401 Timing

1980_Cj7

Original timing marks went from A10 thru TDC to R10. Marks on new cover go from A20 to TDC. Does anyone know if the timing marks were "shifted" on the new style covers to still work with the mark on the balancer? Our 401 is wanting 20 degrees base timing, which seems way too high, unless the marks are 10 degrees off. Didn't get chance to verify where TDC actually is yet since I thought of this, and wondered if anyone knew.

82Waggy

One reference I have suggests 14 degrees initial advance and 38degrees total mechanical advance all in by 3000RPM for a hi-po application. Not sure about the timing mark issue you indicate, but you would think TDC would be in the right place.

AMX69PHATTY

I would think the TDC location on the Timing Cover must remain the same. Do you have both Covers to compare to one another ? If the TDC location is moved, then yeah 20 degrees would now be 10. I have 2 Timing Covers, '69 and '76, both have the 10 degree advanced mark at the bottom just above a long cover mounting bolt boss. I do not have one of the new Timing Covers, but from the picture it looks like the timing marks on it go farther down CCW. On the New one, the timing marks go down past the bolt hole boss. On the old ones it does not. So if the scale on the New Cover goes to 20 degrees advanced it would stand to reason that the scale would be longer in a CCW direction like the picture of the New one shows. Guess you've made sure Distributor is assembled & installed correctly, is phased, mechanical advance is working feely, plug wires are correct ? Any chance the Balancer outer ring may have slipped ? Try opening the Carb Idle screw to make it Idle with only 10 degrees. Too much timing will help idle but will hurt top end power. Not sure what you mean by "seems to want 20 degrees". Do you have a Dial Back Timing Light ? If so I would suggest using it to set Total Advance at about 36 degrees and then see what you get at idle.

zero cool

I've seen different combinations of harmonic balancers and timing marks on Chebby engines to where they don't match each other. I wouldn't put it past AMC to have made similar changes over the years.

1980_Cj7

AMX69PHATTY wrote
Not sure what you mean by "seems to want 20 degrees".

The engine builder told us the best way to time an engine is to hook up a vacuum gauge and adjust the distributor to give the maximum vacuum, then back off 2". That is supposed to be the optimum timing.

When we did that, we got 17", backed it off to 15", then checked with the timing light and are reading 20 degrees BTDC.

Idle is no problem. When we started out at 10 degrees BTDC, the engine was deader than the 258 it replaced. When we advanced it to 15 degrees, however, it ran like a scalded cat. Seems to run even better yet at 20 degrees, but that just seems like an awful lot of timing.

15 degrees base was giving us 35 total at 3000.

Holeshot

So long as your engine starts OK & doesn't ping, 38 total is what you want. If you have a dizzy with an adjustable curve, putting in 18 total distributor advance & 20 initial will give a nice boost in the seat-o-da-pants.

AMX69PHATTY

I agree with Holeshot, if it starts okay when the motors hot and you're not getting any pinging I guess it should be ok. But you're right, 20 degrees initial does seems like an awful lot ........ Using a Vacuum gauge is a good method, but understanding is what matters more than initial is total advance. A Dial Back Timing Light allows total advance to be checked. What Distributor is it ? What type of Trigger ? Points ? Hall Effect ? Unilite ? Does it have a Vacuum Advance Unit ? Has the Mechanical Advance been recurved with Wieghts & Springs ? Aware of Distributor Phasing ? Wieghts and Springs move the Rotor Button relative to the Cap. Vacuum Advance moves the Trigger relative to the Cap. Make sure Rotor Button is pointing directly at a Cap Post when both Mechanical and Vacuum are fully advanced and the Trigger Fires. I took an old Cap and with a hack saw cut a big strip out of the side about an inch or more wide that went more than half way around and used it to look inside to check phasing. What's the compression Ratio ? Able to get #1 at TDC and check the Dampener & Timing Mark ? My original '69 AMC motor Delco Distributor could give about 36 degrees mechanical. Mechanical is limited by a pin in the bottom of the Mechanical Advance Plate that rides in a slot in the plate attached to the top of the Distributor Shaft. It took me a while to figure out what the little brass bushing was for that came in the Mr. Gasket Re-Curve kit . The slot is oversized for the pin, and the kit bushing is made to press over the pin. That way it limits the mechanical advance to only 24 degrees max. So then with 10-14 degrees initial, total advance is 34-38. The stock Wieghts and Springs pretty much never allowed full Mechanical Advance. I don't run a vacuum advance canister. It does sound like that 20 degrees initial is an awful lot. If there is something like 30 degrees in the Wieghts that 50 total ! Thats a lot. :-|

1980_Cj7

Thanks for the replies. I'll try to answer as many of those questions as I can. We pulled the distributor from a Waggie 360 in a junk yard. It was in extremely good condition, so I suspect it is not original but was replaced at some point. We have a Ford TFI adaptor, cap, and rotor on it and are running a TFI coil. Cap and rotor are good quality parts, MSD. It is an electronic distributor, not a points type and it has vacuum advance. We have that hooked up to ported vacuum. Don't know if the distributor was ever recurved but I highly doubt it. We're aware of phasing, but didn't get chance to do it yet. Compression ratio is probably right about 10 to 1. Ross forged pistons and 58 cc heads. Will be checking timing marks this weekend relative to TDC. Haven't checked total timing with base at 20 degrees yet, but when base was 15, total was 35 at 3000. Oh, one other thing, with the timing even at 15 degrees, the engine cranking is very strained. It catches and starts pretty quickly, but really struggles to turn over. At 20 degrees, it cranks fast and normally and starts right up. I'm really suspicious that the timing marks are off, but we'll find out for sure very shortly here.

1980_Cj7

Verified that the timing marks are correct, TDC on the marks on the timing cover is truly TDC on No. 1 piston.

AMX69PHATTY

It should be harder to crank over at 20 degrees than it is at 15 degrees. I wonder if the Vacuum Canister is a retard unit rather than an advance. Are ya disconnecting the Vacuum Canister when setting the Timing ? Then checking the timing again after hooking it back up ? I'm not familiar with the AutoLite style distributors. Now I want to go out and get one to tear apart. I'm baffled. :-|

1980_Cj7

Yes, we're disconnecting the hose from the distributor and plugging it to set the timing. I don't recall if we checked base timing again after hooking it back up, but we did check total timing with it hooked up. We got 30 degrees at 2250 with base at 10, 35 at 3000 with base at 15. Don't recall if we checked total with base at 20. The distributor advance is hooked directly to ported vacuum. We didn't use the CTO valve. We'll check base with the vacuum hooked up if we ever get it running again. Right now we have bigger problems. See the post on "Collapsed Piston".

Holeshot

collapsed piston? common with the stock AM pistons. maybe had one detonating? which cylinder?

1980_Cj7

Number 7. See our other post "Collapsed Piston". It isn't actually collapsed, just worn real bad on one side.