Engine builders' advice req'd - removable piston weights? - Page 5 - PeachParts Mercedes-Benz Forum

Stretch · #61 10-24-2013, 09:10 AM

Quote:

Originally Posted by 97 SL320

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

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Quote:

Originally Posted by 1project2many

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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.

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Here's a quick sketch showing why cutting into the green line area can't be done for long

Apologies for the lack of ISO standard drawing practices!

^^^ This rough sketch shows a quarter cross section of the piston - I hope it is understandable...

Stretch · #62 10-24-2013, 09:23 AM

Quote:

Originally Posted by benedict

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.

It is the bayonette / ratchet type. You are meant to push the tensioner all the way through the outer casing - fit the outer casing - and then AND ONLY THEN(!) fit the tensioner and the spring and the end cap...

http://www.peachparts.com/shopforum/tech-help/341121-achtung-das-schweinhund-baby-benz-thread-5.html

Help my M102 is a whinger!

I've been told that a similar set up exists on diesel engines of the same period.

These tensioners are not just a spring like the OM617a tensioners and not like the hydraulic OM617 / OM616 non turbo tensioners that should be filled with engine oil prior to refitting...

...I know I've kind of bitten myself on the arse for all of this extra work but I do feel I've had enough punishment for a RTFM blip - I've been sold a 2.0 litre head that won't fit my 1.8 litre engine and that seller is being a cock asking for more money for a second hand 1.8 litre one that will probably be as just as bad as the 2.0 litre one he sold me "by accident" with pitted valve surfaces and worn guides etc etc <= so I have little confidence in him. This is a shame I've bought loads of stuff from him previously but have never tried to send anything back. He's lost a good customer.

The cost of head refurbishment here in Holland is going to be between 500 and 700 euros from a reputable place. In fact there's only this "good place"near to me - I don't know of any cow boys!

Anyway now chasing down a "brand new" Carlson head that should be good - bought via paypal so I should have a bit of protection (perhaps) but that bugger doesn't seem to have sent it yet...

...and of course the piston nightmare continues with a different seller (first time used) who has sent me a set of pistons that are incompatible with each other.

This is called banging your head against a brick wall.

1project2many · #63 10-24-2013, 10:21 AM

Quote:

^^^ This rough sketch shows a quarter cross section of the piston - I hope it is understandable...

Ahhh. Crystal clear now.

97 SL320 · #64 10-24-2013, 08:11 PM

Are you able to post pics of each piston? ( are the casting numbers / general shape the same on all? )

Got it on the 4 mm thickness of material.

I'd do a few things here:

It would be a good idea to cover the outer skirts with tape during grinding. Be sure to weigh the piston pre / post tape then calculate your target weight, don't try to remember it as target with tape will be more than desired bare piston.

Make sure of piston weights.

On the heavy ones, remove the casting boss on the left side of your last pic.

Increase the OD of my green cut but only in an area that does not enter or reduce the profile of the skirt ( the red area ) This can be done by hand with a die grinder. The center of the red area is what keeps the piston from rocking left to right, as you travel towards the pin the loads are taken up by each end of the red area. The pin area does nothing for front to rear location.

Remember you only need to get within 10 G not 0 if enough material to remove can't be found.

Stretch · #65 10-25-2013, 10:02 AM

Going from left to right in this picture

614 grams, 617 grams and 633 grams - these are weights with the pins and the rings fitted

In this picture the line continues showing 617 grams, 633 grams and 634 grams (weight values refer to with pins and rings fitted)

So using a bit of a crap method I shoved my digital caliper in as far as it would go and made some measurements of the wrist pin boss area of the pistons

Measurements shown in next post due to number of attachment restrictions...

Stretch · #66 10-25-2013, 10:07 AM

This method is a bit changeable you can get slightly different results with a bit of wriggling but I think is shows where a lot of the extra weight probably is...

Stretch · #67 10-25-2013, 10:12 AM

Whilst it looks like a some metal removal might get me closer to the desired weight of the lighter pistons...

...how about going the other way and adding weight to the lighter ones?

Could a steel bolt with a countersunk head bolted to the skirt be an option? (I think I remember hearing about large lumps of metal being bolted to pistons in ship engines...)

Simpler=Better · #68 10-25-2013, 10:46 AM

Unless you're welding on aluminum it will come off later. Drilling & tapping is asking for a crack in a few miles.

If you can't get Nural on the phone I'd grind down the heavy ones

Stretch · #69 10-25-2013, 10:53 AM

Quote:

Originally Posted by Simpler=Better

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If you can't get Nural on the phone I'd grind down the heavy ones

That seems to be the plan at the moment. I'm a bit concerned about this uncharted territory though - give me a gear box and bearings and I'm a happy man but metal removal with a proxon multi tool...

97 SL320 · #70 10-25-2013, 05:10 PM

You only need to find 9 to 10 G from the heavy ones.

Working the areas I recommended won't reduce strength, just be sure not to leave any sharp internal corners as this leads to cracking.

Got an old piston to practice on?

Before cutting, you could always mark the piston and post a pic to make sure we are talking about the same areas.

Stretch · #71 10-26-2013, 10:47 AM

...bor-or-or-or-or-or-ing...

I've managed to remove 6 grams from one half side of the heaviest piston so far. Most of this material was removed from places that are easy to access.

On Monday I'll see if I can get hold of a milling cutter with about a 6mm diameter to get down into the depths to hoik out a bit more - then I'll start on the other side of the piston...

I have found that those multi-colured stones on sticks that get sold with those mulit-tool machines are kind of OK but the best results come from the little bands of sand paper that you fit on the expanding rubber bungs on sticks.

Ignore the brushes in the picture below - the sand paper things are the bits I mean

vstech · #72 10-26-2013, 10:55 AM

for aluminum, I use wide flute milling bits. the sandpaper, and close flute bits clog up too quickly...

Stretch · #73 10-26-2013, 11:08 AM

Quote:

Originally Posted by vstech

for aluminum, I use wide flute milling bits. the sandpaper, and close flute bits clog up too quickly...

The sand paper has been really good actually. I think it is about 80 grit on one of those little rolls and you can remove about 0.5 grams of material with a single piece. It seems to wear away more than clogging - which is exactly what those little grinding stones do.

The sand paper method is definitely arsing about though - a milling machine is the thing to have - no doubt. This dremmel / proxon multi-tool method is almost inadequate. It is t-e-d-i-o-u-s

97 SL320 · #74 10-26-2013, 12:37 PM

Before you go any farther, post some pics.

Stretch · #75 10-26-2013, 02:30 PM

Quote:

Originally Posted by 97 SL320

Before you go any farther, post some pics.

Well bear in mind it is a work in progress - I'll be smoothing out the bottom parts once they are a tad deeper...

...that sounds a bit strange...

...anyway here's before