ADVrider

Go Back   ADVrider > Bikes > Old's Cool > Airheads
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 08-25-2014, 07:19 AM   #1
Lesser OP
Adventurer
 
Lesser's Avatar
 
Joined: Jul 2010
Location: Brooklyn, NY
Oddometer: 39
R90S Crank Kaput

Anyone have a crank and flywheel to fit a 76 r90s? Also looking for any good threads existing on the procedure. I know a couple really good experienced mechanics and nobody seems to have done a BMW bottom end. Lucky me.

Suffered some catastrophic engine failure about 150 miles from home in the Catskills a few weekends back. Time to start the healing process. Autopsy revealed 5 flywheel bolts shorn from the crank. PO must have reused or mis-torqued them. Looks like components had been galling and wallowing from the loose bolts for a while.

Top end of the bike had been redone just a few thousand miles before I got it. Cylinders were refreshed and rings replaced, cyl heads redone with black diamond valve seats. Motor feels (felt...) tight and goes (went) like stink.



Found this bike two years back and quickly liberated it from a massive full fairing complete with tape deck and cigarette lighter. PO rode it to rallies all over the country for a couple decades before he got a plusher modern BMW and let this one sit a few years before selling it. The finish is a bit rough. There were mice in the fairing pockets when I got it. I rebuilt the carbs and front end with fresh steering bearings and gave her a complete service new with points, condenser, etc. Got lucky and found a freshly painted S fairing and matching front fender, and replaced the rotting original pipes with some knockoff Dunstalls which bark obnoxiously but really open the old girl up, and this has been my roughshod/hotrod runner ever since.

And the bike was running *so* well before it all went wrong. The day she died we'd completed 300 some odd miles of great riding, escaping the city, across Harriman State park, up the Delaware Water Gap, and back down into the Catskills. And then things went boom.



The flywheel sheared in the 15 minute span I swapped bikes with a buddy, who I cannot blame as it looks like this had been going on a while. I was riding his Manfred Hecht built LeMans ahead of him when the 90s crapped out on rt 28 outside a town called Fleishmans, which is another story. We thought it might be a con rod given the terrible clanking noise emanating when starter button was hit. Pickup-trucked it back home after a very long 23-hour day.

During the post-mortem we took off top end, then the timing cover to find everything more or less intact. Slight kiss of piston to valve on one side, but the timing chain is loose as a goose. Then pulled the trans, at which point the flywheel and clutch pack came off on their own.



Perfectly happy to go with a used/VGC stock crank - but I could use some guidance on how to define my search. I am thinking any 1976 r90 crank will do? Anyone know the compatibility of the 1976 r90s crank vs R100's etc?

Bike is a 1976 r90/s. Looks like my vin makes it a 5/76 bike.(4991110)

And of course, if anyone has or knows someone with a chunked motor with a good bottom end including flywheel, please advise. And I'll post back with progress. Going to upgrade charging system and replace timing chain while I've got everything apart.

Before/After Gallery:

__________________
83 r80ST
76 r90s
92 R100R
www.UnionGarageNYC.com
103 Union St, Brooklyn, NY 11231; Tues-Sun
Lesser is offline   Reply With Quote
Old 08-25-2014, 07:49 AM   #2
chasbmw
Beastly Adventurer
 
Joined: Feb 2006
Location: Bath Uk
Oddometer: 1,749
Quote:
Originally Posted by Lesser View Post
Anyone have a crank and flywheel to fit a 76 r90s? Also looking for any good threads existing on the procedure. I know a couple really good experienced mechanics and nobody seems to have done a BMW bottom end. Lucky me.

Suffered some catastrophic engine failure about 150 miles from home in the Catskills a few weekends back. Time to start the healing process. Autopsy revealed 5 flywheel bolts shorn from the crank. PO must have reused or mis-torqued them. Looks like components had been galling and wallowing from the loose bolts for a while.

