This is a cranking compression waveform from a Suzuki DRZ400. I am trying to understand why it looks like this. The valve clearance was out, the 1 exhaust bucket and cam lobe is badly worn so obviously the valve timing is out. The engine was turning over very slowly and uneven as the starter is just about baked as well. I do not understand how it can have 2 peaks. It looks like the exhaust valves were not opening but they are, Any thoughts?

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James H wrote on Dec 23^rd, 2016 at 12:04pm:

the 1 exhaust bucket and cam lobe is badly worn

If the exhaust cam lobe is worn to the extent that the valve  is only opened for a short time the piston is still rising and against a sealed cylinder until the intake opens. IF the INTAKE opend at all.

Did you use the WPS500 psi range 1 in the library?

I wonder if the psdata file would help us here? :-/

Does the DRZ have a decompression valve? New to picoscopes but that may be your second peak.

James put your capture up so we can all take a look. :)

Here you are. A little history. Bike was brought in mostly disassembled for a valve adjustment only and I did an in cyl compression check before I took the valve cover off. - Bike had no flywheel pickup or stator, ign coils, cdi etc, as customer was doing some work on it.  ::) basically just the starter as far as electrical which was also on its last legs. So I couldn't reference the comp waveform to anything. It is really just a curiosity as to why it look like it does as the problems were obvious and have been addressed other than I am still waiting for cams.

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I looked up spec for compression on that bike, looks like it is supposed to be about 135psi. Looks like on your waveform that it is coming in around 144psi. Not really far off considering you said you have an exhaust bucket sticking which will make it hard for exhaust gases to get out.

Still not sure why you have two peaks but I am interested to see what this form looks like after you put your new cams in.

Sorry, don't know bikes.  Is this a four stroke engine?  Could you post up some system operation? :)

Hey I tried to look at the capture and I have the latest software.  Did you use the beta for this capture?  My Pico said it doesn't have the latest software. :)

Yes, it was the Beta software. It is a single cylinder 4 Stroke double overhead cam 4v engine. Cams operate the valves via a bucket and shim arrangement. Had a decompression release but had been removed as they were aftermarket cams.

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