I just scored a CARF MX2

Tired Old Man

Staff member
Ring end gaps.

I removed the piston rings and inserted them into the cylinder with the ends aligned with where they would be when on the piston. I took end gap measurements for each ring at three places, as follows;
Top ring, top of stroke: 0.014", top of exhaust port: 0.015", bottom of stroke: 0.015"
Bottom ring, top of stroke: 0.014" tight, top of exhaust port: 0.015" tight, bottom of stroke: 0.013"

Note that 3w does not publish ring end gap standards. That would be kind of hard to do since they use several sizes of pistons and cylinders for each engine type and only one ring size to handle all of the sizes in that displacement. You can figure that somewhere between 0.018" and 0.020" is on the worn out side. new can be anywhere from 0.003" up to 0.011" depending on what day it was over there. They are not at all particular about consistency with end gaps on new engines.

This engine uses a twin ring piston design. The ring ends are offset ~40*-45* of arc so they work together to provide a pretty good seal in handling light damage. In this case I think they were doing a good job.
 

marksextra

Well-Known Member
Okay, I've done the exam
We'll start with the ring stop side of the piston. Plain and simple, someone, fairly recently, used a hard edged metal tool, similar to a small flat blade screw driver, to compress a piston ring. I say recently because the damage shows little evidence of run wear, and the damage removed per-established oil plating. I can't say who but that individual would be looking for a job if they worked for me. Fingernails work fine if the engine is on the bench or in your lap. Who dunnit? IDK, but it wasn't that long ago.
Could this have been done by Gerhard? I've never taken the cylinder off the motor. Gerhard can confirm that.

Mark, this next part is not going to make you happy, but I'm not going to lie to anybody. There was a lot of wire debris in the top end. I found several pieces of fine wire, consistent with what is found on a stainless steel wire brush on and inside the piston, and at to port plenum locations. There was also some bits of gasket sealant at a couple places, most notably the wrist pin boss. The locations this stuff was found was consistent with being drawn into the engine after something was cleaned with a wire brush.
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Why should this not make me happy? I also saw the wire particles before I sent the parts to you. I may vary well may be guilty of a bit of gasket sealant in a couple places; even though I was super careful. But it may be possible; especially if it's clear. But I NEVER used a wire brush. I don't even own one. That's the nice thing about not lying. You never have to worry about what you said prior. Where or why would you use a wire brush? To re-cap; I only scraped the gasket sealant off with a razor blade. Where would someone use a wire brush on a motor? Is this something Gerhard would have done? or are you saying you think I used a wire brush on the carb plate? I don't get it; sorry.
 
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Tired Old Man

Staff member
Final Analysis

In my opinion the damage incurred at the piston was not enough to generate a significant loss of RPM. A great many of you are using engines as this is written in worse condition. At most I can't see a power loss of much more than a couple hundred RPM, and that is probably a stretch. Someone running a 32-1 oil mix probably wouldn't notice any loss at all because of the improved ring seal with more oil. The scratches were definitely noticeable, could absolutely be felt, and they were indeed old.

Of greater concern is someone being sold a new top because of that damage. Sure, if i was looking at it from a new engine dealer perspective I would tell a buyer the engine had sustained some previous run damage, but I would not tell them they needed a new top. Depending on who I was I might or might not mention the plating void that had been there forever. Hell, I would run it in one of my own and not worry about it.

Ultimately, I'd keep it for a spare in the event I ever hit the dirt and broke something in a bad way. I certainly would not throw it away or consider it junk.

So Barry, you own a piece of it. Mark, I think you left a lot of debris there to get drawn into the engine, and you both got drawn deep into this due to the way some information came back from a dealer. That's my opinion anyway. As I said earlier, there's something here for everyone to be mad at me about, but that the story as I see it.
 

Tired Old Man

Staff member
Could this have been done by Gerhard? I've never taken the cylinder off the motor. Gerhard can confirm that.

