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marksd100
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Joined: 04/29/2017
Posts: 9

Bought a R50/2 about nine months ago that ran only off the left cylinder. Looking for thoughts on next step.

Currently two issues:

  1. Right cylinder runs but low power
  2. Pushrod tube moved out of head

With two young kids I don't get much me/bike time so my diagnosis and tune-up has been over many months. What I've done so far:

  1. Carbs: Rebuilt with new needles/jets etc and honed ports flat. Balanced carbs.
  2. Electrical/Timing: Replaced partially broken advance unit (mechanical). New plug wires and caps. Timed with timing light. Swapped plug wires left and right, including coil left/right trying to diagnose right cylinder issue. Left/Right timing within about 1/4 inch of timing line.
  3. Ran compression test and leak down. Low compression, air coming out of crankcase. Left (110) and right (90). Decided I'd try my first ring replacement so did problematic right cylinder. Took head to local machine shop that had done vintage BMWs. He determined it only needed honed. Put in new right cylinder rings and broke in for about 15 miles.

Here's where it gets a little confusing. It *seemed* to be running better on the right cylinder but maybe not. For sure now it is not. Compression on left still (110) and right side, with new rings, after warmed up 10 minutes is (55,75,85,90 per kick) - unchanged from before ring replacement! Exhaust temperature on problematic right side cooler (as always has been).

And now I have another issue because the one pushrod tubes pushed itself out of the head (see picture below). Strange because I didn't touch them since both were rock solid (so I thought) in the head and correct distance. Adding to this is that the leak down on that cylinder now results in air coming out of that split rubber grommet where the pushrod tube moved. This is with the oil dipstick out so no crankcase pressure.

Did I mis-assemble something? How could air from cylinder end up in pushrod tube? Do I have blow by past valve seats and valve sleeves? Is the pushrod moving a new unrelated problem to my ongoing issue with my right cylinder?

27,000 miles on odometer.

Sorry for long post.

-- Mark
1992 BMW R100GS/PD
1965 BMW R50/2
2005 Suzuki DRZ400S

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schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6540
Mark - What have you done for

Mark -

What have you done for setting the valve clearances? It would seem that you might have clearances that are too tight, holding open the valves and they don't seat. But you should hear that during the leaked down test. If the clearances are too tight, then air is going to escape out the intake (thru carb) or exhaust (out muffler).

Seems that the rocker tube wasn't properly "stuck" in the cylinder head, so it must have drifted. With the pushrod tube seal busted, I can see that air can escape thru there quite easily...that's a direct shot to the camshaft area which all part of the engine compartment.

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

marksd100
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Joined: 04/29/2017
Posts: 9
Hi Kurt, I've set the valve

Hi Kurt,

I've set the valve clearances several times both before the replacement of the rings and several times after since I also had to re-torque the cylinder head after run. They've never really been out of spec on intake or exhaust side.

Regarding air coming out, if I've got low compression, my simple understanding is that there are only rings and valves and spark plug hole that can allow air to escape the cylinder on compression. So if I've got air coming out the push rod tube, I assume that is valve seat problem?

-- Mark

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6540
If air is coming out the

If air is coming out the pushrod tube area, it must be getting past the rings to get into the engine compartment. New rings aren't going to be seated for 500-1000 miles.

As for the clearances, I'm assuming you know how all that goes having the GSPD in the stable. Most newbies don't seem to get setting the clearances at TDC on the compression stroke for that cylinder. Many times people get that wrong.

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

312Icarus
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Joined: 07/15/2016
Posts: 332
Pull the heads and have a

Pull the heads and have a look. Easy to do, and while you are at it you can repair the push rod tube seal.

Icarus

honard
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VBMWMO #9151
Fresno, CA
Joined: 08/03/2016
Posts: 2
Fix it already!

Put the wife in charge of the kids this weekend and get this figured out and fixed. I have to keep explaining to my R50 that in your typical fashion, a weekend job tends to last for ten years! There are many great rides up here that you are missing out on. VAMANOS!

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