M70B54 project

[wokke]

Quite some time ago I was already asking myself if the M73 would run on the M70 peripheries. I squeezed the web and found that it is possible. So I decided that if ever my M70 break downs on me and needs to be replaced it'll be a M73. Roughly 10 days ago I was searching ebay for some spares and more or less stumbled over this complete M73 incl. alternator, AC compressor, starter motor etc. for as little as €250,- and I pulled the trigger. My M70 is BTW running perfectly
My engine bay is the last area of my car which needs to be done properly and this means the engine has to be taken out anyways. So why not stick in an M73 once all the work is done. I decided to buy this engine and roughly one week later (and €120,- less in my pocket for transport) it arrived.



Instead of just storing it away I of course (new toy ) started the disassembly immediately.


Status as of yesterday evening is this:




Since not all hardware is M70 compatible some parts need to be replaced with M70 specific ones:

1. Valve covers.
The M73 has a different crank case ventilation going from the rear of the valve cover into the rear cover of the intake manifold. Theoretically it would be possible to stick with this ventilation system, but then I would have to relocate the intake air temp. sensors. On the M73 those sensors are located in the air filter housings while the M70 location is the rear intake manifold covers.

2. Crankshaft pulley / damper.
The M73 damper does not have the teeth for generating crankshaft position signals. Those signals are generated via teeth on the flywheel in the back of the engine. And this means automatically that also the

3. M70 flywheel
needs to be mounted and

5. M70 lower front cover
with the holders for the crank position sensors is needed.

6. Water pump.
Rumors say the M73 pump can't be used. Valid only if the M73 is used in an E32 simply because the E32 has a different expansion tank and the E32/M70 water pump doesn't have the connection to the expansion tank the E31/M70 as well as the M73 pump have. This means the M73 (not M73N with water cooled alternator) pump can be used and only the upper radiator hose needs to be replaced because of a slightly redesigned inlet to the pump. The M70 pump needs to be machined in order to fit on to the M73 block.

7. Cooling system accumulator (in the back of the engine)
Water temp. sensors of the M70 are also different from the M73. The M73 has one single 4-pin sensor in the water pump while the M70 has two sensors in the rear of the engine (part #11 53 1 736 641). If the M73 waterpump is used (what I highly recommend) just leave the 4-pin sensor in there as a plug.

8. M70 exhaust headers
can only be used if some studs on the heads (not sure how many) are being removed and re positioned. Better alternative IMO is to use the slightly better designed stainless steel M73 exhaust headers and cut the inlets for the aux air system. The hole can easily be shut by welding. A problem is the connection between M73 headers and M70 exhaust system. Even if you have E31/M73 downpipes (most donor cars are E38 and those pipes wont fit at all as i had to find out) they don't have the needed flange to the M70 system. On my first swap i modified the E38 downpipes and it was a nightmare. Meanwhile I get them custom made which is a professional solution and at the end probably not more expensive if I calculate my time.

These are E38 down pipes


These are my custom made stainless steel ones (available at €400,- per set):


9. Oil pan(s)
They are different since the donor car has been an E38. Can be used if your car has only ASC. If it has ASC+T use the M70 oil pan due to a hose in front of it.

10. Engine mounts
Again different due to the donor car being an E38

11. Adjusting pulleys
The wheels of the adjusting pulleys have a different width and diameter (M70 ones are larger in diameter than M73). I recommend to use the M70 assembly.

12. Belts
The M73 belts are wider (6PK instead of 5PK) and of different length than the M70 belts. When fitting the belts make sure to align them properly, so that the 1st groove on the wider pulleys (waterpump...) stays free. Your "benchmark" is the big M70 crankshaft pulley/vibration damper.

13. Servo pump
The M73 servo pump looks different from the M70 pump and has a pulley for a wider belt. M70 pump required.
M73 pump mounts to the M73 oil pan and even if that one is used it needs to be modified where the lower CPS is located and this is exactly one of the two mounting holes for the pump.