Top end of the bike had been redone just a few thousand miles before I got it. Cylinders were refreshed and rings replaced, cyl heads redone with black diamond valve seats. Motor feels (felt...) tight and goes (went) like stink.



Found this bike two years back and quickly liberated it from a massive full fairing complete with tape deck and cigarette lighter. PO rode it to rallies all over the country for a couple decades before he got a plusher modern BMW and let this one sit a few years before selling it. The finish is a bit rough. There were mice in the fairing pockets when I got it. I rebuilt the carbs and front end with fresh steering bearings and gave her a complete service new with points, condenser, etc. Got lucky and found a freshly painted S fairing and matching front fender, and replaced the rotting original pipes with some knockoff Dunstalls which bark obnoxiously but really open the old girl up, and this has been my roughshod/hotrod runner ever since.

And the bike was running *so* well before it all went wrong. The day she died we'd completed 300 some odd miles of great riding, escaping the city, across Harriman State park, up the Delaware Water Gap, and back down into the Catskills. And then things went boom.



The flywheel sheared in the 15 minute span I swapped bikes with a buddy, who I cannot blame as it looks like this had been going on a while. I was riding his Manfred Hecht built LeMans ahead of him when the 90s crapped out on rt 28 outside a town called Fleishmans, which is another story. We thought it might be a con rod given the terrible clanking noise emanating when starter button was hit. Pickup-trucked it back home after a very long 23-hour day.

During the post-mortem we took off top end, then the timing cover to find everything more or less intact. Slight kiss of piston to valve on one side, but the timing chain is loose as a goose. Then pulled the trans, at which point the flywheel and clutch pack came off on their own.



Perfectly happy to go with a used/VGC stock crank - but I could use some guidance on how to define my search. I am thinking any 1976 r90 crank will do? Anyone know the compatibility of the 1976 r90s crank vs R100's etc?

Bike is a 1976 r90/s. Looks like my vin makes it a 5/76 bike.(4991110)

And of course, if anyone has or knows someone with a chunked motor with a good bottom end including flywheel, please advise. And I'll post back with progress. Going to upgrade charging system and replace timing chain while I've got everything apart.

Before/After Gallery:


According to my 1975 parts book the cranks were shared between the 750 and both 900 models, if you get a crank after about 1975 it should have the larger flywheel bolts, but check before you buy it. Buying a complete bottom end would be the easier way of doing it, but you would end up with incorrect engine nos, which on a 90s might be of importance to you. If you go down that route there is a change in the machining of the crankcase where the cylinders fit. I don't know if this is an issue fitting earlier cylinders to later engines.
__________________
Charles
http://i46.photobucket.com/albums/f1...ps6e61ae2e.jpg
R90s 1070 replica, R90/6
1971 Commando Fastback
chasbmw is offline   Reply With Quote
Old 08-25-2014, 07:55 AM   #3
blaine.hale
Beastly Adventurer
 
blaine.hale's Avatar
 
Joined: Feb 2009
Location: Atlanta, Ga
Oddometer: 2,892
Doh! I have a 74 bottom end not doing anything. Too bad it's not a 75+ :(
__________________
1974 BMW R90 /6
1968 Bultaco Matador MK3
1973 BMW R75 /5 Toaster LWB
1969 Bultaco Bandido MK2
2013 Husqvarna Terra TR650
blaine.hale is offline   Reply With Quote
Old 08-25-2014, 07:59 AM   #4
disston
ShadeTreeExpert
 
disston's Avatar
 
Joined: Mar 2011
Location: Silver Spring, Md
Oddometer: 8,276
The most efficient and often cheapest way to fix this is another short block or even a complete other engine.

Pretty sure you can use a crank from mid 1975 through 1980 and keep the heavy flywheel or even use a later set up and lighter flywheel except they get a different transmission. Just trying to say the possibilities are many if you swap parts around but remember if you change one thing it usually means you need to change something else.

