92 1500 Loud Tapping Noise when accelerating

ifixedit · October 6, 2015

Viewing the plugs 1,2 and 5 look the worst, possibly some oil fouling but the things are pretty worn out too and their color could simply be due to not firing properly. Yeah, I'd say it was certainly time to change them, they've got some miles on them.

I'm going to stick with my earlier prediction, collapsed lifter or broken rocker arm.

A couple of questions.... When it is idling, does it make a fairly loud ticking noise, does it especially tick right at start up? If so does the ticking quiet down or keep it up? Does it idle smoothly or is the idle rough? By rough I mean you will feel the entire truck shaking, again especially right after start up.

Edited October 6, 2015 by ifixedit

Jared Stangenberg · October 6, 2015

No tick at idle.

The idle isn't perfectly smooth, but it's not violent either. I've got some loose bits in my interior, so they vibrate pretty good. I can say the whole truck does though.

The exhaust sound does kind of "lope" at idle. I'm not sure if that's the right word. I may go record it to show what I mean.

I've decided against the Risoline additive route. I've got a friend who's supposed to come up tomorrow and help me check out the rocker arms and lifters. He's got more experience with this kind of thing than I do.

*EDIT*

The sound does occur during "power braking". At around 1750 rpm, also coincidently the highest the engine will rev while power braking.

I've not been driving it save to try and diagnose things. I took it out for a short spin tonight and it can cruise at 1500 rpm all day long with no obvious trouble. Go above 2000-2500 rpm and that's when things seem to hit the fan (Figuratively).

I did notice that there's a bit of "lag" between when you push the throttle down and the engine decides to do something about it.

In a literal sense, nothing is hitting the fan, I checked.

You can't see anything in this video, but this is the exhaust sound at idle (in park) after I took it out for the drive to night.

Edited October 7, 2015 by jstange

ifixedit · October 7, 2015

Tough to tell from the video, it sounds like it's idling pretty decently but there does seem to be a slight miss. I think once you get the valve covers off you will find something amiss. Keep us posted on what you find.

Edited October 7, 2015 by ifixedit

1997SierraSLT · October 7, 2015

97Sierra, any particular product you had luck with?

it was just a standard GUNK motor flush if not mistaken.

http://www.gunk.ca/landing_EO.asp

Jared Stangenberg · October 7, 2015

Ok, we've not found any obviously damaged rocker arms, just a little wear from contact with the push rod.

Speaking of pushrods, so far we've pulled 3 and 2 of those appear to be slightly bent.

With the valve covers off (and all rods and rockers still on at this point) and cranked the engine without the ignition coil connected so that the engine rotated from the starter motor without starting. All of the pushrods did appear to lift and move the rocker arms, is this a valid way of checking the lifter movement?

ifixedit · October 9, 2015

Speaking of pushrods, so far we've pulled 3 and 2 of those appear to be slightly bent.

With the valve covers off (and all rods and rockers still on at this point) and cranked the engine without the ignition coil connected so that the engine rotated from the starter motor without starting. All of the pushrods did appear to lift and move the rocker arms, is this a valid way of checking the lifter movement?

First off, if you've got anything other than perfectly straight push rods, you've got a more serious problem. The easiest way to determine if the push rods are bent or not is to roll them on a perfectly flat surface, if they don't roll or roll with a wobble, you've got problems in the valve-train. I'd venture to guess there's a chance your timing chain has jumped a tooth or two which usually results in bent push rods. Rotating the engine will not tell much as even a collapsed lifter will still move up and down as the cam lobe rotates, but those bent push rods would indicate a more serious problem than a collapsed lifter at this point. This may not be easy for you to do, but you need to find top-dead-center of the #1 piston and compare it to the timing mark on the harmonic balancer against the 0 mark on the timing chain cover if it is so equipped. If not equipped or you can't tell, the timing cover is going to have to come off for further inspection, I'd probably be taking it off for further investigation anyways. I'm not sure on these years, but they may have used the cheap nylon timing gears and a tooth or two may have broken off causing the chain to jump. You'll know when you get it apart.

You want to see something similar to this when you get the cover off, scroll down in this link to see the images >>> http://www.chevytalk.org/fusionbb/showtopic.php?tid/198828/

As you rotate the engine, the timing marks on the gears should line up perfectly across from each other.

You said this truck has 204,000 miles on it? Did it recently backfire by chance? In any case probably could be very due for a timing chain and gear set. Unless you already have a harmonic balancer puller and the knowledge to do this job, you're looking at taking it to a mechanic.

Edited October 9, 2015 by ifixedit

Jared Stangenberg · October 22, 2015

You said this truck has 204,000 miles on it? Did it recently backfire by chance? In any case probably could be very due for a timing chain and gear set. Unless you already have a harmonic balancer puller and the knowledge to do this job, you're looking at taking it to a mechanic.

The truck does have about 204,000. It has backfired, but it was as I was running out of gas on the way home from work one day, would that alter the signifcance of that at all?