14. AC compressor
What I say above regarding the servo pump also applies to the AC compressor.
EDIT: M70 compressor is needed. M73 has the AC line connection in a different angle.

Next step is to further take the engine apart and check heads and cylinders.
So stay tuned for further updates.

Cheers
Wolf

[8Tech]

1. Valve covers.
The M70 has a different crank case ventilation going from the rear of the valve cover into the rear cover of the intake manifold. Theoretically it would be possible to stick with this ventilation system, but then I would have to relocate the intake air temp. sensors. On the M73 those sensors are located in the air filter housings while the M70 location is the rear intake manifold covers.

2. Crankshaft pulley / damper.
The M73 damper does not have the teeth for generating crankshaft position signals. Those signals are generated via teeth on the flywheel in the back of the engine. And this means automatically that also the

3. M70 flywheel
needs to be mounted and

5. M70 lower front cover
with the holders for the crank position sensors is needed.

6. Water pump.
I've read that also the water pump of the M73 needs to be replaced by the M70 version but I haven't figured out yet why this is necessary.

7. Cooling system accumulator
Water temp. sensors of the M70 are also different from the M73. The M73 has one single 4-pin sensor in the water pump while the M70 has two sensors in the rear of the engine (part #11 53 1 736 641). The corresponding M73 part can easily be modified though to accept these two sensors. Just drill two holes and cut a M14x1.5 thread into the aluminium. One can even see the correct position in the cast.

8. M70 exhaust headers
can only be used if some studs on the heads (not sure how many) are being removed and re positioned. Better alternative IMO is to use the slightly better designed stainless steel M73 exhaust headers and cut the inlets for the aux air system. The hole can easily be shut by welding. Also the M73 down pipes need to be used which I prefer since the are from stainless steel as well - and can easily be pimped up by glass pearl blasting and sanding with up to 1500 grid paper. I've done two of them yesterday and it took me 30 minutes max. for both. The adaptation of those down pipes to the exhaust system itself will hopefully not turn out to be a nightmare.

9. Oil pan(s)
They are different since the donor car has been an E38

10. Engine mounts
Again different due to the donor car being an E38

11. Adjusting pulleys
The wheels of the adjusting pulleys have a different width and diameter (M70 ones are larger in diameter than M73). I can't say yet if only the wheels need replacement or if the entire assembly needs to be replaced.

12. Belts
The M73 belts are wider and of different length than the M70 belts.

13. Servo pump
The M73 servo pump looks different from the M70 pump and has a pulley for a wider belt. If it can still be used I can't say yet.

14. AC compressor
What I say above regarding the servo pump also applies to the AC compressor.

Next step is to further take the engine apart and check heads and cylinders.
So keep tuned for further updates.

Cheers
Wolf

1. Hopefully you did a typo and meant M73? You should be able to install the M70 covers and breathers if you reuse the throttle bodies from the M70.
2. Correct
3. Correct
4. Apparently the no4 does not exist in the German to English translation!
5. Not sure if that would fit but making some adjustable CPS mounts would be easy and allow for base ignition timing adjustments. NICE!
6. I have no idea!
7. If the position is still in the casting then presumably, the casting is still thick enough.
8. Definately use the M73 manifolds if possible, relocating those studs would not be a nice job.
9. M73 sump is different whether its an E38 or E31. The M73 has a different sump anyway.
10.
11. You can just reuse the narrower belt from the M70. It will not matter if the narrower belt used a pulley thats too wide. All the toothed pulleys use a PK rib pattern anyway.
12. Correct, just get a PK belt the same width as the M70 and a similar length to the M73.
13.
14. Belt should not be a problem, same applies as 11 above and the mounting is different. I would refit the M73 compressor and adapt the pipework if necessary rather than adapt the mounting.

Good Luck.

8Tech.

[X5X]

Paint that silver engine bay yellow

[8eights]

Congrats Wolf, Nice upgrade!

