1995 M3 S50 engine rebuild

[GG///M3]

I’m a big fan of the s50 motor. Glad to see you’re sticking with it.


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[E85STI]

This is a fun process. I did it with my own S50 a few years back. You'll probably need at least a couple valve guides. The exhaust guides do wear. Check the head for warping and cracks, which are fairly common. Valves and springs are most likely good and reusable if still within spec. If it's a street car I'd stick with stock valve springs. For track use you could go with beefier springs but they're $$. I used Supertech springs in my build because I do track only. I wanted a little insurance against valve float or a missed shift.

Going the DIY route with a reputable engine builder saves money and you'll learn a lot about your engine. For reference, my S50 has stock valves and a 3 angle valve job with no other cylinder head work. Bottom end is stock parts too except for ARP hardware. I had the block decked and align honed, and rods and pistons balanced. It's SO smooth and pulls hard (and sounds great too). With stock cams/MAF and a Turner chip it made 225hp and 209lb-ft. Not bad for an S50. The guys at the dyno though it was an S52. When you're finished with this one I'm sure you'll be pleased with the result. Just having a clean engine bay is rewarding too!

I've been trying to decide how much I want to spend on the head rebuild. I'm going with new springs, so I might as well get new valve guides as well. When I take it to the machine shop the are going to deck the head, 3 angle valve job, clean and pressure test it etc. Hopefully it is still in good enough shape to be reused. The car will be driven on the street but I am planning on tracking it the majority of the time. Redoing all of the suspension after the engine is done.

One thing I am trying to decide is whether or not to take apart, clean and reuse the hydraulic lifter or pay the insane amount to get new ones.

[NoLastName]

One thing I am trying to decide is whether or not to take apart, clean and reuse the hydraulic lifter or pay the insane amount to get new ones.

The first time, I disassembled mine and cleaned them. If the top cam mating surfaces are in good shape it's easy enough to clean the internal check valve bits while the head is at the machine shop. Later when I changed cams I had to bite the bullet and buy new ones. $$

[E85STI]

The first time, I disassembled mine and cleaned them. If the top cam mating surfaces are in good shape it's easy enough to clean the internal check valve bits while the head is at the machine shop. Later when I changed cams I had to bite the bullet and buy new ones. $$

I think I will go through each of them, disassemble each and clean the check valve. Did you put them in oil afterwards and pull a vacuum? I've seen some tutorials that people did this to make sure there was no air in them. Not sure this is required.

[NoLastName]

I've installed the lash adjusters pre-filled with oil and empty at different times. Now I do them with just a little oil inside. I never bleed them completely anymore. When fully filled before installation as some people recommend, it pushes the valves farther open than they need to be during camshaft installation. That makes cam installation a bit more difficult because you're fighting the valve springs more. In addition, BMW recommends waiting some time after cam installation before installing the head to allow the lifters to bleed down. Otherwise you risk a valve sticking down too far in the cylinder and making piston contact.


"Attention must be paid to the following if work had been carried out on the cylinder head, for which the camshaft was removed:
Hydraulic valve tappets expand when without load from the camshaft and must be allowed enough time after installation to constrict again. For this reason, fast assembly could cause "closed" valves to still be open and have contact with the pistons.

The following waiting times are necessary between installing of the camshaft and mounting the cylinder head.
Room temperature (20°C) 4 min.
10°C .. 20°C 11 min.
0°C ... 10°C 30 min."


So I figured, why have the lifters way overfilled to begin with when you need to let them bleed down anyway? Hydraulic lifters are self-adjusting. Assuming you did everything right, they pump up to correct height shortly after you start the engine. They might tick for a few seconds on startup but they quiet down as they automatically fill under oil pressure. If you get one that keeps ticking, increasing RPM to 2000+ for a few seconds or a minute or whatever will increase oil pressure and shut it up.

