Setting ignition timing and dwell in 1976 911s 2.7

[NeedSpace]

My engine has been running hot (about 220f) and I read on a post that it could be the result of my timing being off. I decided I needed to check my timing and dwell.

A little history for those who don't know the story...I got a car w/o and engine. Bought a pretty good engine on ebay but it needed a lot of tlc. After replacing a dozen or so parts, the car was running well. I needed to mess with the mixture as the PO had it well out of wack. Then, most recently, my oil cooler exploded. I dropped the engine and replaced it.

My car starts fairly easily. It now idles around 800 upon start up. Once warm, it'll idle nicely at 900 rpm. The weather has been hot, around 90 F outside and very humid, however, before replacing my oil cooler, the car was usually at 190f, rarely going above 200. Now, it is running hot at about 220.

After getting my car to temperature, I attached my Sears Engine Analyzer. This is an old photo but you can see how it is hooked up (my tach is no longer in the engine bay!).



After getting the car to 900 RPM.


I switched to the dwell meter. Dwell was at 35. This is pretty close and within spec (supposed to be 38 +/- 3), but I was hoping to get it closer. You can see there are 3 scales on the right in red, 4 cylinder, 8 cylinder and 6 cylinder at the bottom.


I took off the distributor cap and regapped the points. I used .35 mm (.014).



After tightening it up, I got dwell to 41. In between each test, to get the cam on the high point, I put the car in 4th gear and slowly rolled the car to get the proper point. This worked better than trying to wrench the engine around. Took it apart again, had dwell at 31, then again at 33, then up to 50 than 45. Then back to 41, then 40 before I gave up. Within 2 is close enough for me.

Then I hit timing. This is pretty easy. For my car, it is 5 degrees ATDC at 900 rpms. My timing was off, 0 degrees TDC.

Here you can see me adjusting it. Obviously, I did this with the engine on but I took this photo afterwards.


Finally I had my timing at exactly 5 degrees ATDC at 900 rpm. The yellow mark is TDC. Again, you test this with the engine on, but I had the engine off to take a photo of it.


Many said I had to check timing at 6000 rpms and get 38 degrees BTDC, however, Wayne's Engine rebuilding book does not list this for my engine. This is fine by me because revving the engine to 6000 and checking the timing doesn't fill me with the warm fuzzies.

I hope people find this helpful.

[Lapkritis]

Any change in temps after all this? I imagine significant change in timing makes for a happier drive.

[redstrosekNic]

Don't worry about the idle timing. You should only care about the timing at full advance. Revving the engine to 6K seems intimidating, but it does not hurt it. I had my gf work the throttle and watch the tach while I concentrated on getting a reading on the timing w/ my dial style timing light.

The 5 degrees ATDC is what creates more heat in stop and go traffic. Disconnect your vacuum retard, and only worry about the full advance. My timing was about 15 degrees too far retarded at full advance. Doing everything I just mentioned brought my temps down from my usual 220F down to 180-210F. The 5ATDC spec at idle is great for emissions...not the car

Good luck!

[mreid]

That yellow dot looks like 5* BTDC to me, which is right where it should be without thermal reactors (hopefully no one has those dreadful things any more).

[Bill Verburg]

Dwell on the low side is better than dwell on the high side, as it means that it stays in spec longer. lower dwell comes from a wider gap.

Idle timing on a '76 is done @80 °C, 900rpm, dist vacuum connected and should be 5° ATDC

[NeedSpace]

Originally Posted by mreid

That yellow dot looks like 5* BTDC to me, which is right where it should be without thermal reactors (hopefully no one has those dreadful things any more).

No, no thermal reactors.

I don't think that the yellow is 5 degrees. Here is a photo, it isn't labelled that great, but I assumed the yellow was TDC. Can anyone confirm?

[NeedSpace]

Originally Posted by redstrosekNic

Don't worry about the idle timing. You should only care about the timing at full advance. Revving the engine to 6K seems intimidating, but it does not hurt it. I had my gf work the throttle and watch the tach while I concentrated on getting a reading on the timing w/ my dial style timing light.

