Help with 1972 LT-1 ignition
Thread Starter
Advanced
Joined: Aug 2019
Posts: 75
Likes: 1
From: Germany
Help with 1972 LT-1 ignition
Hi!
And friend and I are trying to fix the ignition on his 1972 LT-1, but are having no luck at all...
When the engine eventually starts, it spits violently through the carb and won't idle or run smoothly.
I've managed to set the dwell angle at 29-30°, but setting the timing is proving massively difficult.
We can get the engine started with the distributor turned more or less all the way anti-clockwise (as seen from above), but as soon as I start retarding it (by turning clockwise), the engine starts spitting flames through the carb.
A visual comparison with my 1971 L48 shows that the distributor on the LT-1 is turned much further anti-clockwise than mine, with the inspection window for the points pointing almost straight forward towards the manifold, whereas on my 71 it's pointing more or less towards the front right wheel.
Is there a way the distributor could have been mounted wrong? We haven't checked OT in relation to the marking on the balancer, but will try so with a dial gauge on spark plug hole #6 (seems easier to get at, and should have the distributor finger pointing 180° from #1 if I'm not mistaken).
Any suggestions would be most welcome!
Cheers
Es
And friend and I are trying to fix the ignition on his 1972 LT-1, but are having no luck at all...
When the engine eventually starts, it spits violently through the carb and won't idle or run smoothly.
I've managed to set the dwell angle at 29-30°, but setting the timing is proving massively difficult.
We can get the engine started with the distributor turned more or less all the way anti-clockwise (as seen from above), but as soon as I start retarding it (by turning clockwise), the engine starts spitting flames through the carb.
A visual comparison with my 1971 L48 shows that the distributor on the LT-1 is turned much further anti-clockwise than mine, with the inspection window for the points pointing almost straight forward towards the manifold, whereas on my 71 it's pointing more or less towards the front right wheel.
Is there a way the distributor could have been mounted wrong? We haven't checked OT in relation to the marking on the balancer, but will try so with a dial gauge on spark plug hole #6 (seems easier to get at, and should have the distributor finger pointing 180° from #1 if I'm not mistaken).
Any suggestions would be most welcome!
Cheers
Es
Drifting
Joined: Aug 2019
Posts: 1,339
Likes: 225
How did this run before you touched it? Yes, it is possible to be like a gear tooth off. I would bring the damper to TDC for cyl #1, then look to see where the rotor is pointing., just make sure the rocker arms are in the fully closed position, If they're not, you're probably TDC for #6, then just rotate the crank one more time. The other possibility is the timing chain.has jumped, throwing the cam. crank timing off.
If it's just the rotor that's off, you might have to turn the oil pump shaft to get it to line up. When removing or installing the distributor. the distributor shaft will rotate a little when it meshes with the cam gear. So you may have to try it a few times to get it to line up. Also, when you do set the timing, make sure the vacuum advance is disconnected and the hose is plugged.
Based on your post, it looks like the distributor is out of sync with the engine. That adjustment window should face the right front tire.
Good luck.
If it's just the rotor that's off, you might have to turn the oil pump shaft to get it to line up. When removing or installing the distributor. the distributor shaft will rotate a little when it meshes with the cam gear. So you may have to try it a few times to get it to line up. Also, when you do set the timing, make sure the vacuum advance is disconnected and the hose is plugged.
Based on your post, it looks like the distributor is out of sync with the engine. That adjustment window should face the right front tire.
Good luck.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
OP CV71H
First ...
... Verify the outer inertia ring on your damper (where the timing groove is) has not slipped ... rubber degrades over time & they do slip.
Bring # 1 piston to True TDC on compression stroke (verify that via spark plug hole) ... and verify that coincides with Zero Groove & Zero tab.
Zero Groove on damper must be aligned w/ Zero on timing tab ... if all that checks, then proceed with your distributor.
First ...
... Verify the outer inertia ring on your damper (where the timing groove is) has not slipped ... rubber degrades over time & they do slip.
Bring # 1 piston to True TDC on compression stroke (verify that via spark plug hole) ... and verify that coincides with Zero Groove & Zero tab.
Zero Groove on damper must be aligned w/ Zero on timing tab ... if all that checks, then proceed with your distributor.