Why should this not make me happy? I also saw the wire particles before I sent the parts to you. I may vary well may be guilty of a bit of gasket sealant in a couple places; even though I was super careful. But it may be possible; especially if it's clear. But I NEVER used a wire brush. Where or why would you use a wire brush? To re-cap; I only scraped the gasket sealant off with a razor blade. Where would someone use a wire brush on a motor? Is this something Gerhard would have done? or are you saying you think I used a wire brush on the carb plate? I don't get it; sorry.

1) It could have.

2) Actually, I was thinking you had used a wire brush on the carb stuff. Don't get excited, it's something many would do and I went there accordingly.
 
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marksextra

Well-Known Member
1) It could have.

2) Actually, I was thinking you had used a wire brush on the carb stuff. Don't get excited, it's something many would do and I went there accordingly.
First off. Thank goodness I took pictures of everything I did.

After that. In the first picture you can see the clear sealant used. This is what I had to scrape off. If you're seeing tiny bits of this; it could have easily been me.

In the second picture; the yellow arrow shows a razor blade that I used to scrape it off with. no wire brush.
 

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Tired Old Man

Staff member
I knew going into this I was going to end up the bad guy in one way or another. OTH, I just don't see how those scratches in the cylinder wall can justify a lot of RPM loss. I do think you got pushed into buying something you didn't really need. I've seen much, much worse and they still made acceptable power.
 

marksextra

Well-Known Member
2) Actually, I was thinking you had used a wire brush on the carb stuff. Don't get excited, it's something many would do and I went there accordingly.
Now if you're talking about the carb itself; you would be able to see if the part of the carb that seats against the carb plate had been wire brushed or not recently; or at all for that matter. The reason I ask is because we didn't use a brush. And if you can't see brush marks on that actual carburetor, then a wire brush was used somewhere else. Logically and by process of elimination; where could that be?
 

Tired Old Man

Staff member
It's possible the repair station could have set the disassembled parts on a dirty work bench. After I received them they remained in the bubble wrap, in the box, until I looked at them over my living room table. At that point they went back into the wrap and box until they went under the scope.

You have no idea how particular I am about foreign debris inside engine components. I used Scotchbrite and cutting oil on the top of the piston
 

marksextra

Well-Known Member
Of greater concern is someone being sold a new top because of that damage. Sure, if i was looking at it from a new engine dealer perspective I would tell a buyer the engine had sustained some previous run damage, but I would not tell them they needed a new top. Depending on who I was I might or might not mention the plating void that had been there forever. Hell, I would run it in one of my own and not worry about it.
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Ok. Here's the way I see it. We don't all have you to check our engines for us. (even though you somehow got sucked into checking this one. Thank you. ) For most of us, we have the manufacturer do it. They're the gospel because they fix thousands of them and they know their own engine; they made it. I know what you're saying though, and I get it. But when the manufacturer says the cylinder is bad; especially when it comes from an experienced one man show like Gerhard; what's a person supposed to say? Argue with Gerhard because there's a difference of opinions between two experts? On top of Gerhards word; I had no reason not to believe him especially given the increased rpm readings others are getting on their motors. There was no discussion about replacement; there was no pressuring me. He said the scoring was causing the loss of performance and the cylinder was trashed. It needed replaced. That was that.
 
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marksextra

Well-Known Member
Now two other things that puzzle me.

The first is the screwdriver damage near the rings. How the heck does that happen? I mean. If Gerhard is taking the cylinder off. He doesn't need to compress the rings right? Unless he put the piston back in the cylinder for some odd reason. I guess it's possible. Wouldn't he know better? Unless he just put it in there after he decided it needed replaced and didn't give a crap. I don't know. Just thinking out loud here.

The second thing I'd like to hear about is why Barry took the cylinders off. I'm not being a jerk asking either. I'm serious. There is no doubt in anyone's mind he has pieces to this puzzle and we don't know what they are. He wanted you to look this over. You did. I've provided ALL the information I can. We need more than I or you can provide.

