cover 600 mile in my diy built engine, consists of acl bearings, wiesco pistions, manley rods, arp head bolts etc.

seems to have a strange hollow like tap, knock only on idle, its constant but u lift revs slightly and its gone, and i mean 100 rpm, im paranoid as i built it, but i think it may just be detonation on idle.

u can hear it more pronouced in car than under bonnet, and if ur not listening in for it ul never hear it, but as i said, im paranoid and listen for everything.

if u go under engine i can hear (and i kno it sounds weird) a tappy noise, as if a nut is bouning / rattling in / against block.

im sure its not slap or anything as when u rev it there is no knock or noise at all, only on idle.

any advise, settle my paranoia, or tests i can do, even thought of droping sump down to av a nose, getting me down. hope it all ok.

 

It DOES sound like piston slap - does it go away when the engine is up to temp.?

PS is nothing to be concerned about - it's bound to be normal on uprated pistons, as they are normally designed to expand to the correct tolerence when at normal operating temp. (therefore ever-so-slightly undersized when cold, hence the 'slapping' against the bores).

My engine is a perfect illustration of this, as I've just had it rebuilt by ZEN with STi 3/4 pistons. On the original WRX pistons, engine as quiet as a lamb... But with the STi ones, really noticeable slap - until up to temp, at which point the noise totally disappears.

 

hello mate ive just built mine 3 days ago, and i know the feeling(although nothing is wrong) it could of been there before but youve never realised? now that you've built it you listen for any slight noise. im the same.

now its just a guess but could it be pinking? its quite possible that you've got the fuel pipes from the filter to the rails the wrong way round? i did this and the car still ran but was pinking. now ive put the bk the right way its fine.

just a thought mate.

 

i have gone parallel fuel mod, so does the fuel come from the filter and feed the back inj 1st or the front and travel bk 2 tank

 

not sure mate as im on standard rails.

 

IMHO

Doesn't really matter, but as mine is SO fast I plumbed front to rear....
so the acceleration will starve the front two cylinders first..... NOT !

LOL

dunx

 

i had similar problem after closer inspection was boost solenoid rattling on idle sounds stupid but just an idea