This can be a somewhat subjective question, I know, but I still would like to know what folks think. I’ve got a slight knocking noise somewhere inside the engine/tranny. I can hear it slightly on startup, I can hear it when I rev the throttle slightly (2k-2.5k or so), but I can not hear it at idle. The sound is there with the tranny in neutral and the clutch in. Seems to be more audible on the driver side….pulled that valve cover and all looks and sounds fine, at least as far as the pushrods/rockers/springs go. I can feel the knock when I put my hand on the waterpump housing (Meziere). I haven’t gotten underneath the car for a full investigation yet but I’ll do that tonight as well as disconnecting the waterpump to rule that out. The oil on the dipstick looks nice and clean with no metal flakes or shine to it.

Relevant info:

95 M6
133k miles
ported LT1 heads (stock casting)
LPE 211/219 cam with 1.6 ProMag RRs
CompR lifters
Hooker LTs
Ford SVO 30#

I was pushing the car pretty good to see how the new injectors were holding up at the top end. The car was nice and strong with no drivability issues until I noticed the slight knock when pulling away from a stoplight, after exiting the interstate.

Any thoughts on what this could be? I replaced the clutch tens of thousands of miles ago and when I did, I installed a pilot BEARING. I know these have caused issues for folks’ tranny input shafts….what are the symptoms when it dries up/wears out?

What’s a collapsed lifter sound like?
What’s a spun cam/main/rod bearing sound like?

Thanks,
Rob
95Z28

 

Lifters always TAP/Tick you will know if its a lifter. If the knock is for sure coming from motor it could be several things. Bearings will give a knock sound at all levels of rpms and will even go away from time to time. The same for mains. Wrist pin will give a knock/chatter. Is it louder when the hood is up and you head close to the motor? Lots of other things can give a knock type of noise; motor mounts, tranny mounts, shock/struts.

Any other helpful info?

 

I did some more investigating this evening mostly all at idle with some revs (2-2.5k) here and there. Using the mechanic's stethoscope I picked up on the way home from work, a buddy and I have agreed that the source of the knock is somewhere around the #1 cylinder.

We disconnected the spark plug wire to #1 and the knock got worse. What the heck does that mean? We hooked that one back up and disconnected #3 cylinder and the knock didn't change. Next, we reconnected #3 and disconnected #2 and the knock got worse but not as bad as when #1 was disconnected. Then we disconnected #1 and #2 and it was the worst knock we'd heard the whole night. This seems to be pretty relevant information for determining what the root of the problem is, but I just don't get it! Does anyone have opinions on this? My thought is a rod bearing but I don't know how the "no spark" made the knock worse.

Thanks,
Rob
95Z28

 

are your pistons hitting???

 

I don't know why they would be....springs are new and in good shape, timing seems to be good, was running great for a couple of weeks since the new heads.

Rob
95Z28

 

Perhaps you have a little wrist pin knock. Stuff like that is kinda hard to pinpoint. As far as the worse knock when 1 and 2 wires were off, consider that they are both next to each other in the firing order and both on the same rod journal, so you had a pretty good dead space in there with the engine running. It is hard to make a comparison because most people don't pull spark plug wires off when their engine is running well. Not saying you don't have a problem, just that it might be difficult to figure out just what it is.

 

Ah, wrist pin knock. Having no background in a knock-searching problem, I hadn't thought of this. It fits well with where I'm hearing the noise.

Even if it's not that, I'm convinced it's something internal to the low end. With what it'd take to gain access and fix, I'd wanna fix it right. With 133k miles, maybe it's time for a shortblock anyway.

Rob
95Z28

 

Ever get this problem all figured out?

 

Yep, and I've got a souvenir piston, rod, bearings on my desk at work!

I spun the #1 rod bearing. Not only did it spin, it started wrapping itself around the edge of the rod cap. A Nu-tek 383 shortblock was ordered and installed shortly after!

Rob
95Z28