Compression every other kick???? Schleicher Cam question.

[1967 R502]

So I am restarting a bike (R50S) which has not been run in a while, but is in excellent shape, always dry stored and the engine has always turned freely. It is equipped with a 328 degree cam. So 6 degrees more duration than stock.

Valves have been adjusted.
Timing is perfect and plenty of spark.

However I can get no ignition.

A friend suggested I go back and check the compression, which had some interesting results. I hooked the gauge into the spark plug hole, and compression only registered every other kick .. or thereabouts. I can get full compression, but the odd thing is that bit about it registering only every other kick.the condition is the same in both sides.

I could also feel this compression/lack of compression on the kicker itself, but I was putting that down to my own short comings.

So, if everything is to spec, the only way it could lose compression is if the valves were open when they shouldn’t be. Or so I am rationalizing.

Granted a sport cam will generally cause lower compression due to the increase in overlap, but this seems quite dramatic.

Being the cam is not stock, do the valve clearances change? I think not, but I’m hard pressed to think of another reason for this weird compression behavior, lack of ignition, and what the cure might be.

Btw, when I mean no ignition, I mean absolutely none. Not a burble. Not a peep. Even after dosing with ignition fluid all I could achieve was a single backfire through the carb after about 50 kicks. Which again only reinforced my position that the valves may be open when they should be shut.

Any thoughts on diagnosis or cure appreciated.

[therealkennyboy]

Was it was previously running with that configuration?

If you have spark and compression, the only thing you haven't mentioned is fuel. Are the plugs (hopefully new) wet after a few (50!) kicks? Did you go through the carbs?

[1967 R502]

Was it was previously running with that configuration?

If you have spark and compression, the only thing you haven't mentioned is fuel. Are the plugs (hopefully new) wet after a few (50!) kicks? Did you go through the carbs?

Yes, previously running.
Yes, carbs were completely cleaned, and the plugs are wet.

[schrader7032]

Seems like compression every other stroke/kick makes sense. It's a 4-cycle engine with a wasted spark ignition...intake-compression-power-exhaust. When one TDC mark comes by, it will on the end of the compression stroke for that cylinder. The next time the TDC mark comes by, that same cylinder will be on the end of the exhaust stroke...the other cylinder will be on the compression stroke. When on the exhaust stroke, the valves will be starting to close, thus no compression.

[therealkennyboy]

>Timing is perfect and plenty of spark.

Ignition timing, I assume. Have you confirmed the magneto timing is correct? If the field doesn't collapse at the correct time, the spark (even though nice and strong) may be occurring at the wrong time?

If it was running when put up, I wouldn't think any significant changes would be necessary to get it back up, just the 'standard' things (that you seem to have addressed)--fresh gas (flush the tank?), carb rebuild, new spark plugs, confirm valve clearances, confirm timing. New plug wires/condensor never hurts.

Seems like you're marching down the correct path--good luck!

[1967 R502]

Seems like compression every other stroke/kick makes sense. It's a 4-cycle engine with a wasted spark ignition...intake-compression-power-exhaust. When one TDC mark comes by, it will on the end of the compression stroke for that cylinder. The next time the TDC mark comes by, that same cylinder will be on the end of the exhaust stroke...the other cylinder will be on the compression stroke. When on the exhaust stroke, the valves will be starting to close, thus no compression.

Well, yes, but also no. The measure here is every other kick. A kick does not equal a crank rotation. In fact, I filmed it, and although it’s variable, one kick… a good one… rotates the crank 1.5 times.

[schrader7032]

I don't know about the ratio of kicks to engine rotation. But it stands to reason that while measuring the compression a given cylinder, that cylinder will only see compression after every other 360 degree engine rotation. I don't know how it works any other way.

[1967 R502]

I don't know about the ratio of kicks to engine rotation. But it stands to reason that while measuring the compression a given cylinder, that cylinder will only see compression after every other 360 degree engine rotation. I don't know how it works any other way.

That’s the problem. It doesn’t result in compression . So the valves must be open or…???

Think about it: a kick rotated the crank 1.5 times or 540 degrees. So during that cycle it must compress at least once. Yet the compression gauge and my foot both register nothing.

[1967 R502]

>Timing is perfect and plenty of spark.

Ignition timing, I assume. Have you confirmed the magneto timing is correct?

Timing is perfect. Differential timing could only be more exact if it were electronic.

However, the “compression question”.,,,

[schrader7032]

Have you checked compression statically? What about pulling the valve covers, removing the plugs, then putting the bike in 4th gear. Pull the rear tire around until you see the intake valve close on the left side. You are now on the compression stroke. Sit beside the bike and put your thumb spark plug hole. As you turn the rear wheel, do you feel compression building against your thumb? You should build compression as you approach OT. Repeat the same thing for the right side.