NA 55 vs 55k Internals (pics inside)
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From: PDX
1999 C43, 2008 P30 E63, 2014 SQ5, 2024 Model Y Performance
Since I have 55k rods/pistons and NA 55 rods/pistons I decided to share with the board what I've found.
Both rods are crack forged. The biggest difference is the oiling port in the NA 55 rod (bottom) which weakens the rod
Notice the difference in wrist pins (NA 55 on top)
The NA 55 (bottom) has higher compression as expected.
NA 55 on right
The 55k pistons look to have really low compression. I have an 06 E55 engine on it's way to me and I will tear it down and put higher compression forged pistons, ARP head studs, and rod bolts in it. This should beef it up a bit. I want higher compression than stock because I want more power per psi and off boost power. I can post differences in the heads, blocks, etc if I get the time. The NA motor was able to hold over 650whp and in my CLK55 was able to trap 138.71 before letting go. I would expect the 55k motor to be able to hold more power but I'm not willing to put the stock 55k motor in my car and risk it blowing up and putting me and the car into the wall.
Both rods are crack forged. The biggest difference is the oiling port in the NA 55 rod (bottom) which weakens the rod
Notice the difference in wrist pins (NA 55 on top)
The NA 55 (bottom) has higher compression as expected.
NA 55 on right
The 55k pistons look to have really low compression. I have an 06 E55 engine on it's way to me and I will tear it down and put higher compression forged pistons, ARP head studs, and rod bolts in it. This should beef it up a bit. I want higher compression than stock because I want more power per psi and off boost power. I can post differences in the heads, blocks, etc if I get the time. The NA motor was able to hold over 650whp and in my CLK55 was able to trap 138.71 before letting go. I would expect the 55k motor to be able to hold more power but I'm not willing to put the stock 55k motor in my car and risk it blowing up and putting me and the car into the wall.
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2002 CL500 to CL55 conversion
big props to blackbenzz for providing a lot of these pictures and information before anybody else
i will say though, ive measured both the n/a 55 pistons/rods with the m113k pistons and rods and in almost every dimension, the m113k rods are slightly thicker. so its more than just the difference of oiling port
m113k pistons also have thicker skirts, thicker ringlands, as well as the different dome pattern for different compression
i will say though, ive measured both the n/a 55 pistons/rods with the m113k pistons and rods and in almost every dimension, the m113k rods are slightly thicker. so its more than just the difference of oiling port
m113k pistons also have thicker skirts, thicker ringlands, as well as the different dome pattern for different compression
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e55 560sec
Crankshaft
The crankshaft was changed due to a new assembly process that lifted the crank and sat it in the engine. Before they were sat in by hand. It caused them to have to changes the bolt spacing slightly as to have more meat around the holes.
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Out Of Control!!
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haters crazy
This is great! Thank you for providing this info to the community. I haven't played with this platform in years but I'm sure it will be helpful to others 👍 Sharing data like this will hopefully get this platform even faster as I know there's lots of untapped potential
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Joined: Jul 2012
Posts: 1,254
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2002 CL500 to CL55 conversion
Knew you had them measured but didn't know the numbers. Thanks for chiming in 
Yes you can. They bolt right up. I think the NA heads flow more. Steve had them tested.
Getting pistons and rod bolts through Weistec. Ceramic coated tops with teflon coated skirts. 9.8:1 C/R is what I decided to go with.
There you go. I do have pics of the differences but they were on my old phone. I will get better pics when the 55k engine come sin and I disassemble it. I will post pics of ported vs non ported NA 55 heads I have on my phone for now.
I agree! You're welcome
Just to add a bit more info and pics to this thread. First off if you plan on running NA heads please make sure you run the shorter plugs because if you run 55k plugs they are too long and will hit!. You will do alot of damage on first start up. This is why I always recommend to hand turn the crank several times before starting the car after doing any engine work.
Pic of NA 55 head ported intake
Pic of unported NA 55 head intake (I will get comparison pics of all 3 when my 55k engine gets here to disassemble)
I promised a pic of the Mahle forged "SLR" pistons so I found a couple on my phone. I bought the block with them in it and was told not to remove them so the pics I took were with the pistons still in the block sorry. There's an obvious difference from the bottom (and they are lighter)
NA 55 piston from bottom in block
From the top they look like a compromise between the NA 55 and 55k pistons... but forged. So the compression is somewhere between the 2.
You'd have to be a detective to notice the minute differences between a NA 55 block and a 55k block. One thing I did run into is that the 06 E55 block apparently has a different crank than a NA 55 (I'm not sure about the other years). The flywheel wouldn't bolt to the 55k crank because of different spacing
(55k on left)
This pic gives you an idea of NA 55 pistons vs the Mahle forged ones in the block.
Pic of ARP rod bolts on 55k rod
This pic is a comparison of one variation of the 55k oil pump (I wanna say S55 but can't remember right now. Either way it's different than E55 because of the different oil pans to fit different cars) and a W208 CLK55. It's hard to tell in this pic but they are not interchangeable because of the different bolt hole spacing! Also the pickups are in different locations. Just a nice surprise I ran into when trying to do a 55k block in my car before. I had to buy 2 oil pumps (which wasn't exactly cheap) and use the front half of one and bolt it to the back half of the other in other for the correct oil pan to fit... but it works!
