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Old March 22nd, 2016, 08:13 PM   #1
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Angry Melted a Hole in My Piston

This thread started as me trying to find out how much compression a ninja 250 should have, the book calls for 139psi - 218psi, and they need about 125 psi to run.

I discovered that my left piston melted do to a lack of coolant (no idea where the coolant went, but in the place of the coolant was a tablespoon of water). My valvetrain looks good, the right side looks good, and the jug can easily be honed. I am undecided if I want to take this as an opportunity to sink another $400 into the bike for a 13.5:1 93 octane build, or if I want to just buy a piston, rings, gasket kit, hone the cylinder, and get her running for some better action later.
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Old March 22nd, 2016, 08:18 PM   #2
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http://www.dansmc.com/compression_test.htm

Water in the carbs?
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Old March 22nd, 2016, 08:29 PM   #3
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I have no idea, but I want to eliminate compression first like you link said. I kinda also wanted to know what a stock ninja ran, because some bikes run a lot more than others.
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Old March 23rd, 2016, 07:54 AM   #4
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I learned the other day that valves way too tight can cause a loss of compression, because they're slightly cracked open when the cylinder is at TDC.
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Old March 23rd, 2016, 08:27 AM   #5
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what was the temperature when it died?
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Old March 23rd, 2016, 08:38 AM   #6
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well...

The pregen has 12.5:1 compression, no? Atmospheric pressure is 14.about 7 psi.

12.5*14.7=183.75.

But since you're using a gauge that reads 0 psig when at atmospheric 14.7 psi, you'll need to subtract 14.7 psi.

183.75-14.7=169.05 psi showing on your compression tester gauge, assuming everything is working under ideal conditions. Given what I've read online and what I've tested, 170 psi is a good number to shoot for.

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Old March 23rd, 2016, 08:45 AM   #7
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Book says 139psi - 218psi.
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Old March 23rd, 2016, 08:45 AM   #8
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This looks like for newgen

Link to original page on YouTube.

but 125 seems low. @ZacharyB may be on to something, How many miles on the bike? If you take the compression tester and if the type is the quick disconnect type, plug that to an air compressor. then you can bring the piston to TDC on the compression stroke, if you hear air coming out the exhaust- then look at those valves, if out the carbs then look at the intakes. If out the crank vent then piston or rings.

Drop a bit of oil down the spark plug hole- see if psi goes way up. - bad rings.

Hope it's just the valve adjustments are off

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Old March 23rd, 2016, 08:46 AM   #9
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Quote:
Originally Posted by choneofakind View Post
well...

The pregen has 12.5:1 compression, no? Atmospheric pressure is 14.about 7 psi.

12.5*14.7=183.75.

But since you're using a gauge that reads 0 psig when at atmospheric 14.7 psi, you'll need to subtract 14.7 psi.

183.75-14.7=169.05 psi showing on your compression tester gauge, assuming everything is working under ideal conditions. Given what I've read online and what I've tested, 170 psi is a good number to shoot for.

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Old March 23rd, 2016, 09:15 AM   #10
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I read 0psi on a compression test on both cylinders which makes my think bad adapter, I tried pushing about 20psi of compressed air with both valves closed, and it leaked fast somewhere, I didn't find out where, but I will take another look.

Side note, the oil reaks of what reminds me of spoiled gas, but I put fresh gas in the bike about 4 days ago when I pulled it out of storage. Also the right plug looks brand new (not white brown or black, its silver on the tip and the electrode looks brand new), the left plug is covered in carbon buildup.
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Old March 23rd, 2016, 09:20 AM   #11
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Quote:
Originally Posted by allanoue View Post
It was about 60° outside, I'm not sure about the bike temp, because my trailtech vapor isn't setup properly yet. It typically reads 19-20 when riding, it was at 23 when it died.
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Old March 23rd, 2016, 09:20 AM   #12
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Quote:
Originally Posted by HoneyBadgerRy View Post
I read 0psi on a compression test on both cylinders which makes my think bad adapter, I tried pushing about 20psi of compressed air with both valves closed, and it leaked fast somewhere, I didn't find out where, but I will take another look.

Side note, the oil reaks of what reminds me of spoiled gas, but I put fresh gas in the bike about 4 days ago when I pulled it out of storage. Also the right plug looks brand new (not white brown or black, its silver on the tip and the electrode looks brand new), the left plug is covered in carbon buildup.
One of two things:

You've only been running on one cylinder this whole time. If one is colored both should be colored.

The cylinder with the silver spark plug blew a head gasket and was letting coolant into the cylinder, which steam cleaned the spark plug.
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Old March 23rd, 2016, 09:26 AM   #13
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So leaky valves, funny smelling oil, and different colored plugs?

