difference between a 1994 and 1991 piston?

[loneranger]

Looking for a piston for a 91 350 sdl per previous post. Cheapest I can find new $295.50. Can get a piston for 94 3.4l for $125 Anybody know the difference between these?

[Stretch]

The differences between a piston for petrol engine (what's that M104?) and a diesel engine piston will be huge. For starters the compression ratio in the two engines is very different. On the whole diesel engines have a higher compression ratio than petrol engines and thus need stronger (and often heavier) pistons / components.

Just looking at the the swept volume displacement and saying "Oh that's almost 3.5 litres so it will do" won't work. Look at the specifications of the engines on wikepedia =>

List of Mercedes-Benz engines - Wikipedia, the free encyclopedia

Mercedes-Benz OM603 - Wikipedia, the free encyclopedia

Mercedes-Benz M104 engine - Wikipedia, the free encyclopedia


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You might be able to get more information about the piston you require on this site

MAHLE Product Catalogue

Mahle may have made pistons for your engine. You'll have to check.

Kolbenschmidt might have made them - I don't have a link for their catalogue though.

[loneranger]

these are both the 3.4L L6 diesel 603.9 engines. I've been working off and on on diesels for 30 years and am not quite that stupid to think I could put a gas piston in a diesel engine. The ring kits for these pistons are the same part number. The only possible difference I can think of is wrist pin diameter and connecting rod width. The top profile of the pistons is identical. Thanks for the sites listed.

[strelnik]

Originally Posted by loneranger

I've been working off and on on diesels for 30 years and am not quite that stupid to think I could put a gas piston in a diesel engine. .

Well, then, you are certainly smarter than all the engineers at General Motors!

They thought they could do it in the 1980s.

[Stretch]

I apologise I was barking up the wrong tree.

I didn't realise they made 3.4 litre OM603s - I thought they were just 3.0 and 3.5s

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If the rings are the same part number then you're about half way there! The Mahle site is good for piston dimension information (if they ever made them)

[compu_85]

Check the weight. Depending on revisions / replacements one of the pistons could have an oil cooling channel.

IIRC there were at least 4 different piston revisions for the 3.5.

And it is 3.5L (well 3.449 if you want to get picky!).

-J

[Stretch]

Originally Posted by compu_85

...
And it is 3.5L (well 3.449 if you want to get picky!).

-J

Ah ha - now I see what's happened...

[Mölyapina]

I think one is from 1994 and one is from 1991. But I'm not sure.

[jusme]

Sixto could weigh in on this to offer some clarity I would think. I have a 91 3.5L out of a 350SD. Your welcome to the piston for free. But, a few headbolts stripped out, and would require quite a long drillbit to reach down through the cam towers to drill them out. On another note, how are you recovering so far?

[loneranger]

Originally Posted by jusme

Sixto could weigh in on this to offer some clarity I would think. I have a 91 3.5L out of a 350SD. Your welcome to the piston for free. But, a few headbolts stripped out, and would require quite a long drillbit to reach down through the cam towers to drill them out. On another note, how are you recovering so far?

Recovery going well, left knee replaced last Nov., right hip in August. In therapy and walking without a cane. Thanks for the offer, I still can't ride that far in a car. If you drill the head off the bolts, the head will lift off, then you can get on the bolt with a pair of vise grips, a block of wood on the block and a pry bar between the vise grips and wood, a little upward pressure and the bolts should unscrew. Don't know how easy the bolt head will drill though. Could be a bugger. You should be able to sell the head if it is OK. I'll have to wait awhile before I could come up to help but will think about it as an option. Thanks for the offer!

[jusme]

Originally Posted by loneranger

Recovery going well, left knee replaced last Nov., right hip in August. In therapy and walking without a cane. Thanks for the offer, I still can't ride that far in a car. If you drill the head off the bolts, the head will lift off, then you can get on the bolt with a pair of vise grips, a block of wood on the block and a pry bar between the vise grips and wood, a little upward pressure and the bolts should unscrew. Don't know how easy the bolt head will drill though. Could be a bugger. You should be able to sell the head if it is OK. I'll have to wait awhile before I could come up to help but will think about it as an option. Thanks for the offer!

Great to hear about your recovery. I'm see if I can locate a drill bit (cobalt pref) long enough to safely pass through the cam towers and drill them out. Here it is on the stand just after the swap when we removed it. It's been in the shop, on the stand, just fighting gravity for months. Look close, I think it knows the end is near. Ha.

[compu_85]

Also, why do you only need one piston?

That said, EPC only shows one part number (A6030301617) for the 603.970, .971, and .972. Odd they don't show any revisions since I've seen other documentation about the oil cooling channel being added back in around 1995.

-J

[loneranger]

Originally Posted by compu_85

Also, why do you only need one piston?

That said, EPC only shows one part number (A6030301617) for the 603.970, .971, and .972. Odd they don't show any revisions since I've seen other documentation about the oil cooling channel being added back in around 1995.

-J

Gross stupidity. I violated one of my own rules, Alzheimer's strikes again. Didn't tape off the holes when I pulled the intake crossover. Put on a new timing chain on, the master link went flying off through the air. Had another master link. Guess where the lost one went. Bang, crunch, busted piston.

[compu_85]

I have to correct myself, there are actually 4 different pistons listed,
A6030301617 - up to engine 971 018445
A6030301817 replaced by,
A6030301917 replaced by,
A6030302117 - as of engine 971 018446

-J

[Rickster1]

Originally Posted by loneranger

Looking for a piston for a 91 350 sdl per previous post. Cheapest I can find new $295.50. Can get a piston for 94 3.4l for $125 Anybody know the difference between these?

Three years!