Replace piston only or entire head?

xenogears

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Location
Fairfax, Virginia
So had the 5ive-t up and running yesterday and ran it for a fairly long session, until it bogged down and died out of nowhere. Was running so well right before it died which makes me think I probably lean seized it somehow or overheated. My first suspicions was dirt getting sucked in due to how dusty it was and the length of the run, but engine looks pretty clean beyond the air filter.

Tried to start it again today, seems to have the same compression as if nothing happened.
Shouldn’t I have lost compression if seized? Or was the piston supposed to get stuck? Can’t remember what’s the expected behavior after a seize, but it sure won’t start up :)

Pulling it apart, I see the piston has some scoring marks. However, the cylinder seems just fine, seems to be silky smooth all over from a visual test/running my finger nails around it.
It’s stock zen32 with a little less than 7 gallons run through it so far.

My question is should I replace the whole head or just piston+ring+gaskets? I have a full rebuild kit but wasn’t sure if I’d be wasting a cylinder for no good reason.

Some of the differences in this run:

1. It was quite cooler yesterday afternoon around here compared to the runs I was doing earlier in the week and before.
2. Just installed an outerwear over the crank. I noticed that the outerwear overall for the 5ivet cage caused me heating in the past and ended up removing it, Makes me wonder if this outerwear made things a little more toasty as well.
3. Had an iffy pull starter that I knew would not pull had I stopped the truck between tanks. So instead of having the 10 minutes or w/e it takes me to refuel and the engine to cool down a touch, I just had her running non-stop. Blew up a little bit after the fifth refill (2h11m to be exact).
4. Chassis is a little tweaked (awaiting replacement), but not causing any issues with driveline that can in turn affect the engine, I believe. 5DF65123-8178-4349-A5FB-CF7DBF03266B.jpeg 5DF65123-8178-4349-A5FB-CF7DBF03266B.jpeg 4589F22F-FFD3-48E4-8951-5462F71525F9.jpeg 691587DB-F98F-46C4-879A-4D2BD07B5204.jpeg C871D7E9-76E5-4325-8D27-5E44336DBA0F.jpeg 8079DA13-A67E-4977-BC90-0F396B15FFC1.jpeg 96B4120F-9CFC-4723-BF20-22842FDF628B.jpeg 88413B7D-CB63-461C-997B-6A9174104486.jpeg 8BF0441A-57FC-4FFB-A485-2C9A73FC3C22.jpeg 9834C992-58D7-464C-95C5-843D4261E599.jpeg
 
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Z.hb71

♥️ Rednecks 😆🤦‍♂️
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So had the 5ive-t up and running yesterday and ran it for a fairly long session, until it bogged down and died out of nowhere. Was running so well right before it died which makes me think I probably lean seized it somehow or overheated. My first suspicions was dirt getting sucked in due to how dusty it was and the length of the run, but engine looks pretty clean beyond the air filter.

Tried to start it again today, seems to have the same compression as if nothing happened.
Shouldn’t I have lost compression if seized? Or was the piston supposed to get stuck? Can’t remember what’s the expected behavior after a seize, but it sure won’t start up :)

Pulling it apart, I see the piston has some scoring marks. However, the cylinder seems just fine, seems to be silky smooth all over from a visual test/running my finger nails around it.
It’s stock zen32 with a little less than 7 gallons run through it so far.

My question is should I replace the whole head or just piston+ring+gaskets? I have a full rebuild kit but wasn’t sure if I’d be wasting a cylinder for no good reason.

Some of the differences in this run:

1. It was quite cooler yesterday afternoon around here compared to the runs I was doing earlier in the week and before.
2. Just installed an outerwear over the crank. I noticed that the outerwear overall for the 5ivet cage caused me heating in the past and ended up removing it, Makes me wonder if this outerwear made things a little more toasty as well.
3. Had an iffy pull starter that I knew would not pull had I stopped the truck between tanks. So instead of having the 10 minutes or w/e it takes me to refuel and the engine to cool down a touch, I just had her running non-stop. Blew up a little bit after the fifth refill (2h11m to be exact).
4. Chassis is a little tweaked (awaiting replacement), but not causing any issues with driveline that can in turn affect the engine, I believe. View attachment 63601
If it was seized the engine wouldn't be able to turn over. I think you overheated it. Personally, I'd try a new piston, ring and gaskets first as that cylinder looks completely fine.
Also a new plug
 
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cbaker65

Takes pipe💈 from stranger's 😨
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Is that a wear on the piston ,If it is ,I would inspect that bottom end for slop!...:unsure:
 

