Engine noise question

[banzaicars]

Having only had my car 2 weeks I don't know whether this is an issue or not. Now the noise in question (please forgive my description):

It is from the engine and happens when the car is cold.

When I rev it past 2000rpm and allow it to fall to idle, as it passes 2000, 1900, 1800 rpm it makes a kind of rattle that I can only describe as a similar noise to castanets (those things Spanish dancers hold!) but isn't all that metalic. The noise isn't there at all either side of these revs.

Forgive my description but the noise isn't offensive or cringe-worthy at all and it totally goes away after about 20 mins of driving - (fully warmed up). It also appears to be more at the top of the engine but to be honest I really can't pin it down at all.

Any help or personal experience is very much appreciated.

The car is a '96 Manual with 53k miles having just had a new clutch and timing belt.

Cheers

Keith

 

[Jin1976]

Is the engine running smoothly? Mine do have a slight rattle but as the engine got warm it goes away. Have you done valve adjustment?

Having only had my car 2 weeks I don't know whether this is an issue or not. Now the noise in question (please forgive my description):

It is from the engine and happens when the car is cold.

When I rev it past 2000rpm and allow it to fall to idle, as it passes 2000, 1900, 1800 rpm it makes a kind of rattle that I can only describe as a similar noise to castanets (those things Spanish dancers hold!) but isn't all that metalic. The noise isn't there at all either side of these revs.

Forgive my description but the noise isn't offensive or cringe-worthy at all and it totally goes away after about 20 mins of driving - (fully warmed up). It also appears to be more at the top of the engine but to be honest I really can't pin it down at all.

Any help or personal experience is very much appreciated.

The car is a '96 Manual with 53k miles having just had a new clutch and timing belt.

Cheers

Keith

 

[banzaicars]

Is the engine running smoothly? Mine do have a slight rattle but as the engine got warm it goes away. Have you done valve adjustment?

Engine runs really smooth.

Haven't done a valve clearance. How could that cause such a noise?

Thanks

Keith

 

[Briank]

This is in left field but when you rev the engine and then let off and it coasts down the flywheel is pushing the engine and then at a certain rpm and manifold vacuum the injectors start fire again and the engine starts producing power. At this transition you will here a little noise from the rod bearings. Is your oil, and filter fresh and are you running the right weight of oil?

 

[Jin1976]

Does this effect how the engine performs? I asked this since I've been using Idemitsu (Honda oil maker) 5w40 Fully Synthetic for years now.

... are you running the right weight of oil?

 

[Briank]

Looser hotter running engines normally use thicker oil and cooler tighter engines run thinner oil. 5W40 sounds like reasonable substitute for the recommended 10W30 and should not be a problem and should not make a negligible difference in the engine performance. Issues come up when people get carried away and go to something like straight 50 weight.

 

[banzaicars]

This is in left field but when you rev the engine and then let off and it coasts down the flywheel is pushing the engine and then at a certain rpm and manifold vacuum the injectors start fire again and the engine starts producing power. At this transition you will here a little noise from the rod bearings. Is your oil, and filter fresh and are you running the right weight of oil?

The car has just been serviced by Honda and I'm assured it has the correct oil.

They also changed the timing belt & clutch.

Could it be the timing belt tensioner? or could it be the whole timing belt set bedding in?

 

[Jin1976]

Mybe it's this one. Check my post here.

http://www.nsxprime.com/forums/showpost.php?p=587060&postcount=7

 

[Larry Bastanza]

Is this noise new after the service was performed??

LarryB

 

[banzaicars]

Is this noise new after the service was performed??

LarryB

I bought the car after having the service done so I cant be sure.

I can't remember it making the noise before though - and I had a good listen

 

[greenberet]

In order to get rid of a similar noise, my mechanic:

1. adjusted the butterfly valves in the intake manifold
2. replaced the lost motion assemblies of the VTEC cams

After the service, the noise was gone. Both were done during the same service, so I don't know which did the trick. If I remember correctly (this was a few years ago), my mechanic said the intake manifold was easy to adjust. He also said that he has seen the lost motion assemblies fail over time and that one of mine was dying. He said it wasn't dangerous for the engine, but I found it annoying so I had them all replaced.

I hope you find the noise and that it's easy to fix!

 

[nis350]

In order to get rid of a similar noise, my mechanic:

1. adjusted the butterfly valves in the intake manifold
2. replaced the lost motion assemblies of the VTEC cams

After the service, the noise was gone. Both were done during the same service, so I don't know which did the trick. If I remember correctly (this was a few years ago), my mechanic said the intake manifold was easy to adjust. He also said that he has seen the lost motion assemblies fail over time and that one of mine was dying. He said it wasn't dangerous for the engine, but I found it annoying so I had them all replaced.

I hope you find the noise and that it's easy to fix!

Surprised the LMS has to be replaced with only 53K miles.

 

[banzaicars]

Thanks for the replies guys.

I'm taking it to the garage next week so will post back.

Regards

Keith

 

[nsxmo]

A couple of months ago, I had a noise that sounds much like this, that started after replacing the timing belt. turned out to be the timing belt tensioner. got to drop the engine 2 times for failing to replace it with the timing belt. so, a word to the wise: if you are doing a timing belt, drop the extra 100$ for the tensioner (unless you just like practice!!). it didn't look or sound that bad in my hand, but screamed on deceleration until the engine warmed.

 

[JD Cross]

My 91 has, what I call, a slow down rattle since I bought it new in 91. I don't know what causes it but unless it's a stornger sound than a rattle I would go for a drive and forget it.

Jim

 

[Jin1976]

Is the rattle coming from under the intake manifold or under the valve covers?

My 91 has, what I call, a slow down rattle since I bought it new in 91. I don't know what causes it but unless it's a stornger sound than a rattle I would go for a drive and forget it.

Jim

 

[JD Cross]

I think on most engines there is something that governs the rate at which the engine slows down so that when you change from acceleration to deceleration there is a softer transition to smooth out the engine and cushion the driveline.
I think this is where the noise is coming from

I'm sure they are experts like Larry B that know more about this

Jim

 

[Whatwasthat]

Ok, my engine does this on slow down too. But I only noticed it after installing my Taitec exhaust, because there was some metal rattle noise coming from the exhaust on engine rev down. It was only my exhuast. Well I changed my oil over the weekend Mobil 1 10W30 I have 50K on my 91 now. Last night I heard this slight knocking sound. I was so freaked, but I listened closely and its somewhere up top. I know my valves need adjusting ( I will be doing that this weekend) but this was a different more knocking sound, it goes away at higher RPM's, so I wasn't so worried about it being my bearings. I noticed when I first start the car, it doesn't make the knock, but when the idle drops down, it starts the knock.

 

[JD Cross]

It might be your injectors.They click away too.

The Canadian Acura magazine recnetly had an article on a Tornto NSX
that had done 500 k km or about 300 k miles
The owner had the head pulled for some valve work.
The bottom end needed nothing.

So I think you should not be concerend about top end noise. There are lots of bits in there to make noise.
Lifters need adjusting, injectors click away and sometime need service
My engine has changed it's sound noticeably over the 15 years I've owned the car. Mostly just got a bit noisier.
I had to replace one ignitor but otherwise the NSX tech, Andrew, at the dealer gets it once a year in the spring.
He goes over it all with the understanding he is to fix anything needed no matter the cost.
He's done the lifters once in 66 k miles and says maybe this year we'll do them again. And maybe remove and check the injectors
Perhaps I have a silly amount of faith in a Honda engine but Acura Canada hasn't had one NSX engine failure yet.

Drive it hard. It doesn't mind.

Jim