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I'm trying to set the ignition timing for my TR4 after my rebuild. I set it statically to 4 deg BTDC, but since there's no mark on the pulley for TDC, and I don't know how far off TDC 4 degrees would be, it's hard to do with a strobe. How far is 4 degrees on the crank pulley? I found TDC by moving #1 to TDC (duh), but I don't know how far off 4 degrees is.
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TR4/4A TR4 dynamic timing
- Thread starter derickson
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aeronca65t
Great Pumpkin
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Measure around the circumference of the front pully in inches (use a piece of string and then measure it).
Whatever this measurement is, multiply it by 4/360 and you will have the length of 4 degrees on your pully (in inches).
For example, if the pully has a circumference of 20 inches, then 4 degrees would be 0.222 inches from TDC. (20" times 4/360 )
Whatever this measurement is, multiply it by 4/360 and you will have the length of 4 degrees on your pully (in inches).
For example, if the pully has a circumference of 20 inches, then 4 degrees would be 0.222 inches from TDC. (20" times 4/360 )
Kurtis
Jedi Warrior
Offline
[ QUOTE ]
I'm trying to set the ignition timing for my TR4 after my rebuild. I set it statically to 4 deg BTDC, but since there's no mark on the pulley for TDC, and I don't know how far off TDC 4 degrees would be, it's hard to do with a strobe. How far is 4 degrees on the crank pulley? I found TDC by moving #1 to TDC (duh), but I don't know how far off 4 degrees is.
[/ QUOTE ]
I think your wasting your time if you're trying to time it with a strobe. For one thing, 4 degrees BTDC will not be an accurate setting at idle. Assuming you have the 25D4 - 40795 distributor, you'll be well into the advance curve at idle. It's my understanding that due to the minor inconsistencies of the centrifugal advance system in these distributors, that dynamic timing is virtually impossible - that's why there's no published spec for it.
I've always had good luck with the "advance it to maximum RPMs, then retard it 100 RPMS" method. After setting it using that method, I fin tune it on the road until I get use a hint of pinging in 4th gear under hard acceleration at speed.
Good luck!
I'm trying to set the ignition timing for my TR4 after my rebuild. I set it statically to 4 deg BTDC, but since there's no mark on the pulley for TDC, and I don't know how far off TDC 4 degrees would be, it's hard to do with a strobe. How far is 4 degrees on the crank pulley? I found TDC by moving #1 to TDC (duh), but I don't know how far off 4 degrees is.
[/ QUOTE ]
I think your wasting your time if you're trying to time it with a strobe. For one thing, 4 degrees BTDC will not be an accurate setting at idle. Assuming you have the 25D4 - 40795 distributor, you'll be well into the advance curve at idle. It's my understanding that due to the minor inconsistencies of the centrifugal advance system in these distributors, that dynamic timing is virtually impossible - that's why there's no published spec for it.
I've always had good luck with the "advance it to maximum RPMs, then retard it 100 RPMS" method. After setting it using that method, I fin tune it on the road until I get use a hint of pinging in 4th gear under hard acceleration at speed.
Good luck!
Geo Hahn
Yoda
Offline
[ QUOTE ]
...I've always had good luck with the "advance it to maximum RPMs, then retard it 100 RPMS" method. After setting it using that method, I fin tune it on the road until I get use a hint of pinging in 4th gear under hard acceleration at speed...
[/ QUOTE ]
Me too. Behavior under load is the timing setting I go by. But if you need a starting point -- about 3/8" should get you in the ballpark.
...I've always had good luck with the "advance it to maximum RPMs, then retard it 100 RPMS" method. After setting it using that method, I fin tune it on the road until I get use a hint of pinging in 4th gear under hard acceleration at speed...
[/ QUOTE ]
Me too. Behavior under load is the timing setting I go by. But if you need a starting point -- about 3/8" should get you in the ballpark.
Hello Derickson,
How did you find TDC, it is very difficult to get an accurate TDC mark with the engine assembled. And if so then any further measurement is not likely to be accurate. Certainly, timing by feel will work, but beware, you will not hear any pinking at speed, only at low revs and under load.
