I added Sta-Bil and the engine started knocking. Uh Oh...

[GoToGuy]

Remember the extra wt. You may have put on didn't happen overnight. Therefore your losing same wt. And or physical fitness improvement will be at a measured pace. Too much too soon. And have the broken bones, stiches zippers to prove it. Lol.

 

[JimFixes]

Remember the extra wt. You may have put on didn't happen overnight. Therefore your losing same wt. And or physical fitness improvement will be at a measured pace. Too much too soon. And have the broken bones, stiches zippers to prove it. Lol.

I say that all the time, it took me 20 years to get to this size, it is going to take time to lose it.

As for the truck, finally got a chance to get out there, I had to repair a transmission line on my Mazda so it was the perfect time to check on the truck.
Started it up, grabbed the mechanics stethoscope, and narrowed it down to cylinder #7.

The sound does speed up with engine speed, I tossed in an old bottle of motor honey I had sitting around to thicken things up a little and within a few moments, the sound had dramatically decreased.

I am going to get down there later this week with the stethoscope and see if I can hear it from below, but I could not get on the ground this time.

I will try grounding out the different plugs one by one and see if there is a change and report back.

Thank you all for your help so far.

 

[RichLo]

If you have it narrowed down that much, you should buy or borrow an inspection camera and check the cylinder wall through the spark plug hole. If its piston slap you should be able to see scoring on the wall

 

[JimFixes]

If you have it narrowed down that much, you should buy or borrow an inspection camera and check the cylinder wall through the spark plug hole. If its piston slap you should be able to see scoring on the wall

WHOAH!

Great idea! I have one of those inspection cameras, how did I not think to use that!

Thanks for the reminder, I will get right on that!

 

[LVJJJ]

That's really strange that a noise like that would start when first using Stabil (I did listen to your video), I've used Stabil for years in my 1965 Chevy Van with a 292. We towed with it in the 1990's all over the western USA but now its in storage. So I put Stabil in the gas, put some fresh gas in it, run the carb out of gas by shutting off the electric fuel pump while running. Has started right up every 6 months or so for the past 20 years using Stabil, gas has never gone bad. I probably put more than I should in. So, why your engine started knocking when using Stabil is weird, maybe just a coincidence. My new 383 started out with a knock when cold but goes away when hot. At first thought it was the larger crankshaft hitting the oil pan but that isn't the case. Actually sounds more like a lifter than metal on metal knock. I adjusted the valves on the passenger side where the sound is coming from, but they weren't out of adjustment so guess that isn't it. If it was piston slap I don't think the noise would go away when it gets hot?

 

[Schurkey]

If it was piston slap I don't think the noise would go away when it gets hot?

Absolutely common for piston slap to go away as the engine warms up. Constant piston slap regardless of piston temperature means the pistons are slapping pretty hard.

I've got a couple of engines with KB pistons, both rattle for five or ten seconds when cold, and then quiet down; and it's not the valvetrain. The noise is deeper-pitched than typical "lifter rattle".

GM made a zillion engines with a known proclivity for piston slap. Pistons have little-to-no skirt for reduced friction. GM avoids warranty repairs or recalls by claiming that the piston slap "doesn't hurt anything". And piston slap only when cold doesn't hurt anything. But constant piston slap can drive the knock sensor crazy, leading to retarded timing, poor fuel economy, and increased emissions.

 

[92Landyacht]

My 2001 GMC Savanna 3500 van has an 8.1L Vortec engine and it has had piston slap from day one. It now has over 230,000 miles and runs just fine. It does consume more oil then I like but it has always used oil for as long as I have owned it at 72,000 miles. My understanding is that GM didn't do such a great job with piston to cylinder wall tolerance on these engines. Knocks for about 10 seconds on a cold start. Sounds a little like a diesel engine when first started. Quiets down soon after.

 

[LVJJJ]

I suppose piston slap is better than rod knock? 383 runs real strong at all times even pulling mountain passes, so I guess the knock sensor isn't bothered. We've kinda hijacked the OP's Stabil problem. Any solutions on that or did I miss something?

 

[JimFixes]

I suppose piston slap is better than rod knock? 383 runs real strong at all times even pulling mountain passes, so I guess the knock sensor isn't bothered. We've kinda hijacked the OP's Stabil problem. Any solutions on that or did I miss something?

No problem at all, I appreciate the back and forth, gave me a lot of info!

I didn't stay off my feet, they got worse, now I am taking it easy, for real. Gonna scope it tomorrow to see what I am working with. Doc got me a couple of hard shell boots I can walk in, he said if he can't keep me from moving, he can at least keep me from hurting myself more. The boots are uncomfortable but walkable, so just by design, they will keep me off my feet.

Feel free to keep tossing out ideas, no one ever accused me of knowing too much.

 

[JimFixes]

Final update on this.

Sta-bill cleaned the crud off a valve (exhaust port valve, piston 7) and it was causing the rocker arm to rattle. Followed procedure to tighten, no more issue.