Any thoughts on this in cylinder compression waveform. 500 Single cyl ATV

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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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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.

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?

Valve clearance is in spec. See attached ignition trace. This is idling and then it quits.

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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-out-and-die-after-a-little-driving.504969/


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

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.

Yeah, I wish I had more insight to offer. Do me a solid and post any updates as to move through this project.

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??

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.

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.

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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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?

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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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=popcorn.gif]

I considered taking a side gig at a local powersports dealer before. I  wondered if that would be a decent change of pace from the auto side.

So, for those interested it was a badly worn exhaust rocker and cam lobe. See attached picture. Piston and cylinder are in reasonable shape. Head needs intake valves and the seats need to be cut.

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James, so glad to hear. And being a neophyte at compression wave forms, I feel good I was in the ball park. But I do think Trevor brought up a thought that I never would have. That was some serious wear but I think the capture headed you in the right direction. Over time if WE, see enough captures like Harley Mike, we can almost 95%  of the time hit it pretty close. This is really nice for the customer before he spends a bundle on guess work.                                                                  
For me as they say, even a blind squirrel finds a nut once in a while.

Hope shop is doing well and keep posting, all solid stuff.

TrevorSchlientz wrote on Jan 23^rd, 2024 at 7:18am:

I considered taking a side gig at a local powersports dealer before. I  wondered if that would be a decent change of pace from the auto side.

Trevor, I think you would enjoy it, and I guarantee you they are looking at this stuff with nothing but a scanner, and even that probably not very well. JMO.

Or at least offer to look at one of their problem childs, get a feel. James here is at the top of  his game but didn't come from the auto side so the learning curve is steeper for him. I notice not a lot of feed back so he is shooting in the dark.

I was helping a guy on  2012 BMW GS few months back, 02 sensor, MAP all of it as pretty much a Bosch system, and everything a guessing game and you need a BMW Scanner. But with a scope you are now coming from a different angle. JMO.

Thanks for the update James.

This was an interesting one.

I shoot a lot in the dark on medium and heavy duty diesels. Larry, has been helping me as well. Really a great mentor who is not afraid to help.

Hopefully we can get an after capture.

Intermittent wrote on Jan 23^rd, 2024 at 10:43am:

Hopefully we can get an after capture.

+1

It seems anytime we see a compression waveform that doesn't look like the classic form it is going to be time to learn why by taking things apart.

fisher wrote on Jan 23^rd, 2024 at 1:37pm:

It seems anytime we see a compression waveform that doesn't look like the classic form it is going to be time to learn why by taking things apart.

The upside, for in this case James, he tells the customer going in, we know we have valve train issue, do you want to pull the trigger and move forward? The wear on that cam is massive, a better question is what caused it?

And the capture will just be one more piece of history to use later on. James is a serious player, last I talked had a dyno, trying to raise the ATV world up to another level, hope he gives us an after capture.

Larry

StitchB wrote on Jan 24^th, 2024 at 12:03am:

The wear on that cam is massive, a better question is what caused it?

My theory is valve clearances too tight. The valve and seats wear down and then there is constant tension on the cam and rocker pad and no clearance for oil. It my experience machines like this are easily neglected for oil changes too so you get a year or more of degradation combined with tight vales and this is the result I would expect.

TrevorSchlientz wrote on Jan 24^th, 2024 at 3:50am:

It my experience machines like this are easily neglected for oil changes too so you get a year or more of degradation combined with tight vales and this is the result I would expect.

Just to add to that, most people just flat out run the piss out of them along with the neglect.

Thanks for the follow up!!

The sad thing is it is owned by a mechanic!!

James H wrote on Jan 24^th, 2024 at 6:51am:

The sad thing is it is owned by a mechanic!!

Now that is funny. If a mechanic why are you working on it.

Tight lifters. Back in the day my dad used to say about loud lifter. If you can hear them they aren't burning. A little different today but clearance is  your friend.

HarleyMike wrote on Jan 24^th, 2024 at 5:31am:

TrevorSchlientz wrote on Jan 24th, 2024 at 3:50am: It my experience machines like this are easily neglected for oil changes too so you get a year or more of degradation combined with tight vales and this is the result I would expect. Just to add to that, most people just flat out run the piss out of them along with the neglect. Thanks for the follow up!!

The term rode hard and put away wet would apply. JMO.

TrevorSchlientz wrote on Jan 24^th, 2024 at 3:50am:

StitchB wrote on Jan 24th, 2024 at 12:03am: The wear on that cam is massive, a better question is what caused it? My theory is valve clearances too tight. The valve and seats wear down and then there is constant tension on the cam and rocker pad and no clearance for oil. It my experience machines like this are easily neglected for oil changes too so you get a year or more of degradation combined with tight vales and this is the result I would expect.

Being that tight,would have thought you would have had a no start before we got this far.

StitchB wrote on Jan 24^th, 2024 at 10:41am:

TrevorSchlientz wrote on Jan 24th, 2024 at 3:50am: StitchB wrote on Jan 24th, 2024 at 12:03am: The wear on that cam is massive, a better question is what caused it? My theory is valve clearances too tight. The valve and seats wear down and then there is constant tension on the cam and rocker pad and no clearance for oil. It my experience machines like this are easily neglected for oil changes too so you get a year or more of degradation combined with tight vales and this is the result I would expect. Being that tight,would have thought you would have had a no start before we got this far.

Yeah, its not a perfect theory.  [smiley=idunno.gif]

Reply #4 says the valve clearance is within specs.

They could have been tight, and as the drive-ability of the machine got worse someone adjusted the valves (damage already done) to try and make it better.

I don't think that kinda wear happened overnight!