Sounds like that uber rich jetting might not be so perfect after all.
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Old March 23rd, 2016, 09:35 AM   #14
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Quote:
Originally Posted by choneofakind View Post
So leaky valves, funny smelling oil, and different colored plugs?

Sounds like that uber rich jetting might not be so perfect after all.
Wanna know what happens with uber rich jetting?? See below....



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Old March 23rd, 2016, 09:40 AM   #15
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It was definitely running on both cylinders, it could possibly be a broken head gasket, but looking through the sparkplug holes, both pistons have the same amount of carbon buildup.

It wasn't so rich that it had oil wash, because it pulled a lot harder with the dj114s then the next size down.
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Old March 23rd, 2016, 09:43 AM   #16
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Quote:
Originally Posted by HoneyBadgerRy View Post
It was definitely running on both cylinders, it could possibly be a broken head gasket, but looking through the sparkplug holes, both pistons have the same amount of carbon buildup.

It wasn't so rich that it had oil wash, because it pulled a lot harder with the dj114s then the next size down.
Pics of plugs please.

FWIW< the bike with that cooked piston pulled like a freight train too....until it didn't.
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Old March 23rd, 2016, 09:57 AM   #17
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Its leaking from the crank vent... :/ I'll take some plug pics, but that pretty much diagnosed the problem.
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Old March 23rd, 2016, 10:02 AM   #18
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This is the right plug.
Attached Images
File Type: jpg 1458752419731-846213246.jpg (71.1 KB, 4 views)
File Type: jpg 14587524542361947406866.jpg (57.6 KB, 3 views)
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Old March 23rd, 2016, 10:05 AM   #19
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Two pics of the left plug, and one pic side by side [left of left right on right (notice carbon buildup on the outside of the plug)]
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Old March 23rd, 2016, 10:21 AM   #20
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Angry

I discovered why the motor sealed, and it has nothing to do with jetting.

I drained the coolant because I wanted to look at the pistons, and this is what came out.

When I filled it up with coolant I filled it to the brim with dark orange coolant, that is a 1 gallon bucket with not even a 1mm thick layer of slightly orange water.

Its safe to say it over heated and seased, then when it cooled off the pistons broke loose and the rings were F***ed.

I havent taken the jug off yet, but I'm positive that's what happened.
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Old March 23rd, 2016, 10:33 AM   #21
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Not jetting directly.....but that could have been an indication you were burning coolant and had to add extra fuel to make it run right.

Explains the cleaned spark plug too.
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Old March 23rd, 2016, 10:37 AM   #22
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Quote:
Originally Posted by RacinNinja View Post
Not jetting directly.....but that could have been an indication you were burning coolant and had to add extra fuel to make it run right.

Explains the cleaned spark plug too.
Dynojet calls for dj114s and the needles in the third clip for this motor with pods and an exhaust, and that's what I have, so I'm pretty sure its not jetting at all.

I also find it hard to believe ALL of the coolant was burnt in that one cylinder in two rides.

I'm not sure where to go from here, at a minimum it needs new pistons and rings, it probably needs a bigger bore or a new cylinder, but I'm not sure what else the heat wasted.

Edit: there was an error on JE's website, they do make +2 and +4 mm pistons for the pregen in +0.1 and +1.1 compression ratio. If I rebuild it I plan on going with the 13.5:1 pistons not sure if I would to 282cc or 265cc.
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Old March 23rd, 2016, 11:40 AM   #23
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Mebbe you should pull the head and have a looky see before assuming the worst.

Might not be as bad as you think. Could have seized due to hydrolock and not cylinder damage. Once the water drained past the rings it could have rolled over again.

Might just need a head gasket.
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Old March 23rd, 2016, 03:12 PM   #24
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Weird fact, the right cylinder has some compression (couldn't measure it with a gauge, but compression non the less). The left on didn't.

I didn't preform the leak down test on the right cylinder.

The 2:1 exhaust might have caused the left cylinder to run rich (can't imagine it running oil dissolving rich), however that doesn't explain why I have no coolant.
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Old March 23rd, 2016, 04:21 PM   #25
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I'm confused as F*** right now and if somebody could explain this to me it would be great.

The left cylinder has a 3/4" hole through the center, carbon buildup around the rim of the cylinder, and the rings are a bit melted, but the cylinder is fine. Sparkplug in full of carbon.

The right cylinder looks like a ninja 250 cylinder with 4000 miles on it and the owner ran good gas and out some seafoam in her every now and then (which is what it is). It also looks like the sparkplug ran for like 5 minuetes (it ran for about 500 miles).

