i have a 1977 f-150 with a 351M and a 4 spd. When I first bought it I got the revs a little high because I didn’t have a tach. I bent a few pushrods (I think around 4 or 5) now I have a tach and I haven’t let it get over 3500 rpm (if anyone knows the redline it would be helpful) but I am still bending pushrods. The guy I bought it from had his buddy rebuild the engine and said they put a cam in it but now that he sold the truck he tried to ask the guy what kind of cam was in it to help me out but the guy won’t answer him because he’s mad about him selling it. I don’t really want to pull the cam as it’s my daily driver and I can’t have it down for too long. Does anybody have any suggestions to help me stop bending pushrods?

 

Without knowing the cam specs, 4,500 rpm redline will be a safe limit.

To prevent the rods from bending again, don't drive the truck ! (LOL)

On a serious note, bending rods at 3,500 rpm implies something nasty like valves hitting pistons.

If you are able to, remove the valve covers and check that the rockers aren't stupidly tight.

And while you're at it, check the cam specs with a dial gauge.

Personally I'd remove the heads one weekend and measure everything including valve spring heights and pressures, but that's just me.

 

I had the redline set at 4200 rpm to be safe. The rockers aren’t adjustable so I just tighten them just a little more than snug. Valves hitting pistons? To my knowledge the 351M is a non interference engine unless I’m wrong

 

Even at 4,200 rpm the rods should not be bending.

Yes, valves hitting pistons sounds extreme, especially when the OE engine has pistons sitting about 4 miles down the bores, but without any details about the cam and engine build, anything is possible !

Did you set the valve lash correctly, at TDC per cylinder ?

Regardless, measure the cam lift with a dial gauge on both intake and exhaust at cylinder one, then at least you'll know what sort of cam you have.

I'm wondering if an incorrectly fitted timing chain will cause bent rods, but I've got brain fade !

 

I’ll try that this weekend if I can. Thanks for the help!

 

Mark your damper into 4 quarters, and start with cylinder one at TDC.

Follow the firing order, which will line up with your 4 lines on the damper (at 90 degree spacing), and set the valve lash to ZERO on each cylinder.

It wouldn't hurt to measure the length of a rod. either. It should be 9.51''.

How did you determine initially that the rods were bending ?

 

It was misfiring real bad and wasn’t running right. Every time I shifted it would shake real bad until I got up to speed. So I took the valve covers off and sure enough I had about 6 pushrods laying in the valley

 

Now I'm sorry that I asked that question.

Did the engine run right when you bought the truck, or has it always run badly ?

Have you tinkered with the engine apart from replacing the rods and setting the valve lash ?

I was going to say welcome to FTE and Happy New Year, but I can't see the screen clearly coz of the tears in my eyes !!

 

Sounds like you need to use a pushrod length checker. Probably want to check all 16 holes too.

Maybe they did something like machining the heads, and then threw stock length pushrods back in it.

 

If this guy stuck a high lift cam into a motor with a stock valve train(springs,rockers,etc.),it could be causing "coil bind", where the spring is compressed so far that it becomes a solid stack. With the valve open fully, there should be clearance between the spring coils.

 

Built a 400 years ago, did mild shave of the head and block. Cam was nothing spectacular on lift. Was bending push rods. pulled apart several times and checked everything. Ended up being coil bind on the exhaust valves because they had a valve rotator on it. Removed valve rotator and installed earlier springs off early 70's 400. never bent another one.

 

Yeah, was going to say that at one time bending pushrods on 351M's and 400's was a wayyyyy too common thing after an engine rebuild took place. Over on ProjectBronco.com years ago I think there were four or five guys in one year that were experiencing that, or knew someone who was. And it just kept on growing in number. All right after a rebuild or major head re-work.

So yea, the PO's friend could have easily done something wrong.

Hopefully it's safe to that point. Originally it should have been fine right up to and beyond 5000 rpm. The long stroke and large bearing diameter and heavy reciprocating weight/mass didn't make it much of a rev machine. But if it could get there, it could handle it. Same heads and valvetrain as a higher winding Cleveland, so if done correctly it should not bend pushrods.

Even non-adjustables have a specific torque rating from the factory.
I forget what it is exactly, but someone here will know. Probably listed in a FAQ too, but I have not found all of that yet myself.
Mine is using the Crane adjustable rocker setup, but it's pretty obvious when one has been converted over to use that setup.

It was when it left the factory 40 years ago. But who knows what's been done since.
You can't presume it's still all good to go. Might still not be physical interference as much as valve dynamics, but nothing is off the table until you've dug into it a little deeper.

Good luck!

Paul

 

Non adjustable rockers on the pedestal style 351M/400 rocker torque:

Make sure you're on the cam's base lobe, take out any pushrod play on that particular rocker - up/down and 'round & 'round....snugging the nut....then torque to 20 - 22 ft/lbs. DONE!

There's more than a few rockers you can adjust at the same time when cylinder #1 is on base lobe.....

 

It needs to hit that torque specification within a specific range of bolt turns too, if it's like a 302/5.0 with the pedestal rockers.
I think it's between a three quarters and one and a half turns, but don't remember exactly. Too soon and the pushrods are too long. Too late and they're too short - or vice-versa - been a few years...

 

I'll just add a comment on the springs. OE 400 springs were designed for stock lift only. Any added cam lift is likely to cause problems.

Suggest you replace the bent pushrods and roll the engine over by hand and watch action of each valve and spring. Good chance you will see what is going on. Very likely you need to get springs better matched to your performance cam.