How much "shake" at idle is acceptable?

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jcolman

jcolman

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My 340 seems like it's shaking a bit more lately. You'll really see it about 15-20 seconds in. Street/strip cam (don't have all the specs except it has 490/490 lift, 262 duration. Manual transmission.

 
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Any videos of the engine with the Auto tranny? Just thinking outloud there could be a balance issue.....

Yes, excessive IMO but there are alot of contributors to that problem...

JW
 
Something is not right. Need to find someone to diagnosis it.

Most likely ignition or fuel related.
 
SLOPAR72 said:
Any videos of the engine with the Auto tranny? Just thinking outloud there could be a balance issue.....

Yes, excessive IMO but there are alot of contributors to that problem...

JW
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When i had the auto in it it would still shake a bit. But now that I have a manual it seems to shake a bit more. It smooths out above idle however.

Here's a video before the transmission swap. You can see the engine at about 2:30 in. looks to run a bit smoother.

 
That is not right... If they shake with a rhythm that is OK.
Check for vaccum leak
Check broken motor mount
Take of valve covers check if rockers are all moving the same.
Then check plugs to see if they are all firing
Check cap rotor
Then if nothing check carb.
 
MidnightSwinger said:
Vacuum leak and/or motor mounts would be my first idea.
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I just checked for vacuum leak and didn't find any. Plus I just noticed that last winter I had the idle set to around 1100 rpm. Now it's at 900rpm. The motor is definately smoother at 1100 rpm.
 
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Ok...

It runs fine then runs bad then does it run fine for a while then run bad again ?
 
jcolman said:
It runs fine above 1000 rpm all the time. Maybe this engine just doesn't like to idle at 900 rpm
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Easiest thing you can do and probably the cheapest is throw a set of plugs in it.... If you have removed a vacuum leak from the list then timing. The video you posted with the Auto tranny is definitely a smooth running engine and the AFR on your interface is showing it's fat but it should have been in Open loop....

JW
 
SLOPAR72 said:
Easiest thing you can do and probably the cheapest is throw a set of plugs in it.... If you have removed a vacuum leak from the list then timing. The video you posted with the Auto tranny is definitely a smooth running engine and the AFR on your interface is showing it's fat but it should have been in Open loop....

JW
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I just had the engine dyno tuned and a custom fuel map was created. New plugs were installed. The car has to go back into the shop for some additional work so I'll have them take a look at it.
 
Mike69cuda said:
When the radio knobs fall off, it is shaking too much…..
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The whole radio fell out! ;)

DSC09456.jpg
 
Dan the man said:
Not enough cam for it to shake. I agree with what has been suggested that could be wrong.
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Ha, May be it's cold and has the chills. The OP may never find out why without a lot of knowledge and some sophisticated test equipment. To the OP, do you have anyone close that has a diagnostic oscilloscope and knows how to read it? If you don't you may never find it unless you just happen to stumble upon it. (or throw enough parts at it for it to go away).

I am guessing it is only at idle. ??? Lean? Who knows.
 
toolmanmike said:
Ha, May be it's cold and has the chills. The OP may never find out why without a lot of knowledge and some sophisticated test equipment. To the OP, do you have anyone close that has a diagnostic oscilloscope and knows how to read it? If you don't you may never find it unless you just happen to stumble upon it. (or throw enough parts at it for it to go away).

I am guessing it is only at idle. ??? Lean? Who knows.
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No I don't. I don't think my shop has one either but I'll check. Yes, the engine only shakes at idle. Runs pretty smooth above 1100 rpms.
 
jcolman said:
No I don't. I don't think my shop has one either but I'll check. Yes, the engine only shakes at idle. Runs pretty smooth above 1100 rpms.
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Unless it is really causing an issue I wouldn't worry about it. You may be chasing your tail.
 
jcolman said:
No I don't. I don't think my shop has one either but I'll check. Yes, the engine only shakes at idle. Runs pretty smooth above 1100 rpms.
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Like the fellow on this thread. He's disassembling his engine to find a shake he (or members here) think might be mechanical or a imbalance. It will be fun to see if he ever discovers what the issue was and at what cost. 340 Engine Shake Note: his problem was a cam and lifter issue.
 
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toolmanmike said:
Unless it is really causing an issue I wouldn't worry about it. You may be chasing your tail.
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I have a potential buyer coming in to see the car in a couple weeks. I want it running right before he test drives it. Right now, it often shakes enough to bounce the passenger side headers off the torsion bar.
 
jcolman said:
I have a potential buyer coming in to see the car in a couple weeks. I want it running right before he test drives it. Right now, it often shakes enough to bounce the passenger side headers off the torsion bar.
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In your first video, how cold was the engine when you started it? Does it go away or get better as it warms up? I see a electric pump but it looks like a carb. I noticed in the second video you started it cold without a choke (or so it seems)
 
put a vacuum gauge on it,set initial timing and a/f ratio for starters. is it actually firing on all 8?
 
toolmanmike said:
In your first video, how cold was the engine when you started it? Does it go away or get better as it warms up? I see a electric pump but it looks like a carb. I noticed in the second video you started it cold without a choke (or so it seems)
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The engine was quite cold. It was winter. No carb….Holley sniper. I was demonstrating how well the sniper handles cold starts
 
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