engine and drivetrain idle engine shake solved!

[KFunk]

I posted this in another thread, but think it may need a thread of its own. I'm pretty darn certain I fixed it.

I'm trying to figure out the e-mail address of another guy with the same problem that I'd tell when I figured it out, but can't find the old e-mails/thread. Mike maybe?

Anyways, my engine has always rocked back and forth since I got it. Its enough to shake the whole car back and forth. At higher rpms its fine. I changed the motor mounts, no effect. Rebuilt the head for other reasons, saw the pistons are intact. Replaced the ignition system with all new parts. Sealed up everything on the intake side, CD's prescription, tuned weber according to instructions. Still it had the same shake. I also checked the frame for cracks around the driver's side engine mount, and it was fine. The engine is the one moving more, and creating the shake. At this point I gave up, and thought that it must be something unbalanced on the crankshaft, and only a major rebuild would solve it.

But all along, my alternator hasn't been very strong. The aftermarket voltmeter has been reading 12V or less. The car still started fine, so I didn't worry about it. But recently I've noticed some stuff like the turn signals wouldn't flash unless I revved the engine. The battery was just fine for starting the car with enough current, but the voltage wasn't what I needed for some stuff.

Then I wondered if perhaps I wasn't giving enough voltage to the ignition system at low RPMs. In any case, I needed a new alternator since mine was giving 12V when it should give 14. I went ahead and got a 320i alt with internal regulator, thus replacing the voltage regulator too. I swapped the urethane bushings from my old stock alt onto the new one, so that part wasn't changed. I started it up, and it still shook and read 12V at first. But after a little driving, it got closer to 14, and guess what, the engine shake was gone!

It took me a while to believe it myself. There's still a slight vibration in the engine, but nothing at all like the big wobble that shook the whole car before. But if I run the battery down, turn on all my accessories, etc., the car will shake slightly more again. I've had to run out and watch it plenty of times. My gear shift still has a slight vibration, but less than before, and I still haven't changed the shifter plate mounting bushings.

I don't know much about charging systems, but I'm pretty happy my engine isn't out of balance internally. Either I was right about not having enough voltage in the ignition system at low rpm, the voltage regulator caused it, or some kind of bearing issues inside the alternator.

Other people may have a different kind of problem. But if you're still chasing something like this, try checkin the alternator.

[herkjerk]

Weird solution to your problem but it makes sense. I would replace your spark plugs. If you weren't supplying enough spark they're probably coked up. Your battery life has probably been severly shortened as well.

[Vroomer]

very odd solution. However that would make sense. I'll put this on my list of things to check.

~Vroomer

[Rosheee]

Man i hope this helps me fix the shake... great post

[KFunk]

Wow, I barely remember this at all.

[TobyB]

I don't think it really happened...

 

t

 

[KFunk]

It did. I was still in Hawaii at the time, and it was running on points with a blue coil and 32/36dgv.  That thing did shake like hell for the first year or so I had it. Probably one of the reasons I got the car so cheap ($700) .  The Bavarian Motor Experts guys in Honolulu basically called it a turd because it idled so rough.  It was quite remarkable when it finally settled into a smooth idle, by doing something seemingly unrelated.

[ray_]

51 minutes ago, TobyB said:

I don't think it really happened...

 

t

 

Maybe it's a fragment, I mean a pigment, of your imagination...

[AndySals]

I have a very similar 'shake' even though it idles at about 900RPM. I have twin 40 Webers so i thought they were out of balance, they're not. It got better when I installed a 123Tune dizzy. My battery isn't great so i'm gonna et a new one and I'll check the output of the alternator at the same time. I hope I have some luck too.

[Rosheee]

On 3/17/2017 at 6:48 PM, KFunk said:

It did. I was still in Hawaii at the time, and it was running on points with a blue coil and 32/36dgv.  That thing did shake like hell for the first year or so I had it. Probably one of the reasons I got the car so cheap ($700) .  The Bavarian Motor Experts guys in Honolulu basically called it a turd because it idled so rough.  It was quite remarkable when it finally settled into a smooth idle, by doing something seemingly unrelated.

So this did indeed solve the problem?

 

Im glad i could help trigger this walk down memory lane..

[KFunk]

It did, at least the bulk of it I think.  What I said at the time was accurate.  It's not incredibly smooth by any means today, but around 2009 I switched to 40DCOE sidedraft carbs that probably aren't tuned perfectly, with 292 cam, 9.5:1 IE pistons, etc.    

 

Another possibility on how the alternator could've affected idle smoothness is through the electric fuel pump.  The voltage it received would've increased (I've always had a volt guage since I bought the car, and idle voltage did go up with the new new alt).    I'm pretty sure it was a Carter rotary pump, but there's an off-chance I had a facet that I used for a brief time.  

I would think that it'd take barely any fuel for the engine to idle, so a weak fuel pump wouldn't affect that much as long as the bowl was full.  Maybe it just did give it an extra bit of flow/pressure though to get it running smoother.  

Edited April 4, 2017 by KFunk

[BlakeNelsonJr]

Which 292 cam are you using? Schrick or IE?

Sent from my SM-G928V using Tapatalk

[KFunk]

7 minutes ago, BlakeNelsonJr said:

Which 292 cam are you using? Schrick or IE?

Sent from my SM-G928V using Tapatalk
 

I've got an IE 292 from new billet now, but that's neither here nor there.  It can idle pretty darn smooth, even though I'm pretty sloppy on tuning.  When this thread was started, I was on what I think was stock cam but who knows.

[percy]

Similar to what you describe, I had a friend with a beautiful '75.  Stock Solex 2bbl and almost stock.  Engine idled poorly and there was an occasional misfire when accelerating.  The dealer and others performed tune ups and claimed that the engine operation was normal, due to the lean carb settings required as part of emission controls.  I noticed a few so-called upgrades, that included a Bosch blue coil and newer Bosch high tension leads and new Bosch spark plugs.  Replacing the coil with the stock OEM coil yielded an immediate improvement, especially considering the (internally resistored) coil was still receiving its voltage supply via the ceramic ballast resistor.  The wires and spark plugs had resistors or were resistor type.  Replacing them also made a marked improvement.  Can't recall whether the rotor had a built in resistor, too.  Moral of that story was aftermarket upgrades can be good, but sometimes OEM is better.

[AndySals]

 I still get shake on idle. My Weber DCOE 40s are perfectly balanced and I've re-jetted hem too. It drives and pulls great it's just at idle.  I have a video on my iPhone 7 but I don't know how to post. I tried earlier on my own blog here but t didn't work.