Seandonato73

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Does the piston only have that one mark? Or are there 3 others like it?
I'd it's only that one mark, or two Mark's on that side, it's a heat seize from not letting it warm up right before getting with it. Normally you would see it on the I take said as well, but not always. I don't see anything wrong with any other parts you've shown us.
 

xenogears

Well-Known Member
Messages
47
Location
Fairfax, Virginia
Does the piston only have that one mark? Or are there 3 others like it?
I'd it's only that one mark, or two Mark's on that side, it's a heat seize from not letting it warm up right before getting with it. Normally you would see it on the I take said as well, but not always. I don't see anything wrong with any other parts you've shown us.
There are 2 identical looking marks, both correspond to the exhaust (left and right). Not sure if it’s a warming up thing though, engine was running non-stop for more than 2 hours at that point :unsure:
buy an esp 32 ported head kit👍🏻
The spare I have on hand is a simple stock head :)
Great point though, I’m just a little hesitant. Still scarred from mod engine reliability issues I had the last time I was in the hobby.
 
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Rep732

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If you have marks on that piston theres gotta be equal damage on the cylinder...new upper kit call it a day..plus its a 2 stroke..running these things at all you have to keep in the back of your mind that any point of running these will be cause for a rebuild if they fail.
 
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Seandonato73

Mr mono shock🤦‍♂️😭
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It's a 2 point heat seize, I see it in saws a lot. It wasnt warmed up enough when you first started running it. The cylinder doesn't expand at the same rate at the piston. So the piston kisses the cylinder right on either side of the exhaust port. It doesn't really damage anything but the piston. Likely the ring looks just fine as well.
If you have marks on that piston theres gotta be equal damage on the cylinder...new upper kit call it a day..plus its a 2 stroke..running these things at all you have to keep in the back of your mind that any point of running these will be cause for a rebuild if they fail.
The cylinder is much harder then the piston or the ring. I've honestly taken pistons out that were more or less glued into the cylinder and cleaned up the cylinder and ran it. You would be amazed how far a cylinder had to be before its junk. I have a 90cc jug down in the basement that was straight gassed, piston looks like someone took 20 grit sand paper to it. Cylinder cleaned up beautifully. Nicasil. And chrome plating are very hard. As long as there are no deep gouges the aluminum transfer can easily be removed if need be. There are no signs of transfer in his cylinder, which again is consistent with what I said was wrong.
 

xenogears

Well-Known Member
Messages
47
Location
Fairfax, Virginia
It's a 2 point heat seize, I see it in saws a lot. It wasnt warmed up enough when you first started running it. The cylinder doesn't expand at the same rate at the piston. So the piston kisses the cylinder right on either side of the exhaust port. It doesn't really damage anything but the piston. Likely the ring looks just fine as well.

The cylinder is much harder then the piston or the ring. I've honestly taken pistons out that were more or less glued into the cylinder and cleaned up the cylinder and ran it. You would be amazed how far a cylinder had to be before its junk. I have a 90cc jug down in the basement that was straight gassed, piston looks like someone took 20 grit sand paper to it. Cylinder cleaned up beautifully. Nicasil. And chrome plating are very hard. As long as there are no deep gouges the aluminum transfer can easily be removed if need be. There are no signs of transfer in his cylinder, which again is consistent with what I said was wrong.
You might be right I tend to warm up for a good 10 seconds before ripping it. The cylinder is pretty much clean I looked really hard for any signs but couldn’t find any. It’s too late now anyways already replaced the piston and bolted it up :cool:
Seems to start just fine, so will see how it goes just need to do that boring break-in thing again...
Thanks for the support gentlemen
 
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It's a 2 point heat seize, I see it in saws a lot. It wasnt warmed up enough when you first started running it. The cylinder doesn't expand at the same rate at the piston. So the piston kisses the cylinder right on either side of the exhaust port. It doesn't really damage anything but the piston. Likely the ring looks just fine as well.

The cylinder is much harder then the piston or the ring. I've honestly taken pistons out that were more or less glued into the cylinder and cleaned up the cylinder and ran it. You would be amazed how far a cylinder had to be before its junk. I have a 90cc jug down in the basement that was straight gassed, piston looks like someone took 20 grit sand paper to it. Cylinder cleaned up beautifully. Nicasil. And chrome plating are very hard. As long as there are no deep gouges the aluminum transfer can easily be removed if need be. There are no signs of transfer in his cylinder, which again is consistent with what I said was wrong.
Very good explanation.
 
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