Re: TDC question
[Re: 6PAX]
#3119567
02/07/23 12:24 PM
02/07/23 12:24 PM
|
Joined: Oct 2007
Posts: 4,210 New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,210
New York
|
@ TDC overlap, the intake and exhaust valves may be open symmetrically (equal degrees from TDC0, or not. Timing the cam to split the overlap duration may not be the best setting. They may be open the same amount, or not. A very small or very old cam (pre-WW2) may have almost no overlap. Don't assume anything with an unknown cam.
Boffin Emeritus
|
|
|
Re: TDC question
[Re: 6PAX]
#3119842
02/08/23 03:56 AM
02/08/23 03:56 AM
|
Joined: Aug 2003
Posts: 43,284 Bend,OR USA
Cab_Burge
I Win
|
I Win
Joined: Aug 2003
Posts: 43,284
Bend,OR USA
|
If the cam is a symmetrical (same lobes on both intake and exhaust) grind and installed straight up they should. I have seen, I think, dual pattern cams with more duration on the exhaust lobe have the same valve lift at TDC when installed straight up, no advance or retard on the LSA I was taught by some old time cam grinders and racers that installing the intake lobe advanced would help the bottom end, retarding it would lose bottom end and gain upper RPM power. I have tried doing that on the local Studka engine dyno years ago on one of my bracket stroker motors with a solid roller camshaft with a Jesel belt drive, didn't really see a significant change going to 3 degrees LSA either way
Last edited by Cab_Burge; 02/08/23 04:02 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
|
|
|
Re: TDC question
[Re: Cab_Burge]
#3119887
02/08/23 10:32 AM
02/08/23 10:32 AM
|
Joined: Oct 2007
Posts: 4,210 New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,210
New York
|
"3 degrees LSA" Unless the engine is DOHC with twin cams, no change to the LSA is possible, it's ground into the cam. Advancing or retarding a single cam always moves both lobes at the same time and the same amount.
Last edited by polyspheric; 02/12/23 01:51 PM.
Boffin Emeritus
|
|
|
Re: TDC question
[Re: polyspheric]
#3120006
02/08/23 03:31 PM
02/08/23 03:31 PM
|
Joined: Aug 2003
Posts: 43,284 Bend,OR USA
Cab_Burge
I Win
|
I Win
Joined: Aug 2003
Posts: 43,284
Bend,OR USA
|
"3 degrees LSA" New LSA means a new cam, it's not an adjustment, did you mean ICL? Yepper, I should have stated moving the LSA 3 degrees from straight up either way didn't make a noticeable difference on that motor that day
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
|
|
|
Re: TDC question
[Re: polyspheric]
#3120312
02/09/23 05:27 PM
02/09/23 05:27 PM
|
Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
|
Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
|
"A picture is worth a thousand words". go to utube & look this topic up & it's show you exactly what you are looking for.
live every 24 hour block of time like it's your last day on earth
|
|
|
Re: TDC question
[Re: 6PAX]
#3120859
02/12/23 10:01 AM
02/12/23 10:01 AM
|
Joined: Jan 2005
Posts: 2,540 Milwaukee WI
TRENDZ
master
|
master
Joined: Jan 2005
Posts: 2,540
Milwaukee WI
|
[align:left][/align] When an engine is at top dead center, should the intake and exhaust valve lifters for cylinder #1 be equal to each other in the length they are sticking out of their bores ? The piston / balancer can be at TDC in two different camshaft positions. If you are seeing two different lifter heights, you need to rotate the crank another 360°and re-check, or you have a cam with two different lobe designs. This is assuming a healthy engine. Any lobe or lifter wear (or different brand/mismatched lifters)will show the same results.
"use it 'till it breaks, replace as needed"
|
|
|
Re: TDC question
[Re: 6PAX]
#3123195
02/20/23 10:35 PM
02/20/23 10:35 PM
|
Joined: Aug 2003
Posts: 43,284 Bend,OR USA
Cab_Burge
I Win
|
I Win
Joined: Aug 2003
Posts: 43,284
Bend,OR USA
|
When the crank timing gear is at 12.00 and the cam gear dot is at 6:00 o'clock your cam is in the overlap position finishing the exhaust stroke and starting the intake stroke on #1 cylinder so both lifters are opening and closing the valves. #6 cylinder, piston, is on the power stroke so you set the distributor so its rotor is pointing at the # 6 spark plug terminal to fire that cylinder. IHTHs
Last edited by Cab_Burge; 02/21/23 02:16 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
|
|
|
Re: TDC question
[Re: 6PAX]
#3123196
02/20/23 10:38 PM
02/20/23 10:38 PM
|
Joined: Oct 2007
Posts: 4,210 New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,210
New York
|
What the valves are doing during overlap, and how to set the distributor rotor, are 2 different subjects.
Boffin Emeritus
|
|
|
Re: TDC question
[Re: B1MAXX]
#3123835
02/22/23 09:30 PM
02/22/23 09:30 PM
|
Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
|
Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
|
leave it dot to dot mesh the gear in when installing the dist. drop it in so that it is pointing at #6 (180 out). now set the damper to 10-15 before then line up magnet to reluctor ridge by rotating dist. housing and fire it up. ^^^ this. actually you can mesh the dist gear anywhere but lining the gear slot up so the rotor is pointing diagonally opposite #1 (toward #8) lets you keep the plug wires in the OE order. (not a dealbreaker but allows the shortest length of plug wires & makes troubleshooting slightly easier (every little bit helps). RR
live every 24 hour block of time like it's your last day on earth
|
|
|
Re: TDC question
[Re: Cab_Burge]
#3123847
02/22/23 10:32 PM
02/22/23 10:32 PM
|
Joined: Oct 2007
Posts: 4,210 New York
polyspheric
master
|
master
Joined: Oct 2007
Posts: 4,210
New York
|
What I meant was: finding TDC for spark purposes is exact, only one answer. The relative positions and events of both valves during overlap varies widely, and has nothing to do with spark, except being roughly 360° away.
Boffin Emeritus
|
|
|
|
|