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22 degrees BTDC.
https://www.slantsix.org/forum/viewtopic.php?t=65358		 Page 1 of 1
Author:  Craig Smith [ Mon Sep 21, 2020 8:18 am ]
Post subject:  22 degrees BTDC.
I just had my '66 Valiant rewired (ignition circuit, ammeter, dash).
Before the work my Super 225 ran great. I had it set at 750 rpm, about 10 BTDC. I was getting about 20 mpg on the hiway.

After the work the engine still ran fine, but I noticed some hesitation from about 55-65, and some popping when I let off the accelerator. When I checked the settings the timing had gone to about 22 BTDC, still at 750 rpm. I could only adjust the timing back to range by taking out the hold down bolt to rotate the distrib. I hooked up a vacuum gauge. It read only 7.

What could cause such a shift in timing?
Thanks in advance for ideas!
Author:  and739 [ Mon Sep 21, 2020 12:08 pm ]
Post subject:  Re: 22 degrees BTDC.
Is it possible that during all that work the vacuum advance got moved from ported vacuum to a manifold vacuum source?
Author:  Joshie225 [ Mon Sep 21, 2020 12:20 pm ]
Post subject:  Re: 22 degrees BTDC.
The damper may have slipped causing inaccurate timing marks. The timing chain may have jumped a tooth retarding the timing. This requires investigation and not just a timing adjustment.
Author:  Craig Smith [ Mon Sep 21, 2020 1:14 pm ]
Post subject:  Re: 22 degrees BTDC.
Hi, the mechanic shouldn't have had to touch any of that.

What do you mean by the damper?

Thanks
Author:  GTS225 [ Mon Sep 21, 2020 2:34 pm ]
Post subject:  Re: 22 degrees BTDC.
Quote:
What do you mean by the damper?
AKA; the harmonic balancer. There have been instances where the outer ring, with the timing mark, has slipped in relation to the hub. What happens is that the rubber between the two fails and seperates, thus the slipping.

I can just hear you thinking HORSEHOCKEY!, but it's true. It's not a common occurrence, but it does happen.

About the only way to check for that is to pull the valve cover, and hand-rotate the engine, watching the #1 valve events, so that you know that it's at TDC, compression to power overlap stroke. Then you take a look at the timing mark(s) to confirm all is OK.

Roger
Author:  Doctor Dodge [ Mon Sep 21, 2020 2:51 pm ]
Post subject:  Re: 22 degrees BTDC.
I always like to find the reason why something failed... or changed but I not going to spend a lot of time on that...
22 BTDC is not correct and will create the problems you describe.
A switch of the vacuum advance hose could "show" the added advance but let's assume you disconnected VA hose when doing the timing check.

Best to re-adjust the timing to see if all comes back to "normal".
I know, more easy said then done, especially if you are out of adjustment "slot" on the distributor.
If so you will have to loosen the bolt on the under-side of the distributor and move the slotted plate.
Worst case, you have to move a tooth on the distributor AND adjust the slotted plate to get to the timing range you need.
A 7/16 "L" type distributor wrench helps with this "process".
DD

Image
Author:  Charrlie_S [ Mon Sep 21, 2020 3:14 pm ]
Post subject:  Re: 22 degrees BTDC.
Is it possible the person doing the rewireing, reversed the wires from the distributor pickup to the module? That would change the timing, with no other changes.
Author:  Craig Smith [ Mon Sep 21, 2020 4:45 pm ]
Post subject:  Re: 22 degrees BTDC.
Good Info!
I was wondering about switched wires myself. I will check that.
Also I took the hold down bolt off the distrib and turned it to about 10 BTDC. Adjusted the rpm's and mix. Vacuum was still very low, about 7". I don't see or hear any leaks. I had to turn back to 22BTDC to put the bolt back in.

I decided to clean the contacts in the distrib top and to make sure the spark plug wires were connected correctly and pushed on all the way. Seems like they were.
Took a test drive. Seemed like a little more power on acceleration. Checked the readings when I got back. Idle still at 825rpm, 22BTDC, the vacuum changed to about 11" for some reason. Still had rough running at about 64mpg.

Tomorrow I'll check the wiring polarity and maybe look at pulling the distrib to give it a look over.
Thanks for the replies.
Author:  plymouthcranbrook [ Mon Sep 21, 2020 8:41 pm ]
Post subject:  Re: 22 degrees BTDC.
I have never seen a vacuum reading on an idling engine at 7 inches. Is it possible that there are two issues here? Have you tried another vacuum gauge to make sure yours works correctly? Is it possible you also have a vacuum leak? They can start quickly and get worse fast. My 52 Plymouth was running great and when I stopped at a light the engine died. It restarted but would not idle. I got it home and discovered a leak had developed in the intake manifold gasket. I replaced it and all has been well since. 4 years now. I suggest you also investigate that possibility.
Author:  SlantSixDan [ Tue Sep 22, 2020 11:23 am ]
Post subject:  Re: 22 degrees BTDC.
Where are you measuring these vacuum readings? Where are you hooking your vacuum gauge?
Author:  Craig Smith [ Tue Sep 22, 2020 7:31 pm ]
Post subject:  Re: 22 degrees BTDC.
I'm pulling the vacuum hose from the carb, then sticking my vac gauge to that.

Today I checked the 1st cylinder to make sure TDC and the timing spot was correct. All good.
I also had a wet spot under the carb float bowl so I replaced the gasket. No leak so far.
After a run I measured 750 rpm and 15" of vacuum, still at about 22 BTDC and still running rough from 55 to 65 with some back fire when I let off the pedal. Runs great on the city roads and seems good cruising at 65-70.

I think the pos-neg wires are correct from the distrib to the ignition box. I'm thinking I will try moving the second bolt on the distrib to enable me to set timing in range 12 to 15 BTDC.
Craig
Author:  SlantSixDan [ Tue Sep 22, 2020 9:05 pm ]
Post subject:  Re: 22 degrees BTDC.
Quote:
I'm pulling the vacuum hose from the carb, then sticking my vac gauge to that.
I thought maybe so. That's not manifold vacuum you're measuring. Pull the choke pull-off hose off its lower connection (on the carburetor body) and put your gauge there instead and you'll start getting valid readings.
Author:  plymouthcranbrook [ Tue Sep 22, 2020 10:21 pm ]
Post subject:  Re: 22 degrees BTDC.
15 makes a lot more sense. Looks like you have a handle on the problem now.
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