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engine drone causes and effects

engine drone causes and effects

(OP)
There was a post in engine and fuel engineering about Engine drone.
I had posted, that I too, had the problem at certain Rpms on a ford explorer.
Pontiacjack and Greg responded to that with similar statements. However I felt that was leading the discussion away from the research the OP was doing.
So I have reposted here for anybody else to jump in.
B.E.

You are judged not by what you know, but by what you can do.

RE: engine drone causes and effects

(OP)
Ok I found the cause,
I had a new rear engine mount fitted in June, so I " Knew " that the rear engine mount could not possibly be the cause.
It was. The mechanic who fitted it had over torqued one of the bolts and stripped the aluminum threads out of the mount housing
so that the bolt fell out, some time, not long, after he did the job. That bolt also held a bracket for the exhaust pipe which now just touched the engine mount without being secured. At certain rpm that loose bracket conducted the engine vibrations to the exhaust pipe. As some of you say " the problem is always in the part you know is ok."
B.E.

You are judged not by what you know, but by what you can do.

RE: engine drone causes and effects

Mechanic screwups have happened to me, also.

Independent of that, both of the vehicles in my fleet (Z28 and Navigator), as well as many vehicles from recent decades, have dead-end branches in the intake tract between air filter and throttle body. They are not spherical, as Helmholtz described, but they are clearly resonators, with a controlled volume and odd shapes constrained by packaging limitations, intended to control intake noise in certain rpm ranges.

Aftermarket 'performance' replacements and early/first year vehicles tend to not have the resonators, and tend to have a noticeable and annoying drone, which I think demonstrates how difficult and time-consuming NVH engineering can be.

Mike Halloran
Pembroke Pines, FL, USA

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