The quoted distributor number, 40795 has a maximum advance (mechanical) of 9-11 degrees at 1200 distributor rpm, so if 4 degrees is spec then with the engine running at 2,400 or more it should show about 13 to 15 degees advance. I would initially set to spec at this speed and then road test and final tune. But you will need some accurate mark to start with.
Alec
How did you find TDC, it is very difficult to get an accurate TDC mark with the engine assembled. And if so then any further measurement is not likely to be accurate. Certainly, timing by feel will work, but beware, you will not hear any pinking at speed, only at low revs and under load.
The quoted distributor number, 40795 has a maximum advance (mechanical) of 9-11 degrees at 1200 distributor rpm, so if 4 degrees is spec then with the engine running at 2,400 or more it should show about 13 to 15 degees advance. I would initially set to spec at this speed and then road test and final tune. But you will need some accurate mark to start with.
Alec
vettedog72
Jedi Knight
Offline
PIMAN
Does all of this hold true for the later dizzy's on the TR6. I have all ways used a dyanamic setting to the static spec. thinking 800 RPM or so would be with out any mechanical advance (and the vac line blocked off). This could be part of my poor performance on the dyno at 85hp. /ubbthreads/images/graemlins/lol.gif
Does all of this hold true for the later dizzy's on the TR6. I have all ways used a dyanamic setting to the static spec. thinking 800 RPM or so would be with out any mechanical advance (and the vac line blocked off). This could be part of my poor performance on the dyno at 85hp. /ubbthreads/images/graemlins/lol.gif
I found TDC by inserting my finger into the #1 sparkplug hole and turning the fan by hand slowly until it felt like TDC, marked the pulley, and repeated several times to get some sense of repeatability. I can certainly use the 'adjust it until it runs right' method, but I'm facing another problem: I can't get the car to idle (even with both carbs' idle screws completely backed out) at less than 1500. I'm trying to determine if timing is contributing.
Kurtis
Jedi Warrior
Offline
[ QUOTE ]
I can't get the car to idle (even with both carbs' idle screws completely backed out) at less than 1500. I'm trying to determine if timing is contributing.
[/ QUOTE ]
My guess would be worn butterflies on the carbs, which would prevent them from restricting airflow enough to bring idle down.
I can't get the car to idle (even with both carbs' idle screws completely backed out) at less than 1500. I'm trying to determine if timing is contributing.
[/ QUOTE ]
My guess would be worn butterflies on the carbs, which would prevent them from restricting airflow enough to bring idle down.
Hello Derickson,
that is a very rough way of checking. The problem being that at top or bottom dead centre there is a large rotational angle for very little piston movement. I use a dial indicator (with the head off) when building an engine to mark TDC. Basically done by going either side of TDC to an equal distance on the gauge, marking the points on the damper then dividing the two marks in half.
Certainly I remember on older motorcycles, static timing was given as a set distance of the piston before TDC rather than an angular dimension.
Alec
that is a very rough way of checking. The problem being that at top or bottom dead centre there is a large rotational angle for very little piston movement. I use a dial indicator (with the head off) when building an engine to mark TDC. Basically done by going either side of TDC to an equal distance on the gauge, marking the points on the damper then dividing the two marks in half.
Certainly I remember on older motorcycles, static timing was given as a set distance of the piston before TDC rather than an angular dimension.
Alec
Kurtis
Jedi Warrior
Offline
[ QUOTE ]
PIMAN
Does all of this hold true for the later dizzy's on the TR6. I have all ways used a dyanamic setting to the static spec. thinking 800 RPM or so would be with out any mechanical advance (and the vac line blocked off). This could be part of my poor performance on the dyno at 85hp. /ubbthreads/images/graemlins/lol.gif
[/ QUOTE ]
I believe a dynamic timing spec is given for most TR6 model years. Moss states a static timing spec of 10 degrees BTDC and a dynamic spec of 4 degrees ATDC for most years (the one's I checked anyway).
I'd guess if you dynamically timed it using 10 degrees BTDC that it would be quite a bit out of time.
