S38 stroker build - SF area

That's a tough world.
I have one in the shop now, complete cam tray grenade after 94,000 miles.
Cams eaten.
We are talking 10 large ones to fix.

In the midst of another in Maui.
15 thousand in parts and machine shop.
Labor is cheap :]


Did you know there are 24 9mm nuts just for the exhaust manifold?

Ever done a valve adjustment on a s38?

Did you ever think of asking your wife for $15,000 for an engine that might blow
up in 2 weeks?

hmmmmm.........
 
+1
I rebuilt mine in an 88 M5 5 years ago and it cost me roughly $6000 in parts and machine shop work. I did all the labor and it took a couple months.
Then I thought I'd had an experienced machinist do the head.
Engine in car and running well but still need to go to dyno and it spit out a valve adjustment disk one cold morning. Never could figure out why. Had to remove cam tray and have hole welded where adjustment disk went through tray.
5 years later and 26000 miles with many trips and tracks at Ofest and it made a horrible noise at startup and I thought it had done it again.
Long story short I finally determined that the machinist used the same valve guide clearance for the intake and exhaust. Exhaust was supposed to be .0002 to .0003 more than intake because of heat expansion.
This caused the valve to stick in the guide and that split second allowed the cam to spit the adjustment disk out. Second time the valve was just plain sticking in the guide and the cam would come around and hit the bucket and make a horrible noise.

Don mentions the 24 nuts that hold the exhaust manifolds on take almost two hours to install with various tools and a bunch of patience.

Head off and complete rebuild.
Not together yet. Mostly because I built an M30 motor for my coupe while the M5 sits in the garage next to it. :-(

So not for the faint of heart or wallet?

But what a wonderful sound they make at 6-7k RPM.

Gary

sfdon said:
That's a tough world.
I have one in the shop now, complete cam tray grenade after 94,000 miles.
Cams eaten.
We are talking 10 large ones to fix.

In the midst of another in Maui.
15 thousand in parts and machine shop.
Labor is cheap :]


Did you know there are 24 9mm nuts just for the exhaust manifold?

Ever done a valve adjustment on a s38?

Did you ever think of asking your wife for $15,000 for an engine that might blow
up in 2 weeks?

hmmmmm.........
Click to expand...
 
Last edited:
Ohhhhhhhhh-
I feel your pain.
It's the best of worlds and the worst of worlds.
Always waiting for the detonation.
A hot date with a super model with schizophrenia and a mean streak.
Ouch
This car was rolled a month after it was bought 10 years ago.
I hope they drained the block.........
 
Failure mode?

So what tends to break in these motors? I've been rather keeping eye open for a nice m635. And know these euro engines need single timing chain and single valve springs attended to. But it is sounding like the DOHC engine is fundamentally weak, even at relatively low miles?
 
They certainly can be scary. That sound though. The feeling over 4k RPM cannot be duplicated. Sure there may be minivans that put down more power than a stock one but there's nothing like that engine. I've never had the courage to get into one myself. I have five M30 cars right now. It will have to do.

That's a heartbreaking story on the shim. I couldn't imagine that.
 
To try and not be so doom and gloom there are many S38/M88 motors out there that are over 200k without failures. My friend Phil in CA had a 300K motor that still ran well. I think on the mye28 forum there was a 400k motor.

For some reason these motors are hard on valves. Exhaust the worst and intakes not far behind. It is very common to have to replace 6-12 valves on a rebuild because they leak.
That's why a pressure and leak down test is so important when buying a motor or car with these motors.

That said it is just as hard to find a machinist that understands these heads?
They are so easy to screw up. Since the valve adjustment is above the valve stem the length and INSTALLED height are critical. All 24 valves need to be within a few thousandths of each other or.... you will have a mess when it comes to installing the shims to adjust the valves.
I have a friend in Florida that has a M6 track car. His motor was built by a respected builder in NC a number of years back. His motor threw a rod (IIRC) because it spun a bearing. So I helped him find another block and a head that needed rebuilding. He also thought he had a good machinist but upon re- assembly he found that he could not adjust the valves because the shims were not thick enough. This means the machinist cut the valve stems so they would all match probably using the shortest stem to match to so when installed all the valves were too short and this required large shims to get the proper clearance. It was not possible and he ask me what to do. The only thing that could be done without buying 24 new valves was to put a device on top of the valve stem called a lash cap. It is basically a cap that fits on top of the valve stem and takes up that gap that was created when the stems were cut too short.
Now you have added mass to the valve train that will cause more wear and make one a little more nervous above 6k rpm.

cam.jpg


The other potential problem is the timing chain guides. There are a few documented incidents of the guides breaking which may break the chain but usually the pistons hit the valves and you've got a rebuild with all new pistons and 24 valves.
The S38 USA motors have double row timing chains and the M88 Euro have single row chains. As far as I know the M88 chain is not a problem but the same guide design can be a problem just like the S38. Yes single (M88 and double valve springs (S38 but with a head rebuild easily upgraded.
Also remember the S38/M88 is just an S14 with two more cylinders.
So a good S14 machinist would understand the issues I mentioned above.

HTH
Gary
 
just like the s14 ... the s38 likes to run high in the revs. it makes its power there. Gary gives a good explanation of what many e30 m3 guys have experienced.
 
Excellent Gary..
I have a s38 to assemble in Hawaii- interested?
 
aeronotix said:
Check this link out: https://www.youtube.com/watch?v=ITS5GkkqgEQ
That will show how vocal the S38 can be (to be listened to with good speakers)
As said below, explosion happens too!
Click to expand...

I've seen that movie numerous times, and as a teenager I recorded that scene on VHS. When my friends would ask me why I loved BMW's so much, I'd show them that.

I was driving my Dad's E39 528i at the time, and wondered why my 24V I6 didn't sound like an S38. Oh the things I learned.

The M30 with Webers in my coupe sounds great, but nothing touches an S38 for sound. Best I ever experienced was an E34 with a Dinan 3.9 stroker, and an Eisenmann race exhaust. If I had the budget, that's what would be in my Coupe, and I'd be ready for it to explode at any time.
 
Nice car chase, but that was most likely not a S38 soundtrack. No where was there the high rpm "shrieking, barking, and wailing" of an "on the edge" S38 drivetrain and exhaust. Probably just a generic car chase soundtrack that could be ordered from the movie industry. Judging from the car's front valance and the dash layout with what looks like the silly economy gauge, most likely it's just a standard e34 sedan with the faked out M5 badge.
 
If I recall correctly from the DVD extras, the car in the scene is a 525 with turbines and an M5 badge, and they recorded an M5 tearing around an airfield and spliced the sound into the plebeian E34.

I've driven all manner of E34's, and that's not an M20 or M50 sound track.
 
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