Engine Shaking...

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Alexhetti

Alexhetti

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Hello all, I'm hoping someone can potentially shed some light on this. So when I bought my car it was in pretty rough shape tuning-wise. Since then I've done a lot of work to it, had the carb tuned and ignition timing set. One issue was the amount of shaking the engine does, specifically during idle, the entire car shakes and rattles pretty aggressively. I changed out the motor mounts, about a 10% improvement in the shaking. I just installed an Msd 6al box with an msd blaster 2 coil and it cut down the shaking probably by about 50-60%... I was not expecting this improvement so this makes me think it's potentially something with the spark plugs/ignition. Any ideas on how to remedy this?

I will add that the 360 has a pretty aggressive cam but it shouldn't be shaking the way it does.
 
Either harmonic balancer is twisted, or you may have an internally balanced flex plate. an aftermarket externally balanced flex plate has a crescent moon shaper cut in it versus an aftermarket internally balanced flex plate is totally round. You might also check for balance weights on the torque converter.
 
Did you double check the firing order?
There are 2 plugs that like to get switched (5 and 8?)
 
Big cams shake... if it’s not rattling your teeth out while driving it’s probably just that. Big cam idle.

assuming it’s actually firing on all cylinders..
 
Alexhetti said:
just installed an Msd 6al box with an msd blaster 2 coil and it cut down the shaking probably by about 50-60%... I was not expecting this improvement so this makes me think it's potentially something with the spark plugs/ignition. Any ideas on how to remedy this
Click to expand...

It's probably NOT the ignition.
It Probably is a poor Idle-AFR,
And the Multi-Strike is re-lighting the fire up to 20 times per revolution.
Fix the Idle-AFR, and the shake will go away.

A big cam always wants additional air. The usual response is to crank up the idle-speed screw. And then the engine gets TOO MUCH fuel from the transfers. So the response to that is to close the mixture screws. But now the Idle speed is too fast, and the response to that is to take away timing. In the end it gets all messed up.
So then, your tuner figures it out and allows the extra air in somewhere else, usually by cracking the secondary blades open.
This allows putting the front back to normal, with additional timing; BUT the dry air entering the secondaries makes the back 4 cylinders go lean, resulting in the shake. and the response to that is to richen up the primaries, making the front 4 cylinders rich, resulting still, in a shake.
In any case, unless you back up the bus and start over by adding the fuel into the Bypass-Air, the result is a rough and usually stinky idle.
Your first defense against this is to have a correctly plumbed and good-working PCV system.
I only tune SBMs, and the biggest cam I have tuned is the 292/292/108 Mopar cam. IIRC; 248@.050. Yeah ok those tend to shake at 550 rpm, lol. But by 750. tuned right, they get to running comparatively smooth, even without a Multi-Strike.

But, ya know what? Because this is a relatively unknown deal, I would start with the basics; and that means a compression test. Which might lead to a LeakDown test. And of course, looking for vacuum leaks, specifically into just one or two ports, and it could be from the bottom, who knows.

And; if you have a big cam,AND a single-plane intake, you really have to have headers; cuz logs can make big trouble.
 
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One little test I like to do if I feel I have a cylinder acting up is to go to the exhaust pipe I use this test to determine which bank is acting up assuming you have dual exhaust IhI put my hand close enough to pipe tip so I can feel the exhaust stroke of each cylinder and listen carefully for discrepancies even with a rowdy cam all notes should be similar.
 
Toluene56 said:
Big cams shake... if it’s not rattling your teeth out while driving it’s probably just that. Big cam idle.

assuming it’s actually firing on all cylinders..
Click to expand...
I was assuming that was the reason for all the movement initially, but after the vast changes it experienced after mouth mounts, the ignition box, and carb tune up, I was thinking it might be something out of the norm. This is the first older car I've had any experience with, but it just seems too aggressive to be normal.
 
Rmoore said:
Have you check to see if it is hitting on all eight cylinders ?
Click to expand...
I'm not gonna lie to ya, I'm not fully aware of how to check this. First classic car....I've only had it for a year. I learn as I go and spend ALOT of time on this forum looking up how to do stuff as I see it needs to get done. I have no automotive background and didn't grow up in the age of fix it yourself, unfortunately. Thats why I'm here asking questions constantly LOL
 
Alexhetti said:
I'm not gonna lie to ya, I'm not fully aware of how to check this. First classic car....I've only had it for a year. I learn as I go and spend ALOT of time on this forum looking up how to do stuff as I see it needs to get done. I have no automotive background and didn't grow up in the age of fix it yourself, unfortunately. Thats why I'm here asking questions constantly LOL
Click to expand...
That's easy

You fire it up, and pull off a spark plug wire
If it changes the way the car sounds, it was hitting on that cylinder

If it does not change the way it sounds, you found a problem

Do that for all 8 cylinder
 
AJ/FormS said:
It's probably NOT the ignition.
It Probably is a poor Idle-AFR,
And the Multi-Strike is re-lighting the fire up to 20 times per revolution.
Fix the Idle-AFR, and the shake will go away.

