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  #46  
Old 10-23-2013, 06:11 AM
Stretch's Avatar
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Quote:
Originally Posted by 97 SL320 View Post
I'm thinking that the seller mixed piston versions. Sometimes pistons have version differences and are intended to be replaced in sets.

I'd return them for a closer matched set.

However, you can easily pull weight from the heavy ones. Chuck it in a 4 jaw lathe chuck with the crown towards the chuck. Run a cutter from the skirt side towards the crown. Have a look at the inside diameter from the skirt side , you will see a cut ring. When removing weight cut only towards the crown and don't increase the diameter.


[RANT]

Unfortunately the seller has decided not to play ball.

They're using the crappy excuse that the guy at Nural says that 20 grams difference is OK.

I know this isn't the case =>



It is total BS for some lazy arsed good for nothing cock head ham shanker to come up with this oh so convenient excuse where they don't have to do anything.

I'm now trying to contact Nural about this.

In the mean time I've filled out the special return form on the seller's website but the bloody thing doesn't seem to work. Another convenient occurrence. I'm getting totally pissed off with these third rate bell ends.

It is a very simple rule - set out in the FSM - maximum weight difference in a set of pistons = 10 grams. Not any other number that might be convenient because some fat sweaty lazy arsed good for nothing waster feels like he can't be bothered.

[/RANT]

Question about highlighted text =>

As I don't have a lathe do you think I can drill small holes in the skirt below the piston rings to remove weight? What's the purpose of the skirt below the wrist pin?

Attached Thumbnails
Engine builders' advice req'd - removable piston weights?-m102-fsm-chapter-03-316-weight-difference-pistons.jpg  
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  #47  
Old 10-23-2013, 08:51 AM
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Stretch, what diameter are these pistons? Hard to tell from photo, 90mm?

I think the first place would be the inside of the skirt area but you would need a lathe so the next best place (without a lathe) would be the wrist pin boss' where you could machine 0.080 (2mm) of the top. Then possibly start chipping away on the underside of the crown with a drill, several small divots.

Do you have anyway of measuring the thickness of the crown?
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  #48  
Old 10-23-2013, 09:24 AM
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Quote:
Originally Posted by Stretch View Post
[/B]

[RANT]

Unfortunately the seller has decided not to play ball.

They're using the crappy excuse that the guy at Nural says that 20 grams difference is OK.

I know this isn't the case =>



It is total BS for some lazy arsed good for nothing cock head ham shanker to come up with this oh so convenient excuse where they don't have to do anything.

I'm now trying to contact Nural about this.

In the mean time I've filled out the special return form on the seller's website but the bloody thing doesn't seem to work. Another convenient occurrence. I'm getting totally pissed off with these third rate bell ends.

It is a very simple rule - set out in the FSM - maximum weight difference in a set of pistons = 10 grams. Not any other number that might be convenient because some fat sweaty lazy arsed good for nothing waster feels like he can't be bothered.

[/RANT]

Question about highlighted text =>

As I don't have a lathe do you think I can drill small holes in the skirt below the piston rings to remove weight? What's the purpose of the skirt below the wrist pin?
Ham chanker. *pffft* (I'll be using that one later)

Hop on customfighters.com forum. They're bike guys but IIRC, a few have shops in your neck of the woods that will do stuff cheap.

Also, a backwoods lathe can be made from a drill press and power sander pretty easily. I've turned down stuff when in a pinch that way.

I wouldn't cross-drill any holes, but I might be persuaded to drill longways to remove weight.
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  #49  
Old 10-23-2013, 09:53 AM
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do you have a dremel tool? you should be able to machine out the inner diameter of the skirt and remove 10 grams from the heavy ones.
I would not remove any material from the pin boss. but the skirt, and the crown are safe places IF they are thick.
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  #50  
Old 10-23-2013, 03:28 PM
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Quote:
Originally Posted by benedict View Post
Stretch, what diameter are these pistons? Hard to tell from photo, 90mm?
88.975

Quote:
Originally Posted by benedict View Post
...

