Friday, September 23, 2011

Finding 8.5 degrees BTDC

This may be found in some shop manual somewhere, or might even be the steps in setting up the ignition timing on some vehicle somewhere in the world. But when I figured out how to re-mark the flywheel in the bike on my 1953 BMW R51/3 after having it lightened, I felt pretty smart.

When I had put my engine back in the frame after having a lightened flywheel put into the engine, it started right up and ran. But in-between 5000 and 6000rpm there was a hesitation, so I took a timing light to see if the timing was advanced or retarded.

For those that have never done this, BMW Motorcycle engines are similar to car engines as there are timing marks on the flywheel. OT is top dead center. S is 8.5% BTDC and the F mark is full advanced. You look through a sight window next to the oil fill and with a timing light, you can see when the spark fires at idle matching the S in the window. As the advance moves, you should see the F mark come into the window. When my mechanic transferred the marks from my heavy flywheel to the lightened one, somehow they did not transfer correctly. At idle the S mark was too far up in the sight window and no amount of adjustment would put it where it needed to be.

Because the advance unit is keyed into the magneto, to make an extreme timing change you have to remove the magneto from the cam shaft nose and rotate it the appropriate direction. This rotates the key way that the advance unit locks into. When I did this, you have to re-set the timing statically. So I set this all up and started kicking away. And Kicking and kicking and kicking. This really pisses you off, because just a half hour early the bike was starting with one kick. Now you are standing there and cursing because you start chasing something simple and now you are off into the woods with a bike that will not start.

After walking away, I was thinking that maybe the timing marks are off. This is the only thing in the whole equation that had changed. To test this I took the spark plug out, got a straw and stuck it in the whole and turned the engine over. And to no real supply while rotating the engine the straw continued to move out as the OT top dead center mark passed through the site window. So if top dead center was not where it was supposed to be, then 8.5 degrees before TDC was not either. And if 8.5 degrees is not where it is supposed to be then no start.

A call to my mechanic suggested remarking top dead center, then remarking 8.5% before TDC. The problem is making marks on a round flywheel which you can only see through a inch round window. My mechanic guessed that the window was about 4% so rotate the engine through 2 window lengths would get me near 8.5%. This didn’t seem like it was going to be too accurate.

It came to me as I was waking up. If the piston went from TDC to BDC in half a rotation of the flywheel, and knowing that the stroke is 68cm, then I know that moving the piston 68cm in the bore will turn the flywheel 180 degrees. So if I need to fine 8.5 degrees before TDC, I need to calculate the corresponding distance the piston needs to be in the bore before TDC. 8.5 degrees is going to be the same percentage of 180 degrees that Xcm from TDC is to the total stroke of 68cm. Calculating X would give me the distance in from TDC I had to measure to get 8.5 degrees before TDC on the flywheel.

Get the Head off, rotate the engine until the piston reaches top dead center. Calculate the % of 68cm which is equal to the percent 8.5 degrees is to 180 degrees and move the piston this measured amount down from top dead center and mark the flywheel.

Set the magneto body back on, advance unit with coil, static time it and one kick (well two/three) later it fires right up.

This was a triumph for me in that I was able to diagnose the problem, find the solution, implement to fix and the satisfaction of the engine firing right up. But this was short lived, as putting the timing cover back on, things did not line up and two parts that use to sync and mesh now grind and whine. This is what owning a vintage motorcycle is all about. Triumph and tragedy all within minutes of each other. So next weekend I will be out in the garage again, looking at the problem, making calls, searching the Internet. Hopefully there will be another triumph, one that is a little longer lasting.

Wednesday, March 31, 2010


This was taken from the discription of bike offered for sale at I have not been able to locate some of this information at any other place, but either way a great machine.

One of the most mythical competition bikes of the 50s, the fabulous BMW 500 Rennsport.The here presented bike is exceptional in several points: This is not only likely to be one of the very rare works type 256 with only 8 examples ever produced, but on top of it this one is in an exceptional running condition. It is frequently ridden by its owner during classic bike events.
In the 50s, the BMW factory produced 25 RS 54 type 253 and 8 type 256. The works type 256 shows the following differences to the privateer RS 54 type 253:* Oversquare engine (70 x 64.5),* Dell’Orto 37 mm carburettors with separate float chambers,* Double ignition (4 spark plugs),*

Earles forks with a straight rear section (instead of bended),* 5 speed transmission,* transmission shaft parallel to the swing arm,* hydraulic rear brakes,* front mud-guard fixed on the frame.
The exact history and palmar├Ęs of this bike are unknown. The famous rider Walter Zeller, official BMW racer from 1951 to 1956, rode the type 256 with success:German Champion 500 in 1951, 54 and 55.Vice World Champion 500 in 1956 behind John Surtess and the MV.Walter Zeller stopped competition beginning 1957. He participated in historic races in Europe from 1979 to 1988 with his loyal mechanic Gustl Lachermeier, who accompanied him throughout his career at the BMW race department.Gustl restored and prepared two marvellous bikes: a 1946 RS Kompressor and a Rennsport type 256 a with an oversquare engine from 1968.Following the owner of this Rennsport, it was also Gustl Lachermeier, who restored this bike in the 80s and it was used by Walter Zeller in historic races.
This extremely rare bike is available in Germany.

