TheSamba.com :: View topic - Piston Slap on New 2.0L Stock Mahle Ps and Cs

Mon Oct 05, 2020 11:56 am

Clatter wrote: VWLover77 wrote: Well, I called the (relatively) local air-cooled VW machine shop.

$85 to clean and measure my pistons and cylinders, $100 to hone the cylinders. Figure another $50-60 for new rings and it's a no brainer.....

New AA pistons and cylinders on order!

Problem here is that the AA you get might be the exact same thing,
Or worse.

Regardless,
You're going to want to measure those and clean them before installation.

My vote goes to saving the older P&L set.
A good hone by a pro, on a seasoned set of older cylinders,
Plus some new USA-made rings,
That beats a set of anything sold these days.
Even at or slightly over the wear limit.
I run those with .006 - .0065 or so, even,
And they don't slap.

Take it FWIW..

PS
Do your old pistons have the steel plates cast into the skirts?
Look inside.

Yes.....^^^^^

For ages.....I keep telling people to quit dropping old cylinders with no warpage, scoring or broken fins in the trash. I came to this perspective earlier than the average bug or bus driver because teh pistons for 411/412's with domes....were getting hard to get even 30 years ago.....and what you could get....were NOT the same quality you could get 35-40 years ago.

There were just so many less vehicle made with domed pistons in type 4 and they had a very short production run. It has always paid off to keep a still decent set of used pistons and cylinders around.

Now....every other type of VW is in the same boat. Turns out your 30-40 year ld cylinders are probably some of the highest quality parts you can get. Ray

Mon Oct 05, 2020 12:25 pm

I tossed two factory sets because that is what we did in 1980. New quality sets weren't much more than a set of rings. Today I wish I had not done that. Probably close to $800 worth of parts that were very usable if you know what to look for. My bad, really bad.

Mon Oct 05, 2020 3:05 pm

SGKent wrote: I tossed two factory sets because that is what we did in 1980. New quality sets weren't much more than a set of rings. Today I wish I had not done that. Probably close to $800 worth of parts that were very usable if you know what to look for. My bad, really bad.

Dude. I am still haunted by the memory of tossing my original 1700 case in the dumpster at the land fill with less than 100k on it....a new one was on the way from a volume rebuilder worse than GEX...I think it was called ECI ..It had at worst a burnt valve...

Mon Oct 05, 2020 11:56 pm

We'vee done it. :(
Dropped valve seat, replace the engine. It made sense when a new head was more expensive than a used complete running engine with all ancilliaries. That got me.

Tue Oct 06, 2020 11:37 am

We all have.

I look back in horror at some of the things I have thrown away...mainly mid to late 90's simply because I either lived in an apartment with a storage unit and could not save it.....and...being pre-internet....could not even find someone to give it away to.

In about a year and half period when I lived in Atlanta....I bought three...non-running, wrecked 411 or 412 cars that were sitting at shops and about to be scrapped. Shop owner says..."worthless to me....gotta move it....give me $100 or $200....and you can have everything you want or the whole car".

So I stripped them on the spot for whatever I could stash....scrapped things I would loved to have...and later even threw some away cause I could not keep it all.... :cry:

Ray

Wed Oct 07, 2020 7:01 pm

SGKent wrote: raygreenwood wrote: VWLover77 wrote: The oil was changed at 8 miles, after the cam break-in and the initial ring seating drive. That oil had a lot of "silver swirlies" in it.
The oil was changed again at around 200 miles when the engine was apart again to fix the camshaft endplay. Some evidence of "silver swirlies", but significantly less than the 8 mile change. Probably from the cam thrust bearing surface which was "eaten" by the rough surface finish on the camshaft thrust surface.
The oil I just drained two days ago at around 800 miles had no "sparklies".

All rod clearances measured 0.002". The rods are not notched.

Given the short skirt height of these new pistons, I'm hesitant to invest any more time or money in them. I'd rather clean up and reuse my old ones if they measure within specifications.

Is that 0.002" bearing to journal oil clearance...or is that 0.002" rod side face to crank cheek clearance?

If is rod side face to crank clearance...either your measurement method was off or you have a problem. Or was it .004" total and you are speaking of the 0.002" for each side...which in that case is excellent.

0.004" is minimum side clearance....to give .002" clearance each side of rod.
Ray

03mm is .0011" . .045mm is .0177"
https://kentcomputer.com/77VW/techbull.pdf

Would #5 in this Technical Bulletin for the Rod be a advisable Mod to a 1800

Wed Oct 07, 2020 7:33 pm

good question. 1600's, 1700's, and 1800's didn't have the same scuffing issues and heat issues that a 2L had. They also didn't wear cam lobes as much from what I understand. 2L sort of stretched the cooling ability of the motor. In addition people started driving faster as time passed, and in 1995, 4 years after that technical bulletin, there was so much pressure for increased speeds that the 55 mph speed limit was repealed.

