M21 Engine Rebuild

[gadget73]

There is definitely a direction of stress. The bottom side of the small end gets the abuse compressing things and the stress from the combustion process so it makes perfect sense that it would be the stressed area.

[z122643]

by the way, what is it that you do for a living that you have access to such very cool tools!? Thanks! -Paul

[gadget73]

I was just assuming you were Q rather than 007.

[kingoftarmace2004]

oh come on! 007 doesn't have hobbies.....

[z122643]

So we are back, after delays finding OEM pistons and me getting the connecting rods finished. Oh and COVID. With the head complete we just need to finish up the block. More pictures soon.

[z122643]

New immediate shaft bearings were a bitch! Front and rear main seals in. Next up pistons and rods.

[gadget73]

"intermediate shaft" I presume is what the oil pump drives from ?

[z122643]

"intermediate shaft" I presume is what the oil pump drives from ?

Yes. I've built a few M20 engines before and I've always found it easier to reused the intermediate shaft bearings. But they were too badly worn on this engine and had to be replaced. The issue becomes that the two bearings when pressed into the block are not concentric, unlike the intermediate shaft.

[gadget73]

how does that work then? The shaft runs at an angle or something ? Or meaning the bearings egg shape in the block and need to be reamed back to round?

[z122643]

how does that work then? The shaft runs at an angle or something ? Or meaning the bearings egg shape in the block and need to be reamed back to round?

The bearings are intentionally undersized. You have to hone the bearings therefore correcting for roundness. The trick is getting two bearings that are about 4" apart to be concentric (on the same central axis).

Here is a write up on the intermediate shaft bearings on the M20 engine. (same block)
https://www.bimmerforums.com/forum/show ... styleid=51

[z122643]

Doesn't look it but gap was good.

[gadget73]

Hone to fit bearings in the block, thats a new one on me. I'm more used to dealing with boring American V8 engines, you just fit the bearings in and if the cam doesn't fit, either the cam is messed up or more likely the bearing install was screwed up. No honing, you just replace whichever part is bad.

[bigtuna]

Your my hero, the nerve of you taking on such a tremendous undertaking... especially that your not in Europe where the parts "might be" more easily sourced. I commend you. Im local to you and would love to see your car./engine I just picked up a 1985 524TD with the original engine Im driving as a daily. runs great ...and live in Laguna Niguel. Fernando

[optig]

Nice color man, I love it! Keep going!

[z122643]

Been some serious delays getting some of the parts. Most have actually come out of Latvia of all places.

[gadget73]

I have also noticed a lot of parts listed on ebay for these in Latvia. Sort of curious how that became the storehouse for all things M21.

[Galahad]

I've gotten a whole lot of car parts from both Latvia and Lithuania - no clue why they're there but the parts arrive

[z122643]

under the "am I just stupid?" category, I bought a new oil level sender and the shield will not fit. There are not enough threads on the studs from the oil pan. Unfortunately I have no pictures of the original and my "buddy" threw out the level sender years ago. Does anyone know what it should look like?

[Ju@n]

I think the shield goes under the nuts, not above them

[gadget73]

not sure about that. Looking at the sending unit, there are studs cast into the sending unit that would space the shield up away from the sender. If you put it together with the shield under the nuts, it wouldn't press the sender into the pan properly, it would just bend the steel shield. Also the whole works would come out of the oil pan if the nuts were removed. I'm guessing there is a connector under there? Seems unlikely they would require the oil pan to be empty to unplug something.

honestly looks like at least one of those studs is cut down. Whats the setup on the inside of the oil pan where those are? Studs just welded to the pan, or is there a plate they thread to or what?


unfortunately i have nothing I can reference, my oil pan is different and best I can figure mine uses the Ford low oil level indictor rather than the BMW one. Mine screws in to the side of the oil pan, same as my V8 Fords of the same era do.

[Mike W.]

Preface, I don't know M21s. I don't even know M20s. But that doesn't look right.

It looks very similar to an M30 oil level sensor, which has an O ring, I'm pretty sure in the sensor, that seals to the pan. In this case you would need two, one on either side of the plastic piece. And Gadget as usual has an insight, one of those studs looks like it's cut off. But I just don't see them using a plastic shield to seal between the pan and the sensor.

[gadget73]

https://www.realoem.com/bmw/enUS/showpa ... Id=11_0168

has the assembly diagram, they don't show nuts between the metal shield and the sensor, but just looking at the shape of the parts I just don't see how that would sit together right without something to keep the metal shield from bending. If it had spacer bushings or something in there it would make more sense to me.

it does appear that the studs unscrew though

[Alpinweib524td]

Looks like the wrong sensor. Grind off the three tits so the plate will mount flush against the sensor.
Here is a picture from my engine that is currently being rebuilt with original sensor installed.
https://drive.google.com/file/d/13iSn1y ... share_link

[z122643]

Got it. Thanks

[thehardcorps]

Just picked up an M21 and love seeing your build come along. I would be very interested in learning more and sourcing your rods. Do you have a company site or can I just PM you?