1995 K1500 5.7 / 350 TBI Engine Knock/Other?

[MisterPie]

Hello,

For reference as the title says, I have a 1995 K1500 5.7L 4x4 TBI / 350 with a 4L60E transmission in the vehicle. Other than the sound itself, the rest of the vehicle is functioning properly. 154 000km on the clock (I'm in Canada).

Don't know if anyone has had this issue before, I just made a video about it which showcases the original sound and the current one. You'll have to skip a little further ahead in the video to hear the second sound. Excuse the language, it's mostly a mix and match of videos I sent to friends.

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I drove to work one morning and parked the truck, then I went to start it up again about an hour later and I got the first sound you'll hear in the video. I figured it was some form of engine knock so I had it towed back home for further inspection. In the second part of the video, it had been sitting for about three days prior to the last time I started it and as you can tell by the video, at first there's no sign of the sound whatsoever. I let it idle for about 3-5 minutes and I even drove the truck back and forth in my garage and there was nothing. At that point I turned it back on and shifted it into reverse for the second time in the video. This time, the metallic sound appeared immediately and the speed at which it appeared seemed to vary with the RPMs of the engine.

I drained the oil and inspected it for metal fragments and there were none. I checked the flexplate for cracks/wear/loose bolts and there were none. I cracked open the intake manifold and checked the pushrods/lifters/etc and everything was in working order. I had one slightly bent pushrod with what seemed to be a seized lifter and I replaced the batch thinking that could have been the cause - to no effect. Nothing is loose as far as I can tell on the underside of the vehicle, no heatshields or any random components. I still have oil pressure and the vehicle moves and shifts smoothly. Has anyone ever experienced something like this before?

 

[1990Z71Swede]

Through Youtube it almost sounds like a REALLY bad lifter or actually several lifters, but that should not be affected to that extent by going into gear, also would typically be worse after car sits for a couple of days.
Wobbly Fan hitting fan shroud? And doing it randomly. Beer can laying in the shroud ?
Going into gear is shifting the motor enough for it to hit? IDK
But that much noise without any signs of low oil pressure, rough running or a transmission acting up seems really odd.

 

[Hipster]

It sounds fast like a rotating assembly knock, I heard 3 days, new to you?, maybe someone dumped some motor honey in it so it stays quiet until the oil starts coming to temp. Bent pushrod is suspect of a lobe going flat, so how closely did you examine them while you had lifters out, and how confident are you in your valve adjustment? Hard to inspect flexplate for a hairline fracture with trans still in the truck. You might have more than one issue going on. Trans pump/bushing screeching? Need to get down and dirty with a stethoscope and try to narrow in on this

 

[MisterPie]

Through Youtube it almost sounds like a REALLY bad lifter or actually several lifters, but that should not be affected to that extent by going into gear, also would typically be worse after car sits for a couple of days.
Wobbly Fan hitting fan shroud? And doing it randomly. Beer can laying in the shroud ?
Going into gear is shifting the motor enough for it to hit? IDK
But that much noise without any signs of low oil pressure, rough running or a transmission acting up seems really odd.

If only it was a beer can haha . Yeah like I said I figured it was something akin to lifter tick, but they were all in working order when I went to pull them, save one with an ever so slightly bent pushrod. What's bizarre to me is the fact that I can let the vehicle set for 3-4 days (maybe less), start it up and have no clacking sound until I go to shift it into reverse. When I had first changed the lifters and done the valve adjustment, the first three minutes the engine was running like normal, then the clacking returned (mind you I didn't shift it into reverse in this case).

