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Eric Scantlebury
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VBMWMO #9275
Joined: 06/17/2015
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Hello all,

As the subject says, I have a cylinder that runs hotter than the other. Is this something to be concerned about or is it normal for these bikes?

capebretonmarkbmw
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Lean fuel mix will do it

When running correctly you will not see the header pipes getting the dark blue color. Mine seem to stay at yellow and a bit of purple and both the same.
If the hot side is also noisier than the other check the valve clearance . It is something to understand and fix so concern is a good word. Mark

schrader7032
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San Antonio, TX
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No, not normal but a few

No, not normal but a few degrees like 10-15 might be in the normal range. If one side is causing the headers to change color and not the other side, that's a problem. Likely you have an issue with the carbs...make sure that the jetting is the same and the carbs have been synched to run in unison.

Another possibility is that you might have differential timing. Since the ignition is a wasted spark situation, the point of firing for one cylinder can be significantly different than the other cylinder. You will need to see when each cylinder sparks relative to the S-mark. To do this, remove both plugs and put them back in the plug cap and lay them on the fins so that the threads are touching...this grounds the plug. Turn the engine on and rotate the engine by hand and as you near the S-mark, listen for the plug to spark and look at the S-mark and where it is. Then rotate the engine 360 degrees to fire the other side (remember both plugs will fire so you can stay on the left side) and again note where the spark is relative to the S-mark. The S-mark should be in the middle of the window for both sparks. If they spark at different places, and the difference is more than say 1/4 of inch, then you have a problem. There is a way to alter this timing, but one way to adjust the timing so that the sparks are evenly spaced either side of the S-mark. Otherwise, you might have one cylinder firing way to advanced or way too retarded. It's not that big of a deal at idle, but the problem is amplified and has worse consequences at full advance.

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

malmac
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Toowoomba, Australia
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also check your compression

I have a right cylinder which has 10% more compression than the left and I have bluing of the pipe on that side. I am going to replace the pistons to try and get back to an equal compression and then I will also worry about carbs and timing.

Mal

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mal - R69s
Toowoomba- Australia

smmotor
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Joined: 07/10/2015
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My left cylinder is hot also

Hi every one,

I bought 1964 R60/2 two week ago with not know history. I start maintenance bike than find out left cylinder running hotter. Bike start in first or second kick, idle perfectly. I checked both side carb for jetting and valve clearance every thing was correct. I have not check trimming yet, any other idea can be helpful.

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1942 BSA M20, 1957 TRIUMPH TIGER CUB, 1961 NSU QUICKLY, 1964 BMW R60/2, 1967 TRIUMPH BONNEVILLE, 1969 BSA A65 LIGHTNING, 1973 BMW R75/5, 1975 BMW R90S, 1993 BMW R100GS PD

808Airhead
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Air fuel mixture and timing

Air fuel mixture and timing will affect temperature.

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Thomas M.
R69s - R60/2 - R67/2 - R51/3

smmotor
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I Find out My left cylinder

I Find out My left cylinder timing is correct in idle speed show S mark with stroboscopic timing light. But right cylinder is not correct. How do I adjust that?

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1942 BSA M20, 1957 TRIUMPH TIGER CUB, 1961 NSU QUICKLY, 1964 BMW R60/2, 1967 TRIUMPH BONNEVILLE, 1969 BSA A65 LIGHTNING, 1973 BMW R75/5, 1975 BMW R90S, 1993 BMW R100GS PD

schrader7032
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San Antonio, TX
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How far off is the other

How far off is the other cylinder? Probably what you have is called differential timing. This is due to wear of the points/advance unit. If the difference is less than say 0.25", what should do is adjust the timing so that one cylinder fires a little before the S-mark and the other cylinder fires just after the S-mark. It's not good to have one cylinder so far off as the timing will be too far off and could cause damage or cause the cylinder to run hot.

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

Bruce Frey
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Texas Hill Country, USA
Joined: 10/27/2006
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If the pipe on the left is

If the pipe on the left is not bluing, it is possible that the right side might be running cold. Do the plugs read the same?

Bruce

butch housman
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Can we back up here, how do u

Can we back up here, how do u know it's running hot?

Is this from reading the spark plugs or r u using a high teck digital, laser guided IR snooper probe ?

Let's hear more abt ur troubleshooting techniques please.
Butch

smmotor
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I check advance unit and

I check advance unit and point every thing looks good bike has about 26000 mile not that much wear. I adjust magneto, now both cylinder timing in idle speed show S mark in window one cylinder is upper and another one is down, and when increase throttle both cylinder show F mark in window so advance unit working fine. This is a best adjust I can do for magneto. I check carbs for Air fuel mixture both is fine. piston compression for both is same about 90. But when bike is worm up, left side is hotter than right side I can hold my hand in top of valve cover for few second but left valve cover is too hot I can hold for one second. right carb is normal temperature but left side is hot also.

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1942 BSA M20, 1957 TRIUMPH TIGER CUB, 1961 NSU QUICKLY, 1964 BMW R60/2, 1967 TRIUMPH BONNEVILLE, 1969 BSA A65 LIGHTNING, 1973 BMW R75/5, 1975 BMW R90S, 1993 BMW R100GS PD

schrader7032
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San Antonio, TX
Joined: 10/27/2006
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What is the distance between

What is the distance between the two marks when running at idle? Is one mark at the very top of the window and one mark at the very bottom of the window? If the marks are too far apart, then you can easily have one cylinder running badly out of time to create extra heat.

At full advance, do you see both F-marks and are they the same distance apart as at idle? Or do you only see one F-mark and the other F-mark is out of the window, not visible? You may need to watch the marks as you slowly raise the RPMs so you can see the position of the marks when at full advance.

If the marks are too far apart, that differential timing can create your problems.

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

butch housman
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If the bike is on the center

If the bike is on the center stand then more hot oil will accumulate in the left side valve cover & that valve cover will be much hotter than the right one. No disrespect meant but I don't think u r clearly determining the temps by feeling it w/ ur hand.

#1 look at the spark plugs, what do they look like & r they the same color ???
#2 buy a cheap ir digital thermometer...abt $30 or so from harbor freight
U will find considerable differences in the temps 10- 30 degrees F even if all is well depending on just how u take the temps, which side has been in the strongest breeze etc.

I am very skeptical that u have a problem unless there is a noticeable difference in the color of the plug insulators. They should be a light brown color.

good luck
b

smmotor
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Here is some picture advance

Here is some picture advance unit, S mark for both cylinder and spark plugs

  • img_1478.jpg
  • right.jpg
  • left.jpg
  • img_1502.jpg
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1942 BSA M20, 1957 TRIUMPH TIGER CUB, 1961 NSU QUICKLY, 1964 BMW R60/2, 1967 TRIUMPH BONNEVILLE, 1969 BSA A65 LIGHTNING, 1973 BMW R75/5, 1975 BMW R90S, 1993 BMW R100GS PD

butch housman
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Ur plugs r badly fouled w/

Ur plugs r badly fouled w/ carbon so one can assume it's running very rich &/or u MIGHT have a very weak spark....probably not.

U do appear to have some differential timing issues, look on Vech's website (Benchmarkworks) for more info on that.

Agn, I doubt u have a temp problem, not w/ sooted plugs like that.

What have u done to the carbs ? Does it flood easily ? In general, how does it run ?
b

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