The Stovebolt Site Forums The Shop Area Engine Shop Engine Tapping Question

I have a 51 Chevy 3100 with a 235 in it. Locally, the truck runs smooth with no tapping. On the freeway I get valve tapping. Checked the oil and all is level.
Does anyone have any suggestions as to what I should look for first?
D

What speed are you driving when the noise starts? You might be experiencing a rod knock, which is much more serious than a little valve noise. Also, slightly over-advanced ignition timing can cause detonation at highway speeds, which resembles valve noise somewhat. Take a check-ride with a well-qualified diagnostic tech.
Jerry

That sounds strange to me. It is usually the other way around. Are you sure it is a valve? If so , do you have good oil pressure? The right oil for your engine? I had one truck that would start that when it needed an oil change. Not much help but good luck.

Might be a bent push rod struggling under highway loads , tapping against the block as it rotates ??

The tapping starts after running the truck about 20 miles down the freeway at about 50-55 miles an hour. Could need an oil change. I haven't driven the truck too much on the freeway. After getting off the freeway and driving local roads, the tapping stops. Sounds like it is coming from the top portion of the engine. The oil gage started to go a bit haywire. At low idle it would go to between 10-15 and after excellation go to 30. Don't know if the gauge is off or not.

I restored a 64 Ford F250 recently and had the original engine rebuilt in that truck and after driving the good ole CA freeway the engine starting tapping too. I took the truck back to the mechanic and he said the top portion of the engine wasn't getting enough engine oil needed for that kind of engine stress. He did something to have more engine oil directed to the the engine and the truck has never done that again.

Guess the old 51 needs to make a trip to the doctors.
I just thought it was weird that the tapping only occurs during freeway driving. I just bought the truck several months ago and was told the engine was rebuilt recently. Was also told that the engine was a 67 to 72 model.
I will change the oil and take a test run but I think it's time for a thorough going over at the doctors if nothing more than for my peace of mind.
D

Were 235's made after 1964? :confused:

If your engine is a 235 with hydraulic lifters, the noise is somewhat common to those engines.It's fairly quiet at low speeds, hiway driving gets the lifters to clacking. Seems the oil pump picks up some air ,feeds it to the lifters, they collapse slightlymaking the noise.

an oil change wouldn't hurt if its been awhile but it sounds like one of the rockers isn't get enough oil at consistant road speeds and RPM's. I would think perhaps a piece of trash may be stuck in an oiler hole? I would pull the valve cover and see what each one is doing. I had one that did somewhat like you mentioned and it just needed adjusting a tat. If hydraulic I've seen a single lifter lose its "prime" and clack like crazy.(spring was broke) Let us know what you find.

High speed lifter collapse is common and can usually be fixed very easily. It is caused by air being trapped in the lifter. At low speed the oil stays at the bottom of the lifter internal reservoir. At high speeds the oil is thrown to the top of the reservoir which puts the air against the check valve so when the lifter recharges after bleed down, which happens a little every time a valve is opened, it is recharged with air. When the engine is returned to a slower speed the air is bled out and a quiet lifter returns. The problem is the air stays in the reservoir waiting for the next high speed run.



Most aftermarket lifters have a vent hole in the pushrod seat that is sealed off by the pushrod. I grind a very small groove on the bottom of my pushrods to allow air to escape from the lifter reservoir through the vent hole. 1950-52 Power Glide engines were grooved from the factory this way.

I agree with the lifter tapping argument...

You need a can of Bardol or Winn's.....Tuneup in a can....careful
don't buy the rebuild in a can

Ustta be you could use a little ATF but it hasn't been the same for years

Rislone That's what I was thinking of 'Frees stickin' lifters'

My tooth is still screwed up and this eatin pain pills is gettin old!!!!!!

Rislone

Hey, Gang

Just for kicks, whenever you hear what you think is a valve tap in the future, check your fuel pump!

I spent a couple of months recently checking with several mechanics, etc. ... 4-5 pro's said I had a valve tap. Finally, I settled on my favorite personality out of that bunch ... he came over and adjusted my valves, which needed a slight adjustment, but in the process we discovered it was the mechanical fuel pump that was making all the noise! We popped a new one in and good-bye "valve tap!"

Also, I"m not sure if this is the case for these motors, but if you have a tick at idle or at part throttle, but not under heavy acceleration, look at your rockers. On Olds motors, the rockers wear out pretty easily (about every 90,000 miles) and start ticking. Sounds like lifters.