[E85STI]

I've installed the lash adjusters pre-filled with oil and empty at different times. Now I do them with just a little oil inside. I never bleed them completely anymore. When fully filled before installation as some people recommend, it pushes the valves farther open than they need to be during camshaft installation. That makes cam installation a bit more difficult because you're fighting the valve springs more. In addition, BMW recommends waiting some time after cam installation before installing the head to allow the lifters to bleed down. Otherwise you risk a valve sticking down too far in the cylinder and making piston contact.


"Attention must be paid to the following if work had been carried out on the cylinder head, for which the camshaft was removed:
Hydraulic valve tappets expand when without load from the camshaft and must be allowed enough time after installation to constrict again. For this reason, fast assembly could cause "closed" valves to still be open and have contact with the pistons.

The following waiting times are necessary between installing of the camshaft and mounting the cylinder head.
Room temperature (20°C) 4 min.
10°C .. 20°C 11 min.
0°C ... 10°C 30 min."


So I figured, why have the lifters way overfilled to begin with when you need to let them bleed down anyway? Hydraulic lifters are self-adjusting. Assuming you did everything right, they pump up to correct height shortly after you start the engine. They might tick for a few seconds on startup but they quiet down as they automatically fill under oil pressure. If you get one that keeps ticking, increasing RPM to 2000+ for a few seconds or a minute or whatever will increase oil pressure and shut it up.

Thank you for the information! This sounds like the way to go from your description.

[E85STI]

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[E85STI]

Removing the rear main seal and crank bolts.

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[BMW Rated]

Is the plan to get it back to OEM specs? Any upgrades while you have it opened up?

[E85STI]

Is the plan to get it back to OEM specs? Any upgrades while you have it opened up?

The idea originally was to just rebuild back to stock like build then I was leaning towards forged internals for forced inductions. I am honestly still trying to make a decision before pulling the trigger on anything. Starting to lean towards a closer to stock build with some decent upgrades to the head and just reusing the rods/pistons but with new rod and crank bearings and rings etc. Decked and honed block of course. But I still need to make my mind up. Hopefully I will get it figured out soon enough.

[BMW Rated]

The idea originally was to just rebuild back to stock like build then I was leaning towards forged internals for forced inductions. I am honestly still trying to make a decision before pulling the trigger on anything. Starting to lean towards a closer to stock build with some decent upgrades to the head and just reusing the rods/pistons but with new rod and crank bearings and rings etc. Decked and honed block of course. But I still need to make my mind up. Hopefully I will get it figured out soon enough.

If you change your mind and go the forged internal route. Are you thinking Turbo or Supercharger?

[E85STI]

If you change your mind and go the forged internal route. Are you thinking Turbo or Supercharger?

If I go the FI route it will be turbo.

[JitteryJoe]

The machine shop will bore and give you the new bore spec's? You'll get pistons & rings to match?
Be sure to deck the block with timing chain cover installed.

[GG///M3]

The machine shop will bore and give you the new bore spec's? You'll get pistons & rings to match?
Be sure to deck the block with timing chain cover installed.

This


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[NoLastName]

Be sure to deck the block with timing chain cover installed.

This

This x2. Timing chain cover MUST be in place when the block is decked! It has to get machined along with the block. That's super important.

[BMW Rated]

If I go the FI route it will be turbo.

I'll have to keep my eye on this always interested to hear or see what individuals do with the S50 motors. Needless to say i'm a bit of a fan for what it is.

[GG///M3]

I'll have to keep my eye on this always interested to hear or see what individuals do with the S50 motors. Needless to say i'm a bit of a fan for what it is.

I remember my built motor s50 from many moons ago.

I think if I were to go FI again I’d go Hyde motorsports blower kit.




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[E85STI]

This x2. Timing chain cover MUST be in place when the block is decked! It has to get machined along with the block. That's super important.

I will definitely make sure the timing chain cover is attached and gets decked with the block as one..

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I remember my built motor s50 from many moons ago.

I think if I were to go FI again I’d go Hyde motorsports blower kit.




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I will check out Hyde Motorsports. I don't really know much about them.

