one cylinder suddenly idling very noisily

[JoeSchmoe]

I did a search on this, but didnt find anything similar.

For some reason this morning, number 4 cylinder (front bank, right next to the timing belt) started idling very noisily. It suddenly became about 3-5x louder than the others. Everything sounded normal last night coming home.

I didnt see anything out of the ordinary this morning. Oil level was fine. No CEL. It started up without trouble and idles smoothly aside from the significantly louder than normal clacking from #4. Valve clearances were adjusted 10 months ago. Car is a '94.

Any ideas on what I should be looking for?

-- Joe

 

[goldNSX]

Does the sound remind you of the valves out of specs? Recheck them and the LBA. There's maybe also a bad gasket, i.e. exhaust.

 

[Larry Bastanza]

If you can actually determine which cylinder it must be pretty loud! I suspect a LMA, Lost Motion Assembly which is part of the VTEC valve train. It keeps the third cam follower preloaded so they are not loose in there, clanking alot. If one gets starved for oil, or fails this is what you would hear.

You can remove the valve cover and check the third(middle) cam follower, by pushing gently on the follower with a screwdriver(with the cylinder at TDC), it should be up against the cam lobe, and you should feel is being spring loaded as you push downward on it's edge. Check the service manual on line to see a picture of it. Compare it to Cylinder #5 if you are in doubt of what it should feel like, assuming of course #4 is really the issue, sometimes sounds do strange things and it can be hard to pinpoint exacly where they are coming from.

I remember a post recently discussing the fact these LMA'a have an updated design change.

If this is beyond your experience level, I recommend you have it looked at ASAP.

HTH,
LarryB

 

[OLDMNSX]

I would start by checking if to see if the spark plug came loose. Not likely, but check anyway. Larry is probably right with the Lost Motion Assembly.

Brad

 

[ffffanman]

Dont Start Your Engine Til You Find Out What It Is!!!!
Check your plugs.
I blew one out and the bill ended at $10,000.00 Canadian.
Trev

 

[JoeSchmoe]

Dont Start Your Engine Til You Find Out What It Is!!!!
Check your plugs.
I blew one out and the bill ended at $10,000.00 Canadian.
Trev

Ouch! What happened? Did the tip of the plug fall into the cylinder?


I did a little more research on some of the other honda/acura forums and it definitely sounds like a bad LMA as Larry suggested. The car is in the shop right now for TB/WP, so it should be pretty easy for them to verify if its the LMAs.

Thanks guys for your responses.

-- Joe

 

[ffffanman]

Can you say "What Plug?"
I dont need 6 stinking plugs to run.
I've got the 5 cylinder model.
Trev
http://www.nsxprime.com/forums/showthread.php?t=76731&highlight=ffffanman+engine+noise

 

[JoeSchmoe]

Can you say "What Plug?"
I dont need 6 stinking plugs to run.
I've got the 5 cylinder model.
Trev
http://www.nsxprime.com/forums/showthread.php?t=76731&highlight=ffffanman+engine+noise

WOW thats some serious damage there. Ouch!

-- Joe

 

[ffffanman]

Thats why I'm on the Scooter!
Trev
Got the Engine Refresh Done at Sos, but thats another post for another day.
Now I say Custom Built!!!

 

[JoeSchmoe]

Sorry I havent post sooner. The shop said the accessory belt idler and the water pump were making a ton of noise. They swapped out the bearings on the idler and the WP was changed as part of the TB/WP service. The engine is now MUCH quieter, although Im still puzzled how those 2 items would create such a loud clacking sound.

Thanks again for everyone's help!

-- Joe

 

[ffffanman]

I changed out that idle bearing myself and posted that on prime.
My noise was a squel from that.
Waterpump, dont know what sound that makes when bad.
I know a cracked belt can make a noise such as a crack crack clack clack.
Glad things are quieter.
Trev