The hole in the piston would suggest lean, but the carbon would suggest rich.

The left side looks like a good running bike, the specs of color on the plug were a nice tan, it was perfect.

Where did my coolant go?
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Old March 23rd, 2016, 06:46 PM   #26
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Any holes/tears in the head gasket?

What shape is the valve train in?
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Old March 23rd, 2016, 06:58 PM   #27
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Quote:
Originally Posted by choneofakind View Post
Any holes/tears in the head gasket?

What shape is the valve train in?
Head gasket looks fine, valve train looks good, a little carbon build up on the valves, but it looks fine.

Really the only thing wrong with the motor is weird smell, left piston, left rings, (there must be aluminium in the oil pan), and the missing coolant.

The piston must have melted because of the coolant, and the coolant is missing because.... I think the jetting is fine.
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Old March 23rd, 2016, 07:00 PM   #28
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Is there a crack in your head/jugs? You said there were only short rides right? to lose coolant that quickly would take a significant leak. Whens the last time you checked the coolant level?
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Old March 23rd, 2016, 07:05 PM   #29
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Quote:
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Is there a crack in your head/jugs? You said there were only short rides right? to lose coolant that quickly would take a significant leak. Whens the last time you checked the coolant level?
I checked it a couple months ago. I drove to school ~20 minuets ride, parked it, drove it to another town and back home 30-40 minuets ride, parked it, drove it to school ~20 minutes, parked it, drove it around town and to PT ~15 minutes parked it, drove it to another town and it blew up on my way home I'd say ~25 minutes. I was likely above 8 grand 90% of that time.
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Old March 23rd, 2016, 07:09 PM   #30
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From my experience the 250 ninja needs at least 125 psi to start and run. Most never reach more than 180 psi. I have had higher with fresh valves and hi compression Pistons.
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Old March 23rd, 2016, 07:11 PM   #31
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Well with my 3/4" wide hole in the top of my piston, I'm a little shy of 125 psi.

Hopefully she's ready for TN April 4-9th.
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Old March 23rd, 2016, 07:29 PM   #32
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Ho much shy ? Like 125 psi shy? Haha I can't wait to see the hole.
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Old March 23rd, 2016, 07:31 PM   #33
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Yeah, about 125 shy. I'll post a picture tomorrow. I was going to take one, but as I opened the camera app my phone battery died.
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Old March 23rd, 2016, 07:35 PM   #34
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Quote:
Originally Posted by HoneyBadgerRy View Post
Dynojet calls for dj114s and the needles in the third clip for this motor with pods and an exhaust, and that's what I have, so I'm pretty sure its not jetting at all.

I also find it hard to believe ALL of the coolant was burnt in that one cylinder in two rides.

I'm not sure where to go from here, at a minimum it needs new pistons and rings, it probably needs a bigger bore or a new cylinder, but I'm not sure what else the heat wasted.

Edit: there was an error on JE's website, they do make +2 and +4 mm pistons for the pregen in +0.1 and +1.1 compression ratio. If I rebuild it I plan on going with the 13.5:1 pistons not sure if I would to 282cc or 265cc.
I have had great luck with 265cc. Ran the engine for two seasons of nitrous hours and hours on the dyno and still going strong.
The 282 should be sleeved. The 282 I have was just punched out. The stock cylinder is super thin now. The chamfer on the bottom is gone making it a real problem getting the rings in. I am afraid it will crack.
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Old March 24th, 2016, 06:34 AM   #35
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So after doing some research, I can't find anybody with a four stroke motor who melted a hole in the piston without either having stupid detonation (which caused other problems) or boosting the hell out of it. I should get some kind of trophy for this (I guess I did though, A piston with a hole in it to go with my display).
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Old March 24th, 2016, 06:57 AM   #36
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So after doing some research, I can't find anybody with a four stroke motor who melted a hole in the piston without either having stupid detonation (which caused other problems) or boosting the hell out of it. I should get some kind of trophy for this (I guess I did though, A piston with a hole in it to go with my display).
Almost a complete hole.....this is from our bike with the Powroll kit. It's a second hand piston we got...crown was way too thin after we looked at it more in depth and it had been machined underneath the dome around the pin bosses creating a weak spot. Didn't find out until it lost power during a race and started missing. I killed it and pulled off the track....just in time before it fully grenaded.

You said there was a lot of carbon on the rest of the piston...running rich can cause this to build up, create a hot spot and cause detonation. Running lean can cause detonation too as well as ignition timing, cam timing and other things.

Although, in this case, I suspect you ran out of coolant, overheated the motor and this is what caused the cylinder temp to rise and detonation to occur.

