changing valve springs...how to tell when piston is at it's top position
Thread Starter
Registered User
Joined: Sep 1998
Posts: 8,319
From: US 1 Mile Marker 52 in the Florida Keys
changing valve springs...how to tell when piston is at it's top position
i'm changing valve springs in the next week or so, i don't have access to a compressor to pressurize the cylinder to hold the valves in place.
i should be able to just turn the crank into position so the chosen piston is is at it's highest point.
what is the best way to do this? is there a way to figure it out using firing order and which other valves are open?
i should be able to just turn the crank into position so the chosen piston is is at it's highest point.
what is the best way to do this? is there a way to figure it out using firing order and which other valves are open?
Registered User
Joined: Dec 2003
Posts: 254
From: Charleston, SC
Re: changing valve springs...how to tell when piston is at it's top position
heh, its been my experiance that if you're using air pressure to hold the valves up, dont worry about piston location.. it will go down when you pressureize the chamber.
if you're using the rope in the chamber trick, you'll know because the crank wont turn anymore... as you turn the crank (by hand) you'll feel the rope compress and then it stops.
if you're using the rope in the chamber trick, you'll know because the crank wont turn anymore... as you turn the crank (by hand) you'll feel the rope compress and then it stops.
Thread Starter
Registered User
Joined: Sep 1998
Posts: 8,319
From: US 1 Mile Marker 52 in the Florida Keys
Re: changing valve springs...how to tell when piston is at it's top position
wasn't planning on useing either method. i was going to combine these two methods...since i won't have the timing cover off to see the marks. i was going to rotate the crank till i felt the piston come to TDC, then use the oreder they list to do the proper cylinders
taken from www.ls1howto.com
Top dead center method
This method requires you to put the piston at the highest position in the bore, so that when you start to compress the spring, the valve can only drop until it hits the piston. When the piston is at top dead center, the valve can't move very far at all.
A) You can place a small stick/rod/straw/something into the spark plug hole and have a buddy turn the crankshaft by putting the stock 24mm crank pulley bolt in and turning the bolt with a wrench. You should be able to feel when the piston comes up to the top.
B) This method is a bit more elegant. Rotate your motor over by hand until your cam gear and crank gear are dot to dot like you set them up as earlier. At this position, piston 1 and 6 should be at top dead center. You can change the 4 springs on these 2 cylinders now using the instructions below. After you change those 4, then, rotate the crankshaft a full 90 degrees, and the cam gear dot will turn 45 degrees, as if it is pointing to 7:30 if it were a clock. Now piston 8 and 5 are at the top and can be changed. Rotate another 90 degrees on the crank and your cam gear dot will now be at 9 o'clock. Piston 7 and 4 can now have their springs changed. And FINALLY, rotate the crank another 90 degrees and the cam gear dot will be at 10:30. You can now change your remaining four springs on piston 3 and 2.
Once again, that's 1 & 6, rotate 90, 8 & 5, rotate 90, 7 & 4, rotate 90, 3 & 2.
taken from www.ls1howto.com
Top dead center method
This method requires you to put the piston at the highest position in the bore, so that when you start to compress the spring, the valve can only drop until it hits the piston. When the piston is at top dead center, the valve can't move very far at all.
A) You can place a small stick/rod/straw/something into the spark plug hole and have a buddy turn the crankshaft by putting the stock 24mm crank pulley bolt in and turning the bolt with a wrench. You should be able to feel when the piston comes up to the top.
B) This method is a bit more elegant. Rotate your motor over by hand until your cam gear and crank gear are dot to dot like you set them up as earlier. At this position, piston 1 and 6 should be at top dead center. You can change the 4 springs on these 2 cylinders now using the instructions below. After you change those 4, then, rotate the crankshaft a full 90 degrees, and the cam gear dot will turn 45 degrees, as if it is pointing to 7:30 if it were a clock. Now piston 8 and 5 are at the top and can be changed. Rotate another 90 degrees on the crank and your cam gear dot will now be at 9 o'clock. Piston 7 and 4 can now have their springs changed. And FINALLY, rotate the crank another 90 degrees and the cam gear dot will be at 10:30. You can now change your remaining four springs on piston 3 and 2.