 

[PlayingWithTBI]

I had a 70 Buick Sylark (back in ~78) with a 350 that had a knock kinda like that. I was told it was piston slap, drove it for about a year before the Torque Converter went out. Had it replaced, and the knocking noise went away. It was the TC all along. YMMV

 

[MisterPie]

It sounds fast like a rotating assembly knock, I heard 3 days, new to you?, maybe someone dumped some motor honey in it so it stays quiet until the oil starts coming to temp. Bent pushrod is suspect of a lobe going flat, so how closely did you examine them while you had lifters out, and how confident are you in your valve adjustment? Hard to inspect flexplate for a hairline fracture with trans still in the truck. You might have more than one issue going on. Trans pump/bushing screeching? Need to get down and dirty with a stethoscope and try to narrow in on this

The sound does seem to appear once the motor/trans has come up to temp. The original problem occurred 2-3 weeks back, and I swapped the lifters and bent rod a week or so ago. I'm in the middle of planning a move between provinces, so it's been a little tricky managing time to work on the truck, since this happened in the middle of everything. As for the examination of the lifters and pushrods, I thought I did a pretty thorough job in checking for wear, deformation and other issues. I inspected all the pushrods top to bottom, cleaned out the insides, cleaned the gunk off the sides, gave them all a few rolls on a flat surface to check how straight they all were and it was only the one that was ever so slightly bent. The bend wasn't even noticeable to the naked eye and it barely failed the roll test. The tops and bottoms of the push rods had what I figured was normal wear, there wasn't any pitting or excessive amounts of material missing. As for the lifters, all of them were fully operational, save the one that was underneath the bent pushrod. There were no signs of excessive wear on the lifters themselves, no pitting, scratches, absolutely nothing. I even took them all apart to inspect the insides as well - nothing except for that one associated with the beforementioned pushrod, which had a spring that wasn't compressing adequately.

I'm pretty confident in my valve adjustment, I was going off my repair manual for the truck and advice from this website regarding the year of my make and model. As for the flexplate, if it is a hairline crack then I'd agree it'd be tricky for a close analysis, as I was just spinning the crank with my face essentially in-between the flexplate and the torque converter haha. I don't have a lot of time left before I move, but I suppose the stethoscope is something to try going forward. I did take a look at my trans fluid yesterday and noticed it smells like absolute so I'm starting to lean towards more of a tc/trans issue than engine knock, but it's really just a guessing game at this point haha.

 

[MisterPie]

I had a 70 Buick Sylark (back in ~78) with a 350 that had a knock kinda like that. I was told it was piston slap, drove it for about a year before the Torque Converter went out. Had it replaced, and the knocking noise went away. It was the TC all along. YMMV

I spoke with a friend of mine and he suggested the torque converter as being part of the issue. Like I said in my reply to Hipster, I checked my trans fluid yesterday and while it's bright red (since I changed it a couple months ago), there are now black streaks when I wipe the dipstick on a rag and the fluid smells pretty awful. He walked me through a test to check and see if my tc is operating correctly by putting the vehicle in drive, having the parking brake/brake pedal maxed out and then flooring the gas to see if the rpms rise above the 1700-1800 mark. He said that if it goes above that (for my make/model) then it's likely the tc. Can anyone chime in on that? Edit* Thanks for the reply!

 

[PlayingWithTBI]

Can anyone chime in on that?

It was too long ago but, it didn't act any out of the norm, except for the knock.

 

[MisterPie]

So I just did the test my buddy told me to try out to test for an issue with the torque converter. Based off the test results in the video, what do you guys think about it? Personally, I'm of the belief that it's a torque converter issue now. Anyone think of another test I can do or any other specific check related to this?

I explained it in the video and in a previous post, but the test is essentially me having the brake pedal to the floor while I pin the gas for a good 2-3 seconds while the vehicle is in drive. The stall speed of the stock 4L60E is between 17-1800rpms, so if I'm able to go above that (which I was), it'd indicate a faulty torque converter.

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Thanks for all the advice so far fellas, I appreciate it.

 

[MisterPie]

Well I decided to take a closer look myself and disconnected the trans from the engine. Thought it was going to be the torque converter but lookie what I found! I wasn't able to tell when I initially took the flexplate cover off because the crack was impossible to see from the angle I was at. I had tapped on the flexplate before but I never heard anything strange. But the moment I disconnected the tc mounting bolts from the flexplate and I tapped it with my hand, all I heard were metallic vibrations. Took a closer look with the tc out of the way and saw the crack in the plate going from bolt to bolt. Not exactly sure how this could have happened from daily driving, but at least we have an answer to the noise now!

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