Following the book “Les BMW Rennsport” by the French Marc Muylaert, Walter Zeller used a works type 256 in the years 1954 and 1955.That type 256 had forks with straight tubes, and not curved ones like the 253. The transmission shaft wasn’t located in the tube of the swing arm but parallel, so that the reactions at braking and acceleration no longer pass by the swing arm itself, but by a long parallel rod supported by the frame. The rear mud-guard of the 256 was suspended on the frame, and not directly on the swing arm, where it would increase the weight of not suspended masses. Last but not least, the 256 was streamlined, which slightly increased its top speed.Regarding the engine, although it had many parts in common with the privateer bikes, the one of the type 256 can be distinguished by its measures, the larger valves, its cam shaft, the rocker arms and the air intake accepting Dell’Orto 37mm carburettors. The power was approximately 60 HP, which means about ten more than the 253.

The Technical Characteristics
flat twin air cooled, DOHC
494 cm3
Bore x stroke
70 x 64.5mm
2 Dell’Orto 37 mm with separate float chambers
5 speed
Diaphragm, Titan fly wheel
138 kg
24 l
2030 mm
670 mm
Wheel base
1370 mm
Heights of seat
700 mm
Top speed
225 km/h
65 HP at 9000 rpm
transmission is a 5 speed (4 speed on the 253).

Thursday, July 23, 2009

Door to Door transport, or close enough

I had been the high bidder on now "My R51/3" and had is shipped from Kansas to Washington. I will not name the carrier to save the innocent. The pick up went smoothly, mostly as I had no part in it. Waiting on the other end was a task. Days, then a week, where is it?

The day it was scheduled to arrive I took and extra long lunch to receive the bike at home. Door to Door service, made the seller and myself happy. The appointed time came and went. Calls to the dispatch did not reveal any more info as to when. More time, more calls. The final call to the dispatch office and they finally gave me the cell number of the diver.

"Hello, I am waiting here for you to deliver my bike."
“I am right in front of your house”
“No you are not, I'm in front of my house”
“I am right here in front of your yellow house”
“I am right here in front of my brown House”
“33rd street?”
“32nd street”
“I will be right there”

Here he comes pushing the bike around the block. “sign here and here, thanks” and there he goes walking back down the street.

Door to door was what I got, next time I will be more specific on which door.

A poem that explains it all

Please if you can tell me who to credit this poem to, I would like to give full credit.

My old BMW came to me in chests,
Each one an adventure, or was it just a mess.
A feast to feed the senses on, a puzzle for the mind,
Each one a rarest treasure, or was I really blind?

There were bits of perished rubber,
Bits of brass and steel,
Spokes and brakes and axles, and a pair of rusty wheels.
The seat was broke, the foot pegs missing, as were many other parts,
This bike is really quite complete,... well, maybe it’s a start.

There are no lights, the Speedo's gone, the mufflers are still missing, but
I'll get them from the local shop, but maybe that's just wishing.
So in my shed I'll labor, and work all through the night,
And if I'm very lucky just one piece will turn out right.

First I took the frame in hand, and checked that it was straight,
Then I put the front forks on, it started looking great.
What next I thought, then wheels in hand, I placed them fore and aft.
I hadn’t any tyers yet, it looked a little daft.

Then the engine to put in place, which way did it fit?
Where was the bolt that held it up? Maybe this was it?
Or maybe that's the one, I should have used before,
There are a hundred others lying on the floor

Then came the gearbox and the tank, the magneto it was next,
Hell it's nearly finished, I think I'll have a rest.
I'll make me, a pot of tea, and sit down by the sink,
Will it ever run again? I really had to think.

The big end's gone, the sparks are dead, the piston it seems broken,
So off I go to the shop they say.... You must be joking.
It's 50 years since we stocked those parts,..
Try that bloke in Woking.

So home I go, and on the phone, I ring around the country,
Then I ring around the world, Hell! this costs some money.
Then at last I find the part, the price is much inflated,
What do you expect the old man said, it's all correctly dated.

The weeks go by and turn to years, the bike at lasts completed,
I know the old girl will run, Ill not be defeated.
So of I go down the road, pushing for all I'm worth,
She fifes up and off I go there's no containing all my mirth.