So you have a heavy flywheel with 11mm flywheel bolts. Those bolts are normally reusable. It looks like the ones that failed were not torqued enough. And your flywheel has 93 teeth to match the 8 tooth starter. These are gonna be a little harder to find. The starter changes to 9 teeth and the flywheel to match has 111 teeth beginning in 1977. Earlier flywheels had 10mm bolts. So your beast only uses a flywheel from 1976 or maybe mid 1975?

There are many more 11mm bolt flywheels that use a 9 tooth starter so if you go the rebuild route having to change the starter may be part of the solution.

I know a guy in Maryland that can do this and may have the time (that's part of the problem. A bottom end rebuild is not quick and it is expensive compared to another engine.)

So this guys name in Maryland is Mark Delaney. He's go a site of sorts; http://www.markdelaney.net/ruths_page

I would continue your search. See what the parts cost and contact a few salvage yards. See what a new engine will cost?

Because this is an original R90S bike get another engine to run and rebuild the original for reinstall later. In other words "do both."
__________________
.
Never memorize something you can look up.
---Albert Einstein

Pay your debt, piratejohn.http://www.advrider.com/forums/showthread.php?t=949341
disston is offline   Reply With Quote
Old 08-25-2014, 02:50 PM   #5
ericrat
Beastly Adventurer
 
Joined: May 2007
Location: Cincinnati, OH
Oddometer: 1,100
Keep the matching frame and engine numbers together, as Disston said.

There are a number of reputable shops that can do this work, Bob's in Maryland, Anton Largiader, Bombar's, Tom Cutter, etc. All are a short shipping distance/roadtrip from you.

Replacing the crankshaft isn't, in itself, an especially difficult problem. Unfortunately, measuring and/or replacing the main bearings is. I would tear down and inspect the bearings. If they look okay, I would buy a used crankshaft and take to a local, reputable shop to have the clearances measured. If they check out, and it is likely that they will, I would put it together and run it. If they didn't I would either replace the main bearings myself or send it out.

I assume you are aware that the main bearings are a one piece "ring" and that this is a "tunnel" style engine case. This makes the main bearing replacement tricky and somewhat non-trivial.

Best regards,

Eric
__________________
Have you visited ride reports lately ?. click HERE
ericrat is offline   Reply With Quote
Old 08-25-2014, 05:07 PM   #6
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,213
Most tuners I have read of call our type engine 'barrel' crankcases. The setup is pretty rare. The best good working barrel crankcase setup can be traced back to the 1912 DOHC four valve Peugeot GP engine that Harry Miller and the real genius behind both Miller and Offenhouser Leo Goossen largely copied. Most tuners call barrel crankcase main bearing setups bearing webs. In multi-cylinder barrel crankcases the inner mains bearing webs split and are bolted around the crank and then interference fit all at the same time into the crankcase ala Offenhouser style. A real PITA!

Normal methods of measuring main clearance won't work with our mains. The mains have to be installed since their interference fit changes their size. You could install the mains and then measure them with a bore gauge but our mains are so soft and making accurate down to ten thousandths of an inch measurements even with a good bore gauge is highly subjective requiring many 'passes'. Very easy to mark up the bearings. I recommend measuring the crank and trusting the manufacturer's installed bearing size all at the same time realizing that BMW does not actually run their mains nearly as tight as they claim.
supershaft is offline   Reply With Quote
Old 08-25-2014, 06:00 PM   #7
Lesser OP
Adventurer
 
Lesser's Avatar
 
Joined: Jul 2010
Location: Brooklyn, NY
Oddometer: 39
Quote:
Originally Posted by disston View Post
Because this is an original R90S bike get another engine to run and rebuild the original for reinstall later. In other words "do both."
Thanks Disston. This is super helpful. I know a different-numbered block would probably be cheaper and easier. And it's not that this bike will ever be entered as a concourse example, but I'd like to get things together. Partly for the morbid curiosity of what this will take to make right. Will post back with any progress.
__________________
83 r80ST
76 r90s
92 R100R
www.UnionGarageNYC.com
103 Union St, Brooklyn, NY 11231; Tues-Sun
Lesser is offline   Reply With Quote
Old 08-25-2014, 07:31 PM   #8
bmwrench
Beastly Adventurer
 
Joined: Nov 2006
Oddometer: 1,958
Any crank with 11mm flywheel bolts will work. I've seen R90s as early as '74 with this size bolt, although they could have had their cranks replaced. Sort of officially, this crank was used from '76-'95.

