What Manifold Vacuum and Timing w/ these mods?

[FullSizeJeeper]

I've got my rebuild in and running, but still not purring like I want. It's a 74 AMC 360, .040 over, summit 8600 cam, crane roller rockers, summit digital ignition, MSD disributor and coil, edelbock preformer intake, timing chain, ceramic headers, 650 carb, port and polished intake, +.10 pushrods to correct value geometery.

I set the timing at 8 degrees BTDC, had low vacuum 5hg in drive at 650RPM, about 8hg at 1000 rpms, 15hg at 2000 rpms. Hard to start and running very hot.

I decided to alter timing. Set the timing in drive at about 650
RPMs, with the advanced vacuum plugged and a vacuum gage on the manifold vacuum. I moved the distributor to achieve maximum vacuum reading then backed off a little. I achieved about 12hg, but the timing was of the scale on the timing cover. I figure about 25 Deg BTDC maybe more. Running much stronger and smoother. A little detonation on hard accelaration. Starts much better.

This seems like a lot of advance, the stock setting is 7 deg BTDC. What should I expect the the above mods when timing and on the vacuum gage?

[82Waggy]

Keep in mind that when you hook the Vac advance back up your timing at low throttle and at idle (high vacuum conditions) will be higher - since you have noticable ping, you should back off the advance quite a bit.

I would guess you do not need more than 32-34 degrees total advance from about 2500-3000rpm up.

If your timing mark is correct, 25 degrees initial is likely way too high.

[1980_Cj7]

Sounds like the EXACT thing we were running into with our 401 with the timing. I'm hoping it was due to our discovery that the machine shop had installed the timing gear incorrectly on the cam and that once that is corrected, the problem will be gone.

[Dusty]

unhook vacum and plug it run engine up to 2500-3k where full mech advance is in. use an advance timing light and set it at 32-34 degrees total. tighten down and let it fall back rpm wise this way you know where your top is. i fought timing issues for awhile. i set my total at 33* at WOT i get just a hair of detonation full load at less than 2k rpm with a manual tranny with the auto i had no detonation. i set my idle at 800-850 in neutral regardless of what the manual says. then adjust the carburator ect to keep it right there, helps with AC on and eliminated a little stubble i had off the line.

i have 22 in vacume at 850 idle

[AMX69PHATTY]

A lean condition can increase engine temps. :-|

[FullSizeJeeper]

I am sure the timing gear is correct. I've put several on and matched the marks up carefuly and rechecked it several times during the build before putting the cover on.

It could definitely be running a little lean. I have not fine tumed the carb, trying to get the timing set first. I realize they go hand in hand, but until I'm close on the timing, the carb will change correct?

So the total advance should be in the 30 to 35 BTDC range? I have an MSD Billet dizzy, do I need to change the springs to get the mechanical to mesh with the vacuum?

Does that vacuum sound a little low?

[AMX69PHATTY]

I'd say the idle vacuum is low. Should be at least about 12 inches at idle.

Timing does not significantly affect carb mixture setting.
Do you have the mixture screws out about 2 or 2-1/2 turns ?
Are the Float Levels set ?

The 35* or so total advance does NOT include Vacuum advance.

Yes, you will have to change springs and advance stop bushing
to re-curve and dial-in the MSD Distributor for ~35* total at ~3000 rpm.
The 35* does NOT include the Initial timing advance, about 10*
so the distributor should have about 24* mech advance by 2500-3000 rpm.

Are the valves adjusted correctly ? Max. of .045 lifter pre-load.
Too Tight would make for low vacuum.

Vacuum Advance goes to ported Vacuum, no vacuum at idle.
Vac Advance is only "engaged" at steady state constant speed cruising.
Any time the throttle is opened slightly further engine vacuum pretty much goes to zero,
until a balanced steady state is re-established at the new throttle opening position.

[FullSizeJeeper]

Yes the valve adjustment may be the problem with the vacuum. I adjusted the rocker arms during the build, but a had a couple of lifters that we not fully loaded. After I had it running, warmed it up, and rotated through the engine adjusting the rockers by paired intake and exhaust. When #1 intake fully open, tighten #6 intake, (1-6, 2-3, 5-8, 4-7). I adjusted the lock nut tight until I just felt resistance when spinning the pushrod. Then tightened a 1/4 turn more. I tried to do the loosen till the clack and then tighten while the engine was running, but I caused more problems than solutions, so went to the process mentioned above. When I did this during the build up, I was finding that more than a 1/4 past first resistance was leaving the valves open slightly, though the crane insructions say 1/2 to a full turn. If I went a full turn the valves would never close.

