I have a friend going to look at a 1975 F250 with a 460. The owner said the engine has "the typical 460 piston slap" but goes away once up to speed. The owner who restores Ford trucks says this is common in a 460 and not something to worry about. I've never heard of this. Is this a common problem and should one be worried?

 

Any "slap" rap, tick, knock or any other noise is something to be concerened about. 460's are not noted for making any noises.

 

Thanks, I'll pass that along.

 

Do they have any noise issues at part throttle acceleration?

 

Once the truck gets up to speed you probably lose the slap in the noise of the truck. I'd mic the engine (if he'll let you) and see what piston it's on. Any piston slap is bad. It's one of those "matter of time" problems before catastrophic engine failure. The only way I'd believe this guy is if the slap was on all 8 cylinders, not just one. The very fact that you can hear it (all eight would be really fast and the individual taps would run together) means that you probably shouldn't go anywhere near that motor.

 

YEAH it goes vroooom! lol just kidding

my 460 is all original (as far as i know) and its quiet as a mouse and ive never heard of any 'typical' piston slap, i think the feller your dealin with has developed skills from a shifty used car lot....

i had a piston slapping in my mazda motor ill pulled the oil pan and found the piston skirts. this was because the rod got bent just enough to touch the skirt.

it could be that a cylinder is worn badly or broken ring maybe?

 

More than likely a rod knock.

 

If it IS piston slap, you should hear it clearly at idle. To diagnose, pull the plug wires individually. When you get the bad cylinder the sound will disappear. Put the plug wire back on, the sound will come back.
With piston slap it's just a matter of time before you have catastrophic cylinder failure.
The excess cylinder clearance allows the piston to sharply rap the cylinder wall on the power stroke. Eventually this leads to fatique failure of the piston skirt oposite rotation. The skirt breaks up and usually allows the rod to go through the side of the cylinder.
This is the type of thing that could happen ten thousand miles from now or it could happen tomorrow. There's no way to tell, but it will happen eventually.
I would say unless you get a really good deal on the truck, walk away.

 

My buddy spoke more in depth with the mechanic selling the truck. He says at cruise speed, 55 or so, the engine will make a rattle, increase throttle and it goes away, decrease throttle and it goes away. The seller says this is something a 460 is known for, "when the engine doesn't have a load and the pistons are just floating". The engine is in a '75 truck, this guy never rebuilt it and it doesn't smoke a bit. I've not heard the engine but it reminds me of my mom's '79 Malibu with the lifter rattling 305. Just plain weird to me.

 

my 460 doesn't do that

GM's have piston slap, the 4.8 & 5.3's in particular, but i've never heard a ford do it, outside of the odd one with a serious problem.

perhaps there is too much vacuum advance dialed in and it is pinging under part throttle?

 

I think that "mechanic" is really reaching.....

 

That's pinging - likely from the EGR equipment being torn out causing a lean mix/steep timing curve, or many other factors.

He doesn't know what he's talking about.

 

I can't say whether this particular 460 had the same problem my old six cylinder did, but it made the same noise. Under load, give it gas and the rattle goes away, back off and the rattle goes away At least temporarily anyhow. Mine was rattling from several different things, needed cam bearings & mains for one. Oil pressure was a huge issue there too.

Also the last time I bought a second hand engine that "ran & didn't smoke"... but the insides of it were trash.

 

This engine has a new edelbrock 4bbl. with all of the smog stuff removed. I'm thinking it's either bad inside or something is wrong with timing/advance. I've told my buddy to walk, it's in a nice truck, they guy want drop the price any.