Hi chaps.

Basically I have a STI V9 spec C bottom end in my classic and since we've had this cold spell I've noticed some slight piston slap. Only does it from cold start and soon goes when there's a little bit of temp in the engine.
Currently using Millers 10W40 FS oil and change it every 3 months regardless of miles covered.

Question is-
Would changing to a slightly thicker oil help. Was thinking of maybe going with a 10/50.

Car is making over 400bhp.

Any advice would be gratefully received as always.

Thanks,
Matt.

 

Tbho Matt I wouldn't worry about it,with the cold weather it wouldn't matter what oil was in there it would still have the piston slap mate.
My forged lump slaps a goodun when cold

 

Yes, the grade of oil has little effect on piston slap.
I hear some slap from a cold start in my 03 STi using 10/50 CFS I just allow the engine to run without load for a couple of minutes then take it to approx. 1700 rpm for half a minute before driving.

JohnD

 

hi got a v8 sti bottom end in mine does the same thing up until reachin operating temp.

 

just a quick question since we talking about forged pistons, will short journeys cause much damage if they dont get up to fully temp? Sorry for the hijack

 

Depends how you drive it, it does no more wear than driving it until it warms up, it still spends the same amount of time cold

The worst thing about many short journeys is the impact on the oil, bore wash from spending too long at idle etc etc.

Change your oil more often if you do lots of short journeys as the lack of heat will result in more contaminants in the oil, some of them acidic which fizz up your alloy

 

top tips , thank you, was worried it might bounce around a bit more and do more damage on short journeys

 

My view: Better slappy than too tight and scuffing the skirts/bores.

Big question: Does it use oil? If not...whats the problem? Just a noise (just don't confuse it with a big end knock ).

I've heard a brand new "loose-built" forged bottom end on a V7 Sti with cold piston slap so loud you'd swear the thing had been driven to Mars and back!

Top tip...park it in a mildly heated garage. My garage never drops below 10degrees as its integrated in the house and has the boiler in there. Saves on fuel too as it doesn't have to dump so much in when warming up and its far nicer on the engine (less bore wash, oil dilution, oil condensation, metal expansion/contraction etc).

 

thanks alot , i was always worried piston slap meant the pistons bounced all over the bore and would damage them eventually, so short journeys would mean borked engine way faster than should be, i feel assured now

 

Re: short journeys...biggest issue is condensation in the oil not boiling off creating a build up of sludge.

(water is one of the main by-products of combustion - thats how its gets in there)

What you get is creamy deposits on the oil filler etc and half-soaked people telling you the head gaskets have gone, when all the cars needs is just a good long run.

So just once every week take the car for a good long drive, no need for 7Krpm redline bouncing....just a good steady 70mph motorway run for over half an hour.

 

The slap is just the piston rotating ever so slightly on the piston pin. The ring end is held in place by the piston rings so the skirt slaps the bores rather than just slide up and down. I think the 97 ish model years had shorter pistons and that agravated the problem. My 97 Forester S/tb did it when I lived in Cyprus, and that place is warm

Ali-B is spot on with the condensation, and this mixes with other combustion by-products and can become acidic (think acid rain but instead of rain, it is emulsifying in your oil). A good run is the best answer like he said, to evaporate it all. Good for your engine and good for your oil. If your car had a service light, it accounts for lots of short journeys and recommends an early oil change, if you do longer journeys, the oil life is extended so you get a longer service interval.

Piston Slap can sound like a quieter version of Big End failure, but when you have had a big end fail you will know the difference

 

An extra clearance of just 0.03mm will produce a noticably noisier engine!

JohnD

 

You're not kidding LOL

 

hi i was wondering if u guy could help!! newbie here,

i put semi synthetic 5w30 oil in my wrx 2003 ppp after buying it as the oil was quite low. i noticed on the service sheets the car always had 5w40 synthetic used at services. since putting the oil in my wrx it seems to be suffering from a knocking/tapping noise at low revs when cold. i think it must be piston slap as it dies down when the engine is warm. seems strange how its started since ive put the new oil in. is it because of the thinner oil ive used or because it is a part synthetic? any idears what i can or should do to stop the tapping,

many thanks

 

Firstly do a full oil change to a good synthetic oil, you should never mix oils!