Wed Oct 07, 2020 8:05 pm

I don't see any negative to adding the notch on earlier engines, all it does is direct the "waste" oil from the rod bearing up into the cylinder and piston, where it can aid in lubrication and cooling. It has minimal, if any effect, on the lubrication of the rod bearings

Thu Oct 08, 2020 7:43 am

I purchased a bore gauge. Here are my results for cylinder bore and piston diameter at the bottom of the piston skirt (as illustrated in the Bentley). This is for the NEW pistons and NEW cylinders.

According to the Bentley, the clearance is simply the difference in the diamaters, and should be 0.0016" to 0.0024" for new parts, with a wear limit of 0.008". So two of mine are a "little" loose. Enough to cause the piston slap noise?

#1
Cylinder Bore: 3.7004"
Piston Skirt: 3.6974"
Diameter difference: 0.003"

#2
Cylinder Bore: 3.7008"
Piston Skirt: 3.6984"
Diameter Difference: 0.0024

#3
Cylinder Bore: 3.7008"
Piston Skirt: 3.6978"
Diameter Difference: 0.003"

#4
Cylinder Bore: 3.7008"
Piston Skirt: 3.6986"
Diameter difference: 0.0022"

On all cylinders, the bore is 0.0005" larger at the bottom than near the top. I checked at multiple locations around the clock and got the exact same readings, so they are quite round at least.

Thu Oct 08, 2020 8:47 am

show us those photos of the arrows when they were installed please.

Also how do the wrist pins fit the rods? Oiled at room temp they should fall thru in maybe 3 - 5 seconds on their own weight. You slide one into the rod to where it is flush at the bottom, and then let go of the pin. It should slowly slide thru on its own weight, and not just immediately fall thru or get stuck.

Thu Oct 08, 2020 9:27 am

Note: Since these photos were taken, I have sent the fuel injectors out to Cruzin Performance for cleaning. I hope that will eliminate the apparent difference in mixtures between the cylinders.

The arrow on #4 is not visible, but you can see by the orientation of the other markings that it's pointing the same way as #3.

Can I check the pin / rod fit horizontally? (The crankcase is full of oil. I can drain it if required to tip the engine up to check the drop.)

Thu Oct 08, 2020 10:18 am

well - I don't know what to tell you. The pistons are a little loose but not so much that they should rattle. The arrows are all in the correct direction. The burn colors on the pistons are normal so all the cylinders are firing. One side seems a little richer than the other. If the wrist pins slide properly then it isn't that. A tight wrist pin will cause the piston to rock more until it warms up.

Thu Oct 08, 2020 10:40 am

I'll check to see how the cold pins slide through the rod bushings.

Thu Oct 08, 2020 10:47 am

SGKent wrote: A tight wrist pin will cause the piston to rock more until it warms up.

Never thought of that, could be why the high mileage POS 1800 in my van is quite noisy for a minute of so after a cold start and then quickly quiets down. The piston to cylinder clearances and the cylinder taper are all near the wear limits so I am not at all surprised that it make some noise, but that it goes away so completely and quickly kind of had me baffled.

Thu Oct 08, 2020 10:49 am

it should be a smooth fit with a minimum of force to slide them thru in either direction. One finger pushing gently. You should be able to move them back and forth with one finger from each hand, not loose but minimal drag. About +/- what it would take to push computer mouse across a smooth surface.

Thu Oct 08, 2020 10:53 am

Wildthings wrote: SGKent wrote: A tight wrist pin will cause the piston to rock more until it warms up.

Never thought of that, could be why the high mileage POS 1800 in my van is quite noisy for a minute of so after a cold start and then quickly quiets down. The piston to cylinder clearances and the cylinder taper are all near the wear limits so I am not at all surprised that it make some noise, but that it goes away so completely and quickly kind of had me baffled.
are the pins worn or tight? Usually they get loose with wear. A piston with 100,000 miles on it will rattle a little mostly because the piston skirts wear and collapse inwards.

Thu Oct 08, 2020 11:46 am

SGKent wrote: Wildthings wrote: SGKent wrote: A tight wrist pin will cause the piston to rock more until it warms up.

Never thought of that, could be why the high mileage POS 1800 in my van is quite noisy for a minute of so after a cold start and then quickly quiets down. The piston to cylinder clearances and the cylinder taper are all near the wear limits so I am not at all surprised that it make some noise, but that it goes away so completely and quickly kind of had me baffled.
are the pins worn or tight? Usually they get loose with wear. A piston with 100,000 miles on it will rattle a little mostly because the piston skirts wear and collapse inwards.

The pins were still quite tight, a light interference fit, which is surprising because the cylinders showed a pretty good taper from the miles on them, the pistons measured out very good though. Never expected this to be more than a scab together fix as I had pulled my old high mileage engine to rebuild it and I didn't like the work the machinist had done on the crank, so I grabbed this one out of the pile, had the valves replaced and threw some new rings on and hit the road in short order. Been something like 5 years and 40-50K miles at this point and doesn't seem to have gone down hill noticeably over the miles. Quiet once warm and using only a quart of oil every 3-4000 miles.

