VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 Zinc additive?

Hi there,

I believe my camshaft is making a bit of noise. I’ve gone through everything else and can’t find anything. Camshaft is a big job for me, so looking for anything else to quiet it before a full tear down. An old timer mentioned adding some sort of zinc additive to quiet a camshaft. Ever heard of this?

For background, this is on my 33 1.5 ton truck, 207 original engine. I busted a valve guide when a pushrod bent months ago and replaced rocker arms and the top of the head with a parts engine. The noise has existed since this time- all other components have been properly adjusted and checked.

Thanks
Adam

Camshafts do not mak noise. If the valves are improperly adjusted they will make noise. In some cases it is not possible to adjust the the valve lash due to things like rocker arm pitted due to contact with valve stem, sticking valves, oil supply etc. A dry timig gear can make a valve type noise.

Dang. I’m out of my element now with this noise. No idea what else to adjust or check, as everything seems in order and I can’t track it down.

Spend $8 and get a mechanics stethoscope from Harbor Freight. Or use the "poor man's" stethoscope. Take a 2 foot piece of 3/8" tubing. Hold one end to your ear and move the other end to various locations on the engine.

For reference, the zinc additive is supposed to compensate for the lower zinc levels in today's engine oils. Zinc is supposed to prevent wear between the camshaft and the bottom of the lifter. It will not do anything to "quieten" valve train noise.

I don't want to start a big posting war here but will offer this guidance. The only time you need to be concerned with cam and lifter wear in these Stovebolt sixes is start-up with a new cam and lifters. The speeds and valve spring pressures are relatively low in these engines so there is more than enough zinc in today's oils especially if the cam is broken in properly.

Thanks Rusty, I’ve got a stethoscope- have listened but can’t find much. Need to find someone near me to help out with an extra ear / experience with these Stovebolts. I appreciate the input. If you know anyone near the Olathe / KC area- let me know!

Adam

My strong recommendation is for you to consider a VCCA membership. This will allow you to find and connect to knowledgeable members in the KC area who are more than willing to share that knowledge.

A key point that I learned very soon after I joined VCCA is that only a small percentage of the members participate in Chat. I also quickly realized that only a very small portion of the people registered for Chat participate regularly. VCCA membership gives you access to a much larger active community.

As an interim solution you might contact Jim Carter Truck Parts in Independence, MO. They might be able to connect you with someone in your area.

Thank you for the suggestion. I will start that process. I’m familiar with Jim Carter and have been there. I’ll reach out as I start down the membership route. I appreciate the insight.

Can you describe the noise? Is it a tap, a knock, a scrape, a squeal, what type of noise are you hearing?

The question is: What caused a bent pushrod and fractured valve guide in the first place? The sound only reared it's ugly head AFTER that happened. Think it may be related?

It’s a tapping. The bent pushrod / guide damage was caused by lack of oil flow to the back of the head. I replaced the rod, top of the head and rocker arms from a parts truck and it now flows oil as it should. There was a light witness mark from the bent rod on top of one of the cylinders, but nothing deep and no rocking on any cylinders so it didn’t concern me. I tightened the new rocker arms to factory spec, and the noise got louder. I then loosened them to feel, to account for wear, and the noise became quieter, and it runs smoother - but still taps when revving and accelerating.

Visually, everything seems fine. I’ve gone over it several times checking the new arms, checking all the rods, ensuring no rods or arms were hitting the covers, etc. I rested at the possibility that when the pushrod failed and valve cracked, possibly the cam got out of round and is hitting as it rotates? I’m not sure that’s possible, but since I can’t see anything- I’m down to guessing it’s internal. Short of a complete tear down, not sure where else to head in diagnosing it.

Currently, I can drive it and it doesn’t affect the regular drives, just noisier than I would like it to be and obviously it’s due to something that isn’t quite right. Outside of the tapping, it sounds like a sewing machine. So it’s close to being where it should. I may try and upload a video somewhere of the sound- anything on my phone is too big to upload here.

The fact that when set at factory spec it got louder and quieter when backed off has me scratching my melon. Have you set the valves on a slowly running engine or stopped Hot or Cold?

If the arc of the rocker arm end at the valve is not correct you will get some ticking.