I haven't had time to deal with this in a good while, my son was born unexpectedly on the 9th (he wasn't due until 11/3). He's healthy and everythings good. I just haven't had time to look at the truck in two weeks.

I've got a good repair manual and I just looked at the section about finding top dead center. It looks like I'll need to do it in order to adjust the rocker arms anyway. I do have a zero mark on the time cover, so I'll check that soon.

Edited October 22, 2015 by jstange

ifixedit · October 23, 2015

I ask about the backfire because it is probably what caused the timing chain to jump a tooth. Now that I think about it, unless you really know what to do, finding top dead center won't do much for you as you have to know how to determine proper cam lobe lift timing in relation to rotation after top dead center. I'd instead get the timing chain cover off ASAP and get a look at things in there, it will probably be pretty obvious once you get in there. You'll probably find at a minimum a badly stretched chain, perhaps a tooth missing from a gear and so on. If things aren't real obvious, you can then roll the engine over and see if the timing marks on the gears line up or not like I provided in the illustration above.

As far as the rocker arm adjustment goes, that's pretty simple. Once everything is back together, simply rotate the engine going one cylinder at a time and just as the lifter for each cylinder's intake and exhaust are beginning to come up on the cam lobe, tighten the rocker arm nut down to zero lash (tightened just enough to get no play between the tip of the rocker arm and the valve stem), this will be your initial setting. Then once you've gone through each cylinder, exhaust and intake rockers adjusting each to zero lash, you can then go ahead and start the engine and do your final adjustment of each rocker. You will want to stop by the auto parts store for some oil deflector clips to attach to the rocker arms so you don't have oil squirting and running all over the place while you make the final adjustment on the rockers. As you adjust each rocker arm nut with the engine running, typically most will call for slowly backing off (loosening) the nuts on the rocker arms one at a time until you hear clicking, then slowly tighten the nuts a quarter turn at a time, pause a second or two, and continue a quarter turn at a time until you've made a half turn total, and you're done. Some will call for the same procedure, quarter turns at a time, and end up at 3/4 of a turn total, I've always gone with a half turn total.

In any case, I'm now betting your timing chain jumped.

Edited October 23, 2015 by ifixedit

Jared Stangenberg · November 9, 2015

In any case, I'm now betting your timing chain jumped.

I finally got the chance to work on the truck some today. I removed the timing cover, but it got dark before I could really check things out. I'll try tomorrow afternoon when I have daylight. The one thing I noticed was that the chain seemed like it had too much slack, but that was just a quick impression.

As a hypothetical question, if I discover the timing has in fact jumped, what parts do I need to make sure I inspect for damage? Valves and Piston heads?

Edited November 9, 2015 by jstange

ifixedit · November 9, 2015

With any luck at worst you've got a few bent push-rods and nothing more. It wouldn't have even been running any longer if you had pistons slamming into valves and so on, that would take a severely jumped (by several teeth) timing chain so I wouldn't worry too much there, the chain is probably badly stretched and is off by one tooth and you might be missing a tooth on the upper gear. Regardless, now that you're in there you'll want to install a new timing chain and gear set, then take every push-rod out and inspect them for straightness, if you need a few new ones you could always rob what you need from an engine at a junk yard. If you opt for used push-rods just be sure they are the exact same length and that the center of the push-rod is clear from one end to the other so the oil can flow through them. If they sit for a long time the hole in the middle of the push-rod can plug up from the dried up gunk, they're easy to clean up and make like new though.

Jared Stangenberg · November 10, 2015

Good to know.

I plan on just buying new pushrods, they're a $1 a piece on RockAuto and about $2 from one of the local stores.

ifixedit · November 10, 2015

Sounds good, keep us posted on what you find!

Jared Stangenberg · November 13, 2015

I got out there again today to take a look at the timing marks,

To my inexperienced eye TDC for #6 didn't look too bad

No matter what I did though I couldn't get it to look perfectly lined up for number #1 tdc, it wasn't too far off but wasn't perfect either (i added color to the marks on this picture)

Also the timing chain seems really sloppy

In hindsight I should have washed the under side of the motor off before starting this.

ifixedit · November 13, 2015

Well, it doesn't appear that it has jumped a tooth, but the chain is very stretched, especially if you can get that kind of slack on both sides of the chain. I'm also looking closely at the key-way and the key-stock on the crank snout, it's hard to tell from the pictures, but both look a bit beat up and out of alignment, I also see what appears to be metal shavings on the key-stock. The key-way in the crank snout where the key fits should be nice and straight and clean with everything lined up, it doesn't appear that way from what I can see, it looks like something there shifted, like the key-stock itself is broke in half closest to the lower gear. Hopefully the end of the crank and key way is not damaged, if it is the thing is a goner or very troublesome to fix at best. Does your harmonic balancer show any damage? Looks to me like there's some kind of damage there and the balancer itself was damaged and or moved out of position and is what was causing the noise?

Edited November 13, 2015 by ifixedit