
Posts: 4,925
Wiki Edits: 0

Thanks: 13
Thanked 47 Times in 36 Posts
Quote:
Originally Posted by johnnyblaze
i could be wrong,but a positive stop tool is for when the head is installed,isnt it inquiring mind2??a dial indicator is for when the head is off...can anyone else comment on this wooden dowl,or whatever else you decide to use,good,no good,accurate,not accurate??
That is correct.

Re-read my previous post, I added some to it a minute ago.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 03-06-2008, 11:02 AM
inquiring_mind2's Avatar
a shade tree mechanic
 
Last photo:
Join Date: Jul 2004
Location: Illinois
Age: 43
Posts: 481
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
yes my bad I explained it wrong. I have used the dial indicator before and thats when the head is off. Sorry for the confusion
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 03-06-2008, 11:10 AM
johnnyblaze's Avatar
Registered User
 
Join Date: Feb 2008
Location: edmonton,alberta,canada
Posts: 32
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
thx..thx..thx..
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 03-06-2008, 01:11 PM
techinspector1's Avatar
Senior Curmudgeon
 
Last wiki edit: DynoSim combinations Last photo:
Join Date: Oct 2005
Location: Hemet, California, USA
Age: 72
Posts: 13,308
Wiki Edits: 326

Thanks: 836
Thanked 1,151 Times in 950 Posts
http://www.crankshaftcoalition.com/w...ff_for_newbies
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 03-06-2008, 01:59 PM
Registered User
 
Last photo:
Join Date: Jul 2007
Location: norcal
Age: 59
Posts: 762
Wiki Edits: 0

Thanks: 1
Thanked 2 Times in 2 Posts
what are you guys talking about??? the positive stop method is the ONLY ACCURATE way to find TDC. it can be done with the head on or off. with the head on--i made some positive stop tools years ago by breaking the porcelean (sp) out of spark plugs and brazing in 2" 1/4 steel rods, screw it into the hole and there's your positive stop. with the head off-- i use a steel steel flat bar that bolts across the cylinder by the head bolts that is drilled and tapped above the center of the cylinder with a bolt threaded in, there's your positive stop.

the positive stop method will give you EXACT TDC, any other method will only get you close (like +/- 5 degrees) would you set your timing +/- 5 degrees and say that is close enough??? i don't think so!!

useing a degree wheel and positive stop i have found a lot of balancers right on. BUT you never know, i am building a 383 SBC and just found the balancer TDC mark is 4 degrees off, so always check for exact TDC. how can you degree a cam or set timing if you don't know where EXACT TDC is???
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 03-06-2008, 04:24 PM
Jmark's Avatar
Registered User
 
Last photo:
Join Date: Sep 2003
Location: phoenix
Age: 61
Posts: 4,925
Wiki Edits: 0

Thanks: 13
Thanked 47 Times in 36 Posts
Quote:
Originally Posted by techron
what are you guys talking about??? the positive stop method is the ONLY ACCURATE way to find TDC. it can be done with the head on or off. with the head on--i made some positive stop tools years ago by breaking the porcelean (sp) out of spark plugs and brazing in 2" 1/4 steel rods, screw it into the hole and there's your positive stop. with the head off-- i use a steel steel flat bar that bolts across the cylinder by the head bolts that is drilled and tapped above the center of the cylinder with a bolt threaded in, there's your positive stop.

the positive stop method will give you EXACT TDC, any other method will only get you close (like +/- 5 degrees) would you set your timing +/- 5 degrees and say that is close enough??? i don't think so!!

useing a degree wheel and positive stop i have found a lot of balancers right on. BUT you never know, i am building a 383 SBC and just found the balancer TDC mark is 4 degrees off, so always check for exact TDC. how can you degree a cam or set timing if you don't know where EXACT TDC is???
Not sure where you got "you guys". I and TDKKart posted accurate info for using a stop and degree wheel OR dial indicator with a degree wheel.

Using the finger method is fine if you are just wanting to get the engine coming up on compression so you can then manually turn the engine to line up the timing marks for dropping in the distributor.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 03-06-2008, 04:52 PM
Registered User
 
Last photo:
Join Date: Jul 2007
Location: norcal
Age: 59
Posts: 762
Wiki Edits: 0

Thanks: 1
Thanked 2 Times in 2 Posts
Quote:
Originally Posted by Jmark
Not sure where you got "you guys". I and TDKKart posted accurate info for using a stop and degree wheel OR dial indicator with a degree wheel.

Using the finger method is fine if you are just wanting to get the engine coming up on compression so you can then manually turn the engine to line up the timing marks for dropping in the distributor.
sorry Jmark, i was a joke (see the smiley). i still think the positive stop method is still the way to go. a dial indicator will dwell 3-4 degrees right at TDC so i think you could still end up 1 or 2 degrees off. and yes, you only have to find true TDC once, after that anything works, line up timimg marks, stick somthing in the spark plug hole to feel the piston reach TDC, feel it with your finger as long as you are just looking for approx. TDC.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 03-06-2008, 05:40 PM
Jmark's Avatar
Registered User
 
Last photo:
Join Date: Sep 2003
Location: phoenix
Age: 61
Posts: 4,925
Wiki Edits: 0

Thanks: 13
Thanked 47 Times in 36 Posts
No problem.

When I did mine and my sons, I used a dial indicator but ran it "in the hole" some. Came "up" and brought it till it touched, then past and "down" till I came to the same reading, divided on the wheel and got it nailed down. Cked the cam and mine was exactally on and my son's was 1.5 degrees off. Close enough.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
383 stroker 73monte Engine 11 05-07-2014 09:08 AM
supercharger.... 73monte Engine 16 07-24-2010 11:27 AM
question about a previouse question elrod1030 Engine 6 03-10-2010 08:35 AM
Ignotion Set-ups Native Gearhead Engine 8 11-29-2003 02:20 PM
nitrous 69BiRd Engine 2 11-28-2003 11:33 PM


All times are GMT -6. The time now is 03:37 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.