[Koizumi]

Wow, that's going to be a lotta fun! And the end result will be really fun!

Cheers

[B10 BITURBO]

Cool

[aliti]

Wokke very cool project , keep us in the loop

[moutine]

Are you going to use original M70 wirelooms, ECU's and entire engine control system? Any modifications into chips needed?

[toomanyparts]

Wolf,

I have a ton of respect for you for the simple fact you are willing to challenge this car on all fronts. As I have said, love the M73.

[mojocoggo]

Are you going to have to make a custom chip for everything to work right? Or could one use your regular M70 chips?

[wokke]

1. Hopefully you did a typo and meant M73? You should be able to install the M70 covers and breathers if you reuse the throttle bodies from the M70.
2. Correct
3. Correct
4. Apparently the no4 does not exist in the German to English translation!
5. Not sure if that would fit but making some adjustable CPS mounts would be easy and allow for base ignition timing adjustments. NICE!
6. I have no idea!
7. If the position is still in the casting then presumably, the casting is still thick enough.
8. Definately use the M73 manifolds if possible, relocating those studs would not be a nice job.
9. M73 sump is different whether its an E38 or E31. The M73 has a different sump anyway.
10.
11. You can just reuse the narrower belt from the M70. It will not matter if the narrower belt used a pulley thats too wide. All the toothed pulleys use a PK rib pattern anyway.
12. Correct, just get a PK belt the same width as the M70 and a similar length to the M73.
13.
14. Belt should not be a problem, same applies as 11 above and the mounting is different. I would refit the M73 compressor and adapt the pipework if necessary rather than adapt the mounting.

Good Luck.

8Tech.

Hi Gerry,

thanks for taking the time to respond to my posting. I really appreciate your help.

1. Yes, definitely a typo. Corrected it in the initial post.
4. If I could count I wouldn't pump so much money into my car.
5. You read my mind. This is exactly what I thought about and what I'll try to do - no what I WILL do.
6. I did some research and it seems like very early E32-M70s had a different water pump. But I still need to verify this.
7. That's exactly the case. The part looks like the not finished M70 part.
8. I will for sure use the M73 manifolds and if I have to change 50% of the car for it.
9. I have to check it I can use the E38 sump with just some mods or if I have to dump and replace it. I only read that it can't be used but I do not see why. E38 and E31 sumps are identical and the front axle hasn't changed from M70 to M73.
11./12. Exactly my plan
14. Again what I plan to do.

Paint that silver engine bay yellow

That silver engine bay turned matte black meanwhile and I admit that I like it. I am probably just going to paint it properly once the engine and everything else is removed.

Are you going to use original M70 wirelooms, ECU's and entire engine control system? Any modifications into chips needed?

Yes, I will.
M70 engine control system, DKs and 4HP24 will stay in the car. The outcome will be kind of a bastard between M70 and M73. I'm sure the M73 will run on my chip set but due to the much higher compression ratio of 10:1 versus 8.8;1 (M70) it is probably better to have a set custom programmed.
Following 8tech's idea I will make the mounting of the CPS variable so I can adjust the basic ignition timing. This might already be enough.

Are you going to have to make a custom chip for everything to work right? Or could one use your regular M70 chips?

see my above reply to moutine.

Meanwhile another day has passed and I have been a little active. New to me is, that the M73 appears to suffer from a well known M60 problem: It tries to get rid of it's oil pump. Out of the three mounting points (two M8 studs with nuts and one M8 screw) two were completely loose. Nut in the oil pan and the screw found a cosy place right behind the oil pump sprocket (already removed in the picture). Luckily it didn't block it.





The block as such is pretty much stripped. All covers as well as cylinder heads removed and block itself 80% cleaned. Next step is to clean all those aluminium covers, glass pearl shower them and then get them anodized for better protection in their new life.
The heads will be stripped completely and everything will be checked and replaced wherever necessary. I'm not sure what to do with the crank and rod bearings. I guess I'll check one of each and then decide if they need replacement or not. The pistons will definitely stay in place because everything looks perfect there.

