engine tapping ...oh no

[IndianaVX]

ok,
my engine runs like a sewing machine...smoothe.....until tonight.
i drove to town, and picked up my brother, and while sitting in the driveway, i heard a faint, rapid tapping, and it seemed to be comming from the drivers side, back by the firewall. i reved it just a tad, and the tapping went away. so we went down the road just a bit, got some drinks, and while sitting there,(he went in), i checked my oil, which was just a hair low, but no tapping, so i grabbed the cable and reved it a bit, and the tapping returned, but just briefly, reved it again, and it didnt increase or get louder, it just quit, and i havent heard it since...
what should i be checking, help me, i am scared to death. its not loud, it almost sounded like when we were kids, we would put cards in the spokes of our bikes to make em sound cool. well, it kinda sounded like that except more metallic.
it sounds like a valve tapping, but only for a few seconds, not constantly.
YOUR HELP PLEEZE!!!

Thanks
david

[Joe_Black]

Is it a sort of ball-bearing-on-plate type of tapping? Or ball-pien-hammer-on-steel-bar tapping? What kind of oil are you using (brand, synth or dino, grade) and what's your local weather during this tapping?

[IndianaVX]

thanks joe for taking intrest...........
i would say, ball bearing on plate, or glass, rapid tapping, for just a few seconds, like ten or so, then i reved, and it went away. when the rev idled down, it was gone. it was evident enough that my brother, who knows nothing about engines, said "that sounded weird, you still have a warranty?" gulp......
using Mobil 1 10-30.....weather is warming up...it was about 60.

[Y33TREKker]

Are you sure it was a mechanical tapping and not an electrical snapping? Maybe something in the ignition?

[IndianaVX]

well, does the coil pack make any tapping noise??? i mean im pretty durn sure it was mechanical, but ive never dealt with these coils over plug setups..... i suppose it could be a rapid snap snap snap snap noise. also, when i started it up this morning, i heard the slightest of rattleing of sheet metal. dont think its related, but i dont know. havent been home again since this morning to check it out.....
thanks guys, ill keep answering if you keep asking....

thanks again,
david

[Tobert]

It could be valve adjustment. Mine taps like crazy, especially on lighter weight oils.

[Y33TREKker]

It could be valve adjustment. Mine taps like crazy, especially on lighter weight oils.

I was just throwing out ideas with the electrical snapping idea. I guess I had just assumed that the 3.5L VX motor used hydraulic lifters, but I see from the cd manual that a solid lifter bucket/shim type adjustment is used, so valve adjustment could very well be the cause.

How many miles on the engine? VX valve adjustment intervals are every 60k miles.

[IndianaVX]

just rolled 63000..........

[Ldub]

Check your exhaust system to find the most likely cause of the sheet metal rattling sound...the heat shield(s) are a known culprit.

[Joe_Black]

If you have a Harbor Freight nearby you can pick up a mechanic's stethoscope for about $6 which can help isolate the source of the sound. You can also find them at NAPA and other auto parts houses for a little more.

If the sound is coming from the head then it's likely the hydraulic valve-lash adjusters, which have a published known-issue of sticking from varnish build-up. The typical "fix" is the use of 0W-30 or 5W-30 Mobil-1 which will remove the varnish over a period of time. The adjuster could also be failing (unlikely at your mileage, but possible), which in a worst-case scenario would cause very rough running as the affected valve stuck open.

Ldub's exhaust shield clatter is another valid possibility, and a while back Johnnyapollo had a noise that would only happen while in drive that turned out to be the exhaust making contact with the right side suspension link.

How long have you had your VX and been using Mobil-1?

[psychos2]

If the sound is coming from the head then it's likely the hydraulic valve-lash adjusters, which have a published known-issue of sticking from varnish build-up.

What??? The only way to adjust the valve is with a type of shim that goes on top of the valve stem. We call them lash caps at work. We do not have lifters on the vx. It is a setup were the cam opens the valves. shawn

[Joe_Black]

I know, that's what I thought at first since that's what I'm familiar with as well from my FIAT/Lancia and Kawasaki DOHC experience. Apparently, and this is according to Isuzu service information and not my actual under-hood experience, our engine has hydraulic self-adjusting "lash caps". I'm about to have lunch with a friend who owns and operates a local major repair shop and will have more info then.

UPDATE: Apparently there is a such thing as a self-adjusting hydraulic tappet bucket for direct-impinging OHC and DOHC applications. When home later I'll look in the service manual for more info.

[IndianaVX]

thanks guys
yes, i am suspicious of the exhaust rattle, not real concerned about it, but it will be found and dealt with....
Joe, i have owned the vx for a year, and changed to mobil 1 2 days after i got it. so its been running mobil 1 for a year. i also run the lucas syn oil stabilizer. and run the lucas gas additive...(forget the name) for cleaning the top end.
there is no noticable power loss, i cant make the tapping. it just happens. have heard it once today.
thanks again guys for the intrest, and input.....its appreciated
lunch is over... gotta get back at it!
david

[IndianaVX]

ok, i think i got AUDIO, and a pretty lousy video, but it is the sound im after....take a listen. its not the best sound quality, and it is loud because i stuck the camera right down in there. camera location is just above the spark plug closest to firewall, on drivers side. i used my stethescope, and it is defenatly loudest there also. i put the scope in the indented groove on the "valve cover?" just above the spark plug. i also stuck it in the indent around the spark plug. both places it was very distinct tapping.
so, if this works, heres my audio clips.......

ok, thats not working....posting the video, that is.....ill try something else

[IndianaVX]

ok, heres the link to some videos with audio of noise.....

http://s169.photobucket.com/albums/u...t=100_1848.flv


http://s169.photobucket.com/albums/u...t=100_1849.flv

the first one is with engine still running after a 5 minute drive.... the second one is after shutting the engine off for about 2 minutes, and i rev, and the sound goes away.

thanks guys
david