Returning home as proud as punch, I stand there and admire,
She's working well all restored, I wonder who will buy her?
Add up the cost against the worth well there's some surprises
I'll have to keep her 50 years until the value rises¶

Wednesday, July 22, 2009


Within just a couple months of owning my 1953 R51/3 BMW, I had wanted to make it go faster. But to make a smooth running low capacity touring bike into race bike has always raised the question of "why?" There are some many other bikes that are so much closer to their racing background then the BMW of the 50's and 60's. Yes, BMW won the Isle of Man in 1939, but that was with a super charged Kompressor engine. Yes, the BMW sidecar was unbeatable all the way thru to the 1970;s. But those were overhead cam engines. It is often repeated that it only takes money to get HP. But that kind of money is spent on speciatly parts and skilled mechinest and mechanics to install and tune. Without the deep pockets to buy horsepower I went looking for those items that make the bike look faster. Aftermarket parts made by Ernst Hoske, like mufflers, hubs and tanks. I looked for tachometers, swinging pillions and fairings. My wish list is always changing with things obtained and things added.High on the list have always been Dellorto carbs. SS1 from the 1950's and 60's vintage to be precice. They had always been the carbs pictures on the most succesfull racing bikes of the time. Names such as Ducati, MV Augusa, Gileri, Moto Guzzi and others. The British bikes always had the Amal GP carbs, such on the Gold Star BSA, Nortons and Velocette. BMW had what looked to be Dellortos, but likley Amal Fishers, built under licence from British Amals.
The velocity stack was what always did if for me. Nothing screamed speed more them a set of velocity stacks. Long velocity stacks with no filtration, gulping in air and turning it into great sounds.
Carburators on BMW have a flange to mate up with the head, bolted top and bottom. I had heard of Dellorto made for BMW, SSFF. These were the SS1 carb. But had only heard of a few that had them. In all cases, people were either looking for help tuning them, or had given up in getting them to run. They would either idle, but not run. Or run like stink, but not idle. Either case, they were not user friendly.
The oppertunity presented itself and I jumped on it. The were offered at ebay, and waiting for the last moment, won the bid.
Now the getting them to run might be a new story. They are on the bike, they have gone to Bonneville to see what they can do, but they run.

Monday, July 20, 2009

Ernst Hoske

There are always those that want to make what the manufacture offers to the public a little better. They either wanted the original to look better, sound different, or go faster. Often this drive for change is in the pursuit of speed. I believe that this has been going on since the beginning of time.

For motorcycles there has always been those that took the original and went racing. These are usually individuals that made the improvements to their stock bikes to help them be competitive. By definition these privateers didn't have factory backing. With the exception of a few, these individuals have always filled out the start list, never finishing at the top of the finishing list. Those that do, often soon find themselves with factory support.

One such racer turned aftermarket supplier was Ernst Hoske. While searching for aftermarket parts offered under his name you find a few race results. He shows up in national races, never seeming to hit the podium on the international stage.

Hoske gas tanks are a highly sought after for BMW motorcycles. They appear to be offered for other makers, but those manufactures have not had the exposure or appear to have the volume of bikes remaining in use today. Hoske mufflers are an item that are offered in a reproduction today and there use is debated by Vintage BMW rider. Those that equate the BMW to smooth running and quiet tour wonder why someone would want these louder then stock pipes on the their bike. With removable baffles, and a reverse cone shape seen on many period racers, you can see that they were offered for those that might want the benefits of a better breathing exhaust offer, without concern for the decibels it created.

Other items offered were tachometers, handlebars, cams and valve springs. This image of the catalog courtesy of You can see the complete catalog in the media section, and some great pictures at this site dedicated to some great old BMW motorcycles.

Hoske offered a oil pan extension piece with tubes cast through the middle to add to cooling. Wheels were also offered, and are high up on my wish list.

It has been debated how much was manufactured by Ernst Hoske in house and how much were sourced from other vendors. Like many vintage aftermarket part, the name has been give value weather earned or not.

A place to find pictures of the many different Hoske tanks The page found on a open source encyclopedia says that Ernst retired after and accident and the business has transformed into "BMW Fuchs"
While searching for parts to make my bike unique, the name Hoske kept showing up. The tanks were huge, and expensive. Everyone wanted one. Those offered on ebay went to those willing to pay. I went searching internationally and did get one from, but it ended up being for a pre 1955 plunger frame R51/3 and would not fit (I would later get an R51/3 with a Hoske tank, wish I would have kept the tank, as it was in better condition.) Other ones offered in the states outside of auctions had asking prices for about half what I paid for the bike.
I did find a nice set of original mufflers, and after getting the jetting right, I have grown accustomed to their sound, and would side with those that believe in louder mufflers for these quiet tourers. When searching for something, you get to learn a lot about the person that created those items.

Can we guide the youth

I have had old BMW motorcycles since the birth of both my children, now 5 and 2.
Will this influence them in their choices of transportation in the future?
What lessons would a child learn growing up around vintage vehicles? Will it influence their sense of style? Their mechanical aptitude?
When I am out in the garage, they will pick up a wrench and want to help, but I don't want them to damage the bike, so they have a plastic wrench that they can use. I have not yet sat them down as I worked on the bike, pointing things out, and how they work.
Will it have the opposite effect. Will they want new things and turn their back on things that are old?
I grew up without vintage items and had posters of new exotic cars. Only when I got older did I grow to appreciate the vintage bikes.
I started with a 1974 BMW, the a 1968, the a 1953 and now I lust after a pre-war bike.
As every parent I am concerned about so many other things that may or may not influence my children. I want them to do the right thing at the right time. But I also what them to have a sense of the past, its place then and its influence on today. I think that it will give them a greater view of the world.