Crank hub replacement

[sapote]

IMO A single bolt long snout design requires an interference fit hub to work properly to transfer torque and because without interference if it slips can easily shear keys/dowels over time but complicates the assembly and disassembly but this approach is used on many engines.

Do we have incidences of the single bolt and woodruff key issue? The key and keyway is a very tight tolerance machined parts.
The 4-bolt arrangement has the sprocket cantilever on the crank face and inherently seems less stable than having the sprocket carried by the crank long snout. It's an interesting engineering problem.

[digger]

BMW changed strategy for the high rpm S engines during time frame of S50B30euro to 4 bolts, whereas S38 3.6 has single central bolt long snout design late 90s vs S38b38 which has S50euro/s54 style 4 M12 bolts because it is better friction drive than a single M18 and less problematic in a high performance engine. The S55 has issues with a single bolt as it is not a robust clamp and the S58 went back to 4 bolts though only M10 this time by looks of it. IMO A single bolt long snout design requires an interference fit hub to work properly to transfer torque and because without interference if it slips can easily shear keys/dowels over time but complicates the assembly and disassembly but this approach is used on many engines.

[sapote]

Only thing that comes to mind, is that when you replace the front main seal, it cannot run in the same groove as before, or risk leaking. You only have 2 or 3 locations to position that seal. At that point, you can just replace the spacer thing where the seal rides, whereas a 1 piece crank... what are your options?

Could be totally wrong, but just a thought.

The non-M crank has the sprocket locked to the crank nose by the keyway, and bolted down, so it is positioned to the seal is relatively the same as the M engine. IOW, the seal is riding on the sprocket, not directly on the crank shaft.

[cobra]

Food for thought: wonder why the S54 doesn't use the solid crank nose for mounting the relatively long sprocket as the non-M crank below which seems to be more stable.

Only thing that comes to mind, is that when you replace the front main seal, it cannot run in the same groove as before, or risk leaking. You only have 2 or 3 locations to position that seal. At that point, you can just replace the spacer thing where the seal rides, whereas a 1 piece crank... what are your options?

Could be totally wrong, but just a thought.

[sapote]

Food for thought: wonder why the S54 doesn't use the solid crank nose for mounting the relatively long sprocket as the non-M crank below which seems to be more stable.

[sapote]

I have a quick update but to answer your questions

• I found the broken pin sheared into the holes of both the balancer and sprocket
• The front crank seal was leaking, I was able to see once I removed it
• the bolts were backed out about 2mm or so
• I cant tell if the pin was welded deliberately but both ends were practically welded in both holes

Today I removed crank hub sprocket and I am bit concerned with the face of the crank here ( see attached photo). There are some gouges by each of the TTYL bolt holes and I'm wondering how bad this is.

Let me know what you all think. This project has been brutal

I look at all the pics again and I think someone had done a butcher job previously on a damaged parts. They welded the pin to the sprocket with uneven surface between sprocket and the balancer, and this caused the bolts to back out.
This crank has to come out for a proper machining to restore the needed perfectly flat surface. If not, the long sprocket carries the heavy load during the quick rpm blips will loosen it up again. The perfectly flat surfaces are required to create the friction force enough to withstand the load.

[bobssecrtsn]

I just went through this when I was refreshing my motor, buy a good quality cam shaft tool, NOT through amazon.

[cobra]

I have seen machine tapers that are gouged worse than this, but as long as you don't have any high spots you should be fine. You will need to clean that up very carefully and gauge it to ensure it's perfectly flat. Then install your new spacer thing and torque but not the yield part yet. Gauge it to ensure it's running true.

As for smoothing it out, I am not sure the best approach. It might require some kind of jig to align a scraper tool flat with the end of the crank and scrape the surface as you rotate it around.

Or, if it's not as bad as it looks, just carefully dremeling out the tiny high spots will be fine.

[digger]

if the gouges sit proud you need to carefully deburr (may require replacement of the dowel sleeve to give a better working area) so the sprockets sits and bears down correctly but not hack the hell out if it

[S54orzo]

I have a quick update but to answer your questions

• I found the broken pin sheared into the holes of both the balancer and sprocket
• The front crank seal was leaking, I was able to see once I removed it
• the bolts were backed out about 2mm or so
• I cant tell if the pin was welded deliberately but both ends were practically welded in both holes

Today I removed crank hub sprocket and I am bit concerned with the face of the crank here ( see attached photo). There are some gouges by each of the TTYL bolt holes and I'm wondering how bad this is.

Let me know what you all think. This project has been brutal

[sapote]

when I went to inspect and confirm I noticed my vibration dampener/crank hub bolts had backed out and were all finger loose. At this point I removed the dampener and saw the crank hub face was significantly scored with the alignment pin sheered off.

1. did you find the broken pin?
2. how far the 4 bolts backed out, far enough for the broken pin to be wedged between crank nose and balancer? If yes, then I don't see how the belt didn't jump off the pulleys.
3. Obviously the balancer still rotating together with the crank, but I see blueish high temperature around the pin base, so what caused the high temperature if the balancer didn't rotate against the crank. Maybe the pin was welded on the crank nose by previous guy.

[Slideways]

Those TTY bolts don't back out by themselves. If someone was in there, I would not be surprised if they reused the TTY bolts. There are certain critical fasteners that should always be replaced. This is one of them.

OP needs a new crank hub, mounting screw, 4 TTY OE bolts and vibration damper. I understand marking everything for a first timer, but this timing system does not need that. There is no special link on the chain nor timing mark on any of the sprockets. All you need is the crank locking pin and the timing bridge. And the chain can just be bunched up in the timing chain guides when the upper sprockets are removed. There is no need to keep tension on it while everything is apart unless you want to rotate the crank to move the pistons away from the valves.

[sapote]

I don’t think this is the case for the leaking seal, unless someone had worked on the seal before.

[S54orzo]

agreed with the timing. IIRC once the vanos is removed this is required. I'll take a look at that DIY. appreciate the reply!

[bigjae46]

There is a DIY somewhere. I believe Heinzboehmer did this by cleaning up the face of the hub. Your looks quite chewed up.

There's no way to do this without retiming the engine. Why risk it? IMO it would be stupid to do all of that work and avoid timing the engine.