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Old March 24th, 2016, 07:19 AM   #37
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My theory is you have an air leak somewhere, a leak down test before dismantling the engine would have been the thing to do. The air leak is mainly/only affecting the left cylinder causing it to run lean. The left cylinder is uber lean, forget about the carbon deposits. Your jetting is probably rich but that would not cause serious problems, just make the bike run a little crappy, you would notice at WOT, but your overall system for that cylinder esp. is lean lean lean.

You either boiled off all your coolant just from the extra heat, or the coolant leaked slowly into the cylinder got boiled off there and then once it was low/gone your coolant leak turned into an air leak into that cylinder compounding the problem. Since the air leak is affecting the left cylinder the right piston doesn't look as bad, the marks on it are most likely just from collateral damage so to speak due to the excess heat of the engine.

If your cylinders are in bad shape or even questionable shape, I would probably just look to pick up a whole used engine off ebay for a reasonable price and be done with it. New engine parts or even just used parts themselves, and engine work are not cheap but whole used engines can be found for decent prices.

Not overly familiar with the jetting on the pre gens or what your setup is like but just for comparison, my new gen has pods, race exhaust, and advanced ignition timing and I run a 108 keihin main jet at about 2000' elevation and in temps down to 20 degrees F. Been running it this way for several thousand miles not even a hiccup.

108 keihin is somewhat comparable to a 104 dj

P.S. when you post pictures of the pistons make sure you take pictures of underside as well and post them
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Old March 24th, 2016, 08:13 AM   #38
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Originally Posted by RacinNinja View Post
Almost a complete hole.....this is from our bike with the Powroll kit. It's a second hand piston we got...crown was way too thin after we looked at it more in depth and it had been machined underneath the dome around the pin bosses creating a weak spot. Didn't find out until it lost power during a race and started missing. I killed it and pulled off the track....just in time before it fully grenaded.

You said there was a lot of carbon on the rest of the piston...running rich can cause this to build up, create a hot spot and cause detonation. Running lean can cause detonation too as well as ignition timing, cam timing and other things.

Although, in this case, I suspect you ran out of coolant, overheated the motor and this is what caused the cylinder temp to rise and detonation to occur.

The piston tops are clean, the carbon buildup in in the top 1/8" of the cylinder on the left side, and on the valve heads on the inside of the combustion chamber. I will clean the carbon off of the cylinder and probbably hone it, and I might try to polish the combustion chamber, I decided not to because I didn't want to lower the compression, but I want to prevent carbon buildup. If i decide to do a high compression build I will forsure polish the combustion chamber, but I might decide to buy a stock kawasaki piston just for my trip, and go high compression when I get a little more spending money.
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Old March 24th, 2016, 08:15 AM   #39
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Originally Posted by subxero View Post
My theory is you have an air leak somewhere, a leak down test before dismantling the engine would have been the thing to do. The air leak is mainly/only affecting the left cylinder causing it to run lean. The left cylinder is uber lean, forget about the carbon deposits. Your jetting is probably rich but that would not cause serious problems, just make the bike run a little crappy, you would notice at WOT, but your overall system for that cylinder esp. is lean lean lean.

You either boiled off all your coolant just from the extra heat, or the coolant leaked slowly into the cylinder got boiled off there and then once it was low/gone your coolant leak turned into an air leak into that cylinder compounding the problem. Since the air leak is affecting the left cylinder the right piston doesn't look as bad, the marks on it are most likely just from collateral damage so to speak due to the excess heat of the engine.

If your cylinders are in bad shape or even questionable shape, I would probably just look to pick up a whole used engine off ebay for a reasonable price and be done with it. New engine parts or even just used parts themselves, and engine work are not cheap but whole used engines can be found for decent prices.

Not overly familiar with the jetting on the pre gens or what your setup is like but just for comparison, my new gen has pods, race exhaust, and advanced ignition timing and I run a 108 keihin main jet at about 2000' elevation and in temps down to 20 degrees F. Been running it this way for several thousand miles not even a hiccup.

108 keihin is somewhat comparable to a 104 dj

P.S. when you post pictures of the pistons make sure you take pictures of underside as well and post them
The cylinders look decent, and I would definitely rebuild instead of buying a used engine. My bottom end only has 4-5k on the clock, and you can buy pistons of differing compression and bore size for $350 a pair, I know a guy with an engine machine shop, so a bore and plane would be pretty cheap, and I would have a better than new engine for less than the price of a questionable used one.
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Old March 24th, 2016, 08:20 AM   #40
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Are you taking the whole engine apart? Perhaps crank and rod big ends are toast too if overheated.
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