Chipper-

I’ve adjusted the rocker arm gaps on both a cold and hot engine. Set them up, drive and then readjusted. When set to factory gap there’s hardly any movement and it’s almost as if too much pressure was being applied, making this noise louder. Backing off, allowing a little wiggle between the arms and rods, quieted everything down.

Your experience does not make sense to me. Normally lowering the gap quiets the valve train noise as there is less movement. It is the same as hitting with a hammer from 0.001 inch versus 1 inch.

The higher noise when adjusted tighter suggests to me either the ends of the rockers are not the proper arc or the lobes on the cam shaft have flat spots. It is possible that the larger gap allows more oil that cushions the noise. That is HIGHLY unlikely in my opinion.

If the engine was mine I would adjust the valves to a little looser that specs and drive the car. If it gets better count your blessings. If not then try again to fix it.

What I would not do is use higher viscosity oil as it will definitely cause more piston pin and ring wear.

Thanks for the additional details. Your description really has me scratching my head.

Please don't take this post the wrong way. It's just that in my experience going back to the basics is often key to solving problems like this.

I know this sounds crazy but are you sure that you are setting the intakes at .006' and the exhaust at .013"? I only did it once but i did set one up backwards one time. It is somewhat of a developed feel. You want just a slight drag on the feeler gauge. I typically check my work using my own "go/no-go" system. For example, on the intakes I have the .005', .006" and .007" gauges extended from the tool. I adjust until I feel a slight drag on the .006". Then I make sure the .005" slides fairly easily. The .007" might fit but you really have to push it.

Another trick would be to adjust the valves using Chipper's vacuum gauge technique. With the engine idling you tighten the adjuster until the vacuum drops, then back off until it reaches back to the highest reading.

One other "back to the basics" question. You noted that you used parts from a parts engine when you did the repair. Do you know the history of that engine? I wnnder if there might be some subtle differences.

Thanks for all the questions and info- Rusty, I did set the intake and exhaust properly, but it's worth a double check as always.

I do not know the history of the parts engine, just that it appeared to be in good shape and turned over- it is the same year and make according to the casting numbers.

I was able to get a link to a video- although this link is only good for two days. This is the truck running at idle, fresh start, not too warm, 41 degrees out, it's in the garage. Let me know if you hear the tapping I'm referring to.

Link: Tapping Noise

What did you set the valves to on your 1933 engine ?

Chev Nut –

I followed my manual and adjusted intakes to .006 inches, and exhaust to .008 inches. Note- that is different from the dimensions Rusty has above on exhaust. My numbers are coming from the 1933 Cars and Trucks Repair Manual. Currently, the valves are backed off on from spec, as it seemed to make a difference on the roughness of the engine and sounds better as well. I'd have to go measure to find out exact, but it's wider than they above.

If the above noise could be connected to the motor bearings- note that I do not have the ability to remove any shims, as the maximum were removed 25+ years ago by the previous owner.

YOU AR CORRECT FOR A 1933 ENGINE.

THE 1934 AND UP IS CORRECT FOR RUSTYS SETTINGS
JjUST MAKING SURE.

To me it sounds more like a knock than valve tapping.

I do not have access to a 1933 Chevy shop manual. So you could be correct. I was basing this on what I know most of the Stovebolt 6’s I have worked on use for valve clearance.

Try to get an official Chevy manual. I have been tripped up by information in aftermarket manuals more than once.

If you are setting at .006” and .008” I would try setting the exhausts only at .013”. Leave the intakes at .006”.

I WONDER I IT HAS A 1934 CAMSHAFT., In the later years Chevolet old the 1934 for replaement in a 1933.

In video engine not idling smoothly. I presume idle mixture set for best idle. How about a compression test? Maybe piston whacked valve when pushrod bent.

This is where my inexperience takes hold. Outside of messing with the vacuum advance and idle on the carb- I’ve not adjusted anything else for her to idle any better.

I’ve also not ever done a compression test, nor do I know how to. This is my first mechanic experience, going on a year owning it and I’ve learned a lot. Still plenty more to learn though.

We all started somewhere with working on vehicles. And have made our share of mistakes along the way!

My guess is that there are lots of good YouTube videos to show how to use a compression gauge and a vacuum gauge. Those gauges are good diagnostic tools to show the health of your engine.

I also recommend that you get a copy of the Chevy shop manual for your truck as well as an operator's manual. You will be surprised at how much routine service information is given in the operator's manual.