The Stovebolt Site Forums The Shop Area Engine Shop Adjusted valves now popping through exhaust?

Cleaned and lubricated rocker arm assembly and reassembled in proper order. Started engine and seemed to run OK, but had a slight hesitation off idle. # 4 intake valve was very tight. Re-adjusted the valves after warming up engine for 30 minutes. Set intake valves at .07" and exhaust at .014". Now I have a what sounds like a continuous popping through the exhaust at idle. Hesitation is gone, and engine revs up fine. Could the valves be adjusted too tight....causing this popping through the exhaust? Valves not seating completely when closed? Any ideas? Forgot to mention, I also have periodic spark knock on #5 and #6.

1949 Chevrolet 3100 with 216 cu.in. engine and SM420 transmission.

Tim

Have you tried the dollar bill trick at the exhaust yet? That might yield information.

Have done the dollar bill test. The exhaust is not drawing in just popping. Didn't do this before removing the rocker arm assembly for cleaning and adjusted the valves.

Hey fixy, how does one determine a spark knock from a specific cylinder ("#5 and #6")? Assume that I know nothing, and you will be very close to an accurate assumption.
Carl

Hey Carl,

Your guess is as good as mine. Really not sure whether it's #5 or #6 just here a periodic knock from the top of one of the two rear cylinders. This just started yesterday along with the popping from the exhaust after I adjusted the valves. Darn thing sounds like a bag of popcorn in the microwave just about ready to eat. Any ideas? Valve lash too tight causing the valves not to seat completely closed. Ran fine before I started making the adjustments. Only made the adjustments because I noticed #4 intake was way too tight.

Your lash settings are tight for an engine that is not new. Also, what procedure did you follow to adjust the valves? You may have them too tight or off adjustment if the engine was 180 degrees out.

Sweet,

Thank you for responding. I am also thinking I have the lash too tight on the valves. The engine has 51,000 miles on it. What are the numbers you suggest for the intake and exhaust valve lash adjustment?

Tim

Tim,

The valve lash settings for various years are linked-to on this procedure.
Heed the first note on the smoothness of the mating surface on the rocker arms.

Good luck,

Tim,

Thank you for your vote of confidence! I've been using the procedures you listed for valve lash adjustment. Checked rocker arms when I had them apart to clean and the valve surface had very little wear. Surfaces are convex. What do you suggest I set the valve lash tolerances to?

Tim

Spark knock happens under load, like pulling a hill at full throttle with the engine lugged down. What kind of sophisticated computerized engine analyzer are you using that isolates a spark knock to specific cylinders?

Valve lash has a habit of tightening up as the engine reaches full operating temperature. I like to do a cold companion cylinder adjustment with the lash set .001" over specification on the intakes and .002" over on the exhaust, then do a 30 minute test drive and check and tweak the clearance as necessary with the engine fully warmed up.
Jerry

Jerry,
No sophisticated engine analyzer. Just heard a very intermittent knock at the rear of the engine. Either #5 or #6 after the valve adjustment. Nothing steady with the knock sound. Could be back firing? I will set the valves as you specified and see if this helps. Thank you for your input! Will keep you guys updated.

Tim

Jerry states the key, the valves need to be HOT.

30 minutes get all parts nice and toasty.

I like the values on Tim's link. Paying attention to the note above, add .005 to your value.

"Spark knock" is actually detonation, and doesn't happen unless the engine is under load out on the road. What you might be hearing could be a valve sticking intermittently and slapping back onto the seat as it releases. Try this- - - -get some upper cylinder lube such as Marvel Mystery Oil or Wynn's Friction Proofing (if they still make the stuff!) and pour several ounces down the carburetor with the engine running at a fast idle until you get a heavy smoke from the tailpipe. Then dump a big slug of the stuff down the carb to stall the engine. If the engine doesn't stall, shut the ignition off quickly. Let it sit overnight, then start up and goose the throttle several times to blow away any carbon deposits on the valve stems that have loosened up during the overnight soak. I use KROIL for this procedure, but I buy it by the gallon.

The exhaust smoke cloud will be epic during this process, so warn the neighbors not to call the fire department!
Jerry

Thank you Tim, Sweet and Jerry!! Got the valve lash set and she runs GREAT!! Jerry your trick worked. Took her for a drive and she runs PERFECT!!

Tim

"I love it when a plan comes together!"

Extra credit if you remember what TV show made that phrase famous!
LOL!
Jerry

That is too easy, Jerry

Who could forget Mr T and friends.

Jerry,

After I adjusted the valves per you instruction, I ran the truck at idle for 30 minutes and then to it for a short test drive. It ran GREAT!! Removed the valve cover and noticed that #6 exhaust valve did not seem to be moving as well as the other valves. Checked the push rod and it was not bent. I believe you are correct, I may have #6 exhaust valve sticking? I have a Ampro upper cylinder lubricator on the truck with it adjusted at 1/4 turn and running MMO in it. will this be enough to free a sticking valve or will I need to pour the MMMO through the carburetor as you specified?