Thread Starter
Advanced
Joined: Aug 2019
Posts: 75
Likes: 1
From: Germany
Thanks!
it ran OK - except for the carburettor, which we set out to rectify.
We swapped the distributor cap and rotor, points and plugs. I mad the mistake of not noting the ignition timing before attempting to adjust it - stupid me!
How far out can the distributor shaft be? Doesn't it have a groove in it so that it can only go in one way?
Cheers
Es
it ran OK - except for the carburettor, which we set out to rectify.
We swapped the distributor cap and rotor, points and plugs. I mad the mistake of not noting the ignition timing before attempting to adjust it - stupid me!
How far out can the distributor shaft be? Doesn't it have a groove in it so that it can only go in one way?
Cheers
Es
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
First, Verify damper's Not slipped. Maybe it slipped, may be not ,.. you cannot KNOW unless you Verify.
As mentioned in post # 2, you may have to rotate the oil pump ... so, the dist can be installed in Many different ways ... Regardless of that, EVERYTHING is based on relationship between Piston position & Zero Groove, so verify that FIRST.
As mentioned in post # 2, you may have to rotate the oil pump ... so, the dist can be installed in Many different ways ... Regardless of that, EVERYTHING is based on relationship between Piston position & Zero Groove, so verify that FIRST.
Race Director
Joined: May 2006
Posts: 18,740
Likes: 2,583
That groove connects to a shaft that connects to the oil pump. If someone pulls the distributor and doesn't mark the location of the body and the rotor it can drop in wrong.
You say you are retarding the timing, are you using a timing light?
read the article below and note the comment on C3 distributor orientation
http://corvette-restoration.com/wp-c...stallation.pdf
You say you are retarding the timing, are you using a timing light?
read the article below and note the comment on C3 distributor orientation
http://corvette-restoration.com/wp-c...stallation.pdf
Drifting
Joined: Aug 2019
Posts: 1,339
Likes: 225
Thanks!
it ran OK - except for the carburettor, which we set out to rectify.
We swapped the distributor cap and rotor, points and plugs. I mad the mistake of not noting the ignition timing before attempting to adjust it - stupid me!
How far out can the distributor shaft be? Doesn't it have a groove in it so that it can only go in one way?
Cheers
Es
it ran OK - except for the carburettor, which we set out to rectify.
We swapped the distributor cap and rotor, points and plugs. I mad the mistake of not noting the ignition timing before attempting to adjust it - stupid me!
How far out can the distributor shaft be? Doesn't it have a groove in it so that it can only go in one way?
Cheers
Es
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Melting Slicks
Joined: May 2002
Posts: 2,476
Likes: 756
From: Laporte, IN
Is the distributor original to the car? If it is at the factory they made a deep mark when the timing was set. It is on the intake and the base of the distributor flange under the hold down clamp.
Thread Starter
Advanced
Joined: Aug 2019
Posts: 75
Likes: 1
From: Germany
Hi Guys,
We'll check the damper on Friday!
I'm using a high-tech timing light with dwell-angle measurement function - the points are set correctly!
I think the distributor is original to the car, and we didn't remove it. I'll check if there are markings visible!
I have a feeling that the OT marking on the damper is off which would explain a lot!
Cheers
Es
We'll check the damper on Friday!
I'm using a high-tech timing light with dwell-angle measurement function - the points are set correctly!
I think the distributor is original to the car, and we didn't remove it. I'll check if there are markings visible!
I have a feeling that the OT marking on the damper is off which would explain a lot!
Cheers
Es
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,095
Likes: 4,449
From: Marlton NJ
Sounds like something is out of position, either the distrib or the crank balancer.
Q: Did it run well before? and has the distrib been removed since? If Yes and No then it must be the balancer
To set everything:
Q: Did it run well before? and has the distrib been removed since? If Yes and No then it must be the balancer
To set everything:
- Use piston stop to gently get close to TDC, mark balancer with pencil in each direction, FWD/Reverse TDC is the middle of that.
- Hopefully that hits the mark on the balancer. If not it is bad, or timing tab is incorrect. If it is exactly 180 degrees off spin engine 1 turn and try it again.
- Set engine to TDC by confirmed balancer mark. Make sure on #1 firing stroke. Valves don't move for 90-180 degrees.
