jammer1984

my car appears to have a strange knocking noise while its cold, i havent had it long but i havent noticed it before, it ticks over fine but when you press the accelerator down theres a strange knocking noise that is in time with the cars trademark burble sound, when up to temperature it sounds fine. It drives perfect when going fast or slow.

any ideas what it is

philhasasti

it sounds like piston slap bud!! nothing really to worry about!!

SunnySideUp

Piston Slap .... sleep easy, it's common and nowt to worry about

RA Dunk

another vote for piston slap, not an uncommon feature with imprezas when cold lol, if it starts doing it when fully warmed up then get worried

jammer1984

what causes it?

dj219957

or....

bad belt tensioner

either cam belt tensioner or air con belt tensioner.

jammer1984

it does it up untill the car hits full running temp, is this normal? im still worried about it

Semper

Pistons are slack in the bore. They have some play and move about a bit as I understand it.

As above it's normal on a forged engine when cold. As long as it's not there when it's warmed up...

GM Piston Slap -- Like a Knock

jammer1984

if its the rod end bearing would it keep knocking when warm?

jammer1984

just been out and checked it out, it only does it when cold. at tickover its fine it makes a knocking sound between tickover and 2500Rpm when reved above that it stops.

dj219957

what year is the car?

jammer1984

2003 sti uk

happydude303

iTrader: (1)

i had piston slap on my 1997 for two years when it was cold and it is not a problem long as it goes away then that, fine it where the pistons are flat and gravity pulls them down more i think i only rebuilt mine because the head went so i though i might as well other wise they still be happy slapping all day long lol. 1997 are prone to it because they had thinner skirts on the pistons so i hear any, give it a good oil change every 3 months it will love you for it

Barnsleywrx

i have started to have this problem since the winter. sounds bit noisier on tick over when just started and hear it up to 2.5k revs but when car been drove for a while and engine nicely warmed up its a sweet as a nut. doews this sound normal cos i get worried with all the rod knock threads. cars only done 22k.

Barnsleywrx

any one?

greekpeterfromlondon

iTrader: (2)

I was working on a customers 95 wrx last week and he was complaining about the same problem. It sounds like the bottom end has a slight knock but goes away when at operating temp. He said it only started in the last 4 to 5 weeks. So if it is piston slap what would cause the cylinder's to expand or wear so fast ?

dj219957

my knocks when cold around 1500-2000rpm. Its a 93 wrx. i have replaced the belt and tensioner but it still does it. the warm weather we have now doesnt seem to have helped either which i was hoping it would.
once its warm the noise is gone. if the noise goes when warm then there is nothing to worry bout really. funny though cos didnt think the pre96 suffered from this, my last one didnt and yet ive heard of quite a few cases recently?

happydude303

iTrader: (1)

all i can say this is the deep fear we all live with owning these cars but most of it is paranoia

merlin24

iTrader: (1)

Provided the noise goes as the engine comes up to normal operating temperature, then its not too much of a worry.
Subaru run a tight O.E Piston to Bore clearance of approx 0.001" and an off-set gudgeon pin boss in the piston to reduce noise.
As things start to gradually wear,this clearance becomes larger and the result is piston slap from cold. Any bruising on the piston skirt from "cold start thrashing" will aggravate the noise/situation further.
Aftermarket Forged Pistons suffer the same to a greater or lesser degree due to the larger Piston to Bore clearance (0.003" + ) needed for the forged pistons and they also tend to have a shorter skirt design ( especially 2.5's ) which will allow more rock in the bore.

Mick

Scooba-roo

iTrader: (1)

I had the same symptoms on the MY00. Knocking when cold, dam thing sounded like a diesel. When I asked the dealer they gave me the classic "They just do that, sir" !! I've never been back there since. After reading several forums, I thought it was piston slap, but then I found some guy in the US said it was the cam belt tensioner. So I asked Subaru to have a look and sure enough it was hanging off. If I had left it any longer it would have fallen off and the caused the cam belt to slip. Now that it's changed it sounds superb.

m@t STImulation

iTrader: (3)

ive got a slaper 2 no nice in the morning but wait till its warm and we are away