Technical What does piston slap sound like?

[randomizered]

100% sure its not det, but at high rpm, I hear a rattly noise. Could this be piston slap? I had it on the old engine as well. It's typically 6K+ and is rather annoying if nothing else.

The panda 100hp may be making this noise, but as i have no sound damping, and a hole into the engine bay noises are much clearer lol

Kristian

 

[fingers99]

Are you sure it's not det?

Often slap is more noticeable at low revs. A sort of "schep" sound!

Remember, the old pistons were literally tearing themselves to bits!

 

[randomizered]

tbh, i have no clue what it is.....but i have messed with timing and afr's/

even at 10AFR and 10 degrees timing, I can replicate the sound.

det also shows up as a very varied afr as combustion is not taking place properly.


It did it on the old block as well.

Timing is verified as is the wideand lambda, and i REALLY don't belive knock could be taking place at those values!!!!!

Any suggestions?

Cheers,

Krisitan

 

[fingers99]

Dunno. To hear piston slap, stand near any air cooled engine as it starts from cold -- usually the bigger pistons, the more slap. This 'cos air cooled engines run bigger piston to cylinder clearances, as a rule. It's not necessarily harmful.

Have you tried seeing what a knock sensor says?

Otherwise, could it be some kind of valve train event?

Whip out the stethescope......................

 

[fingers99]

Dunno. To hear piston slap, stand near any air cooled engine as it starts from cold -- usually the bigger pistons, the more slap. This 'cos air cooled engines run bigger piston to cylinder clearances, as a rule. It's not necessarily harmful.

Have you tried seeing what a knock sensor says?

Otherwise, could it be some kind of valve train event?

Whip out the stethescope......................

 

[Pep0]

In theory

If it is slap it should not be very dependent on throttle, advance, etc, it will vary a bit but i'd be surprised if you could detect.

If it is pinking, it will be dependent on throttle, advance...

If you are geting slap with a warm engine you will be using oil as the control rings will have difficulty, you will be clogging breathers as well.

So I think I'm agreeing with '99...

You will detect if it has been pinking when you next lift the head, the piston(s) will look like cheeze that has been nibbled by a mouse.

Noel

 

[randomizered]

Aye, I've seen pinking/det before

It probably is det to be fair but i cna't understand why? Wonder if others with this engine have similar issues.

I am wondering if with a FBW setup, the engine is actually throttled so it doesn't occur? Of course with my manual throttle, there is no such limit?

Aaron? Arc? Whoever has one of the 1368cc 16v's on aftermarket managment?

Cheers,

Kristian

 

[Pep0]

Well you might have been too good.

If it only pinks at your peak you may have tuned the exhaust and inlets to 'perfection'.

Can you ease off on advance a little, drop the oil and coolant temperatures e.g. 5C, try a lighter grade of synthetic?

When you next rebuild can you do the engineering to pressure feed via a restrictor oil to the underside of each piston.

I know you wont want to drop the compression.

Noel

 

[randomizered]

Well you might have been too good.

If it only pinks at your peak you may have tuned the exhaust and inlets to 'perfection'.

In my dreams :devil:

Can you ease off on advance a little, drop the oil and coolant temperatures e.g. 5C, try a lighter grade of synthetic?

I have dropped advance tp 10 degrees to rule it out. This is a VERY low advance, no point going lower.

I have a thermostatic oil cooler, lower temperature stat, and am now running 5W-40 fully synth.

When you next rebuild can you do the engineering to pressure feed via a restrictor oil to the underside of each piston.

These are fitted as standard on 16 v's

I know you wont want to drop the compression.

Noel

I will one day, when i fit the big exhaust powered hairdryer too it, but not until then

 

[craigb244]

could be just the normal sound of the engine? how about getting someone to stand outside while you drive past at high rpm and see what it sounds like.
I know my car sounds horrid inside at high rpm (no sound deading like you) but outside it sounds fine.

cheapo engines at the end of the day. them rpms wont be far from the stock limiter would they

 

[fingers99]

I'd be inclined to pop it down to a RR. Chances are that their equipment will be a little better than yours, their ears and experience a good bit better.

Much cheaper than another engine rebuild.

 

[randomizered]

Maybe, don't see what they will be able to do though. No money to do it this month anyway, just paid for the LSD

 

[allanhelen]

Didn't you every fit a knock sensor? time to break out the knocksense

 

[randomizered]

Yeah, I had one, kept triggering though Even at idle, so i junked it.

If it could reliably pick up knock i could run timing retard, fuel cut spark cut etc, but i gave up with it in the end. I may give it another bash though

 

[J333EVO]

No don't have any noises like this on our car, though its hasn't been driven in a while as Emma's loves her FTO which is considerably faster, more comfortable, handles better, looks better, sounds better and ..... we are still building a Cinq 1.4 16V and Emma refuses to sell the Sei lol

A r/r can put the engine under load at any speed and the opperator or you are able to stand still and listen to it and not try and stick and ear out of the window and hear over road, wind, other traffic, birds in the trees noises.

 

[allanhelen]

The only down side of the knocksense is that you can't tune out rpm dependant noise, but it is better than nothing

I use a seperate knock/timing controller on the MX-5 and it suprises me at times when it detects up knock where it seamingly didn't before.

You would be suprised how many stories of people that ignore these sort of things i've heard that have had engines blow

 

[Pep0]

If you ignore pinking at 6000 rpm the engine wont last long...

100% no stories.

Noel

 

[randomizered]

Well, this one's done 6,000 of hard driving with it.

The old engine made the same noise, that one did die, but was a pile of crap when i first got it, just like the gearbox was from the same car.

I can't afford a RR at the moment, if it blows it blows, i'll rebuild again at a later date.

 

[Pep0]

The trade off is between lifting the head and radiuising all the edges on the cumbustion chamber, not to drop the compression but to try and remove hot spots, if it is radiused already go larger. You do need to know how much metal the pistons and head have.

If you have backed off the advance and the injectors and fuel pump are not maxed out, a RR wont help, if it is weak you wont get much longer anyway.

(The exhaust valves are probably the culprits, radiusing the top corner, is all I ever did, in my pluky youth, but you young whipper snappers are devils. Replace exhaust guides, etc. if they are separate items, otherwise new head. You could change cam overlap, to try to cool the valve more.)

Alternatively regrinding (and radiusing) the crank, etc. later.

How many miles did the last engine do? Curious not snide...

Noel

 

[fingers99]

The reason I suggest taking it to a RR is for the diagnostic skills of the operative.

To my mind -- given you now have secure employment -- it's crazy not to borrow the money off the bank: a LSD is not much use without an engine to put it in!

And we never really worked out why the old engine pulled its pistons apart........