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Piston Slap on New 2.0L Stock Mahle Ps and Cs
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VWLover77
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PostPosted: Tue Sep 29, 2020 6:05 am    Post subject: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

Lots of diesel-like piston slap noise when the engine is cold, but it goes away after it's good and warm. Brand new Brazilian Mahle pistons and cylinders with around 900 miles logged. (Stock 2.0L Type IV for 1978 Bus).

Comments? Suggestions?

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1978 Westy
1971 Super Beetle Convertible


"If more of us valued food and cheer and song above hoarded gold, it would be a merrier world." - J.R.R. Tolkien
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SGKent Premium Member
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PostPosted: Tue Sep 29, 2020 9:15 am    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

solid or hydraulic lifter? Piston slap is rare and more like muffled marbles being shaken. Also did you check the pin fit. One other thing, if the arrows are put in backwards (away from the flywheel) then the offset is wrong and you will get noise and wear.
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VWLover77
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PostPosted: Tue Sep 29, 2020 10:03 am    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

Hydraulic lifters.

I have no better description than it sounds like a diesel when cold - especially when it's revving up from idle under load. It's not an unhappy sound, but it's not right.

I tried to capture it in this recording....
https://youtu.be/7fcTfgX55q0


When I assembled the engine, I made sure the arrows all pointed toward the flywheel. (I took photos along the way and just double checked.) Pin fit was good per the Bentley "push fit" criteria.

Those scrape marks on the sides of the pistons can't be normal, can they? The old pistons I replaced do not show anywhere near that level of abrasion after thousands more miles.
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1978 Westy
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PostPosted: Tue Sep 29, 2020 10:17 am    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

find a local automotive machine shop with a bore gauge for boring cylinders, and have them measure the pistons and cylinders. Should be about .0018" +/- clearance or so. If they are .0025" to .003 inch or more then it would be the rattle. Those look to be totally different construction than the Mahle sets I have owned. As to scrape marks, without knowing it they were washed well and blown dry, the scrapes can be caused by detritus on assembly.

see this bulletin for the clearance

https://ratwell.com/mirror/www.dolphinsci.com/techbull.html

Hydraulic lifters will make that sound if they are not pumped up. Did you bleed them before installing them? Set the lash properly for hydraulics?
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raygreenwood
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PostPosted: Tue Sep 29, 2020 10:44 am    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

SGKent wrote:
find a local automotive machine shop with a bore gauge for boring cylinders, and have them measure the pistons and cylinders. Should be about .0018" +/- clearance or so. If they are .0025" to .003 inch or more then it would be the rattle. Those look to be totally different construction than the Mahle sets I have owned. As to scrape marks, without knowing it they were washed well and blown dry, the scrapes can be caused by detritus on assembly.

see this bulletin for the clearance

https://ratwell.com/mirror/www.dolphinsci.com/techbull.html

Hydraulic lifters will make that sound if they are not pumped up. Did you bleed them before installing them? Set the lash properly for hydraulics?



Was thinking the same thing on the pistons....kind of short /stubby skirts?

Also wondering if the cylinders have any taper. Ray
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VWLover77
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PostPosted: Tue Sep 29, 2020 11:19 am    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

Unfortunately, I've had enough hydraulic lifter issues over the years to know their various sounds. Shocked I did bench bleed these prior to installation and set them to 2 turns past valve stem contact. They are OE VW from Brazil and they have been fantastic so far. No bleed down even after sitting for a couple of weeks.

As you can see from the photo, the pistons are definitely Mahle Brazil. Revised design to cut cost????

I will get the Ps and Cs measured.

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VWLover77
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PostPosted: Tue Sep 29, 2020 11:31 am    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

But good call on the piston skirt height! Check out the difference between the old piston on the left (also Mahle Brazil) and the new one! Maybe I should rering and reuse the old ones!

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1978 Westy
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PostPosted: Tue Sep 29, 2020 11:55 am    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

with the skirt difference I would say that could be your rattle if the clearances are too large.
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VWLover77
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PostPosted: Tue Sep 29, 2020 12:38 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

The piston and cylinder kit I purchased was:

"For VW Transporter Vanagon Engine Piston Set Mahle 029198075"

Doing a web search, this is "the" part number for stock 94mm Ps & Cs with dished pistons. BusDepot, AirCooled.net, Pelican Parts, and many others refer to this kit PN.

