The Autonerdz Community Forums - in cyl compression

James H Senior Member Picogroup Offline Bike Nerd Posts: 165 Waterloo Ontario Canada Gender:	in cyl compression - thoughts Jan 17^th, 2024 at 8:16am Any thoughts on this in cylinder compression waveform. 500 Single cyl ATV
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TrevorSchlientz

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Re: in cyl compression - thoughts
Reply #1 - Jan 17^th, 2024 at 12:16pm

Tell us more about this machine and what's happening in this capture.

Are you looking for a specific fault or a cause for a symptom?

How are you achieving such a high cranking speed?

What happened at the 2 second mark where the compression suddenly rises?

The notch/slope at 24° ATDC is interesting. Its there when the compression is both low and high.

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James H

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Re: in cyl compression - thoughts
Reply #2 - Jan 17^th, 2024 at 12:27pm

It's a 2002 Arctic cat 500 Auto quad. The problem is hard starting, and when you get it running it will run for about 5 seconds and then shut off. Similar to if you shut the ignition off. However, spark still remains. It's a carb, and a fuelling problem was ruled out. You can restart it, but it will only run for 1 second or so and then shut off again. It's a bear to restart after that.

In the graph, the higher compression is wide open throttle. The lower humps are with the throttle closed. Cranking speed has been achieved via a remote starter on the end of the crank, as the electric start is trashed on the unit.

There is a decompressor, however with the high cranking speed, it's not a factor.

We checked for a plugged exhaust, however both the muffler and pipe are free flowing.

We also did a leakdown test, which had 20% leakage. Checking through the entire range of the stroke provided the same result. The air filter in the unit was trashed and there was dirt ingested in the intake. It has been cleaned out now.

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TrevorSchlientz Autonerdz Administrator Picogroup Offline I'm an Autonerd Posts: 1,403 Grand Rapids Michigan USA Gender:	Re: in cyl compression - thoughts Reply #3 - Jan 17^th, 2024 at 1:12pm Have the valve clearances been checked? All throughout your capture it looks like the cylinder has a leak with the leaning towers. Do you have any other captures? Secondary?
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James H Senior Member Picogroup Offline Bike Nerd Posts: 165 Waterloo Ontario Canada Gender:	Re: in cyl compression - thoughts Reply #4 - Jan 17^th, 2024 at 1:42pm Valve clearance is in spec. See attached ignition trace. This is idling and then it quits.
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TrevorSchlientz

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Re: in cyl compression - thoughts
Reply #5 - Jan 18^th, 2024 at 1:10pm

Just getting into the secondary capture and I can't see anything that seems important. I'd like to see the flywheel that is responsible for generating some of those signals.

Did a like Google-fu to learn more about this machine and found something that seemed interesting. The short answer from the following link is that the O.P. had a failing voltage regulator that was causing his machine to die. (Take with 1 tsp salt. Its the internet after all.)

https://www.arcticchat.com/threads/solved-2002-500-4x4-automatic-decides-to-cut-...

Do you have a pressure transducer? Do you have any credible way to check the spark timing?

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James H Senior Member Picogroup Offline Bike Nerd Posts: 165 Waterloo Ontario Canada Gender:	Re: in cyl compression - thoughts Reply #6 - Jan 19^th, 2024 at 7:53am Trevor, thanks for looking at this. I am pretty sure that ignition isn't a problem. I think its mechanical based on the compression waveform. I think I need to pull it apart.
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TrevorSchlientz Autonerdz Administrator Picogroup Offline I'm an Autonerd Posts: 1,403 Grand Rapids Michigan USA Gender:	Re: in cyl compression - thoughts Reply #7 - Jan 19^th, 2024 at 11:55am Yeah, I wish I had more insight to offer. Do me a solid and post any updates as to move through this project.
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StitchB

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Re: in cyl compression - thoughts
Reply #8 - Jan 19^th, 2024 at 5:11pm

James, is this a 2 stroke, thought it was? That said when it is up and running the tower actually does not lean at the top 1/3 of the capture, again have never looked at 2 stroke wave form if again it is 2 stroke. If this is a reed valve, (have no idea) From the top 1/3 down it bulges out, again if coming down off compression what does this mean, vacuum changes. That also stated the base line of PSI drastically change from low RPM to high, again if a two stroke maybe that is the way it looks.

