Sunday, October 23, 2011

1956 BMW R50 barn find recommision

About late spring I arrived at the shop to find that Duncan had bought a 1956 R50 BMW barn find. The owner had moved to the West coast and the bike had been in storage for 38 years here in New England. It was heavily caked with black crust from the dust, mouse traffic and years of neglect. But the overall patina was perfect by my way of thinking. In fact you don't see them left close to how they were found.
After a bit of arm twisting Duncan reluctantly agreed to sell it into my care. Obviously a bath would be a good thing but a full on restoration of repainting, chroming and dent pulling would be out of the question. I'll try to leave it as close to the condition Duncan found it and just do repairs that will make a safe road worthy machine. Since the R50 has a magneto ignition a quick check for spark gave good encouragement for a rapid fire up. The engine still had oil and after checking the float bowls were clear I tipped some gas into the bowls. Several kicks later it fired up and gave a short but enjoyable ride around the shop parking lot. Good show for 38 years of sleeping!

After a good soaking to removed the years of filth and mouse droppings buildup, I removed the bars and seat for preservation. The bars had a cool reflective strip on the cross bar but were quite damaged and not safe for street use. The seat would last a few miles before turning into dust. Rather than put a new set of chrome handlebars which would stick out I chose to use a set that was black so at not to detract from the overall patina of the bike. An aftermarket sprung saddle will work until a more appropriate seat is found.
Of the few things that needed to be addressed were the several fluid fill and drain plugs; many were stripped and bodged with wooden plugs. Almost every one of them had seen some sort of abuse. The first one to be dealt with was the oil pan. The drain plug was filled with a tapered pluming fitting so the pan would need to be replaced. After draining the black gold from the crankcase it became clearly evident that the slinger rings will need to be addressed first.

Almost every time you find a pre-1969 BMW motorcycle count on doing a slinger ring cleaning. The slingers are the only filter after the oil pump strainer/pickup. There are two slingers, one on each end of the crankshaft and BMW meant for these to have a service interval in which the engine would be stripped down to the crankshaft. Its a time consuming job needing some special tools to get the job done. Cycleworks in Kansas sells a wonderful kit that has all the tools need for the job []
Here's a view of the timing gears. The upper gear is for the cam this also hold the breather disc for the crankcase. The lower gear is for the oil pump, mind if your doing this job that the retaining nut is left hand thread. In the center is the steel timing gear and bearing. The gear is on with some authority so use a heat gun and get it good and hot before you remove it. Also underneath the small bearing there is a circlip and a few shims, these will need to be removed before you pull the gear. The small bearing just pries up and off.
A fun little find that kept in following with the fill/ drain bodge was the mismatched pistons. Even the wrist pins were of different weights too. It was running on an overbore and needs to go up the next level if these barrels are used. I'll use a set of less worn out pistons and barrels with new rings in the meantime until I can find a set of pistons and a place to rebore the barrels.
After the main bearing carrier is removed you can see the front slinger ring and that its filled with debris in the next picture.
The early cam followers seem to ride full on the cam, later cam lobes are thinner so that the follower only ride to one side of it. This helps rotate the follower and keep the wear to a minimum. The followers were dished and worn though the hard face. I'll use a later cam and reconditioned followers.
With the two cams side by side you can see the difference in the spacing of the lobes. The cam on the right is the early R50 cam whereas the cam on the left is a later R50/2 part.
With everything stripped down and cleaned up for the reassembly. Happy parts, happy times.
The crankshaft installed into the case. Don't forget to put the shims between the front slinger and the main bearing carrier.
Front bearing carrier and oil pump gears.
Front bearing carrier being pressed onto the crankshaft with the Cycleworks tool.
The heads were well worn out and needed exhaust thread repairs so I robbed a reconditioned set from my 1959 racing R50 engine project. In fact, that where alot of the parts came from; crankshaft, barrels, pistons, oil pan, cam, cam followers...etc. Better to get and keep a good solid machine on the road than to let bits sit on the shelf waiting and dreaming for someday.
The next stage was to tear into the transmission to fix both fill/drain plugs. Getting into the trans was not disappointing. The output flange had spun on the the shaft and both needed to be replaced. all the bearings needed replacement along with all seals which will allow the use of 80w90 gear oil. Removing the shift lever to replace its seal revealed that the lever has a small crack just like the kick start lever.

So with the engine and transmission ready to go back into the frame the old R50 is well on its way being a zen experience on the back roads of New England. Now all that needs to be done is the final, wheels, swing arm, head bearings.... etc.
There is a side comment and observation that I would like to make about this project. There is a fine line of preservation versus repair or restoring a old machine. In this situation I felt that the condition and patina should be left mostly alone. There are some things that had to be changed due safety concerns, unpractical use, or even just plain worn out. But overall, my feelings were to leave as much as is.
On the other hand it would be easy for someone to spend the time and energy repairing the engine and transmission to the point that they would logically move to the next step of painting the frame and bodywork; a logical step based on the money and time spent reconditioning the drive train. Some of the best intentions can go astray and one is left with a pristine machine devoid of imperfections yet they might be unwilling to ride for fear of damage having investing so much.
With all the repairs needed this machine would have been better parted out. Its condition not even worth a second thought for restoration but in my mind that is the best type of machine. I hope the next care takers enjoy it as well.

1 comment:

Emmet said...

great story! I feel the same way about my '71 Triumph Tiger- it runs excellent and has an aged patina about it. The paint's worn and cracked, the exhaust is ratty, and any/all chrome is pitted. If I were to invest the time and money into bringing it back to its original state, I wouldn't have ridden it 200 miles in the rain ;)