While complete engine rebuild, is it necessary to extract the rear main bearing holder?
Don't think it was ever done before by PO's.
I can see in drawings that there is a gasket beneath.
If so, how do I pull it out? Any special tool needed, or can I go with a regular arm puller?
It has what seems to be 4 aluminum shoulders.
- rear_main_bearing_holder.jpg (400.52 KiB) Viewed 554 times
Engine Nr. 529466
I bought the book to not only support Chris and Barbara, but it pretty much has everything you need from basic to advanced repairs.
I found it to be a great read when I'm just sitting around doing nothing.
Although I won't be doing a major rebuild on my motor/transmission/etc etc, I just appreciate that someone has taken the time to write a very detailed "Bible" on our machines.
With having less and less people able to do the repairs, thank goodness we have this book to refer to.
Your bearing holder will likely need to be replaced if it has any appreciable wear on it. Your picture isn’t clear enough to tell definitively but if you can feel a lip with your fingernail where the rear edge of the bearing sat, then it should be replaced. there is a fine groove that I can feel with my fingernail The rear bearing can theoretically move axially back and forth very slightly and over time causes wear in the carrier can it? it is held in place with lots of bolts. So putting a new bearing in an old worn carrier can potentially accelerate wear on that new bearing. I’ll have to look in the literature to be certain but I don’t think there’s a maximum ID wear limit listed for that carrier....I’m not near my books right now maybe someone else can say for certain. These carriers are a little less than $200 if bought in the US, quite a bit cheaper from certain European vintage parts suppliers. yes they are expensive Most motors with significant mileage need new ones from my experience. Installing the new one you can simply line up the holes with the studs and tap it in with a soft faced hammer. Or, again, you can press it in with a press if that feels better for you.
I will again appreciate your thought here.
Engine Nr. 529466
As far as what holds the crank in place, there are no bolts to hold it in. What locates the crank fore and aft inside the case is simply the interference fit of the two main bearings onto the crank, and then the interference fit (“slight pinch fit” according to BMW) of the bearings in their carriers. The crank is further tightened up and finally located by means of the steel timing gear as a press interference fit pulling the crank forward and effectively sandwiching the front main bearing between the gear, and the front slinger and spacer ring. In other words, when the crank is placed in the heated case (factory manuals call for 180 deg F.) and the timing gear is pressed in place, and all the bearing interference fits are to factory spec, in theory, the crank shouldn’t move at all. But I’m leaving out some details of fitting the crank properly so this doesn’t get too long, but if everything isn’t installed right, the bearings can be put in a “bind” and accelerated wear begins immediately after the expensive engine rebuild is complete. I’m not an engineer, and maybe someone with some theoretical mechanical design background can shed more light, but I’m assuming that due to the slight imperfect rocking moment of the power pulses from the connecting rods being offset, I’m thinking that this puts enough fore and aft forces over many miles and years of use to cause the crank bearings to begin loosening up slightly both in the case, and also on their crank journals, that the crank then moves ever so slightly as well as the bearings, were only talking about maybe a couple thousandths of an inch, and so over time the physical wear and damage occurs on both the carriers and the crank journals. Some evidence that this occurs, other than obvious wear found on these old engines, is that for the higher compression R50S and R69S engines a barrel roller bearing was used in the rear, presumably to allow for higher axial loading to account for this phenomena. Some feel that bearing is an outmoded design for this particular application, that’s certainly up for debate, the factory BMW engineers felt it was an appropriate solution, however that was nearly 70 years ago. There’s a lot to all this crank stuff some of it has much to do with feel and subjective assessment, and some is bound by simple factory tolerance specs.