The compression release, how does it work??

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HarleyMike

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Re: in cyl compression - thoughts
Reply #9 - Jan 20^th, 2024 at 2:51am

StitchB wrote on Jan 19^th, 2024 at 5:11pm:

James, is this a 2 stroke, thought it was? That said when it is up and running the tower actually does not lean at the top 1/3 of the capture, again have never looked at 2 stroke wave form if again it is 2 stroke. If this is a reed valve, (have no idea) From the top 1/3 down it bulges out, again if coming down off compression what does this mean, vacuum changes. That also stated the base line of PSI drastically change from low RPM to high, again if a two stroke maybe that is the way it looks.

The compression release, how does it work??

I believe its a 4 stroke.

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James H Senior Member Picogroup Offline Bike Nerd Posts: 165 Waterloo Ontario Canada Gender:	Re: in cyl compression - thoughts Reply #10 - Jan 20^th, 2024 at 3:44pm Hey Larry, it is a single cycle 4 stroke carbureted engine. The decompressor is automatic and holds the exhaust valve open slightlty during the intake stroke to reduce cranking compression. You can not see it in the waveform as I am turning the motor over with a remote starter and the rpm is too high.
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StitchB

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Re: in cyl compression - thoughts
Reply #11 - Jan 20^th, 2024 at 8:27pm

James, okay that clarifies it. What I see and will have some others look is very high compression. Never seen that in a gas engine, not saying it isn't . And is it high because I don't see the exhaust valve opening at all. Or better put 1/3 the way down from compression what I see is it being pulled open, JMO. That stated the attempt of the exhaust valve to open is late, as you stated I don't see plugged exhaust because basically I don't see exhaust. Over head Cam, I have no Idea, but that is my opinion. I know subaru Cams can break.

Almost like a valve spring coming and going or a seat coming in and out. Think the head needs to come off. Would like to know the outcome.

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TrevorSchlientz

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Re: in cyl compression - thoughts
Reply #12 - Jan 22^nd, 2024 at 1:59pm

That hitch in the expansion stroke makes me think that the crank slowed down, not that a valve opened.

Considering that anomaly is at 135 psi and is illustrated as horizontal-ish I would take that to mean there was 135 psi for a longer period of time.

What if this engine is binding up?

What I would give to have a 60 tooth crank sensor and tone ring on every engine....

I wonder if we could have used the amperage through the auxiliary starter?

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StitchB

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Re: in cyl compression - thoughts
Reply #13 - Jan 22^nd, 2024 at 3:45pm

Trevor, very interesting, great observation. That said, what if the device turning it is actually producing that anomaly, and not the subject we are testing. I Suppose if binding what in the system , (the motor) is the culprit. Once the head is off, or the plug is out, does it turn with no hitches.

Initially I asked if this was a 2 stroke, my thought being they are known in the fueling process to have piston slap, just thinking out of the box. I also googled this motor and thought it to be a twin, James states a single.

I originally had some contact with James as I have bikes and email from time to time when confronting a question.

He has a dyno and was cognizant of the complexity of the later model bikes, and in truth many of the shops really aren't up too speed like the automotive circle, that is why purchased the pico.

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TrevorSchlientz

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Re: in cyl compression - thoughts
Reply #14 - Jan 23^rd, 2024 at 7:16am

StitchB wrote on Jan 22^nd, 2024 at 3:45pm:

Trevor, very interesting, great observation. That said, what if the device turning it is actually producing that anomaly, and not the subject we are testing.

Thank you. I think you're onto something there.

I think all we can do now is sit back and wait for James to give us an update. Smiley

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