Thermoquad tuning

[thethee]

Okay today was my first time using a timing light. My current initial timing was set at 19 degrees BTDC. I tried to back it off a bit towards 10 degrees but the RPM went down as I did. When I tried advancing the timing further the RPM went up! Vacuum advance was disconnected and plugged at the carb. Should I set it to 20 degrees? That feels like a lot.

Also, it was hard to get an accurate reading as the timing mark on the balancer kept jumping around with the timing light. Is this normal or does that point to a whole other problem? Or does that have something to do with the timing light itself?

 

[Big_John]

Okay today was my first time using a timing light. My current initial timing was set at 19 degrees BTDC. I tried to back it off a bit towards 10 degrees but the RPM went down as I did. When I tried advancing the timing further the RPM went up! Vacuum advance was disconnected and plugged at the carb. Should I set it to 20 degrees? That feels like a lot.

Also, it was hard to get an accurate reading as the timing mark on the balancer kept jumping around with the timing light. Is this normal or does that point to a whole other problem? Or does that have something to do with the timing light itself?

Not sure why it was jumping around, try moving the clamp to a different spot.

Yes, advancing the timing and conversely, retarding the timing will affect the RPM as you have just found out.

So, now you have to balance the idle speed/mixture/timing to the right spot to make it all work right. It's going to take a little patience to do, and you may have to do it in steps, but it can be done.

Idle screws out a couple turns from bottomed out might be where I would start. Maybe a half turn less.

 

[70bigblockdodge]

A big bore low compression engine will take more timing. 19 will be too much and it will ping and knock at highway speed so no good. 10 is too low except a higher compression good cylinder head.
I have always shot for around 14 as long as it does not effect starting.

 

[commando1]

I long ago stopped trying to nail tuneup specs right on the money.
Especially timing with a timing light.
As Dave said above, I twist the distributer until it stops pinging under full load and still start and idle decently.

 

[thethee]

Not sure why it was jumping around, try moving the clamp to a different spot.

Yes, advancing the timing and conversely, retarding the timing will affect the RPM as you have just found out.

So, now you have to balance the idle speed/mixture/timing to the right spot to make it all work right. It's going to take a little patience to do, and you may have to do it in steps, but it can be done.

Idle screws out a couple turns from bottomed out might be where I would start. Maybe a half turn less.

Okay I was under the impression that the initial timing was set for the highest rpm's but I guess that is not the case, noted. I will just set it around 14 degrees then.

 

[thethee]

After looking online I may have found the cause for the erratic timing mark. Pulled the distributor cap and there is some rotational play in the reluctor but there is quite a lot of play up and down. The timing chain is new so I think the distributor is worn and it's time for a new one.

 

[Big_John]

I long ago stopped trying to nail tuneup specs right on the money.
Especially timing with a timing light.
As Dave said above, I twist the distributer until it stops pinging under full load and still start and idle decently.

Yea, but how many years have you been doing that?

Experience gives us that ability but we have 50 years of "just give it a crank until it runs right and you have to start somewhere. My advice is to start conservative, get it at or close to where the factory says it ought to be and then tweak from there.

I think that in this case, he's got the idle up high so the advance is kicking in and the advance kicking in is bringing the idle up higher. Been there, done that and haven't we all?

And of course, we're doing this via the intrawebs, miles and miles apart, so no one is looking over shoulders or hearing the results themselves... You or I would have already been down to cars and coffee at the Dairy Queen with it.

 

[thethee]

I have my idle around 730 rpm

 

[thethee]

Pulled the distributor this morning because I doubted the wayward timing was from the timing light.

The pump drive gear and bushing look good, no side to side movement when seated. There is a tiny bit of play between distributor shaft and slot in gear drive but that appears cause of the design.

Opened the distributor. Reluctor gap was tight, could not get 0.2mm gauge (0.0078 in) in between. Vertical shaft play is around 0.006in which is the limit to replace according to my FSM. Removed pick-up and plates. It has one small spring and one large spring. The large spring has no tension on it and it looks like it can easily slip off the pin. When I remove the center plate the one weight is held by the spring but the other one moves freely.

I think it's best to get a new distributor

 

[Big_John]

Pulled the distributor this morning because I doubted the wayward timing was from the timing light.

The pump drive gear and bushing look good, no side to side movement when seated. There is a tiny bit of play between distributor shaft and slot in gear drive but that appears cause of the design.

Opened the distributor. Reluctor gap was tight, could not get 0.2mm gauge (0.0078 in) in between. Vertical shaft play is around 0.006in which is the limit to replace according to my FSM. Removed pick-up and plates. It has one small spring and one large spring. The large spring has no tension on it and it looks like it can easily slip off the pin. When I remove the center plate the one weight is held by the spring but the other one moves freely.

I think it's best to get a new distributor

That distributor is probably fine and not causing any drastic timing issues. Any new one won't spec any better, I can almost guarantee that.

