knock/piston slap...is this true?

[Scorcher2005]

Well i was looking at buying a lightning. One of the ones i was looking at has a built motor and some mods. The guy says it has a "knock" at startup but goes away after warming up. Someone else said it shouldnt be a knock at startup just a little pistone slap. Totally normal...Most builders open the ring gaps a bit to be able to cram more boost without the ring welding itself together. Is this true or not? Should i be worried about the issue?

 

[blkhorse]

forged pistons expand at a different rate and require more piston to wall clearance than stock. they can be noisy when cold,not saying that this is the cause of the knock on the truck,but possible. find out who built the motor,what brand pistons etc and contact the builder and ask them. if unsure have a third party diagnose

 

[Scorcher2005]

8.5:1 compression ratio, JDM built motor with cp pistons, manely h-beam rods, forged crank, pro steal rings and bearings, apr main studs and apr rod bolts

 

[Wolvrin704]

The Triton 5.4's have a rep for piston slap at startup. I remember 5.4 guys talking about it all the time when I frequented an F150 forum.

 

[Scorcher2005]

Ya, but its not really a Triton. Its even built...but it should be good?

 

[blkhorse]

like I posted earlier,contact jdm,ask them if some noise is normal for their engines,then take it to a third party(hi-perf shop etc)and get their opinion before you spend the money. nobody on the internet can say your okay with that.

btw.. ring gaps having nothing to do with the noise, the noise, if piston slap is from the piston "rocking" in the bore

 

[the98stang]

if the knock goes away after like 20-30 secs you are fine. Just have the engine compression tested before you buy it to make sure the engine is healthy.

 

[blkhorse]

some piston slap never goes away,some go away at operating temp,if the knock goes away after 30 secs I would be very concerned,thats more of a low oil pressure/bearing issue

 

[04YELLOWGT]

I have it at start up also, pretty much all forged motors do this. Like already posted its the forged pistons not completly expanded that your hearing. As long as its gone at normal opertating temps there really isn't anything to worry about. I would still get it checked out by shop to make sure everything else is ok, there are so many things that can go wrong with a built motor its hard to just look at it to know.