Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

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Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby Jay420 » Tue Apr 02, 2019 2:45 pm

Hi all,

I'm left frustrated after the engine rebuild of my 1.4 TSI 160bhp Scirocco. So the engine was rebuild 1000 miles ago because of low compression in 2 of its cylinders due to exhaust valve leakage and piston coating wear. New cylinder head and pistons were used in the rebuild. But right after the rebuild I started noticing knocking noise on cold starts upon accelerations. This noise mallows down when the car gets warmer. I think it is piston slap as all the symptoms fit. Rattle upon acceleration on cold starts.
I have spent a lot of money for this rebuild and I'm now stuck with this new issue that can be detrimental to the engine causing premature piston wear and cylinder damage. The garage that performed the rebuild are VW Audi specialists and they believes to have done everything properly. I am freaking pissed off about it as everytime I drive, I can't seem to shake the thought that I am damaging the engine with every drive.

My questions is, What now?
Is piston slap really dangerous?
Is there a possible move forward for me?

Kind regards
Jay420
 
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby Cuprabob » Tue Apr 02, 2019 4:52 pm

I assume the company who rebuilt the engine warrant their work?

Do they acknowledge there is an issue when you demonstrate the symptoms to them?

If they don't acknowledge there is an issue then you may want to get an independent engineer to write a report confirming there is an issue and consider legal action.
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby Jay420 » Tue Apr 02, 2019 6:42 pm

Hi @Cuprabob
Yes, the garage do warranty their work but they are also trying to convince me that this is an inevitable concequence of honing the cylinders as required for new piston install. And due to honing the clearance between the pistons and cylinder walls is larger causing piston slaps and are insistant that this is expected and unharmful to the engine.
But i dont get how piston slaps can be unharmful?
I am to take the car back to te garage for one of their expert mechanics to have a listen and diagnose whether it is or isn't piston slap.
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby vladandrei51 » Wed Apr 03, 2019 5:51 am

Did you put in forged pistons or cast (OEM) pistons?

I've rebuilt the engine using Wossner forged pistons and I also have piston slap on cold startups until the car warms up a bit and from what I gather is normal in my case. Just take it easy until it's fully warmed up (which you should do anyway)
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby Jay420 » Wed Apr 03, 2019 7:40 am

OEM pistons.
Yes, Mine does the same. Rattle at cold start and mallows down once the engine has warmed up. But wont that extra clearance cause oil to penetrate into the chamber and burn? Because that was the reason the engine was rebuilt in the 1st place.
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby vladandrei51 » Wed Apr 03, 2019 8:01 am

I am not sure. I haven't done a lot of kms since I finished the break-in preiod (~1100 km) but for what is worth, during that time, it didn't burn any oil even though it was to be expected (1500 km spaced out into 3 oil changes)

I can check the level when I get to the car and get back to you ;)
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby Jay420 » Wed Apr 03, 2019 9:24 am

Thanks @vladandrei51.
Quick one, is frequent oil change necessary to break the car in? As Im about 1000 miles into it now without an oil change? Neither was I advised to change oil after break in period by the techicians.

Kind regards
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby vladandrei51 » Wed Apr 03, 2019 9:43 am

I used Miller's break-in oil and the oil changes were as following:
0 - 100
100 - 700
700 - 1500 km

They also advise not to go longer than 800 km without an oil/filter change (using their product).

Pretty much everyone says using a synthetic oil during the break-in is a big no-no since the rings can't properly seal (since there's limited friction), I had a chat the guys from Millers and reassured me that their oil will provide adequate lubrification to other components during this period considering I don't surpass the 800 km (you shouldn't keep a mineral oil much longer in regardless) and the break-in additives will do their job with the rings in the meanwhile.
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby Jay420 » Wed Apr 03, 2019 10:00 am

Thanks @vladandrei51.
I will change oil/filter soon. However I assumed the avoidance to use synthetic oils to break in a rebuilt engine was a Myth. I will inquire the garage whether they used synthetic or mineral oil.
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby vladandrei51 » Wed Apr 03, 2019 10:07 am

There's always a lot of debate on how to do a break-in, for how long, an easy or a hard one (Beating the shit out of it) etc, there are a lot of theories, however, the vast majority of people agree that mineral oil is the way to go, and that's what guys from Millers told me also, so I thought better safe than sorry.
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Revised Timing-Chain

Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby Jay420 » Wed Apr 03, 2019 12:07 pm

