M10 + E12 Carnage & Rebuild

[ajordan282]

Hello 02ers - I have posted a bit in the FB group about my journey but thought I would document my situation here among the die-hards and get some advice on how to proceed!

 

Specs on the car:

• 1973 Body
• 1975 M10 Block
• 1973 E12 Head
• 9:1 CR Piano Tops (US Spec)
• 1972 Plastic Intake Runners
• 1971 Kugelfischer Pump

 

History:

I recently bought a 20+ year dormant 1973 2002 Base with a Tii drivetrain including K-fish.  The plan for the car is a preservation - not full restoration.  It smoked blue pretty bad and idled high but ran when I picked it up. The brakes were stuck so I tackled that first then checked the fuel system for cleanliness, it looked good.  Took a 3 mile drive.  Blue smoke seemed to go away (was thinking there was just a bunch of oil in the cylinders from bad valve guides or whatever).  That said, car leaked like a sieve, so I sealed up several oil and coolant leaks.   Also rebuilt the WUR with the kit sold here (kudos, great kit!).  Fired it up after fixing leaks and found that rebuilding the WUR lowered the idle, but also that it smoked white, consistently from the tailpipe.  Coolant was also dripping off #4 exhaust stud.  It could have been doing this before I fixed the leaks, hard to tell.

 

I pulled the head hoping to do just a head gasket job, and found a chunk missing from piano top piston #2, as well as some damage to the head.  The head gasket appeared intact.  The head is at the machine shop and has been pressure tested good.  He did a quick check of flatness and said it was not bad, but may be worth decking.  He believes the head to be reusable.

 

I pulled the engine and disassembled.  I found (unsurprisingly) a cracked compression ring in piston #2 which explains the hole.  I also found a cracked compression ring in piston #1.  I am getting ready to take the engine to the machine shop.

 

Questions and Findings:

• 10/6/23 - Piston replacement recommendations?  I plan to replace all 4.  I am not even a tuning wizard on carb'ed vehicles and am completely new to the K-Fish - so concerned about the downstream effects of changing compression ratio and having to retune, etc.  Likely stick with 9:1 unless I get overwhelming feedback otherwise.
  • 10/17/23 - Popular opinion is that 9:1 isn't much different than 9.5:1.  OEM piano top cast pistons are hard to find but are out there.  BMW Oldtimerteile sells repop cast pistons at a great price but supply is limited.  Top End Performance can do custom forged pistons in roughly a month.  IE lead time is 3-5 mo.  Some restoration shops may have them on the shelves and may sell them if you ask nicely
• 10/6/23 - Are there any particular places to look for cracks in the head/block that would cause white smoke/external coolant leak I described?  With the head gasket appearing good, and the machinist claiming the head pressure tested good and doesn't look super warped...I am concerned that either something is being missed or the block is cracked.
  • 10/17/23 - Water jackets and bolt holes are common places for issues.  Head pressure tested good.  Block magnafluxed good. Upon milling found that head had been whiz wheeled, likely the weakness that caused breach in HG seal.
• 10/6/23 - Should I send out injectors for testing while the engine is apart?  Could dirty/bad injectors cause this type of engine failure?
  • 10/17/23 - YES! I found that injector #2 was broken after sending to Marty @ H&R Fuel.
• 10/6/23 - Should I send out K-Fish for testing while the engine is apart?  Could dirty/bad k-fish cause this type of engine failure?
  • 10/17/23 - Maybe! Generally it seems if K-Fish is running, it is not causing large issues.  That said I sent mine out anyhow and found it was out of time.
• 10/6/23 - I plan to replace timing chain, sprockets, guides, and tensioner.  Is this reasonable?
  • 10/17/23 - Yes.
• 10/6/23 - I plan to replace oil pump sprocket and chain, as it has a good amount of play.  Should I also replace the oil pump?  Any cheap-ish options for this?
  • 10/17/23 - 320i oil pump is probably a good idea.  Check for proper actuation, the new ones can be improperly made.
• 10/6/23 - Other do's and don't's for Tii rebuilds?
  • 10/17/23 - Maybe replace big end connecting rod bolts.  Some say you're cray if you do, others say you're crazy if you don't.

 

The Fun Stuff:

 

Edited October 17, 2023 by ajordan282
Updating with answers.

