M103 3.0 to 3.6 Build Discussion

[t walgamuth]

i would try to find out WHY the heads are not interchangible. sometimes a minor amount of machine work would make it work.

i remember swapping heads left to right on my 51 caddy motor. the castings were the same but there was a tapped hole for a fitting on the firewall side. when put on the head from the other side we had to drill and tap on the back and plug the front. but the heads werent "interchangible" according to the book.

anyway i think the 103 104 blocks are pretty similar so knowing specific differences might allow you to do some simple things and use the setup you want.

good luck.

tom w

[waybomb]

Originally Posted by Ortolan

One side of the cylinder could probably be machined but the problem is that the other side is where the oil nozzles must be mounted.
http://www.peachparts.com/shopforum/...?do=big&p=1491

Make your own nozzles out of stainless steel tubing. Tap the block's oil holes, install a fitting at the end of you fabricated piston oilers, and there you go.

[JasonOne]

Has there been progress on this project? I have a few M103 motors I can get a hold of from my uncle. Was thinking of building one custom and swapping it for the stock and one in the car now.

Thanks,
Jason

[basix]

I'm about to start this project next week, hope to punch out a m103 3.0 to a 3.4, this without boaring the cyl. Head being ported/polished now,euro sport cam on the way. Hope to have motor done and in the car by end Feb.

[Ortolan]

Originally Posted by JasonOne

Has there been progress on this project? I have a few M103 motors I can get a hold of from my uncle. Was thinking of building one custom and swapping it for the stock and one in the car now.

Thanks,
Jason

I purchased a complete 3.2L M104 last week which was delivered to my mechanic before he closed shop for the holiday period. When he reopens we will try to use this engine with the C36 parts. I will also see if the 84mm crankshaft & rods from this can be swapped into my old M103 for a more conservative displacement increase (extra 0.1L).
Bottom line on the previous swap attempt was that M103.983 crankcase & pistons + C36 crankshaft and conrods will not work, the rods hit the cylinders before getting to 90BTDC.

The guy I bought the C36 parts from in Germany remains steadfast that he has built a 3.6L M103 and that the problem won't occur if the cylinders are bored to 91mm and C36 pistons are used. Another German I spoke with says you need to use the crankcase from a 300GE model. What we know for sure is that a 3.6L M103 CAN be built.
This suggests that:
A) The extra 0.75mm of cylinder space on each side will allow the rods to pass.
B) The pin offset on the C36 pistons is different to the stock 3.0L pistons and this creates a lower rod angle at 90BTDC.
C) The 300GE crankcase has the cylinders placed higher and is what Brabus/Renntech etc use when building their 3.6L engines.

This may be the answer but the problem is if I bored the block and bought C36 pistons and it still didn't work I wouldn't be able to return the engine to it's original state.
Maybe someone in the USA can call up Renntech and ask what parts they use. I didn't get a response from my email.

[JasonOne]

I'll call Renntech. Aren't they in Florida? I'll check the site and then give them a call. I would like to build a 3.2 or 3.6 out of a spare 3.0 M 103. Please let me know what I can do to be of any assistance. I've helped build mercedes engines before, 300Ds that were transplanted into Series 2A Land Rover 109"s. Friends of mine were sourcing trucks and motors from Germany and Switzerland. Both my friends speak fluent German so it was easy to get a hold of things over the phone.

Regards,
Jason

[300EVIL]

Originally Posted by Ortolan

I purchased a complete 3.2L M104 last week which was delivered to my mechanic before he closed shop for the holiday period. When he reopens we will try to use this engine with the C36 parts. I will also see if the 84mm crankshaft & rods from this can be swapped into my old M103 for a more conservative displacement increase (extra 0.1L).
Bottom line on the previous swap attempt was that M103.983 crankcase & pistons + C36 crankshaft and conrods will not work, the rods hit the cylinders before getting to 90BTDC.

The guy I bought the C36 parts from in Germany remains steadfast that he has built a 3.6L M103 and that the problem won't occur if the cylinders are bored to 91mm and C36 pistons are used. Another German I spoke with says you need to use the crankcase from a 300GE model. What we know for sure is that a 3.6L M103 CAN be built.
This suggests that:
A) The extra 0.75mm of cylinder space on each side will allow the rods to pass.
B) The pin offset on the C36 pistons is different to the stock 3.0L pistons and this creates a lower rod angle at 90BTDC.
C) The 300GE crankcase has the cylinders placed higher and is what Brabus/Renntech etc use when building their 3.6L engines.

This may be the answer but the problem is if I bored the block and bought C36 pistons and it still didn't work I wouldn't be able to return the engine to it's original state.
Maybe someone in the USA can call up Renntech and ask what parts they use. I didn't get a response from my email.

