Help! Bang Bang Bang in my air cleaner! Uh oh.

[dieselbegreat]

Please help me diagnose this problem:

Merging onto I-87 after driving 65 mph for three hours with no problems something broke. Loud rapping - thought I threw a rod at first but oil pressure is normal, no vibration except a loud exhaust popping (from single cylinder) you can really feel on the air cleaner coming up through the manifold. Everything else seems normal.

I'm thinking something to do with intake valve, maybe broken rocker arm, valve spring or retainer which can hopefully be fixed. I can bring it back up to 65 mph and it runs pretty smooth, but at idle it's really noisy. I guess I'll probably loosen each injector line one by one until it gets quiet and then I'll know which cylinder it is.

[NH2112]

I'd say you have either a loose rocker arm or a broken valve spring that isn't quite holding a valve shut. The popping is probably gas escaping before the compression stroke or combustion pushes the valve shut, and the reason it smooths out at higher RPM is because the valve can't drop as far before the next compression stroke. I suppose it could be a collapsed lifter, too, but that's a bit less likely.

[crew84]

Hey, do not forget an injector stuck open leaking sounds like a rod knock. When you do the breaking open of each of the injector lines and find out which one it is then try replacing the injector if you have another. It will be cheaper than tearing it down.

[NH2112]

True, but an injector stuck open won't pop back through the air cleaner. It has to be something keeping the intake valve open when it should be closed.

[ToddMeister]

Could also be a broken push rod on an exhaust valve.

[dieselbegreat]

hmm. A malfunctioning exh valve would inhibit the burning exhaust gases from being pushed into the exhaust and instead, when the intake valve opens, allow the recompressed burning exhaust to enter the intake manifold with a bang. Makes sense. If that's the case (bent pushrod, broken spring, etc.), this is probably going to be fixable without COMPLETE a teardown. That would be nice. still have to remove the lines to get the valve covers off tho. waiting for spring temperatures...

Everyone's suggestions are appreciated very much.

[78Chev]

Would a compression test isolate the cylinder with the weak valve spring if that's the case?

[G. Gearloose]

When I broke an exhaust valvespring on a built 302, it soulded just as you describe, (minus a little muffling action from the carbagator.)

NH2112; my wife reading over my shoulder promped me to ask you to thank your buddy for his service, for us both. Wish him best.. smile.gif

[dieselbegreat]

The more I think of it, without actually taking a look, the exhaust valve must be the culprit.

Gearloose:
Yeah, using my aluminum intake for an exhaust manifold is not good. Don't think I'll run it too much.

78Chev:
I'll just pull the glow plugs and see which cylinder has two compression strokes! :D
Once the cylinder is isolated a compression check should show whether a valve is stuck closed or open (and probably bent).

[dieselbegreat]

I pulled the valve cover on the driver's side because the popping was originating from the #1 cylinder. I found at least 4 bent pushrods with the exhaust for #1 the worst. (See photo link below.) The other side had been completely rebuilt (rings, valves, etc.) by a dealer about a year and a half ago and all was fine when they put it together.

I sure could use some good pushrods (enough for one side) if anybody has some 6.2 spares lying around. I'll pay ya.

http://www.monkeywig.com/chuck/public/pushrods-wide.jpg

[john8662]

So, now that the problem was found. What causes pushrods to get bent like that? Nice Pics! I have seen used sets of 6.5 pushrods on ebay quite often, might look there, they were cheap too.

[dieselbegreat]

Many consider the pushrod to be the "fusable link" in the valvetrain which just bends if anything goes wrong. Bent pushrods can be caused by valves sticking/binding in their guides (maybe cold or heat related), valves floating at high speed and possibly colliding with pistons (especially at high RPM with a cold engine), binding or off-center rocker arms, misfire, etc. Someone on the web even theorized that a malfunctioning exhaust valve can lead to a bent intake pushrod because of the extreme cylinder pressures holding the valves shut when the camshaft is trying to make them open. Like I said, they just bend.

No pushrods on eBay right now. So I'm hoping someone on this forum is able to mail me some this week. smile.gif

[ 02-28-2004, 03:57 PM: Message edited by: dieselbegreat ]

[john8662]

OK, I was just wondering, thanks for explanation. I still wonder which of the things caused your engine to bend the pushrods and if it will do it again. I looked on ebay for you also, I didn't turn up anything either. By the way, Your quotation in your signature cracks me up! Thats the truth man!

[dieselbegreat]

Thanks. Hmm. Maybe it was that six grand hole shot I pulled out of my driveway the other morning! :D

[waorth]

If you're still searching, there are pushrods&rocker arms on ebay (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=46098&item=2464846013) right now.