The 5 degrees ATDC is what creates more heat in stop and go traffic. Disconnect your vacuum retard, and only worry about the full advance. My timing was about 15 degrees too far retarded at full advance. Doing everything I just mentioned brought my temps down from my usual 220F down to 180-210F. The 5ATDC spec at idle is great for emissions...not the car

Good luck!

OK Red, if I decide to go the route of 6000 rpm, where are the timing marks for 38 degrees? Are these them? Which one. It looks like, from the left is 30 degrees, on the right is 35 degrees. I guess you just estimate a little ahead of 35 to get at 38?

[NeedSpace]

Originally Posted by Lapkritis

Any change in temps after all this? I imagine significant change in timing makes for a happier drive.

Andrew, haven't checked it yet. Out with the family this afternoon.

[NeedSpace]

Originally Posted by Bill Verburg

Dwell on the low side is better than dwell on the high side, as it means that it stays in spec longer. lower dwell comes from a wider gap.

Idle timing on a '76 is done @80 °C, 900rpm, dist vacuum connected and should be 5° ATDC

Bill, so even if closer to spec @ 40 being 2 degrees away, you still think being at 35 degrees 3 degrees away is better?

[Bill Verburg]

Originally Posted by NeedSpace

Bill, so even if closer to spec @ 40 being 2 degrees away, you still think being at 35 degrees 3 degrees away is better?

I'd always want to err on the wide gap/low dwell side, 2° low on the dwell means the gap is already closed up a bit and will get tighter as the rubbing block wears.


the marks Left to right are
5° ATDC, Z1 or TDC, not sure and furthest right is 35° BTDC

[NeedSpace]

Originally Posted by Bill Verburg

I'd always want to err on the wide gap/low dwell side, 2° low on the dwell means the gap is already closed up a bit and will get tighter as the rubbing block wears.


the marks Left to right are
5° ATDC, Z1 or TDC, not sure and furthest right is 35° BTDC

OK, thanks...will do.

[thumbdoctor]

Agreed, wide gap is preferred as it will close as:
1) Points pit and degrade
2) Breaker cam to rubbing block diminishes
3) Dizzy shaft bearing has wear
I checked my '77 ~ 2.7 pulley with timing tape and furthest to the right is close to 35° BTDC

[thumbdoctor]

Hope you don't have an engine full of rodent treats like I did !

[Walter_Middie]

NeedSpace,

1 deg timing = 1 mm at the edge of the crankshaft pulley.
5 deg BTDC will be 5 mm to the right of the Z1 mark
Spec for initial timing is 5 deg ATDC w/ the distributor vacuum connected and oil temps ~80 deg C, idle 900+/-50
Total timing is 32 to 38 deg BTDC at 6000 RPM

TDC is marked Z1, to the left is ATDC (after top dead center), to the right is BTDC (before top dead center). The mark furthest to the right is 35 deg BTDC and is probably the furthest timing should be set @6000rpm w/o vacuum hose connected. (actual spec is up to 38 deg BTDC but 35 is safer to avoid pre-ignition or detonation)

To see if you have vacuum in the hose to the distributor, put the hose in your mouth and you will feel the vacuum. The vacuum pod on the distributor is a retard control for emissions and should retard the timing about 5 degrees. Watch the timing light as you connect the hose to the vacuum pod to see if it is working. If you adjust the initial timing w/o the vacuum hose hooked up (or working) TDC is about where you will want the initial timing to be.

The advance weights can also get dirty and gummed up. If the dist advance weights are working properly, it will advance freely from idle to 6000 RPM and you should reach 28 degrees advance at 3000 RPM, 31 degrees at 4000 RPM, on up to 38 degrees at 6000 RPM. Set the timing at high RPM and then don’t worry about the idle timing with or without the vacuum retard connected.

