an unfortunate update to my long restoration process

[brant914]

Update....

got the motor partially disassembled....
it does look like the right connecting rod bearing was the problem

it apparently did not spin on the journal.
and when removing the rod cap.. I found it in many many pieces...

the picture of the right rod journal of the crank is also attached.
there is limited scoring... as the bearing never spun
and the photo was taken at maximum enlargement, from about 4 inches away
so looks bad...
but nothing you can feel with a fingernail.

do they make undersized bearings for airheads?

all of my air cooled cars offer undersized bearings, in case a journal has to be cut, and the bearing used to save the component.

 

[gtgt_bangbang]

ouch . I'm about to fire up a new one, say a little prayer this don't look like mine next month.

been a little while since I 'm read in, but if I recall BMW cranks this vintage were surface hardened at size.

A crank re grind would blow through the hardening. I imagine there are shops these days that could harden but I dont think salvage bottom ends are too rare.

Have you got any suspicions on root cause? Its time to inspect other journal. If its not toast too, maybe give you some clues.

Old hands; is this what the $2000 oring buys ?

 

[20774]

Old hands; is this what the $2000 oring buys ?

No such o-ring on a /5. That came along with they changed the filter area on the /7s.

 

[stevenrankin]

Max

I have been told Max BMW is now working on crankshafts. I am NOT sure if this means only /2 or if they have the means to work on yours. I do not have direct experience but looking at Max's microfiche there are different size bearing shells available.

I am giving second hand information here so take it for what it is worth. One of the customers of my friend's shop installed new bearings himself and the result was back and forth play in the connecting rod which was noticeable as a noise. The consensus is when he did this he should have had the crank worked on to assure proper fitment. Of course the problem is, there are no shops in the area that can work on BMW cranks.

I think it might be time to again contact Matt, or Max, Max to assess if they can indeed do any machine work on your crankshaft if needed. Again, second hand knowledge and rumor is most machine shops can't properly work on BMW crankshafts.

Good luck. St.

 

[brant914]

the other connecting rod looks good
the bearing shows slight wear... but not significant.

root cause?

well the bike sat 26 years before I fired it.
I rebuilt the oil pump
and showed oil pressure on the warning light for the 47 miles I rode it.
primed it with the starter and showed oil pressure during that also.

my guess is that prior to my 47 miles... it was likely ran low on oil, or lost pressure somehow...

of course easier to blame the previous owner....
but I didn't see any problems with pressure what so ever
and the slight sound I had was noticeable on the very first trip around the block when I rode it... the first mile... of the 47

so it helps me sleep at night to blame the previous owner


all of the german porsche cranks I've worked with in the past are hardened also
they have the ability to cut the journals and reharden...
so maybe this will be an option for this one...
of course it first needs a micro polish and good measurement before its cut.
I should of looked at max's bearings...
good to know they show them as available.

brant

 

[20774]

I have been told Max BMW is now working on crankshafts. I am NOT sure if this means only /2 or if they have the means to work on yours.

Latest ON has an ad for Max that mentions crank rebuilding. Says "baseline runout testing, disassembly & inspection, rod/bearing/pin replacement, reassembly & truing, CWT computerized balancing." Doesn't sound like they'll grind a crank, though. Give them a shout anyway...maybe they have some ideas.

Some guy toasted his crank on a /7 top end rebuild and documented things on the Boxerworks forum. There was a discussion late in the thread on people who could regrind cranks. Can't find it now, though.

 

[brant914]

probably won't have another update for a long time....

but did get my motor disassembled.
the crank looks better than I expected it to
... the machinist will measure and determine if it has to be replaced.

got an entire airhead motor into 3 boxes for shipping out.....

 

[stevenrankin]

Thanks

Thanks for the continual updates, good luck. St.

 

[Omega Man]

probably won't have another update for a long time....

but did get my motor disassembled.
the crank looks better than I expected it toView attachment 89195
... the machinist will measure and determine if it has to be replaced.

got an entire airhead motor into 3 boxes for shipping out.....


View attachment 89196

I really would use the fiberglass reinforced packaging tape over that clear packaging tape. That is if it is going by one of the common shipping companies.
Good luck.
OM

 

[brant914]

that is great advice...
I'll pick some up tonight.. and give it another layer before things ship tomorrow!

thanks
brant

 

[gregfeeler]

that is great advice...
I'll pick some up tonight.. and give it another layer before things ship tomorrow!

thanks
brant

Good luck!