Wow, That Sucks! Are you sure you have the right rods? I do remember something about having to modify the lips of the cylinder bottoms to clear the rods. I'd get some more advice before scrapping the M103 block.

[basix]

I'm attempting this build now. I just dropped in the crank and it fits and spins freely... Problem is with the rods, I thought the m103 2.8 rods would work but they are to long, actually longer than the stock 3.0 rods. Any ideas of which rods are the correct to use. With the 350SDL crank and stock rods the piston pops out of the cyl by about 1/16", with the 2.8 rods the piston pops out about 1/4"...
Gonna play around on the EPC and see whats up... If anyone has any ideas PLEASE reply...

[Ortolan]

I went down to my mechanic again today and compared the connecting rods up close.
The C36 rods I received are the same length as my stock 3.0L M103 rods.
I measured the rods (between the centre of each hole) at 145mm and the pin height (centre of pin to top surface of piston) at 34mm. These measurements were done very quickly and crudely using a ruler so they may be wrong by +/- 2mm.
My new 3.2L M104 engine is being taken apart this week so I will compare the rods & pistons from this engine when it's ready. I may also ask my mechanic to test the 3.2L rods with the C36 crank and 3.0L M103 pistons in the M103 block.

If the 92.4mm crank pushes the pistons out of the block by 1/16 (1.588mm) then the pistons should stop 4.487mm before the top of the block using the stock 80.25mm crank (the change in TDC position is half the increase in stroke, ie 6.075mm).

If the M103 has a 9.2 compression ratio, then the total volume of each combustion chamber at TDC is about 60mL (using the formula CR = (volume of chamber at TDC + displacement) / volume of chamber at TDC)
22.7mL of the chamber is thus located within the unused block with the remaining 37mL or so split between the piston valve recesses, head gasket and cylinder head.

For my 84mm to 92.4mm stroke increase my TDC position will be 4.2mm higher in the block (probably flush with the top of the block based on your info). This means that to maintain TDC position I need to use rods which are 4.2mm shorter or pistons with a pin 4.2mm closer to the top.
However, since increasing displacement while maintaining the same chamber volume will increase compression from 10:1 to 11:1, I will need to increase the chamber volume.
If I want to drop the CR to 9:1 for the turbos (and I probably do) then I need to increase the chamber volume to 73mL (36mL of it within the block) which means the 4.2mm has to become 5.7mm.
What stock rods are 5.7mm shorter than 3.2L M104 rods?

Is my math and reasoning correct?

If the 2.8L rods are longer it means the 2.8L engines probably use the same pistons as the 3.2L.

[waybomb]

I think your math is ok.

But, are you allowing for the quench area? Changing the quench can cause serious mixture burn issues.

[Ortolan]

Does the M104 use much of a quench area? I've seen the pistons which appear to be flat top with valve recesses. I'm trying to recall seeing the underside of the the cylinder head.

[Ortolan]

Here's some comparison photos of the 3.0L M103 crank & rods vs the 3.6L M104 parts.
The C36 parts are the ones that look new and grey.
(images are around 200KB each)
http://members.iinet.net.au/~ortolan/300E_vs_C36_1.jpg
http://members.iinet.net.au/~ortolan/300E_vs_C36_2.jpg
http://members.iinet.net.au/~ortolan/300E_vs_C36_3.jpg
http://members.iinet.net.au/~ortolan/300E_vs_C36_4.jpg
http://members.iinet.net.au/~ortolan/300E_vs_C36_5.jpg

[sLoweredK300e]

so the c36 rods are teh same as the 3.0 litre m103 rods.

Can you not get a set of c36 pistons? or at least the specs?

[300EVIL]

Originally Posted by Ortolan

Does the M104 use much of a quench area? I've seen the pistons which appear to be flat top with valve recesses. I'm trying to recall seeing the underside of the the cylinder head.

Yeah, the M104 piston is flat other than the fly cuts for valve clearance. The head has a soft pent shape.

With the numbers provided by basix, it sounds like the rods are the main issue in the combination. Has anyone had any luck contacting AMG or Brabus?

You can definitely see the extra throw on that crank. Pretty cool! Did you get the M104 apart yet?

[Ortolan]

Visually, the two rods are the same length +/- 1mm. The guy I purchased them from in Germany says the C36 rods are actually 1mm shorter (I believe it but it makes me wonder why AMG didn't just use stock 3.0L rods). He also said the wrist pin hole in the C36 pistons is higher than with the stock pistons (it would need to be). He's going to email me a photo of the two pistons together which I will post here.

My M104 is still being taken apart as of this morning. I'll visit the workshop tomorrow to check on progress and take some more photos.