Once again, that's 1 & 6, rotate 90, 8 & 5, rotate 90, 7 & 4, rotate 90, 3 & 2.
Moderator
Joined: Jul 1998
Posts: 6,247
From: Charlotte,MI USA
Re: changing valve springs...how to tell when piston is at it's top position
Originally Posted by teke184
i'm changing valve springs in the next week or so, i don't have access to a compressor to pressurize the cylinder to hold the valves in place.
i should be able to just turn the crank into position so the chosen piston is is at it's highest point.
what is the best way to do this? is there a way to figure it out using firing order and which other valves are open?
i should be able to just turn the crank into position so the chosen piston is is at it's highest point.
what is the best way to do this? is there a way to figure it out using firing order and which other valves are open?
Thread Starter
Registered User
Joined: Sep 1998
Posts: 8,319
From: US 1 Mile Marker 52 in the Florida Keys
Re: changing valve springs...how to tell when piston is at it's top position
thanks al
i was planning on putting my finger over the plug hole, when it begins to suck in it should be at TDC.
would you beleive i got that from watching "monster garage"? lol.
i was planning on putting my finger over the plug hole, when it begins to suck in it should be at TDC.
would you beleive i got that from watching "monster garage"? lol.
Thread Starter
Registered User
Joined: Sep 1998
Posts: 8,319
From: US 1 Mile Marker 52 in the Florida Keys
Re: changing valve springs...how to tell when piston is at it's top position
well i got things disassembled, and have cyl 1 springs swapped. it was a bit of a pain doing those tiiny locks, but not horrible. granted that is the easiest cylinder...
i figured TDC by watching the valves, when #1 exhaust closed, and then #6 closed a little later (turning the crank). i pulled the springs on #1 and they barely dropped, same on #6.
now i have to find a kind soul to help me with the ones under the cowl. i think it will be easier messing with the locks with a second set of hands holding the springs compressed.
i figured TDC by watching the valves, when #1 exhaust closed, and then #6 closed a little later (turning the crank). i pulled the springs on #1 and they barely dropped, same on #6.
now i have to find a kind soul to help me with the ones under the cowl. i think it will be easier messing with the locks with a second set of hands holding the springs compressed.
Registered User
Joined: Jun 2001
Posts: 1,209
From: TX
Re: changing valve springs...how to tell when piston is at it's top position
Also recommend the rope method. Just pop all the rockers and plugs. Then get thin rope like for clothes lines. Feed in some rope in a cylinder. Rotate the engine. When the rope stops the engine rotation = TDC. Firing or non firing not important.
This method doesn't care where the dots are. Or the valves, cause the rockers are off.
Your method of finding TDC firing reminds me of back in the day when I ran solid cams, like the Z28 second design off road cam in my 57 Bel Air. IC EO for adjusting the valves. Ah the memories of the sweet music of solid lifters.
This method doesn't care where the dots are. Or the valves, cause the rockers are off.
Your method of finding TDC firing reminds me of back in the day when I ran solid cams, like the Z28 second design off road cam in my 57 Bel Air. IC EO for adjusting the valves. Ah the memories of the sweet music of solid lifters.
Last edited by angel71rs; Oct 7, 2004 at 09:32 PM.
Thread Starter
Registered User
Joined: Sep 1998
Posts: 8,319
From: US 1 Mile Marker 52 in the Florida Keys
Re: changing valve springs...how to tell when piston is at it's top position
long as i pay attention to the open/close of the proper cylinders, this method seems to be working well. and not as time consuming as the "rope method" since the engine bay is so packed.
Thread Starter
Registered User
Joined: Sep 1998
Posts: 8,319
From: US 1 Mile Marker 52 in the Florida Keys
Re: changing valve springs...how to tell when piston is at it's top position
one close call with a valve....almost dropped into the cylinder!!!!!
somehow when the exh and then the intake closed the piston was still not on top
interesting..but i was able to turn it over and the piston pushed the valve back up...thank heavens
only #7 to go...then torque to spec and see how it runs
Thread
Thread Starter
Forum
Replies
Last Post
dbusch22
Forced Induction
6
Oct 31, 2016 11:09 AM
chevroletfreak
LT1 Based Engine Tech
202
Jul 4, 2005 05:00 PM