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1995 D90 NAS

It first started with my engine making a tapping sound at idle that increased in speed when I stepped on the gas but soon disappeared or became unnoticeable due to a change in frequency.

Anyway, my local mechanic removed the valve covers and intake plenum and removed/cleaned the rocker arms and oil passages and noticed no unusual wear that would be detrimental to continued use. He individually held down each lifter and saw oil fill appropriately. He halfway suggested that I could replace the lifters for about $1000 but that would not guarantee solving the issue so I didn't.

Nothing changed for a week. Now since yesterday, gradually the tapping sound has gone away but my engine now sounds like a chopper/motorcycle without a muffler, much louder and rougher, especially with acceleration and with exhaust fumes more evident in the cabin. None of the warning lights are lit.

Can the 2 issues be tied together? I'm definitely not going to drive it once I get home and take it to a mechanic.
 

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Exhaust leak... wheel exhaust is cool, start up, check for leaks at headers/joints with back of hand. Careful gets hot quick. Can use a rubber hose up to your ear like a stethoscope.

------ Follow up post added June 21st, 2015 01:23 PM ------

Sound goes away as everything expands and seals better.
 

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Discussion Starter #3
Thanks Adam. Can it be a partial leak as the wheel exhaust is still spewing out hot gasses?
 

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"When" exhaust

Yes partial Leak. But if it sounds like a motorcycle its a good size leak.
 

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90% of the time its the triangular gasket between the header and pipe.
The tapping sound is a completely seperate issue. Often times its gunk buildup due to infrequent oil changes. Use engine flush "follow directions on bottle" or 2 quarts of atf, let idle for 30min then flush and refill with fresh oil and new filter. If knocking sound still persists then you have mechanical damage and would ideally need to change the lifters as a set. Most prob 2 or 3 are bad. Ive changed just tye affected lifters before for cheap customers. If your engine has over 80k you would also need to pay close attention to the cam to make sure tye lobes are in spec.
 

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The ticking and motorcycle noise are one and the same from the sound of it. When you have just a small exhaust leak it is a very definite "tick,tick" and sometimes goes away as the manifold gets hot and parts expand, tightening up and sealing. The leak has now gotten bigger so is much noisier.

As mentioned, most likely the manifold to header gasket but could also be manifold to head gasket.
 
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