[Son of Marty]

Don't buy your pistons until the machinist determines how much overbore you'll need then don't let him bore the block until he has the pistons in hand. You can raise the C/R with out having to recalibrate the pump. A pretty flat head will be iffy I'd have it decked, if you decide to have the head decked be sure to send the front cover to be decked at the same time. The block is pretty tough but check for cracks around the head bolt holes. Check the head for erosion around the water passages, from the pictures the water passages in the head look good but clean everything up and see. On a Tii you'll have to keep the cam real mild or stock big cams really screw up the k-fish system. As for sending the pump and injectors in I would concentrate on the engine internals and try the k-fish see how it works being external to the engine you can always get them rebuilt later if needed. Just my 2 cents worth.

 

PS, You'll have to disassemble your oil pump and take a look.

 

Marty  

Edited October 6, 2023 by Son of Marty

[Tommy]

These pistons discussed recently would look intriguing to me.

 

[ajordan282]

10 minutes ago, Tommy said:

These pistons discussed recently would look intriguing to me.

 

I have already saved this post!  Definitely a frontrunner at the moment.  Thanks for chiming in! 

[ajordan282]

38 minutes ago, Son of Marty said:

Don't buy your pistons until the machinist determines how much overbore you'll need then don't let him bore the block until he has the pistons in hand. You can raise the C/R with out having to recalibrate the pump. A pretty flat head will be iffy I'd have it decked, if you decide to have the head decked be sure to send the front cover to be decked at the same time. The block is pretty tough but check for cracks around the head bolt holes. Check the head for erosion around the water passages, from the pictures the water passages in the head look good but clean everything up and see. On a Tii you'll have to keep the cam real mild or stock big cams really screw up the k-fish system. As for sending the pump and injectors in I would concentrate on the engine internals and try the k-fish see how it works being external to the engine you can always get them rebuilt later if needed. Just my 2 cents worth.

 

PS, You'll have to disassemble your oil pump and take a look.

 

Marty  

 

Thanks so much for the response. I will look carefully around head bolt holes.  The timing cover is with machinist in case of decking!

 

I have read about the temperament of cammed tii's, high flow exhaust tii's, aftermarket intake tii's...and don't plan to deviate from stock.  To the point where I'm afraid to even increase CR.  I just want a good running reliable (as can be lol) car.

 

The only reason I ask about the Kfish/injectors is for fear that they aren't outputting enough fuel and could be causing a lean condition on one or two cylinders that resulted in ring/piston failure.  I plan to install an AFR gauge when putting the car back together, but am worried that this wouldn't alert me as to mixture issues on specific cylinders, just on the collective exhaust gas mixture. Maybe I am being oversensitive about this, just looking for some input on what risk I'm putting the engine at by not checking FI system now.

 

I have a factory service manual so I will review that for inspection of oil pump!  Thanks!!!

[slowbert]

3 minutes ago, ajordan282 said:

I have a factory service manual

 

 

[ajordan282]

2 hours ago, slowbert said:

 

 

I love the digital copy. But I like to put my hands on something so couldn’t resist getting a paper copy. 

[TobyB]

ummm-

the head might look pretty straight, but what does your machinist propose to do about the ring-chunk-gouges?

When I did that to an engine, I found that the perforations went awfully deep...

Yes, you could certainly smooth it and use it, but it's going to be a lot more detonation- prone on that cylinder.

 

As to what caused it: wear.  The rings wear the lands in the piston, and eventually don't have enough support

to resist twisting, and eventually the twisting gets so bad they break, and then make a bid for freedom.

 

t

 

[ajordan282]

5 hours ago, TobyB said:

ummm-

the head might look pretty straight, but what does your machinist propose to do about the ring-chunk-gouges?

When I did that to an engine, I found that the perforations went awfully deep...

Yes, you could certainly smooth it and use it, but it's going to be a lot more detonation- prone on that cylinder.

 

As to what caused it: wear.  The rings wear the lands in the piston, and eventually don't have enough support

to resist twisting, and eventually the twisting gets so bad they break, and then make a bid for freedom.

 

t

 

Thanks for the response!!! Machinist suggests smoothing head then skimming a few thou, and using the stock thickness head gasket. He has smoothed it in below pic,  but not yet decked.

