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1967 R502
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Joined: 01/25/2018
Posts: 19

For a while I've been suspecting my 1967 R50/2 has had compression issues. I did a conventional compression test and it looked like the left cylinder was weak. I followed this up with a leak down test today and what I found confuses me.

1. Engine warm, Air filter off, Spark Plugs out, Throttle open. Fly wheel is at OT. Bike is in 1st gear and I stand on the brake. 100PSi Compressed air goes in, and comes right back out the intake tubes!.

Say what? Intake valve is supposed to be closed at OT, right?

2. Thinking that the flywheel has slipped, or that some doofus (me?) mounted it wrong in in the past. I turn the flywheel to "F". Noise from the intake tubes stops.

3. So I check to see if the engine is really at OTC, the old fashioned way. A straw goes into the spark plug whole and I rotate the crank until I can visibly see that the piston is at the top...and guess what? It matches OT.

So what is happening here?

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6540
Only one side has the valves

Only one side has the valves closed...that's the side that is on the compression stroke...and you should be able to wiggle rocker arms. The other cylinder valves are not completely closed...that cylinder is on the exhaust stroke.

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

1967 R502
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Joined: 01/25/2018
Posts: 19
Thanks... however the air is

Thanks... however the air is coming out the intake valves not the exhaust valves. Which is quite puzzling

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6540
Well, I don't really know the

Well, I don't really know the state of exact valve positioning on the off-side cylinder. Could be intake is more open than exhaust??

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

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