Long story short I have a 78 f150 with a 400. Its been hopped up a bit by the previous owner when it was rebuilt by pro machine in Utah in 1996. The only thing I truthfully know about it is it has a rod knock. It has an interesting push rod set up. The push rods have adjustable tips in them. On one particular rod the tip keeps getting galled up from the rocker. Ive replaced the tip multiple times, checked rod lengths, reset lash multiple times using the procedure in my service manual to no avail. Starting to think its the lifter.


Now im starting a restomod. Do I ditch the 400? I don't care at all about the numbers matching. Im a torque first guy, this truck sees a lot of work in country life style. Id like to keep around 15 mpgs. This truck has overdrive. everything is great about it except the engine knock. I have about 2000$ to get my whole engine troubles figured out whether that's starting from scratch or rebuilding the 400

 

I say keep it it'll do what you want and it's cheaper to rebuild than rebuild and swap

 

If you have a 400 getting 15mpg you should for sure keep it.

 

Agree rebuild sounds best.

The adjustable pushrods could be there 1) for a mechanical flat tappet cam...not common on a truck engine but possible 2) To adjust for deck and head milling... originals pushrods too long 3) To really dial in lifter pre-load with a hydraulic cam... not common on a truck engine but possible 4) The PO just liked them. 5) Other. You can hopefully figure it out when you pull it down.

On re-assembly of the engine you/your shop can use the adjustable rods to check for correct length and order accordingly (with new rockers). Summit sells pushrods by length in small increments or Smith Brothers can make a custom set in a few days.

Also just wondering if you are sure you have a rod knock vs valvetrain noise.

 

It's definitely a knock. It's the same rod everytime. I've pulled the valve cover off and reset the lash after installing a new tip 3 times now. I get about 100 miles after changing the tip before the knock comes back and the tip is ruined. I've been really baby-ing it worried about throwing a rod and causing major damage.

 

Run it with the valve cover off to make sure it is oiling itself.. sounds like a clogged push rod to me.. If you want 15 MPG you won't be finding it with that 400.. 9-10 MPG at best

 

Will try with valve cover off. I get 15 with it right now. Drove it 900 miles from ND to WY 65 mph 15 mpg

 

Wait - is the "knock" being caused by the tip of the pushrod going bad? That is not a rod knock. When you say "rod" and not wanting to "throw a rod", are you talking about the pushrod? Because when we say "rod" and "rod knock", we are talking about the CONNECTING rod, in the bottom of the motor. You don't say "rod" when you mean pushrod. Just want to get the terminology right.

If when you say rod knock, you mean the pushrod, you do not need to rebuild your motor to solve that.

 

Sorry about the confusion. Yes its just an issue with my push rod. No issues with my connecting rod. I'm not opposed at all to leaving it alone if I can get it to shut up. It runs really strong and holds good oil pressure. I've never had to deal with this type of issue so I don't exactly know what to expect.

 

I agree with JDeshler, it's gotta be an oiling issue.

 

Your pushrod that is burning tips is plugged. Run a stiff steel wire through it to clean it out. Or maybe it doesn't have a hole on one end or the other. Or possibly the lifter that is supposed to feed it oil doesn't have a hole in the middle of the cup.

These engines don't have a rocker shaft and as far as I know the only way they get oil to the rockers is through the pushrods.

Not a big problem once you find the blockage.

R.

 

I'll check for blockages hopefully next week. I'd be really happy if that's all it was.

 

If the rest of the engine is good except the rockers/pushrods, I'd be tempted change rockers and pushrods in place. Not too hard to do in the truck. Rockers first, then measure pushrods with your adjustables and order a set of regular pushrods in correct length.

 

That's exactly what I will do. I am not a fan of this adjustable set up.