The most important timing is at 6,000 RPM, whether the spec in your shop manual is for idle or not. This is true for all engines – not just certain ones. Set this and don't worry about where the idle is timed at. As you are learning, getting the most advance without detonation at high RPM gives you the best performance.

For those that don’t like to hold the RPMs at 6000, or if you don’t have an assistant, I use an alternate method of setting total advance. For max advance, measure the distance from Z1 to the other marks on the crankshaft pulley in mm. Each degree of timing is about 1 mm at the edge of the crankshaft pulley. There should be a 35 degree mark about 35 mm to the right of Z1 on your pulley - make a white mark with chalk or paint. Keep the distributor just snug so you can move it.

After marking the pulley, I start the engine and line up the timing light on the timing marks. Then reach over to the throttle and briefly open it all the way then release. The engine will rev up and then return to idle. What you will see on the timing marks is the advance moving toward the 35 degree mark and then stop, before the engine RPM begins to drop. This is your total timing. You won’t be able to measure the timing with such a short blip of the throttle, but you will have a good idea which direction and how much to move the distributor in order to get the total timing to stop at your desired mark. Once you have moved the distributor to a new position, rev it up again. This is a little trial and error, but I have done it many times, and it only takes a couple of adjustments to get it right – and you don’t have to sit at 6000 RPM for several seconds while you play around with the timing.

Best of Luck

[redstrosekNic]

Originally Posted by NeedSpace

OK Red, if I decide to go the route of 6000 rpm, where are the timing marks for 38 degrees? Are these them? Which one. It looks like, from the left is 30 degrees, on the right is 35 degrees. I guess you just estimate a little ahead of 35 to get at 38?

I'm not sure which marks they are. I have a timing light with the adjustable dial, so I only use the TDC mark. This type of light makes it much easier to get the timing exactly where you want it.

[Walter_Middie]

But a dial light works best just using the Z1 mark.

[E Sully]

[Jerome74911S]

Originally Posted by Walter_Middie

1 deg timing = 1 mm at the edge of the crankshaft pulley.

This is very useful and should be easy to employ. Is it always true, however? The pulley in the pictures that NeedSpace posted appears to be of a slightly larger diameter than the one on my engine. Do they differ, in which case the 1 mm = 1 degree would not hold? Does this rule then apply to NeedSpace's pulley? My pulley has only a Z1 mark, and no others, so I'm interested.

[JK McDonald]

Hey NeedSpace, As you sort out all the spec's and final timing numbers that makes your engine happy why not install one of the many point eliminator kits. You will have to go through the set-up procedures again but with no points to deal with, dwell will no longer be an issue.

There are lots of brands available on the market. I've helped install several in some of my friends early 911's and we've not seen any problems to date. The CDI ignition unit in your 76 seems to really like the change over. Some owners still carry a spare set of points in their glove box as a "comfort factor" just in case of a kit failure.

If you also install a set of the platinum tip plugs you normally don't have to do much toward a tune-up under the rear deck for quite a while.

Good Luck, Michael

[NeedSpace]

Originally Posted by JK McDonald

Hey NeedSpace, As you sort out all the spec's and final timing numbers that makes your engine happy why not install one of the many point eliminator kits. You will have to go through the set-up procedures again but with no points to deal with, dwell will no longer be an issue.

There are lots of brands available on the market. I've helped install several in some of my friends early 911's and we've not seen any problems to date. The CDI ignition unit in your 76 seems to really like the change over. Some owners still carry a spare set of points in their glove box as a "comfort factor" just in case of a kit failure.

If you also install a set of the platinum tip plugs you normally don't have to do much toward a tune-up under the rear deck for quite a while.

Good Luck, Michael

I may do the conversion at some point. I did convert my old mercedes to electronic ignition with great results. I previously had problems with my car in wet weather and not starting. The car has never run so well.

I am going to stick to points for now for the education of it. I want to learn more about how they work and how to tweak them. Also, to be honest, they haven't been much of a bother. That said, if they start becoming an issue, I'll yank em.