Removing metal from the new crank may change the balance of the crank and therefore add vibration to your ride.

Don't do that !

Posted by: @wobbly

Removing metal from the new crank may change the balance of the crank and therefore add vibration to your ride.

Don't do that !

That was the conclusion i came to which is why i said it seemed like a bad idea.  Actually it seemed like the worst of the ideas i had.  Thanks for confirming that.

@14517 Apologies if I offended. I hoped it was obvious to you, but I couldn't be sure due to the order of listing. Didn't know if that was some kind of ranking or what. I simply figured better safe than sorry.

Can't really help you any further, as of all the hundreds of engines I've been into, never once have I needed to open up an Airhead. The only suggestions I can make is 1) to replace the conical spring in the oil by-pass at the "bottom" of the oil filter well. And 2) update the cam chain tensioner plunger spring. 

I would love for you to update up us on your progress.

@wobbly No worries.  I wasn’t offended. I’m not that easily offended.  I did appreciate the imperative not to grind down the crank.  I was pretty sure that was a bad idea, but its nice to have someone dissuade me from a really bad idea. ? 

First time i have worked on the bottom end.  I’m not really sure what happened to cause the oil failure.  It didn’t leak oil, it didn’t burn oil, it had oil, so...when the oil light came on i was a two miles from home and tried to ride it home.  That was the first really bad idea.  I ended up pushing it the last mile.  Pulled the left head (thats the side that had all the noise), and found that the connecting rod moved back and forth against the crankshaft bearing.  Took off the connecting rod to find the bearing melted.  Examination of the connnecting rod showed significant “blueing” about 2/3rd the length of the rod.  Removed both heads and found the right cylinder, bearing, connecting rod to be fine.  Left (front) bearing and connecting rod were not good.  The journal had some minor markings, so i looked into a crankshaft and found a refurbished one online, with the bearings, so i bought it.  Buyer beware.  The crankshaft i bought is in excellent shape, but I’m convinced it cannot be installed in my engine block.  I’m guessing i have a minimal length tolerance block and that is a maximum width tolerance crankshaft, but that just guessing/making excuses.  

My son-in-law, who is a mechanic suggested i smooth out the original crankshaft front bearing journal with crocus cloth.  I did so and its now very smooth.  However, since i needed to remove the crankshaft to check the front main bearing and i had the other crankshaft, i decided to install it.  The main bearings for the purchased crankshaft are slightly smaller than what i need (its been machined down to STD 1) so if i go back to the original crankshaft i need different bearings, need to pull the ones i just installed and ...At least i know how to do that now ?.

Thanks for the tips about the spring at the bottom of the oil filter well.  I’m not even sure how to get that out. Help there would be appreciated.

I have attached a picture of the left connecting rod for your “entertainment”

Posted by: @14517

Thanks for the tips about the spring at the bottom of the oil filter well.  I’m not even sure how to get that out. Help there would be appreciated.

Start by buying a new spring, ball and cap. Then grind a screw driver tip to have a parallel blade, and have it precisely fit the slot in the new cap. A standard home screw driver with a wedge blade cannot apply enough torque to remove the old cap. You get one shot at removing the cap, and if you bugger the cap's slot in doing so, you're stuck. So a wide blade that fits the full width of the cap, which is precisely ground to exactly fit the slot is worth your time. 

Then, with a wrench set to turn the screwdriver shaft, and the crankcase held securely, you can easily unscrew the old cap. (I do not try to remove the punch marks, and simply plow through them.) Use a stick magnet to remove the ball and spring. The spring typically comes out in bits. Clean away aluminum shards with compressed air.

There are 2 caps in use. (Early and late model.) Closely compare the old and new cap before beginning assembly.

The new spring and new ball can be placed into the well in heavy grease to hold them in position. The new cap is a precise fit due to the general machining and the distortion of the 2 punch marks. Grease can be used to hold the cap to the screwdriver as it's lowered into the well. Offer the new cap to the threads. Then with very light inward pressure applied, turn the new cap counter-clockwise until the threads are felt to 'click'. That tells you the threads are ready to engage. At that point greater inward pressure is applied and the cap starts its thread engagement in by turning clockwise. Again with a wrench on the screwdriver blade so as to apply enough torque. The new cap should bottom out with about 10ft-lbs of torque, and end up flush with the surface.

Hope this helps.

@wobbly Thanks for the instructions.  I looked at it yesterday and thought a large screwdriver would work.  I’m sure your instructions have prevented me buggering up the threads (or at least made that less likely ?). 

Since there are two different styles of caps, how to i know which cap to buy before hand?

Also, I was thinking of replacing the spring and rod assembly on the front bearing carrier, which lubes the chain.  A few months ago i replaced the timing cover seals because i found oil in the ignition cavity. That cured the problem, but the oiling failure made me think that the overpressure valve on the front bearing carrier might be faulty, leaking too much oil onto the timing chain and causing low oil pressure throughout the system.  Not sure about the cause and effect, but figure it should be easy to replace while i have the engine on the bench and the front bearing carrier out.  I cant find any information on how to remove that either.  If you have some advice on that it would also be greatly appreciated.