I'd set the reluctor gap correctly and put it back in.

How much is the timing jumping around?

 

[thethee]

That distributor is probably fine and not causing any drastic timing issues. Any new one won't spec any better, I can almost guarantee that.

I'd set the reluctor gap correctly and put it back in.

How much is the timing jumping around?

Yes I was planning on giving this distributor another try before I order a new one. Especially since I have this one and a new one would take at least a week to get here. The timing mark isn't evenly jumping around if that makes sense, but the biggest difference between two marks is around 10 degrees I think.

Took some pictures to better explain what I meant with regards to the two springs and the big one being very loose. I don't know if that is normal or not.

 

[Dana]

Yes, those look factory to me.

 

[70bigblockdodge]

Those springs are normal. The light one controls low rpm advance and large one is final few degrees higher in the rpm range.
You can get a 1/2" shaft collar with a set screw and it can act to push dist shaft up to bottom of housing.
Set it softly on shift down near blade tip and insert dist, the collar will self adjust while pushing up on shaft. When you pull it out just tighten the set screw all the way.
This seems to work better on electronic dist. than points. You should also have .008 clearance on reluctor.

 

[Big_John]

Ditto on the springs being normal. That is how they work. The light spring controls it and the heavy spring is just there for the ride until higher RPM is reached.

Again, sometimes changing position of the timing light clamp will have a marked effect on how consistent the strobe is flashing.

 

[70bigblockdodge]

Again, sometimes changing position of the timing light clamp will have a marked effect on how consistent the strobe is flashing

Down near the plug is usually better. On a big block 1,3,&5 all run down front of the head and by the steering box

 

[thethee]

Thanks a bunch guys, I'm learning a lot. I will reassemble the distributor and will try a different spot for the timing light clamp tomorrow. Will let you know what that does!

 

[thethee]

Reassembled the distributor and back with new questions.

Tried to set the reluctor gap to 0.008 inch but couldn't. I set the gap the widest it would go with the adjustment screw, but I'm still only getting a gap of around 0.005 inch. Don't really see a way to make it bigger since the coil is mounted on 1/8 inch metal strip and trying to bend it out may damage the coil. Figured it wouldn't be that bad for now. But then I gave the vac advance some vacuum and the gap closes further and the reluctor is even hitting the pickup. So I took the distributor apart again to take a closer look at the pickup and this is what I found:

Hard to see, but the tab is slightly tilted and I think it's due to repeated contact with the reluctor. Again, new to timing, and I don't know if this is bad or not.

 

[Big_John]

Something is wrong here. The vacuum advance should not change the gap.

I'm not 100% sure on this, but I believe that if the reluctor and pickup were in contact with each other, the car wouldn't run. I could be wrong on that... But I do know that there would be much more damage or wear marking on the pickup if that had happened for even a few minutes worth of running.

 

[thethee]

Vacuum advance uses a linear motion to rotate pickup around offset to the axis of the reluctor so that the gap changes is only logical, but like this it gets really close. It looked like it was touching at first but my 0.05mm (<0.002 in) feeler gauge wil go through so probably wasn't any real contact. Does make some ticking sounds, but inconsistent.

So yeah, something is wrong here.

But before I fixate too much on this, what actually changes with a wider/narrower air gap than the specified 0.008 inch? Should it matter how close the gap is, as long as there is no contact?

 

[Big_John]

Vacuum advance uses a linear motion to rotate pickup around offset to the axis of the reluctor so that the gap changes is only logical, but like this it gets really close. It looked like it was touching at first but my 0.05mm (<0.002 in) feeler gauge wil go through so probably wasn't any real contact. Does make some ticking sounds, but inconsistent.

So yeah, something is wrong here.

But before I fixate too much on this, what actually changes with a wider/narrower air gap than the specified 0.008 inch? Should it matter how close the gap is, as long as there is no contact?

I have never found a good answer to that question and I have looked a few times.

However, I have read that one of the reasons for the .008" spec was to allow for any gap change as the vacuum advance moved the assembly. I've never been able to find any solid source for that claim though, so I kind of dismissed it, but this discussion does make me wonder...

It has been shown that variance in the reluctor diameter will change the gap, and that is often found in cars that have been running just fine. It also makes some sense that 99.9% of the mechanics that have checked the air gap, did it in one spot on the reluctor and not all eight, so again, .008" might be the compromise that Chrysler has figured would allow for all the tolerance "stack up".

IMHO, there's probably not too much difference as long as the gap exists and the gap isn't so big the magnetic reluctor and pickup still do their job by telling the ECU it's time to fire. Unlike points where dwell time for the coil is determined by how long the points are opened/closed, the dwell time is set by the ECU and the pickup has nothing to do with dwell.

The gap does get smaller for later cars. .006" for 1977(? IIRC) so there may be something there... But I don't really know.