1992 240sx: Can't get rid of this knocking!

[slipnfall]

Hi Folks, I simply can't get rid of this pinging/knocking noise above about 3-3200rpm, under medium-high load. The engine was completely rebuilt about two years ago, and has had synthetic ever since. This noise appeared *right after* I adjusted my shims. They are *all* within spec, if anything on the tight side of the scale. I'm just going to list all the factors that are worth mentioning:

1)'Have always run 93octane.2)Walbro+FPR(removed stock FPR)3)2.5" exhaust with test pipe, no shields in place. I've re-tightened my exhaust manifold bolts(near head).4)upper timing chain guides have been gone, never installed5)I recently installed an OEM upper chain tensioner. No change(even though I put a new one in with the rebuild(aftermarket kit)) I have a lower tensioner on order6)Car seems to run perfect: great compression, good MPG, no detonation visible on plugs7)has been doing this for about 9-10k miles now, no change in noise or severity8)Recently removed clutch fan/shrowd, so no possibility of it hitting on anything

It's noisy enough to hear above my exhaust driving, again at about 3-4k and on up. It seems to be easier to hear with all the windows up(?)

Even though my engine *should* be much quieter now with the shims adjusted, the engine bay is very noisy(esp. around cam/injector area) Any thoughts on this? Do you think they could really get *that* loud?

It's hard to tell really where it's coming from while driving, but it *sounds* like it is the top side.

I'm really starting to worry if this is something mechanically major.

Thanks for reading.Jamie

[slipnfall]

bump for some suggestions.

[elwesso]

Does it sound like a chain related sound (marbles in a coffee can and shaking) or a rhythmic tapping....

[slipnfall]

It sounds exactly how it does when idling: like loud injectors mixed with high valve lash. But it appears loudly at higher RPM. Weird.

[elwesso]

Can you recreate it under NO LOAD?

[slipnfall]

Well I don't take my RPMs that high at no load very often... definate no though the last I remember. Are you leaning towards knock?

[elwesso]

If it does it under NO LOAD, then you have some other problem (not cam related)..... A cam related problem would certainly be apparent regardless of load.....

Go check it under the same condition under no load and see what happens....

[slipnfall]

Your statements somewhat contradict themselves. :-) Anyways as soon as I hit 3200 in 3rd gear it made noise to 4k. So I put it in neutral and popped it to 4500, no such noise.

I'm have a feeling it may be my lower chain tensioner. When there's load on the crank there's excessive slack on one side, and perhaps the tensioner isn't making up that slack? Just a though.

[rogoman]

Check your oil pressure. If it's low, then it'll affect the chain tensioner.

[slipnfall]

That reminds me: I forgot to mention I'm running Mobil1 0W40. I've heard in the Q forums that mobile 1 has a tendency to increase valve train noise. I wonder if this is the case here? I'm waiting on my next oil change to install my oil pressure sending unit, so maybe I'll switch over then.

Thoughts?

[elwesso]

I actually get more lifter tap on my Q45 with 5w30 then i did on 0w40..