Walter

[dieselbegreat]

Thanks for letting me know. Those are the solid rockers from the early to mid '80s. Are they interchangeable (as a complete assembly of course) with the later stamped rockers I have?

[dieselbegreat]

All right. For anyone who is interested, I just put in 8 brand new pushrods I got mail order $7.52 ea. from Dal Slabaugh at VanDevere Olds (GM parts cheap and fast). You can reach him at lockitup@bright.net to create an account. (couldn't wait for used ones right now).

The engine starts and misses, then as it warms up after about 20 seconds it starts to pop again. :mad: I suspect there are even worse pushrods or other problems on the right side now and will open it up when I have a warm day. Oh well.

Hey, I looked for a place to "bar the engine over" to see if the valve action was smooth (it was anyway) but couldn't fiind a place to stick a socket on. How are you supposed to do it?

BTW, my glow plugs wouldn't come on and I couldn't figure it out. :confused: Then I found the temp inhibit switch at the front of the engine on the passenger side of the coolant crossover - not the back of the engine - and wiggled the connector which I had touched earlier when I unhooked the pink wire. Voila! Cycles normally now. Must remember to fix that connection.

[ 03-13-2004, 05:06 PM: Message edited by: dieselbegreat ]

[britannic]

Either put a socket on the harmonic balancer bolt, or use your hand to tension the alternator belt and use a socket wrench on the alternator's pulley nut.

[britannic]

I was rereading your post and was thinking: that's a lot of bent rods all of a sudden - is something leaking into the combustion chambers to cause hydrostatic lock or something? Did you drive through a deep puddle and ingest a ton of water or was it a bird strike :D (think fighter jets)?

[dieselbegreat]

britannic:
Ahh... well, my crank doesn't have a big honking bolt in the center, just a hole. Re the bent pushrods, the thing sat all last summer and fall waiting for a guy to do a little body work on it. There was a lot of new rust under the hood when I got it back and I suspect that moisture got in there from sitting so long and rusted the valves to the seats, bending the pushrods when the engine was started. I've heard that happens. Otherwise, who knows?

[britannic]

Well your next problem running without the harmonic balancer bolt for any length of time, is going to be a busted crank and whatever collateral damage it wreaks on your poor old engine :eek: !!

[dieselbegreat]

Definitely, but I think there is a bolt from what I was told, except the balancer pully is mounted in such a way that the bolt is recessed behind it. Ever hear of that?

[britannic]

No, never heard or saw of such a thing. It is hard to see without removing the radiator or pulley, but neither is necessary to wind it with a socket though. Reach up from underneath with a mirror and you should see it in the middle of the pulley. It may be covered in dirt, so be prepared to scrape it out first. The pulley has a hole in the middle of it and is bolted to the balancer with 4 bolts around the outside of the balancer's main bolt.

[waorth]

Did you already see/feel the 4 pulley bolts which britannic describes? If yes, remove the pulley. This will get you better access and visibility to the damper and the (missing) bolt.

Walter

[john8662]

The 88 6.2 is just like my 86 6.2, it has the dampner pulley on top of the harmonic balancer. If you're just looking underneath its hard to see the balancer bolt as its covered up by the dampner pulley. So, it WILL look like your bolt is missing, I'll bet everything is intact. But to get at the bolt, you're gonna have to remove your belts, then the pulley.

The milspec 6.2's had a pressed pulley that mounted to the harmonic balancer, this is true of early 6.2's from 82 to 84 and early 85. Most 85 and up had the rubber dampner that bolted to the harmonic balancer to increase belt life and reduce vibrations and noises.

[britannic]

You learn something every day :cool: , thanks John!

[dieselbegreat]

Yeah - what John said. ;)

[dieselbegreat]

Finally pulled off the other valve cover today and found the pushrod to the #8 exhaust valve had bent enough to fall out of the rocker arm. The plastic insert which holds the rocker in place had failed. All the other pushrods on that side look okay. I guess I'll order a set of inserts from GM. I hope the camshaft is unharmed.

[dieselbegreat]

Just to record my findings for others, I didn't notice the rocker arm shaft was cracked and had bent upward allowing the rocker arm on #8 to go sideways. I ordered one whole used assembly which includes 4 rockers already mounted, from Avant Salvage in GA, for $25. They will overnight ship which is very convenient and they are real friendly to deal with. Making sure to evenly tighten the shafts down I put it all back together. It started right away and idled smooth as glass! 250 mi ROAD TRIP TODAY!

One important lesson is that I wouldn't have known that the other side had a bunch of bent pushrods unless I had pulled the wrong valve cover first. Makes sense to check both sides when things start happening.