TOPIC:

Before you get crazy, do a comparison test on a "good" cylinder or two, so you can hear what air leaking past the rings (ie, coming from the oil fill/crankcase) sounds like. I did a similar test on mine (filled the cylinder with air, listed for the sound of it escaping), and ended up with what sounded like air coming from the crankcase.

Come to find out, however, that I got the same sound no matter WHAT piston I did that to, ie, you're going to get a bit of air leaking around the rings regardless. My problem ended up being completely unrelated, a bent connecting rod.

Get the ignition sorted first. Still curious about the low compression readings, but if you were having ignition issues on 2 and 5, that may be part of the problem.

There's something going on here with the numbers. You've got a low of 87 psi. and a high of 110 psi, BUT you should have around 130 psi. on a good tight engine, SO what's going on?
20% leak down across the board sort of makes sense with the numbers you're recording on the compression test, so being the Devil's advocate I'm going to suggest that your compression tester is recording lower than it should. One thing that a lot of people don't know is that the Schrader valve in the end of the hose that goes into the cylinder sparkplug hole, is not the same as a Schrader valve that is used in a tire valve. The spring which closes the valve is much lighter in the Schrader valve for the compression tester and if it's been changed out for a Schrader valve for a tire valve it will read low by about 30- 50 psi. The first thing I would do if I were in your shoes is replace the Schrader valve in your compression tester and make sure you buy on for a compression tester.

So can we assume that you checked for leakage at the carb and the exhaust pipe to confirm the valves are sealing?

20% leak down is not great but it's not bad enough to account for compression readings in the 80-95 psi range. 20 % of 130 psi is 26 psi. so in theory all things being equal, if you measured 104 psi on a cylinder of 20% leak down then both tests confirm the other's result.

The service manual is a little vague stating the compression ratio is 9.9 to 1 and the service limit for compression is 117 psi to 171 psi. But what you really want to know is what a tight engine should measure when brand new, broke in and a leak down rate as low as possible. So technically speaking a compression ratio of 9.9 to 1 "in theory" is atmospheric pressure which is 14.7 psi times the compression ratio 9.9 which comes out at 145 psi. Then you have to account for the intake valve closing after bottom dead center. So cylinder filling is not 100%. So I would expect the true compression reading should be around 130 psi. on a really good engine.

Just some things to consider. Hope this helps sort out your dilemma.

It is probably more than coincidence that the Dyna ignition wires to the number 2 & 5 coil burned. These are the same two cylinders that appear not to have a burn in them. Even with only 80 psi compression on those two, the exhaust pipes for them should get hot if the cylinders have the correct air/fuel mixture and a hot spark.

Maybe time to really scrutinize the ignition for cylinders 2 & 5, starting with the coil.

SIXPIPES wrote: Well I have carried out the test and can confirm that I have air coming from the oil filler case, however the readings were all around 20% loss. Did not make a lot of sense to me as 2 and 5 are only showing 80 - 87 psi on a compression test.
These will now have to wait anyway has my Dyna box started hissing and then a nice plume of smoke came flowing out - all the damage was around the output connector that sends the signal to the coil 2 - 5.
So now I will have to buy the German ignition kit and start again. Still not giving up though.
I do not suppose anyone has the blue Dyna ignition box for sale?

Any chance Dyna can repair the 2 burnt pins in your blue box (I suspect it's a Dyna 2000). If nothing else they would be interested in the fact that you burnt out the 2 pins and may be able to provide some insight here for you.

something is defiantly suspect with your engine, but we still don't know exactly what is going on. keep in mind a cold engine will often show lower compression than a warm one. Your leak down numbers are not so bad, but something still isn't adding up.

What are your valve clearances?

Did you call dynatek about repairing your ignition? They may be able to service it, it used the same components as the 4 cylinder ones?