So I have someone coming over to help with Vavle adjustment tomorrow. With the Summit 8600, will that bring the vacuum down some?

[FullSizeJeeper]

I have the floats at the stock levels in the Edelbrock manual, I've read on here that they may need to go a little lower for better offroad preformance.

I am at 2 2/3 turns currently. That is were I set them during the rebuild and have tried adjusting them a couple of times but the valve issue was causing some issues with the vacuum reading.

I will post some vacuum readings at different RPMs after I reduce the timing some. Could I be off a tooth on the dizzy, which is making it want to time so far advanced? As I said the 25* is a guess, just have a basic timing light. So once it goes off the scale, its all guessing. It runs at 10* but lacks power and idles pretty rough. :-|

[1980_Cj7]

I am sure the timing gear is correct. I've put several on and matched the marks up carefuly and rechecked it several times during the build before putting the cover on.



The way they screwed ours up is they put the key in the oil groove in the cam timing gear instead of the keyway. The timing marks still lined up, cuz they just turned the cam until they did. Don't get me wrong, I'm not saying you made this same mistake, but our symptoms were exactly like yours in every respect. Sounds so much like ours it's scary.

Ours would run at 10* initial advance, but had no power, and strained to turn over when trying to start it. If we turned the initial advance up to 25* (we have an adjustable timing light), it turned over normally, and made a lot more power, but pinged. We didn't keep it at 25*, just tried it there. Around town, temperature ran fine, but out on the highway cruising, it would run hot.

It's back in a different machine shop, due to detonation tearing up the engine. Look up a post in here called "Collapsed Piston" and check out the pics. On tearing it down, they discovered the timing gear being on wrong. Hope to have it back any day now. This time I'm personally putting a degree wheel on it before it goes back in the Jeep. If that would have been done the first time, we probably wouldn't be having it rebuilt the second time in only 300 miles.

[FullSizeJeeper]

Were you getting oil to the cam gear? You said they used the oil passage, so was it not spraying the Dizzy to cam gears? I'm getting plenty of oil there. I really don't want to pull the cover, but would rather do that than rebuild the engine.

[bulletbuilder]

Low manifold vacuum AND a 'hot' running engine upon initial start up, would generally mean 'retarded cam timing'. IMO, pull the timing cover and double check your cam sprocket keyway(s) again. Better safe than burn down your new motor.
Larry

[AMX69PHATTY]

I guess installing the Cam Sprocket on the Oil groove rather than the Keyway could be considered "retarded" ? :?:

Not being mean, just thought that sounded funny :wink:

Man, I hope that's not the case for you dude.
They oil groove is not near as deep or tall as the Keyway
and the notch in the cam sprockets rear face wouldn't line up with the oil hole in the cam's front journal that feeds the dizzy
so if it's on wrong the dizzy wouldn't be getting any oil.

You could maybe pull a valve cover and use #1 cylinder and watch to see when the valves start to move and mark the dampener with a maker at the open and close points of the Intake and Exhaust valves. The measure the circumference of the dampener and distance between marks and calculate the angles and compare them to the cam card as an option to see if it's anywhere close. Kinda "hoakey" but would give some general idea of the cam timing and beats pulling the timing cover.

[FullSizeJeeper]

Talked to Summit, they recommend 10* BTDC on the 8600 in a 74 360 in a heavy rig like a FSJ. If the vacuum should be a minimum of 14ish?

I'm wondering if the problem I'm having adjusting the rockers would be caused by the cam being off the proper keyway. Trying to picture this. When the #1 intake is at full lift, the #6 intake lifter should ALWAYS be at the bottom of the cam lobe correct? The timing sprokets position should not effect cam to valve timing only the timing between valve openning and piston stroke?

I'm still wondering why these rocker arms are so tochy on the adjustment. If I go a 1/2 turn past 1st ristance on the turning pushrod, my vavles do not close. Any feedback?

[FullSizeJeeper]

AMX69PHATTY,
I was thinking the same thing. I'm pulling the vavle cover in the morning. I have been studying the cam and timing gears, have stock set and an old edelbrock set. I am 99% sure I did not lineup the oil hole on the keyway. I am getting plenty of oil on the dizzy gear.

The only thing I may have done is used the wrong mark on the crank. The edelbrock crank sprocket has three keyways and 6 marks. If I use the mark right above the keyway versus the mark offset from the keyway, then the when the crank came to TDC the cam would already be two teeth beyond TDC for the cam. Would this retard or advance the timing?