 

I see your point about detonation. Perhaps another reason I should try to find a piston set that doesn’t increase compression further. Still on the hunt, as the set above raises CR half a point. I forgot to search the existing pistons for markings before dropping them off with machinist. But I did measure the piano dome, I think at 4mm - which lead me to believe they’re 9:1. Machinist asked that I dig up OE part numbers as he may have a source. 

Additionally, I’ve been doing some reading on connecting rod bolts. Machinist says reuse them. It seems there are folks both strongly for and strongly against that sentiment present here on the forum, some who’s opinions vary over the years lol. Any advice on the matter appreciated. 

[AceAndrew]

33 minutes ago, ajordan282 said:

 

Additionally, I’ve been doing some reading on connecting rod bolts. Machinist says reuse them. 

 

 

To quote south park...

[ajordan282]

10 hours ago, AceAndrew said:

 

To quote south park...

shaka bro 🤙🏽 

 

Hearing one bad experience would convince me in a heart beat. But I didn’t find any. So I’m still considering doing something dumb. 

[Son of Marty]

This is the dilemma rebuilding engines, cost VS blowupability I know the prosses nickels and dimes you to death but where do you stop? Plus these days you always wonder if the quality of the new parts are the same as the old ones?

[AceAndrew]

9 hours ago, ajordan282 said:

shaka bro 🤙🏽 

 

Hearing one bad experience would convince me in a heart beat. But I didn’t find any. So I’m still considering doing something dumb. 

 

..... out of hundreds of m10 rebuilds I've sold parts for when I was at IE, I would be the first (or at least within the first 5) guy to hear when something broke. 

 

  While infrequent, I would get calls/photos on rod bolts giving way.  Rare on street builds (I can think of three-ish instances), but enough to where I'd just rather not start climbing the f-around/find-out curve.

[R.I.P.B.M.W.]

39 minutes ago, AceAndrew said:

 

..... out of hundreds of m10 rebuilds I've sold parts for when I was at IE, I would be the first (or at least within the first 5) guy to hear when something broke. 

 

  While infrequent, I would get calls/photos on rod bolts giving way.  Rare on street builds (I can think of three-ish instances), but enough to where I'd just rather not start climbing the f-around/find-out curve.

   Following along with Ace's recommendation (+1), I wholeheartedly agree with replacing the stretch rod bolts. I would imagine the stretch portion of the bolt shaft will get even thinner when retorqued to/or higher than the spec (as some might want to do). In my experience I've only seen one rod exit the side of a block from a wrong gear selection on a high speed downshift and its over revving the motor. The other stretch bolt incident was with a Volvo flywheel and its stretch bolts. All the parts for the flywheel/clutch repair came in on Friday, except the ordered flywheel bolts. Vehicle had to leave that Friday to head north and service advisor and customer made the decision to reuse the old flywheel stretch bolts. The next week we heard that halfway into the trip the flywheel bolts let go and... instant carnage. Save a little money now or, maybe, try to find a good used 47+ year old m10 motor later. Replace all stretch bolts=piece of mind.

[ajordan282]

20 hours ago, Son of Marty said:

This is the dilemma rebuilding engines, cost VS blowupability I know the prosses nickels and dimes you to death but where do you stop? Plus these days you always wonder if the quality of the new parts are the same as the old ones?

THIS. I’ve gotten to the point where I don’t trust much of anything made in the last 3.5 years (I call them Covid parts, Covid cars, Covid appliances, Covid building materials, etc etc etc). Reliability was plunging before, but the process has been accelerated since. I’d hate to believe such issues have permeated ARP and other historically reliable MFGs. But the f*ckery seems to run deep. 

 

12 hours ago, AceAndrew said:

Rare on street builds (I can think of three-ish instances), but enough to where I'd just rather not start climbing the f-around/find-out curve.

 

10 hours ago, R.I.P.B.M.W. said:

   Following along with Ace's recommendation (+1)

😬😬😬

 

I’m now convinced my shit is going to blow up either way 😂 

 

I am planning to go ahead and replace the oil pump. As I understand it the 320i pump is the exact same, just swap over the pickup assy.  I assume the pickup will be the same elevation in the pan - I am aware that changing pickup elevation can also have some *dire* consequences. 
 

How concerned should I be about detonation as far as maintaining the 9:1 comp? 9.5:1 piston availability is making that route tempting. But I don’t want to have to go thru this process again. I have no issue running pump high test foreva and eva. 

Edited October 8, 2023 by ajordan282