[E85STI]

Main journals, bearings, oil squirters and rear main seal.

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[BMW Rated]

Ahh the joy of having the knowledge to do this....I wish!! Also thanks GGG///M3 for sharing. I never heard of "Hyde Moto Works" so this is interesting for sure! Let the research begin!!!!

[E85STI]

The biggest dilemma for me is trying to decide on forced induction or n/a. As much as I want to go absolutely freaking nuts and do everything while I'm "in there already", I also know it is a slippery slope. Don't get me wrong I love the car, but I just can't rationalize spending unlimited amounts on my project/toy/fun vehicle.

If I make the decision now to get forged rods and lower compression pistons, I am committing myself to go the forced induction route. Yes, I want forced induction but that seems to be at least another 5-10 grand depending on the "kits" out there from places such as CES Turbo Systems or AA. I still plan on dropping and fully rebuilding my rear suspension and getting a good set of coilovers or possibly strut/spring combo. So I am mostly thinking out loud at the moment. Just not sure what I will do yet.

[GG///M3]

Ahh the joy of having the knowledge to do this....I wish!! Also thanks GGG///M3 for sharing. I never heard of "Hyde Moto Works" so this is interesting for sure! Let the research begin!!!!

I may or may not be going with their kit in the future. We’ll see


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[E85STI]

Other than some tiny surface rust spots and the buildup at the top of the cylinders, everything looks pretty good. The factory cross hatching is still very prominent. Definitely taking it to the machine shop to get it cleaned, decked and honed. Pretty sure I should also get it line bored as well.

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[BMW Rated]

I may or may not be going with their kit in the future. We’ll see


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I took a quick look at it and it seems that the tuning may be a bit of an issue and power dropping off at 5200 RPM's. I need to research it some more though.

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The biggest dilemma for me is trying to decide on forced induction or n/a. As much as I want to go absolutely freaking nuts and do everything while I'm "in there already", I also know it is a slippery slope. Don't get me wrong I love the car, but I just can't rationalize spending unlimited amounts on my project/toy/fun vehicle.

If I make the decision now to get forged rods and lower compression pistons, I am committing myself to go the forced induction route. Yes, I want forced induction but that seems to be at least another 5-10 grand depending on the "kits" out there from places such as CES Turbo Systems or AA. I still plan on dropping and fully rebuilding my rear suspension and getting a good set of coilovers or possibly strut/spring combo. So I am mostly thinking out loud at the moment. Just not sure what I will do yet.

I'm in the same boat in terms of keeping it NA or going forced induction. You have the one step up because i don't have the know how on rebuilding an engine which I would want to do before adding any more stress to it but the $ can run up really, really fast easily as clearly you already know.

[JitteryJoe]

The biggest dilemma for me is trying to decide on forced induction or n/a. As much as I want to go absolutely freaking nuts and do everything while I'm "in there already", I also know it is a slippery slope. Don't get me wrong I love the car, but I just can't rationalize spending unlimited amounts on my project/toy/fun vehicle.

If I make the decision now to get forged rods and lower compression pistons, I am committing myself to go the forced induction route. Yes, I want forced induction but that seems to be at least another 5-10 grand depending on the "kits" out there from places such as CES Turbo Systems or AA. I still plan on dropping and fully rebuilding my rear suspension and getting a good set of coilovers or possibly strut/spring combo. So I am mostly thinking out loud at the moment. Just not sure what I will do yet.

Turbo is a big commitment and you should make that decision now. I did a complete engine rebuild (everything was done) recently. I opt'ed for NA with higher compression pistons and higher lift cams plus a bunch of other stuff. If M3FORUM was operational you could take a look at the journal. The result was plenty for me. A high rev'ing engine with good power. Turbo will definitely get you a lot of grunt. You can double (or more) the HP output. Really depends on what you want. I'm not a fan of FI on these motors but a lot of people swear by it. Also, a super charger is probably less invasive and was offered as an add-on by Dinan. You won't get the same power but likely less money and an easier fit. You have options. Good luck!