Intermittent Noise from Engine Area

[djdrock]

I will do my best to describe the noise I heard today from my 1991 with 39K miles.

With all of the snow, I have not driven the car in 4 days due to snow etc. Decided to take it to work this morning (withdrawal is not fun after a great summer in the NSX.)

Okay...drove it to work this morning, thought I might have heard a little bit of a strange noise when I started it this morning, but nothing to get in a twist over. The car sat outside today for about 6 hours in 20 degree weather, drove it a couple of miles to lunch, and noticed a stange sound as it sat idle. I mostly noticed the noise standing outside. Drove it to back to work, where a former NSX owner and I took a look at it. The sound is a bit of a knocking whirling sound, that is coming from the engine side where the alternator and pulleys are. I could not hear the sound as much as I moved my ear closer to the valve cover. The sound continues as we increase the rpms. Alternator seems to be charging fine, as no extra load, inclucing the AC changed the sound or voltage. Same noise whether the clutch is engaged or not.

Oil level is perfect. No decrease in performance and no funny smells. Oil pressure is fine.

So, I drive it home, about 25 miles or so, stand outside of it while it is idling, and the sound is gone. So, I might be on a bit a wild goose-egg hunt here trying to pinpoint it. I do have an appt. with Acura tomorrow, but wondered if anyone had any thoughts.

I read as many posts as I could find regarding engine noises, including one which mentioned cold weather and a pulley that went bad.

The car had about a $2000 maintenance on it before I bought it including a new water pump, timing belt, belts and hoses etc...This was about 13000 miles ago.

Thanks in advance!

 

[Doc308]

It could possibly be belt noise in the cold or, in my case, a bad idler pulley. From your description, it sounds just like the sound I had in my car last week. Get a long screwdriver and use it as a stethescope . In my case, it was most discernable touching the driver tip to the bolts/nuts closest to the pulleys. If you hear it under the valve covers, it could be a sticky lost motion assembly.

 

[djdrock]

Doc...thanks for the tip. Went out to start it after 4 hours of being in warm garage, and no sound. Who knows?! I will check with Acura and mention your thoughts to them.

 

[djdrock]

The NSX tech has been out sick with the flu, but his right-hand man agreed. Unless they can hear the noise, it will be difficult to say. He checked the belts in that area, and also agreed that it could be the idler pulley.

My car has not made the sound since.

 

[icefire]

it could be a sticky lost motion assembly.

How much trouble is it to replace or clean the lost motion assembly?

 

[Doc308]

PM Larry Bastanza for an answer to that. Of course, given it's location , one has to remove the valve covers--beyond that, I don't know.

 

[NormRD]

I think i hear this sound as well time to time. Probably will have it checked out after the new years.

Doc308, how much was it to fix the bad idler pulley?

 

[Doc308]

The dealer charged me around $100 for the pulley and $50 labor ( they charge $80/hr). Not bad considering what it could have been if it were a rod knock!

 

[nsxhk]

I am interested in fixing the lost motion assembly too. If I'm not mistaken, it's quite a big job. I too wonder how much it would cost.

What will a sticky lost motion assembly do to the engine anyway other than making annoying ticking sound?

Henry.