I checked this several times and was confident it was right before I buttoned it up. I like to think I'm not retarded, but at 4am in the garage with a mind spaner on the work bench, LOL.

[1980_Cj7]

Were you getting oil to the cam gear? You said they used the oil passage, so was it not spraying the Dizzy to cam gears? I'm getting plenty of oil there. I really don't want to pull the cover, but would rather do that than rebuild the engine.

Don't know, didn't really check for oil, was more concerned with what was scuffing the pistons, and had no reason to think anything was wrong with the timing gear, but, I suspect not. The divet on the back side of the timing gear was no where near the hole in the face of the cam journal, so I don't see how much if any oil could have been getting out to the front of the engine. The kicker was I test fitted all of this stuff before taking it to the machine shop, and even opened up the divet on the timing gear because it wasn't lining up with the hole in the cam to my satisfaction.

If I were you, I'd degree the cam. That's what I'm definitely doing this time when we get the engine back. I've been reading in here where many people have had to set their timing gear other than straight up just to match the specs on the cam card. Maybe that is what's happening with yours. Best of luck. Hope you don't run into what we did. Keep us posted.

I know pulling the timing cover is a PITA, but not nearly as much as pulling and rebuilding the engine again.

As far as your valves, you say you replaced the push rods with longer ones. Could they be too long and causing your adjustment problem?

[82Waggy]

The only thing I may have done is used the wrong mark on the crank. The edelbrock crank sprocket has three keyways and 6 marks. If I use the mark right above the keyway versus the mark offset from the keyway, then the when the crank came to TDC the cam would already be two teeth beyond TDC for the cam. Would this retard or advance the timing?


It sounds like the cam is advanced a couple of teeth if I understand your description correctly.

With the #1 piston at TDC, the appropriate marks should line up. You should refer to the timing gear set instructions to determine which keyway and set of marks is used to install the cam "straight up", and then use a degree wheel to establish TDC and verify valve timing events on #1 cylinder in accordance with the cam card.

With three keyways, you should be able to install the cam "straight up", or 4 degrees advanced or 4 degrees retarded (typical options). When yo say there are six marks, I assume you mean you have three on the crank sprocket, and three on the cam sprocket. Depending upon the keyway used, you would then line up the appropriate pair of marks - the marks are matched relative to the keyway used and should line up when the piston is at TDC.

Some timing sets have more advance/retard options at varying degrees, and there is also the option of using an offset keyway to split the advance/retard degrees further.

With as much variation as there seems to be with AMC timing sets and cams, I think it wise to always use a degree wheel.

[FullSizeJeeper]

82 waggy,
There are six marks on the crank sprocket, one above each keyway and one offset for Standard, +4*, and -4*. My only concern is I used the keyway mark rather than the offset mark. I took pictures of this to have incase something like this happened, but when developed, they came out to dark to see anything. I need to get a digital camara. My camara is not as old as my jeep, but close :roll:

[82Waggy]

82 waggy,
There are six marks on the crank sprocket, one above each keyway and one offset for Standard, +4*, and -4*. My only concern is I used the keyway mark rather than the offset mark. I took pictures of this to have incase something like this happened, but when developed, they came out to dark to see anything. I need to get a digital camara. My camara is not as old as my jeep, but close :roll:

In that case, I think you need to go back in and verify you have chosen the correct set up. Sounds like you have the option for nine settings in 4deg increments.

[FullSizeJeeper]

Yes, I'm going to try the valve cover trick AMX suggested above 1st. The key as I understand it is to match the cam profile to the engine. I'll do a compression check at the same time a report back this evening. Its not that hard to pull the cover, but I'm pretty sure that I have it done correctly, the symptoms are making me 2nd guess myself though ](*,)

[FullSizeJeeper]

Alright, now I'm getting somewhere, finally got a guy over to help out today. It helps having someone more knowledge than yourself sometimes!

Anyway, had/have a couple of issues. First had the EGR hooked to maniflod vacuum and was pulling my vacuum down by staying open at idle. Teed that off the ported vacuum from to the dizzy and cut out the EGR TBI switch altogether. That helped alot.

Next we richened up the carb. I was running a little lean on that.