Plan to yank it next spring and give it a new cam and P&C's and will see what the heads look like at the time.

Thu Oct 08, 2020 1:35 pm

Wildthings wrote: SGKent wrote: Wildthings wrote: SGKent wrote: A tight wrist pin will cause the piston to rock more until it warms up.

Never thought of that, could be why the high mileage POS 1800 in my van is quite noisy for a minute of so after a cold start and then quickly quiets down. The piston to cylinder clearances and the cylinder taper are all near the wear limits so I am not at all surprised that it make some noise, but that it goes away so completely and quickly kind of had me baffled.
are the pins worn or tight? Usually they get loose with wear. A piston with 100,000 miles on it will rattle a little mostly because the piston skirts wear and collapse inwards.

The pins were still quite tight, a light interference fit, which is surprising because the cylinders showed a pretty good taper from the miles on them, the pistons measured out very good though. Never expected this to be more than a scab together fix as I had pulled my old high mileage engine to rebuild it and I didn't like the work the machinist had done on the crank, so I grabbed this one out of the pile, had the valves replaced and threw some new rings on and hit the road in short order. Been something like 5 years and 40-50K miles at this point and doesn't seem to have gone hill noticeably over the miles. Quiet once warm and using only a quart of oil every 3-4000 miles.

Plan to yank it next spring and give it a new cam and P&C's and will see what the heads look like at the time.
an interference fit would be quite tight. When out of the engine the general tests are:

1: with the rod flat on a surface for support the pin is inserted all the way to where it is flush with that surface, and wiggled. It should not be a noticeable rock.

2. Oiled the pin is inserted and held about even with the bottom of the bushing. When it is let go it should fall by gravity on its own slowly thru the bushing but not instantly drop. Meaning there should be some resistance but not enough that it sticks in the bushing. I'd guess 3 - 5 seconds to drop thru on its own weight. That way it is loose but not too loose. If you let go of it and it just free falls then you'll probably fail on test 1 also.

It is purely a feel thing. I'd hone the bushing to about the right size then fit each pin to the rod on a free floating bushing. On Chevy's etc that didn't have a free floating bushing, one heats the small end of the rod while it is in a vise until it starts to change to just past a straw color then immediately slides the wrist pin thru the piston into it making sure the pin is captured about evenly when the rod cools - which is usually in about 6 - 8 seconds. On those the piston and pin have to be ready to go and in the right direction before heating the rod. Air cooled VW's use free floating pins and replaceable small end bushings. They use circlips that hold the pins. The flat side of the circlip faces out but unless one was missing or loose it would not cause a knock. A tight pin might, if it was tight in the piston and the rod. Usually the pins are too tight a fit in the pistons when new in my humble opinion. The manufacturer assumes they will eventually wear in.

All that said, if it were me I'd be splitting the case to see if there are any other issues like too much thrust on the cam or bearing problems. I had a light knock on my first 2L build and it turned out to be too much runout in the new cam gear. That was walking the cam and crank back and forth. It wasn't until I found a thread where Colin had the exact same thing happen to him that I was sure that was it. Replaced the cam gear with a factory aluminum one and the light knock went away.

Thu Oct 08, 2020 7:17 pm

I lightly oiled the wrist pins and the rod bushings. The pins glide through the bushings (horizontally) with minimal finger pressure and a weighted smoothness. Release finger pressure, and they immediately stop. They feel like a perfect fit.

I then measured the skirt diameters of my OLD Mahle pistons, with the longer skirts. Their diameters would result in the following clearances. (This is NEW cylinder diameter minus OLD piston skirt diameter):

0.0037"
0.0035"
0.0035"
0.0040"

Sloppier than the new pistons for sure, but just for fun, I ringed up an old piston with the new rings, got acceptable side clearance for all three, and installed it in a NEW cylinder. Now, watch and listen to this little video comparison of the piston rock along the wrist pin axis..... New piston on the left, old one on the right. Is this because of the longer skirt on the old piston? I think I like my old pistons better....

Thu Oct 08, 2020 10:46 pm

probably. Shorter length would mean more rock just like a shorter wheel base car is affected more by bumps than a long wheel base. If you raise a 1' 2x4 1' off the ground at one end you have a 45 degree angle, but if that 2x4 is 20' long then the angle is much less.

Shorter length also means less heat transfer into the oil and to the cylinder walls for cooling the piston, but less friction too. I have no idea why they changed the design. That is one area in racing that we left to the piston manufacturers. On Monday you might call someone like JE Pistons and ask for a technical rep. They may put you thru and you can ask a quick 1 minute question. JE makes custom pistons for type 4 engines I believe so they can tell you what they would be using in a similar situation. Just a suggestion. You have a lot of time invested in this so maybe they can help with advise.