6 replies [Last post]
mutater22's picture
Joined: 05/28/2008
Posts: 4

I am the new owner of a 1962 r/50. The left cylinder seems to run much hotter than the right. not knowing what to do,or what the problem may be. I grabbed the manual.
After reading the manual and looking at the spark plugs. the left side was grey in color and the right side was black. ( I dont know if that helps.)
I replaced the plugs. cleaned the carbs. replaced the gaskets. tried to tune in the carbs.( much better idle after that) but still the left side seemed to heat up faster and hotter than the right.
I also think the previous owner was running with no air filter. since it took me over an hour to dislodge the cover, which was rusted shut. and no filter.
I dont know if this will require a qualified mechanic, or if this is something I may be able to fix myself or if this is normal. I knew the engine would get hot tuning the carbs since we were stationary, and air cooled is air cooled, it just didnt seem correct.
This is a new realm for me, so please forgive my ignorance.
Any help would be greatly appreciated.

Thank you. bewildered BMW in mass.
a.k.a Kevin.

schrader7032's picture
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6896
hot cylinder

This should probably be posted under the Vintage forum so that others are sure to see it and offer their suggestions.

The cylinders should run about the same temp as you suggest. Most likely you have a difference in the carbs that's causing this...I would think the left one is running leaner than the right. Or maybe the right side is running too cool. You say the left plug was greyish (light tan is the color you're shooting for) while the right was black. Grey is not too bad but black would indicate too rich...or possibly oil fouled.

Did you confirm the settings in the carb, such as jet sizes and especially the position of the needle that sticks out below the slide? Do the floats actually float? You should measure how much of the needle sticks below the slide...it should be the same on both sides. The needles should be held in position by a small clip on top of the slide. You'll see a number of holes...these are used to position the needle up or down. If you see many holes above the slide, that's a rich condition. If you don't see any holes, that's a lean condition.

This website is a good one to consult for the /2...Duane has some good insight on these bikes.


Type carb into the search engine and look into how to balance the carbs. This is an important step to getting the bike running right.

How's the timing? You'll need to go through the steps to set the magneto timing, the static timing, and then to check how the timing is under higher RPMs. Also be sure the valve clearances are set correctly.

How many miles on the bike? What do you know about any of the previous maintenance history? The no-filter episode doesn't bode well. If there are significant miles on the bike and the slingers haven't been cleaned, this will be something to consider in the future. The bike has no filter system and the slingers are a way of settling out the larger particulates. If the slingers get too full, they can starve the bearings for oil. This type of work requires that the bottom end of the engine come out...it takes a certain amount of skill, knowledge, and tools to do this. Most people can disassembly the top end, but for my money, the bottom end should be left to skilled mechanics.

Unless there's some real nasty deep problem, these bikes will run fairly well even though they are not tuned within an inch of their life. But keep working at it...you should be able to do most things yourself with help like the above website and people on various forums.

Kurt in S.A.


Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

EuroIron's picture
VBMWMO #7266
Joined: 04/23/2007
Posts: 414
hot cylinder

from what I am reading it sounds like the right is a bit rich and the left a bit lean

one other thing you may wish to consider

retarded ignition timing will reduce chamber temp but increase exhaust temp

advanced ignition timing will increase chamber temp but lower exhaust temp

it is possible for the timing to be incorrect from one cylinder to the other

it would also be somewhat possible for one side to have it's valves opening much more than the other

so checking both valve adjustment clearance, as well as max lift at least, wouldn't be a bad idea

maybe somebody ran one side loose and ended up knocking a lobe or two down

will you need a "qualified mechanic" ???

that depends on you, these things are about as simple as any

mutater22's picture
Joined: 05/28/2008
Posts: 4
thank you

Sorry for posting in the wrong forum.
I would like to thank both parties for their help.
This forum has been most helpful to this novice.

Thank you again. I will let ya know how the repairs go.

Peace. Kevin. In MA.

Allan.Atherton's picture
VBMWMO #2709
Joined: 10/27/2006
Posts: 507
Re: hot cylinder

"mutater22" wrote:

I am the new owner of a 1962 r/50. The left cylinder seems to run much hotter than the right...

It sounds like you have not ridden the bike, only idled and revved it while troubleshooting. When riding, it is not easy to tell that one cylinder is hotter, and usually this is judged by pipe color. The fact that you can feel a temperature difference so easily at idle could mean that the right cylinder is not firing. Try pulling the cap off the left spark plug and see if the engine still runs on the right cylinder.

tricyclerob's picture
VBMWMO #6717
Joined: 10/27/2006
Posts: 70
hot cylinder

After reading your post, I had the impression you were running the engine while stationary for some time. I would strongly suggest getting a decent sized fan to place at the front of the bike to cool the engine while running/tuning . I don't think a small[12" type] table fan is enough. I use a 36 inch shop type floor model, but I know others have used squirrel cage type fans salvaged from a/c equipment. Either that or really limit the length of time you work on the engine while stationary, allowing for some cool dn.time. rj



"I like new stuff... especially after it gets old"

Bruce Frey
Bruce Frey's picture
VBMWMO #6316
Texas Hill Country, USA
Joined: 10/27/2006
Posts: 574
hot cylinder

To assist in troubleshooting, I would start with a set of new plugs.

If you have one cylinder that does not warm up as quickly as the other or runs cooler, try swapping the plugs wires and caps from one side to the other.

Do a compression test.

If the compression is close to the same in both cylinders and the plugs, wires and caps do not make a difference, I think you are down to carbs or differential timing.

Good luck,

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