You can see the spacing issue in this pic if you look closely. (Na 55 oil pump on a 55k block)
And just for fun here's a pic of the NA 55 piston that broke and got lodged in the cylinder the first time an NA 55 motor let go on me. I haven't removed the piston from the most recent one since I'm leaving it in the block when it becomes a table. It adds character lol
Hopefully all this info will help some people in the future and save them alot of time and $$$
Yes you can. They bolt right up. I think the NA heads flow more. Steve had them tested.
Getting pistons and rod bolts through Weistec. Ceramic coated tops with teflon coated skirts. 9.8:1 C/R is what I decided to go with.
There you go. I do have pics of the differences but they were on my old phone. I will get better pics when the 55k engine come sin and I disassemble it. I will post pics of ported vs non ported NA 55 heads I have on my phone for now.
I agree! You're welcome
Just to add a bit more info and pics to this thread. First off if you plan on running NA heads please make sure you run the shorter plugs because if you run 55k plugs they are too long and will hit!. You will do alot of damage on first start up. This is why I always recommend to hand turn the crank several times before starting the car after doing any engine work.
Pic of NA 55 head ported intake
Pic of unported NA 55 head intake (I will get comparison pics of all 3 when my 55k engine gets here to disassemble)
I promised a pic of the Mahle forged "SLR" pistons so I found a couple on my phone. I bought the block with them in it and was told not to remove them so the pics I took were with the pistons still in the block sorry. There's an obvious difference from the bottom (and they are lighter)
NA 55 piston from bottom in block
From the top they look like a compromise between the NA 55 and 55k pistons... but forged. So the compression is somewhere between the 2.
You'd have to be a detective to notice the minute differences between a NA 55 block and a 55k block. One thing I did run into is that the 06 E55 block apparently has a different crank than a NA 55 (I'm not sure about the other years). The flywheel wouldn't bolt to the 55k crank because of different spacing
(55k on left)
This pic gives you an idea of NA 55 pistons vs the Mahle forged ones in the block.
Pic of ARP rod bolts on 55k rod
This pic is a comparison of one variation of the 55k oil pump (I wanna say S55 but can't remember right now. Either way it's different than E55 because of the different oil pans to fit different cars) and a W208 CLK55. It's hard to tell in this pic but they are not interchangeable because of the different bolt hole spacing! Also the pickups are in different locations. Just a nice surprise I ran into when trying to do a 55k block in my car before. I had to buy 2 oil pumps (which wasn't exactly cheap) and use the front half of one and bolt it to the back half of the other in other for the correct oil pan to fit... but it works!
You can see the spacing issue in this pic if you look closely. (Na 55 oil pump on a 55k block)
And just for fun here's a pic of the NA 55 piston that broke and got lodged in the cylinder the first time an NA 55 motor let go on me. I haven't removed the piston from the most recent one since I'm leaving it in the block when it becomes a table. It adds character lol
Hopefully all this info will help some people in the future and save them alot of time and $$$
only upon tearing down the engine did I finally see the cracks in the ring lands. The cylinder walls still looked great and I decided to re-use my n/a 55 block instead of the 55k block I picked up
my issue in my opinion was too much fuel, I used a stethoscope in the spark plug hole of cylinder 6 and saw liquid fuel pooling on top of the piston. I discovered that the fuel in this condition can create tiny, unwanted explosions until the piston or piston rings eat themselves
I believe my rings could’ve been re-used actually but I bought all new rings. Wasn’t cheap, even with my employee discount I think the rings were still over $500
regarding differences between the n/a 55 blocks and 55k blocks, they are very very similar. Here are some more differences I’ve found between the two setups
-front timing cover is different
-oil pump mounting is different
-oil pans can be different depending on chassis
-55k motor has a bit more bracing built into the block, during casting, that I guess would help the rigidity of the block
-55k motor has a bit more bracing built into the block around the motor mount flanges
Last edited by ctravis595; Nov 9, 2020 at 08:30 AM.
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Junior Member
Joined: Feb 2021
Posts: 16
Likes: 2
From: Pocahontas, AR
2006 slk 55 amg
Since I have 55k rods/pistons and NA 55 rods/pistons I decided to share with the board what I've found.
Both rods are crack forged. The biggest difference is the oiling port in the NA 55 rod (bottom) which weakens the rod
Notice the difference in wrist pins (NA 55 on top)
The NA 55 (bottom) has higher compression as expected.
NA 55 on right
The 55k pistons look to have really low compression. I have an 06 E55 engine on it's way to me and I will tear it down and put higher compression forged pistons, ARP head studs, and rod bolts in it. This should beef it up a bit. I want higher compression than stock because I want more power per psi and off boost power. I can post differences in the heads, blocks, etc if I get the time. The NA motor was able to hold over 650whp and in my CLK55 was able to trap 138.71 before letting go. I would expect the 55k motor to be able to hold more power but I'm not willing to put the stock 55k motor in my car and risk it blowing up and putting me and the car into the wall.
Both rods are crack forged. The biggest difference is the oiling port in the NA 55 rod (bottom) which weakens the rod
Notice the difference in wrist pins (NA 55 on top)
The NA 55 (bottom) has higher compression as expected.
NA 55 on right
The 55k pistons look to have really low compression. I have an 06 E55 engine on it's way to me and I will tear it down and put higher compression forged pistons, ARP head studs, and rod bolts in it. This should beef it up a bit. I want higher compression than stock because I want more power per psi and off boost power. I can post differences in the heads, blocks, etc if I get the time. The NA motor was able to hold over 650whp and in my CLK55 was able to trap 138.71 before letting go. I would expect the 55k motor to be able to hold more power but I'm not willing to put the stock 55k motor in my car and risk it blowing up and putting me and the car into the wall.