 

My 6 Sti forged lump slaps all the time, never uses oil or Down on power and has done it since re build near 20k ago, I think of it as just a noise and proof it's forged lol

 

thanks!!

i did the oil change and still the tapping noise arhhhh its driving me mad, as ive not had the car very long. ive found a vid on youtube which is the same problem or sound im getting in every way. is there any chance u guys could have a listen. the sound of the tapping starts at 45 seconds when he revs it a little. THANKS http://www.youtube.com/watch?v=PrdMpLPUu3c
oh and mine is not quite as bad as this tho. it seems to be tapping on his while hot where mine is not or its very hard to here... HELPPPPPP

 

That ticking is normal, the knocking you can hear later in the vid isn't though. Doesn't sound like piston slap either to me, sounds more serious.

 

the ticking sound is normal yeah and it does sound bad the knocking later on in the vid. i dont have the knocking u can hear while its ticking over just the tapping sound whenhes reving the car. this vid is more like the tapping i hear


http://www.youtube.com/watch?v=oQELTwI6Qk0

 

This vid is piston slap. And I assure you I've heard ALOT worse! (bear in mind every brand new Rover K-series left the factory sounding like that..and nobody batted an eyelid on those )

I think I have a audio clip of mine somewhere that sounds just the same....and that was just 10K miles onto a factory short engine replaced under warranty for guess?....Yup piston slap! (I suspect the dealer was drumming up extra work and making full use of a TSB to make some extra money off IM). If its not using any oil, I suggest you live with it, as even after a engine tear down and rebuild, if its not blueprinted, it may still do it if the bore piston/bore clearances are at the upper (but acceptable) tolerances, so could be money down the drain.

Bear in mind a wider piston/bore clearance is preferred to one that is too tight as the latter causes big problems that can wreck the bores and pistons or if extreme even cause total seizure and a rod to bend (or break and be ejected out the block).

I wouldn't use a heavy/thick oil, as that just impedes oil flow and causes more cold start wear from pump cavitation. However 5w/40 fully synth is preferable to a 5w/30 semi

The other vid you posted (not the one above) is a deeper knock and alot more concerning.

 

thanks a great help wouldnt a thicker oil fill the gap between the pistons and block more helping on the tapping sound on start up..

 

Read Ali's post again.

 

It sounds the exact same in my experience mate, you eventually get used to it and learn to get in, drive it and turn up the radio

 

ok i did a vid of my own car now lol see what u guys think ive done this one when it was cold. not started since lastnight it was 4 in the afternoon when i started it. i know the fuel is low i went and had some fun lastnight

http://www.youtube.com/watch?v=RDhSv...qqRhXKqR-DzKzk=

this one was done after about 5 mins of urban driving u can still here the tapping a very little bit.

http://www.youtube.com/watch?v=zcoZ-...qqRhXKqR-DzKzk=

now the last vid is after a good drive fully warmed up.

http://www.youtube.com/watch?v=vf3cl...qqRhXKqR-DzKzk=

 

That's fine, exactly what I'd expect. If there's little oil use (say, 1 litre per six months or 3000miles), there is no problem in my opinion.

The skirts on Subaru pistons are pretty shallow, not too different to a motorbike/race engine. So it does allow for more movement (i.e "slap") at the top and bottom of each stroke.

 

yeah i will keep an eye on the oil but after having a rx8 its second nature too check oil levels lol. thanks for the advice.

 

Hi Matt

My P1 taps badly till engine is hot! Piston slap is unavoidable When you have forged pistons as they require more clearance as they expand more when hot, especially the low silicon mahle ones! Even in summer my car sounds terrible till warm, but if you want bigger power, then you have to accept it std engines should not have any slap, unless the piston skirts are worn, I've heard that std ones lose there hardening which creates slap!

I have actually improved mine alot with mobile 1 formula oil

 

yes well clearly they dont do it standard as such, but its more how does it happen? i think its fast driving before the cars warmed up fully that may cause them to wear. what grade oil is it 5w40 synth?

 

http://allwheeldriveauto.com/subaru-piston-slap/

so there u go it is normal in a subaru of a certain age/mileage and its the way they made the pistons. a shorter piston reduces the bang to help fuel/mpg. trouble with short pistons is they can slap because of there short size eg a longer piston with the same wear wouldnt slap as easy. is that what u guys are getting from the vid lol.