Tim

It sounds like you may have a flat cam.
You may want to check the travel of that pushrod compared to another exhaust pushrod.

A sticky valve will cause erratic, intermittent noise due to the valve not seating all the way, and a bad miss due to low compression. Definitely check the cam lift at the pushrod side of the rocker arm. Harbor Freight and most of the other discount tool places have magnetic-base dial indicators at bargain prices, and I've had at least one of them as long as I can remember. Set up the indicator directly above the valve adjusting screw and check how far it moves as the engine is turned through two turns of the crankshaft. I like to use a piece of steel flat bar bolted to the head with the vale cover attaching holes to give the magnetic base a sturdy mounting surface. All the valves should move approximately the same distance, within a few thousandths. Intake and exhaust lift might not be the same, but all the intakes should be similar- - - -ditto for exhaust. If there's a noticeable lobe lift difference between cylinders it's time for a cam and lifter change.
Jerry

Jerry,
The popping through the exhaust stopped after readjusting the valve to your procedure, so did that rear top cylinder clack/knock? Checked #6 exhaust valve movement with magnetic mount micrometer. The rise and fall of the #6 exhaust valve was within .001-.002 of the other exhaust valves as best I can see. What I am seeing is the # 6 exhaust valve moving slightly erratically like it is sticking. Removed all the spark plugs and turned the engine over by hand slowly. When # 6 exhaust valve opens and closed when the rocker arm comes up the valve is sticking down and popping shut, but not at all times. Checked for broken valve spring. Spring is good. Could be weak. Push rod is turning straight, no noticeable bend. Valve appears to be straight at the stem section as it goes up and down. Very little if any variance in the movement of the stem when it goes up and down. Just pops shut periodically one the rocker come to the up position. Valve sticking with carbon deposit in the guide? Should I try the MMO treatment or Seafoam?

Tim

I would remove the seal on that valve to allow more oil to lube that valve, at least for a while.

Yours is a classic example of valve stem carbon deposits. I'd suggest the procedure I described about flooding the intake with penetrating oil and letting the engine sit overnight to soften the carbon deposits, then giving the engine a few hard full throttle runs and wind it up in the lower gears to blow the deposits away. As long as you don't go crazy on the RPM you're not going to hurt it. These engines were designed to run- - - -the way people pamper them these days, it's no wonder they get gunked up.

KROIL would be my first choice. Sea Foam is a good fuel tank additive, but it's not aggressive enough to dislodge a carbon buildup. www.KANOLABS.COM

Jerry

I think HRL is dead on with what happens to these engines which we baby. They come with 3 speeds too far apart, 4.11 rear ends which really makes the engine sing at 50 MPH. They were designed and engineered to carry heavy loads and to be tached out before you shift.
Who does that to their precious "Baby" today? No wonder they get carboned up.
Carl

I'm gonna second HRL and 52Carl on the benefits of occasionally working our trucks. Back in September I hauled a dozen bales of hay, a smoker and 55 gal drum of water about 150 miles into the hills of Arkansas while the wife pulled horses for a two week camp/ride at National Chuck Wagon Races in Clinton Ar.

My 51, 3600 is stock with the exception of a T5 tranny (.72 5th gear). To keep pace I ran 65 a lot, and in the hills it was generally on the floor, sometimes in 3rd to keep her horse trailer in sight.

Since then it runs quieter and I swear the oil leakage/usage had dropped by 50% or more.

Amazing! Most folks here think a 216 Babbit-pounder is as fragile as an ivy league liberal arts student looking for a "cry room" or a "safe space"! I'll bet you didn't even have to stop and pick up any connecting rods that came out the side of the engine!
ROTFLMAO!
Jerry

Heck NO, the amazing thing is how the ol truck was reported to be grinning the few times we passed slower vehicles.

Moparguy, are you saying you have a T-5 behind a 216? I'll bet you now get every bit of the ponies out of that baby now.
I have a T-5 behind a '53 235, and it is amazing how pleasant that truck is to drive now.

Moparguy, are you saying you have a T-5 behind a 216?

Carl,that's right. The truck is a documented 45,000 mile unit (I'm responsible for about 4k of those). The only two upgrades I've made are new 16" wheels with modern 215/85/16 tires and the T5 with a one piece drive shaft. Of course there's been tons of work to make it a safe stoppable daily driver.

I'd be hard pressed to say which upgrade was best, but both have made it a joy to drive. And yelp, even with the 4.57s I have to use all 82 hp occasionally.

That's awesome! I have a similar setup, only with a 235 and a 4.64 gears and couldn't be more pleased.