PIMAN
Does all of this hold true for the later dizzy's on the TR6. I have all ways used a dyanamic setting to the static spec. thinking 800 RPM or so would be with out any mechanical advance (and the vac line blocked off). This could be part of my poor performance on the dyno at 85hp. /ubbthreads/images/graemlins/lol.gif
[/ QUOTE ]
I believe a dynamic timing spec is given for most TR6 model years. Moss states a static timing spec of 10 degrees BTDC and a dynamic spec of 4 degrees ATDC for most years (the one's I checked anyway).
I'd guess if you dynamically timed it using 10 degrees BTDC that it would be quite a bit out of time.
Kurtis
Jedi Warrior
Offline
The only way I know to check is to remove the carb and look through it (from the intake end) with the butterfly fully closed. You'll have to raise the needle piston... and point it at a light source. You should see a very thin, faint circle of light. Anything more and you probably have a problem.
Before you do that, you might check to make sure they are synced properly. If the carbs are linked, and one butterfly is still open while the other is fully closed, I'd think it could cause a high idle problem as well.
What kind of carburetors do you have?
Before you do that, you might check to make sure they are synced properly. If the carbs are linked, and one butterfly is still open while the other is fully closed, I'd think it could cause a high idle problem as well.
What kind of carburetors do you have?
They're SU H6 carbs, and I checked the sync. Even disconnected from each other, the idle is above 1500.
I'll pull the carbs to check the alignment/wear.
Also, is there someway to check the centrifugal distributor advance for wear? I'm wondering if the timing's off even if I static timed it correctly.
I'll pull the carbs to check the alignment/wear.
Also, is there someway to check the centrifugal distributor advance for wear? I'm wondering if the timing's off even if I static timed it correctly.
Offline
I think this has already been pretty well covered.
You should be able to back off the idle stop adjustments to the point where the engine dies. If not:
The linkage may be binding
The butterflies are not fully closing
A common problem is that the fast idle cam (linked to the choke) is not fully returning or it's adjusting screw is not set correctly.
There is wear in the shafts & or bearings
Other vacuum leaks in manifolds or attachments
With the air valves (pistons) removed you should be able to look in & see if the butterflies are centered & fully closing. Carb to carb linkage loosened.
With the engine idling,
A squirt of oil on the ends of the throttle shafts where they enter the carbs should show if the shafts are leaking.
The same for any other attachments to the manifolds & the carb & manifold gaskets themselves.
Timing alone would not cause a fast idle that could not be corrected with carb adjustment.
D
You should be able to back off the idle stop adjustments to the point where the engine dies. If not:
The linkage may be binding
The butterflies are not fully closing
A common problem is that the fast idle cam (linked to the choke) is not fully returning or it's adjusting screw is not set correctly.
There is wear in the shafts & or bearings
Other vacuum leaks in manifolds or attachments
With the air valves (pistons) removed you should be able to look in & see if the butterflies are centered & fully closing. Carb to carb linkage loosened.
With the engine idling,
A squirt of oil on the ends of the throttle shafts where they enter the carbs should show if the shafts are leaking.
The same for any other attachments to the manifolds & the carb & manifold gaskets themselves.
Timing alone would not cause a fast idle that could not be corrected with carb adjustment.
D
Hello Derickson,
a simple check of the advance is to remove the top plate of the distributor (where the contact set is fixed to), then see if the bob weights below are free, if they are you will get your advance. Look on the 'beak' of the mechanism and you will see the advance figure stamped on it. (Should be 11)
One other check not mentioned a with your HS6's, make sure the piston is free to drop fully down. Using a finger in the intake, push the piston up and release, it should drop smoothly down and stop with an audible click. If not then the jet(s) may need centreing.
Alec
a simple check of the advance is to remove the top plate of the distributor (where the contact set is fixed to), then see if the bob weights below are free, if they are you will get your advance. Look on the 'beak' of the mechanism and you will see the advance figure stamped on it. (Should be 11)
One other check not mentioned a with your HS6's, make sure the piston is free to drop fully down. Using a finger in the intake, push the piston up and release, it should drop smoothly down and stop with an audible click. If not then the jet(s) may need centreing.
Alec