vibration after header install

[mxdave91]

I installed a set of pypes long tube headers over the weekend, and now I have a pretty good in-cab vibration. It vibrates when I just rev the car in neutral, and also while accelerating and decelerating. It's pronounced enough that I feel it on the seat, steering wheel, and floorboard. The headers clear everything, but i'm wondering if maybe the lead pipes or cat-back are now touching somewhere. I didn't have enough time to let it cool down and check for clearance issues today, but I wanted to know if this type of vibration could just be an inherent trait with off road long tubes, or if my problem could in fact be that the exhaust is touching somewhere? I put headers on two different Z06 corvettes and I never noticed an issue with vibration afterwards. Also, could I have messed something up when reinstalling the motor mount brackets, and maybe that's causing my problem? Thanks in advance...

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[ManBearPig]

The first thing I'd check would be the motor mount brackets. And of course the obvious clearance issues.

The motor mount brackets have to be tightened when they do not have the full weight of the engine on them. You may want to jack the engine just enough to take the pressure of the mounts and double check the bolts.

 

[mxdave91]

Now that you mention it, I only removed one motor mount bracket at a time, but when I reinstalled them, I tightened the bracket to the motor mount first via the single nut, and then tightened the bracket to the motor via the four bolts. I probably should've done that in the opposite order.

 

[ManBearPig]

I'd think there's a good chance that may have something to do with it.

I found that when removing and reinstalling the mount brackets, the four bolts underneath wanted to bind badly if there was weight on the engine.

I'd start there...still work one side at a time but jack the engine enough to take the load off the mounts, loosen everything up and tighten the four bolts underneath first, let the engine down, then tighten down the single bolt up top.

 

[mxdave91]

That makes a lot of sense, Brian, and I actually think that's my problem.

Let me also pick your brain about header gaskets. I reused the factory metal gaskets because the car is still pretty new, and I like the metal gaskets better than the soft, thick ones that they send with most headers. The passenger side seems fine, but I notice a small leak from one of the rear drivers side primaries. would you recommend just ordering a new metal gasket set and replacing the drivers side, or are there better gasket options out there? I also considered putting a little high temp permatex on both sides of the gasket in case the header flange surface is slightly nicked or untrue. Thanks

 

[ManBearPig]

I don't know much about the header gaskets, other than factory is usually best. I have had my drivers side header off twice and reused the same gasket each time. I prayed for no leaks there and have been fortunate so far. If it were me I'd probably replace the gasket with a new OEM gasket, though.

 

[mxdave91]

Going to recheck the torque on all the nuts, and if everything looks good i'll just order new factory gaskets. Thanks for all the help, Brian.

 

[mxdave91]

I reinstalled the mount brackets today the way we discussed earlier and I still have the vibration. My exhaust is probably no closer than 1/4 inch at the closest point. Not sure if this would be close enough to make contact under load or not. It even vibrates in neutral if I rev it gently to 1500 rpms. It almost feels like the motor is out of balance.

 

[ManBearPig]

Thanks for posting the update, but sorry to see it didn't do what you needed.


I'm pretty much at a loss if the motor mounts and brackets are on correctly and there's no clearance issues. Is there any chance the exhaust is somehow bound up? The OEM midpipe has a piece of flexpipe to prevent additional NVH, but shouldn't really be necessary? When I say bound up I mean if one of the midpipes from the header is off center but the h-pipe is sitting in the car straight, you may have the exhaust forced into place and could be transmitting vibes throughout the whole car. I'm grasping at straws here but you may want to loosen all the exhaust connections and make sure they aren't under tension.


My gut says there's still something off with the motor mounts, but I can't imagine what that may be.

 

[mxdave91]

Exhaust could be bound up, because I left the mid borla resonator connected to the rear pipes and reinstalled it as one unit (just being lazy). Maybe i'll separate all the pieces and reinstall them one at a time working from the header leads back. I, like you, however, still feel as though the motor mount brackets are somehow the culprit.

 

[ManBearPig]

If everything slid into place nicely I'd doubt the exhaust is bound up anywhere.

You didn't remove the motor mounts themselves did you? Just the brackets, right?

Focusing on the mounts makes the most sense but they're pretty straight forward bolt-on affairs. When you loosened everything up did you get the brackets 100% loose? Like loose enough to wiggle the bracket around?

Now that everything is back together...maybe it would help to loosen the top two nuts at the same time (with the full weight of the engine on them)and make sure there isn't pressure on either of them. They are slotted so you can shift the engine if needed...maybe one of them got tightened down when under pressure and there's constant tension on the rubber mounts?

Again just grasping st straws. Those top two are easy to get to though. Worth a shot.

 

[mxdave91]

Never loosened the actual mounts, just the brackets, and yes, I did loosen the brackets enough to wiggle them around. I guess I could try loosening the two mount nuts, since it's only about a 5 minute job.

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