- Check that rotor is pointing to #1 terminal in pic below. If not pull distrib.
- Distrib rotates a tooth when inserting, keep trying until rotor points at #1 spot. Easier if you mark desired #1 position with masking tape. Oil pump shaft may need to be bumped a little with a long screwdriver for slot to engage at correct position.
- Rotate housing til vac can and window look like pic below. This is the only way vac can can fit inside the shielding on a corvette. I believe the window points to cyl #2.
- Rotor is now pointing at your new #1 distrib cap terminal. Install wires,
- You can even pre-set the timing with a continuity light (with points) before engine fire up. Points should open (no continuity to ground) (fire the plug) at exactly "X" degrees TDC.
- If you need to move the vac can after that, to get it to fit in the distrib shield, move the distrib 1 tooth and try it all again.
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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- find tdc and locate timing mark so you know you are on the firing stroke
- look at rotor to find #1 on the cap
- retrace every plug wire to make sure you are putting them on the cap in the right order 18436572
- look at the above diagram from Leigh to locate chevy cylinder order. Other car manufacturers are different if you are used to working on a different make
- then try and start and time with the light.
Racer
Joined: Jan 2016
Posts: 290
Likes: 78
Find tdc for #1. Balancer mark should line up with 0°. Rotor should point to wherever you have #1 plug wire at cap. If balancer lines up but rotor don't you jumped time. If rotor lines up but balancer don't, balancer has slipped. This all assumes distributor hasn't been disturbed before work was done.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You MUST set timing before setting dwell and before adjusting the carb. If you have trouble setting the timing, you are wasting your time doing 'other' adjustments.
To set timing, you MUST know that the "O" (top dead center) mark on your timing scale is close to correct. Do an internet search on HOW to set your engine to TDC. Also, since the engine is a 4-cycle system, the ignition spark must be set on TDC-compression (rather than TDC-exhaust).
Once you are sure that ignition timing is correct, then set the dwell (points system only). After that you can move to carb adjustments: set idle mixture screws FIRST; then set choke; fast idle; curb idle. Good luck.
To set timing, you MUST know that the "O" (top dead center) mark on your timing scale is close to correct. Do an internet search on HOW to set your engine to TDC. Also, since the engine is a 4-cycle system, the ignition spark must be set on TDC-compression (rather than TDC-exhaust).
Once you are sure that ignition timing is correct, then set the dwell (points system only). After that you can move to carb adjustments: set idle mixture screws FIRST; then set choke; fast idle; curb idle. Good luck.
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Lars
V8FastCars@msn.com
Last edited by lars; Feb 19, 2020 at 06:32 PM.
Thread Starter
Advanced
Joined: Aug 2019
Posts: 75
Likes: 1
From: Germany
That groove connects to a shaft that connects to the oil pump. If someone pulls the distributor and doesn't mark the location of the body and the rotor it can drop in wrong.
You say you are retarding the timing, are you using a timing light?
read the article below and note the comment on C3 distributor orientation
http://corvette-restoration.com/wp-c...stallation.pdf
You say you are retarding the timing, are you using a timing light?
read the article below and note the comment on C3 distributor orientation
http://corvette-restoration.com/wp-c...stallation.pdf
That's not correct. The diagram shown is for HEI - not for points distributors. Do not use the diagram shown above for a points system. For correct info on how a points distributor should be installed, e-mail me for my paper.
That's not correct. The dwell must be set before the timing is set. Dwell affects timing, but timing does not affect dwell.
Lars
V8FastCars@msn.com
That's not correct. The dwell must be set before the timing is set. Dwell affects timing, but timing does not affect dwell.
Lars
V8FastCars@msn.com
A quick question: which is the standard location for #1 on the cap?
Safety Car
Joined: May 2008
Posts: 3,753
Likes: 721
From: Lafayette Louisiana
Much Thanks!
That's not correct. The diagram shown is for HEI - not for points distributors. Do not use the diagram shown above for a points system. For correct info on how a points distributor should be installed, e-mail me for my paper.
That's not correct. The dwell must be set before the timing is set. Dwell affects timing, but timing does not affect dwell.
Lars
V8FastCars@msn.com
That's not correct. The dwell must be set before the timing is set. Dwell affects timing, but timing does not affect dwell.
Lars
V8FastCars@msn.com