Do you have anyway of measuring the thickness of the crown?
It is 6.7mm (more or less)



The wall thickness is about 4mm at the thinnest points

The under the recess on the inner side there's a thickness of about 4mm to the inwards bulge to the wrist pin recess - so I can't cut away too much there...
Attached Thumbnails
Engine builders' advice req'd - removable piston weights?-m102-piston-measuring-crown-thickness.jpg  
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  #51  
Old 10-23-2013, 03:34 PM
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Quote:
Originally Posted by Simpler=Better View Post
Ham chanker. *pffft* (I'll be using that one later)

Hop on customfighters.com forum. They're bike guys but IIRC, a few have shops in your neck of the woods that will do stuff cheap.

Also, a backwoods lathe can be made from a drill press and power sander pretty easily. I've turned down stuff when in a pinch that way.

I wouldn't cross-drill any holes, but I might be persuaded to drill longways to remove weight.
Quote:
Originally Posted by vstech View Post
do you have a dremel tool? you should be able to machine out the inner diameter of the skirt and remove 10 grams from the heavy ones.
I would not remove any material from the pin boss. but the skirt, and the crown are safe places IF they are thick.

I do have a dremel type thing - better actually a Proxon - I'm dead posh me...

...problem is there's not much I can really remove without making things paper thin.

Here are some quick spread sheet calculations.

1) Drilling 4mm diameter holes in the wall (thickness is 4mm)



2) Hacking off the lower skirt bits





I don't think this is a good idea though...

...20 grams is just too much to remove. 10 grams is pretty bad and I'm struggling to find enough metal for that...
Attached Thumbnails
Engine builders' advice req'd - removable piston weights?-estimated-number-4mm-holes-needed-remove-20g-material-piston.png   Engine builders' advice req'd - removable piston weights?-m102-nural-piston1.jpg   Engine builders' advice req'd - removable piston weights?-estimated-weight-loss-removal-piston-lower-skirt-portions.png  
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1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Last edited by Stretch; 10-23-2013 at 03:44 PM. Reason: Messing about with numbers
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  #52  
Old 10-23-2013, 05:09 PM
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Do not remove the lower skirt. You could cause piston slap and / or scuffing wear in the bores. You could contour the skirt but that's not where I'd be working.

Look at the pin bosses. From 2:00 to 4:00 looks thinner than 8:00 to 10:00. There's a fair amount of unmachined area there to cause variance.
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  #53  
Old 10-23-2013, 06:21 PM
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I would not feel comfortable removing any weight from those pistons. I'd try to find a better set. ARe the original pistons too far out of spec to reuse? I have re-used my benz pistons at least 75 % of the time when going through a motor. There are specs for measuring wear and determining if its acceptable.
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  #54  
Old 10-23-2013, 09:07 PM
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You could tapper the inside hole of the wrist pin.
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  #55  
Old 10-23-2013, 10:00 PM
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Nooooooo. Never drill holes in pistons or remove skirts.

Remove material from the green areas _TOWARDS_ the crown, don't increase the diameter.

The skirts keep the pistons square to the bore, this keeps the rings square to the cylinder wall resulting in good sealing and ring life.
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Engine builders' advice req'd - removable piston weights?-piston.jpg  
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  #56  
Old 10-24-2013, 03:30 AM
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Quote:
Originally Posted by 97 SL320 View Post
Nooooooo. Never drill holes in pistons or remove skirts.

Remove material from the green areas _TOWARDS_ the crown, don't increase the diameter.

The skirts keep the pistons square to the bore, this keeps the rings square to the cylinder wall resulting in good sealing and ring life.
I thought so too - I had a gut feeling this isn't a good idea.

The problem with the green line area you've added to the picture is that on the areas where the there's a bulge for the wrist pin attachments there's only a 4mm thickness of material at that thinnest point.