A big cam always wants additional air. The usual response is to crank up the idle-speed screw. And then the engine gets TOO MUCH fuel from the transfers. So the response to that is to close the mixture screws. But now the Idle speed is too fast, and the response to that is to take away timing. In the end it gets all messed up.
So then, your tuner figures it out and allows the extra air in somewhere else, usually by cracking the secondary blades open.
This allows putting the front back to normal, with additional timing; BUT the dry air entering the secondaries makes the back 4 cylinders go lean, resulting in the shake. and the response to that is to richen up the primaries, making the front 4 cylinders rich, resulting still, in a shake.
In any case, unless you back up the bus and start over by adding the fuel into the Bypass-Air, the result is a rough and usually stinky idle.
Your first defense against this is to have a correctly plumbed and good-working PCV system.
I only tune SBMs, and the biggest cam I have tuned is the 292/292/108 Mopar cam. IIRC; 248@.050. Yeah ok those tend to shake at 550 rpm, lol. But by 750. tuned right, they get to running comparatively smooth, even without a Multi-Strike.

But, ya know what? Because this is a relatively unknown deal, I would start with the basics; and that means a compression test. Which might lead to a LeakDown test. And of course, looking for vacuum leaks, specifically into just one or two ports, and it could be from the bottom, who knows.

And; if you have a big cam,AND a single-plane intake, you really have to have headers; cuz logs can make big trouble.
Click to expand...
So when I got my carb tuned by a local classic shop, the shop owned said that I did have an exhaust leak... he didn't say exactly where it was coming from but it was there. I have a 600 cfm eddy carb and super-comp hooker headers. Really wish I knew what kind of cam was in the engine that would make my life a lot easier. Previous owner said he THINKS it a 288 duration with a 413 lift. Dont know how that would affect your advice but I hope maybe you can get something out of it. Next time I take my car to the shop I will have them do a compression test and leakdown testvbecause I have 0 experience in performing that successfully
 
diymirage said:
That's easy

You fire it up, and pull off a spark plug wire
If it changes the way the car sounds, it was hitting on that cylinder

If it does not change the way it sounds, you found a problem

Do that for all 8 cylinder
Click to expand...
Wow okay, I will do that this week and let you know the results!
 
AJ/FormS said:
And if you get an idea that the pipe is sucking yur hand up; either "now and then" or "regularly", then,you got yourself a bad exhaust valve going on.
Click to expand...
When I get back in the garage I will check this... seems like a pretty easy way to test the exhuast.
 
K.O. SWINGER said:
One little test I like to do if I feel I have a cylinder acting up is to go to the exhaust pipe I use this test to determine which bank is acting up assuming you have dual exhaust IhI put my hand close enough to pipe tip so I can feel the exhaust stroke of each cylinder and listen carefully for discrepancies even with a rowdy cam all notes should be similar.
Click to expand...
I do have dual exhaust, I will try this out next time in back in the garage
 
Alexhetti said:
Sorry, I've just got back online (busy day)... I'll post a video tomorrow for you guys. I know that's more help than a vague description can offer.
Click to expand...

Here's a video of it when it was at its worst... Pre carb tune, no multi-spark ignition, and when the timing was off. Also, please don't roast me for my black engine bay. Promise you I hate it more than you do lol
 
Alexhetti said:

Here's a video of it when it was at its worst... Pre carb tune, no multi-spark ignition, and when the timing was off. Also, please don't roast me for my black engine bay. Promise you I hate it more than you do lol
Click to expand...

I suspect that the outer ring of your crank damper(balancer) has shifted and you no longer are getting and accurate reading on your ingition timing. Common problem
As I understand some multi spark setups need a specific type timing light?
Was your engine timed with a digital timing light?
 
Alexhetti said:
Next time I take my car to the shop I will have them do a compression test and leakdown testvbecause I have 0 experience in performing that successfully
Click to expand...
The Leakdown MAY not be required. If the compression test is relatively even, and relatively high I wouldn't bother.
But if you get a significant variation among the pressures, then it might be worth a look.
If it goes to the shop, I would have them do a vacuum test on the crankcase with the engine idling. I do this by flipping the PCV out of the grommet and sealing the engine; then install a vacuum gauge on the dipstick tube.
There should NEVER be a vacuum in there, under these circumstances.
There should be a slowly building pressure in there; do not let it get much past 3psi, as the pressure can blow seals out.
If you do get a vacuum, then the intake manifold is leaking from the bottom, and will have to come off.
If you do not get pressure at idle, rev it up a bit. Still no pressure? then the CC is already leaking, and you need to find and fix it, cuz most likely with the PCV hooked up, she will be sucking in dirty air.
 
AJ/FormS said:
Hey nice shake,lol.
Thas a whole lotta shaking going on.
Click to expand...
Yup, exactly my concern. It had improved DRAMATICALLY since I got all that stuff done to it and the MSD box made the most impact.. Sounds like a completely different car too. Still some shaking but not nearly as much. I just want to get to the bottom of what is causing it lol I'll upload a recent video with the improvement if my phone will ever let me send a video
 
512Stroker said:
I suspect that the outer ring of your crank damper(balancer) has shifted and you no longer are getting and accurate reading on your ingition timing. Common problem
As I understand some multi spark setups need a specific type timing light?
Was your engine timed with a digital timing light?
Click to expand...
No ignition timing changes since after I installed the digital box. I just converted to it yesterday. As for the timing with the electronic ignition, I couldn't tell you. These are questions I never asked the shop since I pretty inexperienced in engine performance and tuning knowledge :(
 
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