BUILDING S52 - HAVE S50 Block, S52 Crank, S52 Cams - WHAT PISTONS/RODS/ETC IS NEEDED

[GGug12345]

So I have been reading about specs and I would like some advice on my options. As the title says I have an s50 block, s52 crank and s52 cams, trays and journals. I am trying to do this on a budget as two little girls in diapers and daycare leave me no choice. I am guessing I need s52 pistons and rods along with an m52 head? I see a set of s52 piston and rods for $300 on eBay but was wondering if I could use some pistons out of another motor say an m52? What I believe I’m gathering is the wrist pen location on the pistons might be different on an s52? The 328/528 rods seem to be the same other than weighing a little more but what about piston options? The goal is to throw together a basically stock s52 and have as a spare or swap for later. On a side note I have a stock s50 in my track e36 m3 and a m50b25nv sitting on an engine stand. Any help, advice and thoughts are greatly appreciated.

[MauiM3Mania]

Moved from the E36 sub-forum.

[Hova]

Oh boy. Well, lots of options, but you'll find that any of them will likely nickel and dime you. The one that makes the most sense is boring the motor out to 86.4mm

An M52 head will work just fine with S52 cams. You should deck the block and head while they are out and at the machine shop.
I know S50 wrist pins are at a different location than S52 pistons, if you run stock rods and stock S50 pistons, you'll smash into the head with S50 pistons.

With S52 pistons, S50 or S52 rods, and bore out to 86.4mm will land you an S52 clone.
The crank sensor is the only real issue you're going to run into, on the S50 block it's on the front, on the OBD2 S52 crank it's on the back.

S50
Bore: 86mm
Stroke: 85.8mm
Rod Length: 135mm


S52
Bore: 86.4mm
Stroke: 89.6mm
Rod Length: 135mm

[pbonsalb]

The bores are different among M52, S50 and S52 so the pistons don’t interchange due to diameter. The strokes are also different so the pistons dont interchange due to pin height. The rods are all the same.

The only budget build is M54 3.0L internals into an M50/52 block. The M54 3.0L crank is the same as S52, but the pistons are 84mm. You get 3.0L.

If you want 3.2L you will have to bore your S50 block. No big deal. I turned an M52 block into an S52, a greater overbore than from an S50.

[gdavid]

The s50US bore (86m) is not the sames as the s52 (86.4mm) or the m50/52 (84mm) engines, so swapping pistons between them is a non-starter. The wrist pin height would be wrong as well (would not work with the s52 crank's travel). The m50/s50 blocks do not have the hole in the block for the internal crank position sensor the the m52/s52 engines use, I have heard the trigger wheel on the crank will hit the m50/s50 blocks unless they are removed or the block is notched. You can run the external crank position sensor and OBD1 controls instead which was a pretty popular mod until OBD2 tuning developed further. I'm not an expert on any of this but but know enough to point out potential issues, none are insurmountable but notable.

Edit- I was slow in my response and didn't intend to repeat the accurate advice given above

[pbonsalb]

Euro M52 may use an external crank sensor like on the US S52. Running OBD2 on an S59 block should not be a problem.

[ScotcH]

He says he's got a stock s50 in his M3 now, so using the OBD1 crank trigger is the way to go. Everything else said is on the money ... just bore it out to s52 piston spec, that's your cheapest option. Machine work should only be ~$300-400 for that work, and you'll have a fresh block to work with.