To remove (most of the) 20 grams of aluminium I need to remove to get the weight closer to the lightest piston a volume of about 0.75 cubic centimeters needs to be gone => this seems way too much material for the dimensions of the existing structure.
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1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!
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  #57  
Old 10-24-2013, 03:41 AM
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Quote:
Originally Posted by t walgamuth View Post
I would not feel comfortable removing any weight from those pistons. I'd try to find a better set. ARe the original pistons too far out of spec to reuse? I have re-used my benz pistons at least 75 % of the time when going through a motor. There are specs for measuring wear and determining if its acceptable.
I'm not at all comfortable about it - hence the thread! I was hoping that if those bits of steel could be safely hoiked out then I'd be able to loose the 20 grams I need - it seems like they are there for a different reason though!

The story with the pistons is this =>

I have a 1.8 litre M102. This has conical shaped piston crowned pistons. You need a head with a conical shape to match these pistons. Even here in Europe 1.8 litre heads seem to be rare - but there are many of the 2.0 litre head options available. I killed the 1.8 litre head by not reading the FSM properly - fitting the tensioner incorrectly and snapping the cam etc etc etc...

The bore and stroke of the 1.8 and 2.0 M102 engines is the same (differences in swept and unswept volume are due to head and piston design) so you can swap out the 1.8 pistons with 2.0 pistons and fit a 2.0 head to convert a 1.8 to a 2.0...

...I have found a Carlsson never used ported and polished head for a 2.0 engine for not much money at all. With the cost of the four brand new 2.0 pistons (THAT SHOULD HAVE BEEN GOOD!!!!) I should be able to get a working engine for less money than the cost of machining and refurbishing a cylinder head.

That was the plan - as usual there's no such thing as a hassle free cheap lunch...

Quote:
Originally Posted by 1960mog View Post
You could tapper the inside hole of the wrist pin.
I don't think that will give me enough metal removal. 0.75 to 1 cc is a lot. I think 1project2many is right in saying that the only place to remove the metal is around the wrist pin bosses - I'm not sure if I have the gonads for that though...
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1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!
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  #58  
Old 10-24-2013, 04:42 AM
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I spoke with my local engine builder (builds race engines for speedboat racing and has done heads up for me on a few occasions)

He didn't have the time to go into it too much but said if he was making a piston from scratch and it was to be 89mm then he would make the crown thickness 9mm and cut it back (for balancing purposes if needed) to 7mm. He would not advise going any thinner (on the crown) than 4.5mm.

If you say the thickness of the crown is at 4mm in some spots already, then there really isn't going to be much you can shave from there.

He has in the past machined off from "anywhere that is safe to do so - wrist pin boss's the inside of the skirt and the underside of the crown"

If you were to speak with Nural, do you think they might exchange your set for a [better] mated set?
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  #59  
Old 10-24-2013, 04:59 AM
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Originally Posted by Stretch View Post
fitting the tensioner incorrectly and snapping the cam etc etc etc...
You are not the first! My parents s420 was destroyed because the chain jumped a tooth on startup from an incorrectly fitted tensioner by an Indy.

What type of tensioner was it? The ratchet type that requires activation once it's installed or the hydraulic type. Please give us the heads up.
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  #60  
Old 10-24-2013, 07:20 AM
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If you cannot return or exchange these pistons, and they are unacceptable as-is, then they are junk. You spend only time to work on junk pistons and whether you install them or not, you gain valuable experience before you're done.

What 97 SL320 is referring to is the factory's balancing method. It's a single cut to save time and money. If you look at the difference in thickness of the pin boss between that machined area and the portion toward the center of the piston, it appears substantial. I wouldn't be afraid to continue the factory operation. I would still try to identify where the differences are between pistons before metal removal.

Just out of curiousity, are the specifications you're citing for the maximum weight variation for the 1.8 or 2.0 liter engine? Are both engines subject to the same limits?

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Last edited by 1project2many; 10-24-2013 at 07:32 AM.
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