The same piston part numbers are cast into the bottom of both my old and new pistons: 68021
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PostPosted: Tue Sep 29, 2020 1:11 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

there should be a blue or pink paint swatch on the top of each cylinder. I don't see it on yours. Was the case a sealed case when you bought it? This is a strange situation. Also you seem to have varying amounts of carbon on the pistons, and I don't understand why that is. They should be about the same.
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VWLover77
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PostPosted: Tue Sep 29, 2020 4:27 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

The Ps and Cs came in sealed Mahle packaging. complete with the anticounterfeit holographic sticker on the box. Wrist pins were in the pistons, pistons with rings installed were in the cylinders, and each cylinder kit was in its own bag. All the circlips were together in another small sealed bag.

Also, the old and new piston wrist pin hole locations are in the same place. Any difference in the photo is an optical illusion.

There's too may variables in play to comment much on the carbon - one of which is that I gave two of the piston tops a good scrub with a dry paper towel to see how baked-on the carbon is.
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PostPosted: Tue Sep 29, 2020 4:39 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

From your excellent images I would assume those were destined for a stroker
/ full counterweight crankshaft application ???
& maybe mispackaged .
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Wasted youth
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PostPosted: Tue Sep 29, 2020 5:13 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

What were your P&C build measurements? What are the design specs for those? The vertical scratches are not uniform, pronounced and seem aggressive to me for young pistons. Seems kinda sloppy and loose. No good reason in my mind why a piston wall should be getting that kind of non-uniform and aggressive wear with less than 1,000 miles. Wonder what those will look like at 85,000 miles.

Maybe the short skirts are allowing the pistons to flop around in there. I’ve never built a stroker motor, but it seems to me there was at least one good reason why original pistons had longer shirts: added stability.
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PostPosted: Tue Sep 29, 2020 5:15 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

timvw7476 wrote:
From your excellent images I would assume those were destined for a stroker
/ full counterweight crankshaft application ???
& maybe mispackaged .


Possibly, but the part numbers cast into the the bottoms of the old and new pistons are the same. (68021)
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1978 Westy
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PostPosted: Tue Sep 29, 2020 5:25 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

VWLover77 wrote:
timvw7476 wrote:
From your excellent images I would assume those were destined for a stroker
/ full counterweight crankshaft application ???
& maybe mispackaged .


Possibly, but the part numbers cast into the the bottoms of the old and new pistons are the same. (68021)


Did you check you skirt clearances and ring clearances when putting the engine together?
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PostPosted: Tue Sep 29, 2020 5:37 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

I googled the part number and all the vendors selling them show the same stock photo of those pistons with the short skirts. They are labeled as stock pistons for 2l bus-vanagon as the OP says. The deeper scratches look like they might be grit/debris.
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VWLover77
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PostPosted: Tue Sep 29, 2020 5:45 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

The only checks I made, for better or worse, were the top two ring gaps of all 4 pistons (removed from the pistons and installed in the cylinders). All 8 measurements were in spec.

I trusted Mahle on everything else. The piston diameters are dot-matrix engraved on the top of each piston. All 4 are marked "93.97". But there are no markings on the barrels indicating their bore diameter.

I can assure everyone that the Ps & Cs were very clean when installed.

Trying to measure the deck height was frustrating because of how much I could rock the pistons in the cylinders with just finger pressure.
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PostPosted: Tue Sep 29, 2020 6:24 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

VWLover77 wrote:
Trying to measure the deck height was frustrating because of how much I could rock the pistons in the cylinders with just finger pressure.


Alarm bell.
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PostPosted: Tue Sep 29, 2020 6:54 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

If you have a skirt clearance of .0015" and a piston height of 2.000" then how much rocking can you have? That would work out to ~.003" from rock at the top edges of the pistons perpendicular to the pins.

Last edited by Wildthings on Tue Sep 29, 2020 7:16 pm; edited 1 time in total
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PostPosted: Tue Sep 29, 2020 7:05 pm    Post subject: Re: Piston Slap on New 2.0L Stock Mahle Ps and Cs Reply with quote

VWLover77 wrote:
The only checks I made, for better or worse, were the top two ring gaps of all 4 pistons (removed from the pistons and installed in the cylinders). All 8 measurements were in spec.



I can assure everyone that the Ps & Cs were very clean when installed.


Ok...not that we do not believe you....but please tell us exactly what you did to clean them. The scuffing looks like what you get from grit left in hatch marks. Ray
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