Rod knock?

[VBNSX]

I've built many other engines before.. but toying w/ this nsx is my first experience w/ a v6.

At idle there is a small knock.. my presumption was.. ah! rod knock.. but in my experience rod knock has always followed the engine.. the higher you rev, the more insane the knocking noise gets. But this one goes away past idle... it only does a small knock at idle.

I would think valves but that noise always protrudes from the top.. not the bottom...

Any ideas?

thanks,
-x-

 

[Briank]

VBNSX

You may only have low oil presure at idle and tired bearings. Is your oil fresh and the proper grade are you using the correct honda oil filter. What kind of presure are you reading pressure at idle and at speed on the gauge. You may have to attach a seprate gauge to confirm, the in car gauge is not that good. You could have a bad pump or relief valve spring.

Brian

 

[nsxtasy]

It's also possible that you're hearing the normal sound of an NSX.

Have you tried listening to someone else's to see if it makes the same noise?

 

[VBNSX]

Oil pressure.. I'll look at it next time.. (the exact reading)
Oil is fresh... I did the 60k on it.. fuel,air,oil, spark plugs.. etc...
Using green cap mobil 1 oil (easier to remember by color)..
Guess I'll have to go hunt for a small oil pressure gauge..

As far as listening to other NSX's.... well I don't know anyone around here who has one.. (just my luck)

I guess I'll keep people posted..

thanks,
-x-

 

[Larry Bastanza]

The VTEC system has a set of unique devices called LMA's (Lost Motion Assemblies) These are spring loaded, oil cushioned little gizmo's that take up the play in the VTEC cam followers when you are not in VTEC. May sound a little more like a tap then a knock.

You can go here:
http://www.nsxprime.com/FAQ/Reference/1991_svcman/1991servman.pdf Page 6-36

On a totally separate note:

If it's truly a "knock" I would also check your front and rear motor mounts. That is something that will go away as you rev it, since the mounts will get preloaded, and it has been a problem for many owners.

If it is the mounts, the best thing is to loosen the front and rear mount bolts a few turns, rev the engine a few times to settle it's position, then retorque to spec. Many an NSX "knock" has been cured this way.

HTH,
LarryB

 

[Elite]

So you rebuilt this motor? If so, what is your piston to cylinder wall clearance? What you are hearing may be piston slap. It is not a problem just an annoyance. Normally used in race motors. Mo - Elite.

 

[VBNSX]

nawh.. it's stock.. (as far as I know) I bought this used...
hmmmm...

thanks,
-x-

 

[sjs]

Rod knock is quite different than "typical" valve train noise which might be better described as a "tic" or "tap".

You say it goes away above idle, but if you increase the RPMs slowly does the rate follow the revs as it fades away? What does it sound like as the revs fall back towards idle, louder, quieter or the same?

BTW, piston slap is only acceptable in a performance engine with forged pistons where additional clearance is provided because the expend more when hot. Once up to temp even they should be pretty quiet. So I would say that in a stock NSX engine it is more than an annoyance and likely telegraphs accelerated wear.

 

[jrehner]

Figure out the problem?

I read all these threads to learn something---I saw a lot of possibilities presented--Have u determined what the "knock" derived from as yet?