Do keep the case and matching number frame together. Should you ever sell the bike, this will make it far more valuable.
bmwrench is offline   Reply With Quote
Old 08-25-2014, 08:57 PM   #9
_cy_
Beastly Adventurer
 
Joined: Sep 2011
Location: Tulsa, Oklahoma
Oddometer: 5,341
sorry to hear about your R90S crank problems .. looking at pic's this problem took awhile before it finally separated.

thinking back .. what tell tale signs did you get that something was not right?
_cy_ is offline   Reply With Quote
Old 08-25-2014, 09:24 PM   #10
Thorazine
Likes exhaust fumes
 
Thorazine's Avatar
 
Joined: Sep 2013
Location: Smoggy Valley, east of Smog City, Southern Calif.
Oddometer: 628
Quote:
Originally Posted by _cy_ View Post
thinking back .. what tell tale signs did you get that something was not right?
Yes. Curious to hear this . . .

Also--really like the pics, especially the front shot. Real nice.
__________________
Bones aren't important; we like motorcycles.-- M'boy D @ 4 y/o

* Posts submitted under the moniker Thorazine are for entertainment purposes only, and may include exaggerations, prevarications or bald-faced lies. -- Thorazine - '74 R90/6
Thorazine is offline   Reply With Quote
Old 08-25-2014, 09:38 PM   #11
_cy_
Beastly Adventurer
 
Joined: Sep 2011
Location: Tulsa, Oklahoma
Oddometer: 5,341
recently took my R90S out while waiting for throttle parts to arrive on G/S.
R90S had been parked not wanting to put miles on ... what a joy to ride!

parts arrived and G/S is all put back together again .. R90S goes back into standby @ 8328 miles ...


_cy_ screwed with this post 08-25-2014 at 09:49 PM
_cy_ is offline   Reply With Quote
Old 08-25-2014, 11:43 PM   #12
Bill Harris
Confirmed Curmudgeon
 
Bill Harris's Avatar
 
Joined: Sep 2008
Location: backwoods Alabama
Oddometer: 6,435
Quote:
Originally Posted by 'Wrench
Do keep the case and matching number frame together. Should you ever sell the bike, this will make it far more valuable.
Even if it is more expedient at this time to go ahead a replace the engine as a short-block, keep and "properly" store the matching-number block. It will be valuable if and when the bike is sold.

Quote:
Originally Posted by Cy
what tell tale signs did you get that something was not right?
I didn't want to mention this, but yeah, it must have been making quite a racket and vibrating and clutch juddering and RMS seeping.

--Bill
__________________
'73 R60/5 Toaster
Luddite. Not just a philosophy, a way of life...
Bill Harris is offline   Reply With Quote
Old 08-26-2014, 01:13 AM   #13
chasbmw
Beastly Adventurer
 
Joined: Feb 2006
Location: Bath Uk
Oddometer: 1,749
Quote:
Originally Posted by disston View Post
The most efficient and often cheapest way to fix this is another short block or even a complete other engine.

Pretty sure you can use a crank from mid 1975 through 1980 and keep the heavy flywheel or even use a later set up and lighter flywheel except they get a different transmission. Just trying to say the possibilities are many if you swap parts around but remember if you change one thing it usually means you need to change something else.

