Boxerworks.com

For those who have trouble seeing in there minds how a crankshaft is re ground please see the link below, this man is clearly a great machinist and would make a great tutor, I do like his machine much better than the last one I operated.

https://www.youtube.com/watch?v=12UdcpXHxPM

sooo....
So much advice, so many opinions...
all valid...
however... long story short...
CAN ANYBODY POST A LINK TO A FACILITY (WITH A PROVEN TRACK RECORD) THAT WILL CORRECTLY REGRIND A TYPE 247 AIRHEAD CRANKSHAFT?
I DOUBT IT!

kmisterk-
Consider something along these lines (with stock sized shells) if your crank is only lightly scored.
https://www.youtube.com/watch?v=wb-S0VPLPM4
Not to BMW standards but WTF, it'll work just fine.

gspd wrote: ↑Mon Jul 04, 2022 7:00 pm
https://www.youtube.com/watch?v=wb-S0VPLPM4

You and my brother both sent me this link, and it will likely end up being the route I take.

So, here's the damage:



And an overview of the parts' appearances:



The scoring on the spun bearing journal vs the good bearing:

Link to Imgur Album

And as a bonus, I made sure to get a good look at the internals of the Oil Filter Cavity to make sure it looks kosher. As far as my uninformed eye can tell, it seems okay in there.



So, my fellow boxer enthusiasts, here's where we stand.

From what I can tell from the teardown and the condition of the parts as a whole, here's what I found.

Clearly, the left-side con-rod bearing was spun (the bearing shell end was sticking up about a half-inch above the "seam" of the two halves) and, as you can see in the second video at ~8 seconds in (the video of all the parts), the bearing shells for that con-rod were destroyed.

When running a fingernail across the journal for which this bearing was destroyed, subtle grooves are felt, but my fingernail technically never *caught* on them, they just detected their presence. *super* light scoring.

I'm likely going to go the route of the video GSPD shared with me, as it seems to be the most cost-effective, "good enough for me" fix, as I really don't want to do a full crankshaft swap, let alone have to buy one.

Did I miss anything? Anything y'all see in any of the images/videos that I missed?

Thanks!

kmisterk wrote: ↑Tue Jul 05, 2022 3:46 am I'm likely going to go the route of the video GSPD shared with me, as it seems to be the most cost-effective, "good enough for me" fix, as I really don't want to do a full crankshaft swap, let alone have to buy one.
Did I miss anything?

Earlier on I stated "Can't say 1000%, but my experienced ears would bet ($100?) that the knock in the video IS a big end bearing knock, nothing else sounds like that. Even on shitty computer speakers."
I wish someone had taken me up on my bet.

You're on the right track, but I have one thing to add that wasn't mentioned in the redneck video...
In the video the crank is removed from the engine making it easy to blow out all the oil passages before re-assembly.
Seeing as you're not removing the crank, I suggest you block the oil feed holes by filling them with ONE piece of rope or leather tassle or something similar so you don't end up blocking them with grinding paste and debris. Make sure you use a large enough piece so that it can totally be removed intact with a dental pick or similar tool after the polishing is done. DO NOT use pieces of Kleenex or paper towel or anything that might disintegrate upon removal.

Post a pic after the polishing is done.

Before re-assembly, wrap a bit of cloth around each crank journal (held in place by a loosely fitted rad hose clamp or tape) to be 100% sure that all passages are clear and oil is getting to both journals when briefly spinning the engine with the starter motor.
DO NOT ATTEMPT THIS WITH THE CONRODS INSTALLED!!!!

Before



In progress



Hoping to get this a bit smoother but I needed to give my hands a break.

Ugh.

I think this is the best I’m going to get the scoring.

Doesn't look that smooth yet.
What are you using for abrasive?
Did you try some 600 grit sandpaper with tape wrapped around it, like in the redneck video?
Try to smooth it out a bit more without removing too much material, if that makes sense.

gspd wrote: ↑Sat Jul 09, 2022 9:15 pm Doesn't look that smooth yet.
What are you using for abrasive?
Did you try some 600 grit sandpaper with tape wrapped around it, like in the redneck video?
Try to smooth it out a bit more without removing too much material, if that makes sense.

I was using 220 grit with WD-40 but otherwise yes.

HOLY CRAP!!!!
220 is WAAAY to rough!!!!
That's what caused all those deep scratches.
You should NEVER have used anything coarser than 600.
Then 1200 or 2000, and then polishing compound.

Hope you haven't scrapped it.
The idea is (was?) to polish it smooth, not to grind it down.