So @vladandrei51
You are not worried about the piston slap? and the damage it can do to the cylinders and the pistons? As it will cause premature wear.
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby vladandrei51 » Wed Apr 03, 2019 12:13 pm

People say it's to be expected for forged pistons, I'm not sure about cast pistons tbh, sorry :shrug:
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3" catless downpipe & 3" catback (custom)
S3 intercooler
De-Cat / De-Res
03C906036M Injectors
NGK BKR7EIX Spark Plugs
NGK U5002 48003 Coil Pack
Revised Timing-Chain

Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby Jay420 » Thu Apr 04, 2019 2:42 pm

So,
I'm still argueing with the garage. Their lead Tech confirms it to be piston slap and again is insistant that its harmless.
I asked them to do compression tests on the cylinder just to be sure that there isn't any compression leaks due to the extra clearance and here are the results:
1:185psi; 2:175psi; 3:180psi 4:185psi. According to the garage, the values are well within tolerances.
Does anyone know it to be correct? And what are the optimal compression ranges for a 1.4 TSI engine?

Kind regards
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby blower » Fri Apr 05, 2019 12:07 pm

I rebuilt my 1.4 TSI twincharger with wossner forged pistons. I get very little if any piston slap, maybe a tiny amount for a minute but i think the noise i hear is more the classic valve tapping due to the hydraulic lifters draining down overnight, rather than piston slap.

I didn't need the bore cut, as i changed my pistons as a precaution (and a project for myself) - i hadn't had piston failure to force the need to change them.
If they had to re-bore and hone the cylinders they should have fitted enlarged pistons, wossner and many manufacturers of forged pistons offer 2 sizes, the original bore size and a slightly enlarged set designed for those who had to rebore the cylinders.

Your cylinder pressures are both correct and good for this engine. Those pressures are what i got on my engine (before the rebuild) at 30k miles.
Expected range on a new engine is about 180-190psi - VW tolerance is 145psi to 215 psi, a very wide margin, but your pressures are spot on.

It is known for many manufacturers of forged pistons to suffer from piston slap when cold - wossner pistons however usually suffer the least as they are made of a different alloy that doesn't expand as much when hot, so they don't need extra clearance when cold.
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby Jay420 » Fri Apr 05, 2019 1:48 pm

Hey @blower.
How is stage 2 going for you?
Thanks for the reply. My car suffered from low compression in 2 of its cylinders which was 1st thought to be due to piston wear but after the car was openend up it turned out to be cylinder head issue and not the pistons, as the exhaust valves on 2 of the cylinders were leaking. So I went for a new cylinder head and just out of caution like yourself, also opted to have the pistons replaced. The cylinders were in good condition and didn't need a rebore so the normal 76.5mm pistons were used. The garage is stating that by simply honing the cylinders produced that extra clearance for the pistons to slap. Where as I would have thought that putting new pistons in would reduce the clearance slightly as the older pistons had 90000 miles of wear on them.
Hydraulic lifters was 1st thought to be the culprit of the noise but it does not fit the symptoms so was ruled out.
The piston slap on mine is occurs on cold starts and is only there upon accelerations until the engine heats up. The moment my foot is off the throttle the knocking stops. I am booking the car in with VW to get a second opinion.
Thanks for the confirmation on cylinder compression. Appreciate your response.
Kind regads
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Re: Piston Slap after rebuild Scirocco 1.4 TSI Twincharged

Postby percy_tc » Sun Jun 06, 2021 2:42 pm

blower wrote:I rebuilt my 1.4 TSI twincharger with wossner forged pistons. I get very little if any piston slap, maybe a tiny amount for a minute but i think the noise i hear is more the classic valve tapping due to the hydraulic lifters draining down overnight, rather than piston slap.

I didn't need the bore cut, as i changed my pistons as a precaution (and a project for myself) - i hadn't had piston failure to force the need to change them.
If they had to re-bore and hone the cylinders they should have fitted enlarged pistons, wossner and many manufacturers of forged pistons offer 2 sizes, the original bore size and a slightly enlarged set designed for those who had to rebore the cylinders.

Your cylinder pressures are both correct and good for this engine. Those pressures are what i got on my engine (before the rebuild) at 30k miles.
Expected range on a new engine is about 180-190psi - VW tolerance is 145psi to 215 psi, a very wide margin, but your pressures are spot on.

It is known for many manufacturers of forged pistons to suffer from piston slap when cold - wossner pistons however usually suffer the least as they are made of a different alloy that doesn't expand as much when hot, so they don't need extra clearance when cold.


Could you please infrom me your experiences with Wössner forged pistons?
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