[argonaut]

Wolf, have a search around for "Kapitan" - user on this board, I think he recently did a similar conversion and he posted some information about your question number 6 (Water mpump) I thin kthat the impeller is different but I can't remember exactly how.
Cheers
Jason

EDIT, I saved you the search, here's a link to the thread I mentioned: http://forums.bimmerforums.com/forum....php?t=1722825

[wokke]

Thanks Jason for your hint.
I had read Kapitan's thread before but will do it again.
What I understand regarding the water pump is that the impeller on the M70 pump is larger than the one on the M73 pump. What I do not know yet is why the M73 pump can't stay but has to be replaced. Must be a tubing issue IMO. But I'll find out.

Cheers
Wolf

[DriftGirl]

Wokke!!!

[CaifanSC]

What did you use to clean up the head surfaces and the cylinder tops? What did you do to avoid any of the debris to go down the cylinder walls?

[wokke]

What did you use to clean up the head surfaces and the cylinder tops? What did you do to avoid any of the debris to go down the cylinder walls?

I used a rotating sander with 800 grid paper for cleaning the block surface. The heads I will take to a machine shop to have them checked and cleaned.
In regards to the debris I didn't do anything special because I'll be pulling the pistons anyways in order to check the rings.
For the pistons I used a metal tool to scrape off the black stuff and then some fine steel wool for the "finish".

Some minor progress today:

[dudu850]

Some minor progress today:

Have you said "minor" ??? What do germans understand by "major" ??

[wokke]

Minor just because I wouldn't call it a milestone and there is still a lot of work in front of me

[argonaut]

Nice and shiny looking Wolf, impressive stuff :-)

[koenig d]

WOLF; do you have any pics of the heads?

[wokke]

WOLF; do you have any pics of the heads?

Not yet since I haven't touched them besides taking them off the block.

WATER PUMP DIFFERENCE
Thanks to a members documentation about a M70 engine swap I now know the difference between the water pumps. The inlet (connection to upper radiator hose) is different.
The below picture shows one more difference because it#s an E32 M70 which does not have the connection for the expansion tank.

M70 (E32) water pump


M73 water pump

[Bryson]

Definitely replace the rings Wolf! If for no other reason than to keep that damn oil scraper ring from getting coked up and no longer doing it's job. Chances are that your cylinder walls are fine but I would recommend rings. I have new ones here for my next engine.

Also, m70/m73s are known to exhibit ring land wear on some, definitely check for land wear, especially for the compression ring. Wear will lead to a lifelong oil burner! A friend recently did a steel sleeved m70 rebuild (would not recommend this method personally) and has issues with land wear on the stock pistons.

If you want to get crazy, ceramic coating the piston tops will help prevent predetonation and will lower oil temps..

[wokke]

Hi Bryson,

pulling the pistons is one of the next activities and I'm already searching for a supplier for rings. I'm not willing to pay the outrageous BMW prices if I can avoid it.

Ceramic coating of the piston tops sounds like a nice idea but I have no clue who does it here in Germany. I also don't think that pre detonation is an issue. Our fuel must be of highest available quality looking at the price

Cheers
Wolf

[wokke]

WOLF; do you have any pics of the heads?

now I do have pics of the heads.

BEFORE (or better not done yet)









AFTER (not finished yet - valves need to be installed)









I now need to find a proper tool to compress the valve springs for the valve installation. I'm thinking about one of this type and get a tube which I will temporarily install instead of the cam shaft.

[Bryson]

I would bolt something to the valve cover studs so that you don't have to risk damaging the cam journals. This way you'll be levering against something that can take the load.

Great update Wolf, thanks! Could you do a comparison shot of m70 and m73 exhaust runner outlets? I've always wondered it they made any changes to the original shitty exhaust runner design