I have a 1979 4.9L 300 six with only 110,000 miles on it. Once in a while over the years I would hear a gentle knock in the top of the engine which I assumed was a rocker arm. It showed up at cold starts/idle, then went away.

Now it is noticeable at idle much of the time even when the engine is hot. There is also lifter noise mostly when the engine is cold. What's the best way to deal with this?

I know there are rocker arm kits but I don't have any experience with this. If I replace one or more rockers do I need to mess with valve adjustment or can you just lube everything and torque to spec?

 

Sorry for the delayed response, but have been away. 110,000 miles is not very much with these engines. Start with easy [inexpensive] things... are you using a good quality 10W30 oil? Are you using a good quality oil filter [i.e. Motorcraft FL1-A]?

Sometimes, adding a quart of Marvel Mystery Oil [or something similar] at oil change time will help clean sticky lifters and quiet them down. Some people add a quart of automatic transmission fluid [if oil level is low] and drive for a few hundred miles. The detergents in the transmission fluid help to clean the engine internals.

Be careful [stay away] using some of the 5 or 10 minute quick engine flushes. They are strong and may dislodge gunk so quickly that the oil pick-up screen becomes blocked/clogged.

If all else fails, try a thicker oil like Rotella 15W40. That might be too thick for your winter driving, but should be fine in the summer.

 

I've always used either Havoline, Valvoline, or Castrol 10W40 oil and either Purolator or Motorcraft oil filters. I change both at 4,ooo miles or 1 year, which ever comes first, using 6 quarts of oil plus filter.

I tried a quart of CD-2 oil additive which is supposed to free stuck lifters, quiet engine noises, ect. CD-2 claims that today's oils lack detergents and (naturally) recommend adding it every oil change to keep your engine clean and quiet. While it did unstick the lifter the other lifters, which had been quiet, began making noise.

After 100 miles I changed the oil again and added a quart of Lucas Oil Stabilizer which is so thick it can used as engine assembly lube. That has helped quiet the engine some but sometimes with a cold engine or even occasionally when I pull into the garage with a hot idling engine I can hear some tapping/knocking sound which leads me to believe I have either a worn or loose rocker arm.

So how do I get back to having a quiet engine? First check the torque of the rockers and inspect them for wear? If I find a worn rocker do I just replace it with a kit? I don't have any experience with this type of thing.

 

One suggestion - if you don't have one, go buy a mechanic's stethoscope and use it to determine exactly where the noise is coming from, instead of using a shotgun approach like oil additives. You could find that your rocker arm issue is actually a lifter or broken valve spring. While messy, I would remove the valve cover to do this diagnosis so you can pinpoint the noise and determine if anything looks like it is operating differently than the rest of the parts.

 

any updates?

 

Sorry, no. Right now I'm up to my eyeballs with body work on this truck while the weather is dry. I hope to get it repainted before winter.

I took out a front sunroof and welded in the steel panel that had been cut out 30-some years ago. That turned out okay, but when I did the same to the sunroof in back there had been extra metal cut out creating gaps plus the metal is formed less rigid back there... That led to warping which I'm dealing with next

With the hot weather the engine has been quieter lately. I sometimes notice some tapping on cold start up but not as bad as before. As long as it's behaving okay it's on the list of things to get done but I don't know when...