Lastly; if the wire brush particles were not put there by Gerhard during him dismantling of the engine; then they were there during the run. What, if any, impact did they have in any damage that occurred?
 
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marksextra

Well-Known Member
There was a lot of wire debris in the top end. The locations this stuff was found was consistent with being drawn into the engine after something was cleaned with a wire brush.

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Could this have been done by Gerhard?
1) It could have.
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Could you explain if you think these particles could have been in there during the runs I made or if you think their location makes it more possible for a dirty workbench at AI to have put them there?
 
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Tired Old Man

Staff member
More the work bench. There was nothing at the top of the piston to suggest that anything had made it there and been bashed around. The stuff had not been there long.

Mark,

I only reported what I saw and what I know. As to who did what I can only state the two long grooves were old and likely picked up during ground operations like T/O and landing. As to why someone would use a screw driver to compress a ring on such a small piston, it happens all the time. Who dunnit is not something I can establish.
 

marksextra

Well-Known Member
More the work bench. There was nothing at the top of the piston to suggest that anything had made it there and been bashed around. The stuff had not been there long.

Mark,

I only reported what I saw and what I know. As to who did what I can only state the two long grooves were old and likely picked up during ground operations like T/O and landing. As to why someone would use a screw driver to compress a ring on such a small piston, it happens all the time. Who dunnit is not something I can establish.
Well, thank you for taking the time to look at the engine. I don't think you reported anything surprising; as the evidence up to and including your inspection supports your conclusion.:thumbsup: Maybe the one exception might be the potential amount of loss of power the scoring caused.(since you and Gerhard disagree)That number will not be known until I re-test the motor with the same prop. The average rpm was around 5700-5750 and Gerhard reported over 6000rpm during his test on (I think) he said a Beila. I was using a Mej. So the only sure way to know is by testing it again. It'll be a fun test though. Can't wait.
 
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red7fifty

BadAss Member
Pat, great forensics on your examination of Marks piston and jug, feels like I'm watching 20/20 or Dateline.
Your findings and report of such, seems very factual, without any BS. :thumbsup:

Now, for the B.S.......I host that on my blog page, :)
:prrr:
 

BVargas

3W Flyer
Now two other things that puzzle me.


The second thing I'd like to hear about is why Barry took the cylinders off.
Mark, Barry does not take engines apart. Reason,,, he never flew it enough and he would rather have a new engine than change out spark plugs because he's a multi Billionaire.

just saying.


BV
 

marksextra

Well-Known Member
Mark, Barry does not take engines apart. Reason,,, he never flew it enough and he would rather have a new engine than change out spark plugs because he's a multi Billionaire.

just saying.


BV
Well. Not that I don't believe you but I'll keep my comments relevant to this discussion. I would rather Barry say that he's never taken it apart if he hasn't.

If Barry had this motor since new; which I was led to believe he had since you told me you thought the engine had less than 3 gallons through it; and he didn't take the engine apart as you say; then he must know who did take it apart or how these tool marks got on both cylinders.
 

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Mithrandir

Circus Staff
Lifetime Supporter
I am unaware of Barry ever taking the jugs off.... If for some reason he wanted the cylinder base
peened.. he woulda asked someone like Bill or Shuler to do it...

I have had much worse cylinder/piston scuffing with no apparent performance difference...
I didn't tach it b efore and after... but the plane flew the same.....
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marksextra

Well-Known Member
It was done around the entire cylinder base flange. I'm guessing it was manufacturer because there was absolutely zero remnants of any sealant in any of the stake pockets.
I am unaware of Barry ever taking the jugs off.... If for some reason he wanted the cylinder base
peened.. he woulda asked someone like Bill or Shuler to do it...
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Pat thought the peening was done at the manufacturer.
 
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