So you have a heavy flywheel with 11mm flywheel bolts. Those bolts are normally reusable. It looks like the ones that failed were not torqued enough. And your flywheel has 93 teeth to match the 8 tooth starter. These are gonna be a little harder to find. The starter changes to 9 teeth and the flywheel to match has 111 teeth beginning in 1977. Earlier flywheels had 10mm bolts. So your beast only uses a flywheel from 1976 or maybe mid 1975?

There are many more 11mm bolt flywheels that use a 9 tooth starter so if you go the rebuild route having to change the starter may be part of the solution.

I know a guy in Maryland that can do this and may have the time (that's part of the problem. A bottom end rebuild is not quick and it is expensive compared to another engine.)

So this guys name in Maryland is Mark Delaney. He's go a site of sorts; http://www.markdelaney.net/ruths_page

I would continue your search. See what the parts cost and contact a few salvage yards. See what a new engine will cost?

Because this is an original R90S bike get another engine to run and rebuild the original for reinstall later. In other words "do both."
I'm pretty sure that the flywheel bolt change to 11mm came very early in the /6 production cycle I.e end of 74 or early 75. My June 75 has the bigger bolts.
__________________
Charles
http://i46.photobucket.com/albums/f1...ps6e61ae2e.jpg
R90s 1070 replica, R90/6
1971 Commando Fastback
chasbmw is offline   Reply With Quote
Old 08-27-2014, 08:55 PM   #14
Lesser OP
Adventurer
 
Lesser's Avatar
 
Joined: Jul 2010
Location: Brooklyn, NY
Oddometer: 39
Postmortem

Quote:
Originally Posted by _cy_ View Post
thinking back .. what tell tale signs did you get that something was not right?
Quote:
Originally Posted by Bill Harris View Post
...must have been making quite a racket and vibrating and clutch juddering and RMS seeping.
Quote:
Originally Posted by Thorazine View Post
Yes. Curious to hear this . . .
Hungry for blood and gore! Alas I have none to tell of.

The kicker is that I had traded bikes with a friend (a hotrod LeMans MK1) when the flywheel finally spun - so I don't know how it felt at the time of catastrophe.

Leading up to this critical 15 minute swap the bike felt great. No vague/sloppy clutch feel at all. Conceivably the only time I'd have felt the growing slop in the crank/flyweel marriage would have been during downshifts or upshifts following hard downshifts. But I didn't, and in fact this was overall one of the tightest Airhead motors I've ever ridden. Super responsive and plenty of grunt. Top end had been redone a few k miles prior. And the transmission had been replaced with a rebuilt unit from an RS, I believe. And it felt tight and strong.

When I'd turned around and looped back to my buddy and busted bike on the side of the road he couldn't explain what had happened. At first thought it might have been a spline or a drivetrain problem. I of course had to hit the starter to see what the sound was even though he warned me not to. It was a horrible death clank that I guessed was a con rod. Turns out it was the teeth of the flywheel skipping around in the bell housing of the transmission. No real RMS leakage as he shut it down right away.

There was a lot of long-runs in 4th gear that day and the bike felt incredible. When we autopsied the bike we first pulled the top end. Was surprised to find everything mostly tidy and tight.

It appears there was a slight kiss between the LH Exhaust valve but didn't look disastrous. I knew my timing chain was stretched out so next step was to pull the timing cover expecting carnage. Again - nothing. Stretched yes but not broken.

Then I pulled the trans and the flywheel came off with it. Eureka.

Got a couple leads on cranks. Won't be a fast fix...
__________________
83 r80ST
76 r90s
92 R100R
www.UnionGarageNYC.com
103 Union St, Brooklyn, NY 11231; Tues-Sun
Lesser is offline   Reply With Quote
Old 08-28-2014, 05:13 AM   #15
bmwrench
Beastly Adventurer
 
Joined: Nov 2006
Oddometer: 1,958
Not to had to your troubles, but you should disassemble the cylinder heads. Valves contacting pistons, unless the motor is over-revved, frequently means sticking valves, something Black Diamonds are infamous for.
bmwrench is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 11:51 AM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014