Next we timed with an advance light were it was running best and it was at 29* with 55* total. Took it down to 10* degrees, and it would back fire, worked it up in increments and it likes it at 23*-24* - no pinging or backfire. With a total of about 50*

Pretty sure I need to degree that cam. Summit said the intake should open TDC, close 34* ATDC
exhaust open 49* BBDC, close 5 BTDC :-s . I had this cam in this same motor for a couple of thousand miles and didn't degree it had ran fine 111!!!

It also had a stumble on WOT before the vacuum advance kicked in so we lighten the springs to kick that advance up a little quick. She runs much smoother now and will put you back in your seat. But it should not be at 24* BTDC. So I will be researching this site and the AMC Forum (which is back up) to make sure I know what I'm doing and take the cover off and make it scream.

Thanks everyone for all the input. I feel alot better openning the cover when I have a clear objective, not just looking for what could be the problem. I'm starting to get excited this baby is going to rip when the valves are openning on time! She has more power at this moment than she ever has.

One last question for this post. My mechanic friend does not seem to think running it softly with the timing at 24* will hurt in the next week. I plan to do this next weekend, but may need to some run errands next week. Will running it a low RPMs during the break in period with late valve timing be bad? I'm so close I don't want to screw up now!

[FullSizeJeeper]

One last piece of the puzzle. We did a compression test and the values are still very close al at the 165 to 170 range. So I feel like my valves are adjusted pretty well. Its just the retarded cam thats missing stuff up. Not the retarded home mechanic. :razz:

[1980_Cj7]

Is it still pinging? Don't run it if it is.

[AMX69PHATTY]

If the lifters are pumped up from running the engine then they will not bleed off immediately when adjusting the valves. That's why when adjusting them, they would open the valve when going 3/4 turn past zero lash. After a while under spring pressure the lifter should bleed off and allow the valve to close.
The .020 to .045 lifter preload is just to get the lifters inner plunger from off of the intenal snap ring that holds the plunger in the lifter body when they are loose and in the box, and to keep the plunger from "bottoming out" on the snap ring when they pump up. If you have 3/8-24 Rocker Studs, then 1 turn turn equals .042", if 7/16-20 Rocker Studs, then 1 full turn equals .050", so in both cases 1/2 to 3/4 turns should be good. I know when I did mine with the intake manifold off, there was very little resistance from the plunger when zero lash was reached. I could look and see exactly when the plunger started to move off of the internal snap ring. Would be hard to judge from just feel with the intake mounted, but the lifters were not pumped up since the motor had not been ran. Might be easier to go by feel once they're pumped up I guess.

A stumble right off of idle is usually the accelerator pump out of adjustment,
or too little of an accelerator pump shot.

Man that's way too much timimg advance, can't be good for it.

Have you checked the distributor Phasing ?
The Distrib Cap is keyed to the housing and does not move.
I used an old dist cap and hacksawed a big strip out off the side of it si I could see what was going on inside.
When the mech advance is all the way in, the rotor button should be pointed directly at a spark plug wire post. It's tricky cause when sitting initial the whole dizzy is turned, which moves the "switch" (points) relative to the dist shaft "bumps" or "triggers" relative to the crank, mech advance moves the "Bumps" or trigger or reluctor relative to the "switch", and vacuum advance moves the "switch". Three different things moving there. When Phasing the distributor, when full mech advance is in, when the "trigger" trips the "switch" the rotor button should be pointed directly at the post in the cap. On my '69 Delco dizzy it wasn't very close to being properly phased stock unless there was full vacuum and mechanical advance, and total advance of both was basically never achieved because the weights were light and the springs heavy and engine vacuum was low due to the big cam. I removed the vacuum advance altogether, installed heavy weights and light springs, phased it, and locked down the "switch" plate in that postion. The Vacuum advance normally hold the "swith" plate in position, so with it removed it was free and had to be tied down with a little metal strip and a screw in a vacuum canister mounting hole.

I know what you mean about 6 marks on the crank sprocket and 3 settings. Each setting has a mark by the keyway, and another corresponding mark by the tooth that goes with that keyway.

[FullSizeJeeper]

Yes 24 is way to much, but no ping. My understanding is by not degreeing the cam, I'm openning my valves are late and the engine is not running very efficently. We are adjusting for the late valves by advancing the timing. Thus it is firing closer to the valve timing. It seems this would cause potential probelms because it is firing way before the cylinder reaches TDC. This could stress the lower end and cause excess heat correct?

AMXPhatty
I will reread you phasing post when I'm fresher. I think I understand but it been a long day (several months) dealing with the engine). I'm going to try and grasp the cam dailing procedure first and take care of that and go from there.