Corey

@14517 The correct cap, spring, and ball are chosen by ordering your parts from the correct year parts manual. I used Max BMW's on-line parts fiche system to good effect, but there are several of those on-line parts books now.

https://shop.maxbmw.com/fiche/fiche.aspx

A complete check of your oiling system is certainly required. As a matter of common sense, yes, I most certainly would replace EVERY spring within the oil distribution system. Also check the mechanical power linkage (cotter, bolt, key... whatever) between the rear of the camshaft and the oil pump. 

The thing you want to keep foremost in your mind is this: The failed main bearings are only a symptom of poor oil delivery. Your main job is to find the root cause of the poor oil delivery, or it will simply happen again with the new crank. 

...the oiling failure made me think that the overpressure valve on the front bearing carrier might be faulty...

That's really nothing more than wishful thinking on your part... UNTIL you get the new part and see that the new spring is 1/2 longer than the old spring. In other words, you need to find the "smoking gun" that proves beyond any doubt you have corrected the root problem. 

Time to put on your detective hat.

$2,000 o-ring at oil filter ?

No. 1 rod is the first to fail with low oil pressure !

Posted by: @6344

$2,000 o-ring at oil filter ?

No. 1 rod is the first to fail with low oil pressure !

You pretty much nailed the cost!

That’s a good tip about the oil filter o-ring.  That is consistent with the results.  The No 2 rod, journal and bearing are undamaged.  THe front main bearing was iffy, but the no 1 rod journal was slightly scratched, the bearing melted and connecting rod “blued” to the point of concern.  I have already disposed of the oil filter and there wasn’t an “extra” o-ring in the filter cavity.  The filter cover didn’t leak.  Is there another o-ring i should be looking at/for?  

My first try at detective work was checking the oil pump.  All parts measure within spec and are smooth and the woodruff key way in place when i took it apart.  No signs of failure of the oil pump.  I’m going to replace the oil filter bypass valve and the relief valve that allow oil to drip onto the timing chain.  Will inspect both to see their condition, but I’m going to replace regardless.

Got some parts on order, but its going to be awhile as I’m headed to visit grandkids soon.  I hope to get both springs out of the respective valves for examination before i depart.

Really appreciate all the help and advice.

I went back to Snowbum’s technical articles and re-read the $2000 O-ring information.  From my read that doesnt apply to my 1975 R90/6.  You still nailed the approximate cost, with me doing all the work.

It looks like you bought a/5 crank. They will not fit in a/6 case the throws are bigger.

@8166 I have been out of town for a month taking care of grandkids, but..

I have checked the release valve in the oil filter reservoir and it seems to be fine.  Ive also checked the bypass valve on the front bearing carrier - also seems fine.

I talked to the vendor i bought the first crank and it was for a 1975 non-USA.  From what i have found, USA models went to the “1976” crank in 1975.  I sourced another used crank and have installed it and associated bearings. Replaced the thrust washers on the crank, setting the float per the recommendations i found on Brook’s airhead garage, attributed to Tom Cutter. I sourced used connecting rods and installed them with new bearings.  Decided to install the Siebenrock 1000cc upgrade kit, so i have done that.  Oil pump specked out fine, but...replaced all those parts just because also replaced the oil pressure sensor switch.  Engine is now reassembled, sitting on the bench in my garage.  I’m waiting for grandsons to come over and help me lift and install in the frame.  I hoping for that to happen this weekend.

At this point, given that everything seems to work, I’m “assuming” I ran it low on oil (I’m embarrassed to admit that might be true).  

Once i have it in the frame, I will installed the diode board, points, etc, install the tank and carbs and start her up and see how oil flows (or doesn’t). If i validate that things are OKI, ill finish assembling the bike.  If oil doesnt seem to be flowing correctly, then Ill take it apart again.

I got this bike from a friend’s wife, after he died and I’m fixing it in his honor, having a lot of fun and learning a ton.  I have other bikes to ride (K1600 and GL1800) so there isn’t a time frame, just when its done.

Thanks for all the help and advice.

Corey

Posted by: @14517

Once i have it in the frame, I will installed the diode board, points, etc, install the tank and carbs and start her up and see how oil flows (or doesn’t). If i validate that things are OKI, ill finish assembling the bike.  If oil doesnt seem to be flowing correctly, then Ill take it apart again.

The traditional way to do this is to install the crank journals covered in motor oil, STP, or some type of engine assy lube. Then, when the engine is back in the frame and everything is connected back up, with the spark plugs removed, allow the electric starter to turn the engine over until the oil pressure lamp goes out. That can only happen when the oil galleries (including the oil filter) are completely full of oil and the pressure has risen to at least 5 psi. 

Hope this helps.

@wobblyI did use assembly lube on all the journals when putting it back together.  Thanks for the tip on running the engine without plugs to let the galleys full with oil.  I was kind of wondering how to “prime” the oil pump and get oil flowing, so that helps a lot.