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what could cause this???

  • Thread starter Thread starter NATEO
  • Start date Start date
N

NATEO

Guest
its my 82 GS750e. any ideas what could cause the piston to melt? I have a new top end to put on, but I want to make sure its not just going to melt another piston...

also, provided I use the matching block, can I swap pistons from my parts engine? or is that going to require more work than just swapping parts?

Thanks

natespiston1vq5.jpg

natespiston2nj2.jpg
 
dang!!
zv.gif
that is bad!!
you are not suppose to ride it till it quits!

that looks like detonation failure, could also be from a fault in the piston.
generally a lean condition failure happens in the center of a piston where they are the thinest.
 
to much ether? wow that doesn't look good. what do the other three look like? i would be concered that other parts are bad like ol pump getting metal in it, maybe even getting chunks in the bearings to. If it was me i would see about finding a new motor and strip this for parts.
 
first timer said:
to much ether? wow that doesn't look good. what do the other three look like? i would be concered that other parts are bad like ol pump getting metal in it, maybe even getting chunks in the bearings to. If it was me i would see about finding a new motor and strip this for parts.
Click to expand...

the other 3 look fine, and except for the obvious wear on the cylinder wall, it doesnt look like there are any particles anywhere under the piston... the engine I am getting the head/block/pistons from is pretty much junk... it is missing a bunch of stuff, and while I know I could take parts off the blown engine, this parts one is in really tough shape...


if I were to go against all recommendations (I have been known to do that... see where it got me?) would swapping pistons require rehoning and new rings? or would using the matching block prevent that?
 
NATEO said:
if I were to go against all recommendations (I have been known to do that... see where it got me?) would swapping pistons require rehoning and new rings? or would using the matching block prevent that?
Click to expand...

well if the pistons and rings from the "parts" engine are good, then you should be fine. you might want to do a light hone but it is more important to use all 4 pistons and the cylinder block (make sure to put in same order) as the donor pistons will be worn in to that blocks cylinder.
 
Assuming your crankshaft is O.K., swapping pistons is possible in another bock as far as I know. Both pistons and block are easy enough to measure for proper spec. and piston/wall clearance.

You'll need new wrist pins and circlips. Rings as well, make sure to measure for proper gap. Cylinder honing is required.

Take a good look at your connecting rods where the wrist pins go and check for any abnormal wear, that piston took a beating. That can be measured as well.

Sure wonder what happened. That's nasty.
 
Holy sh!t Batman! Looks like it got dropped into molten lava!
 
make sure to save that as a nice souvenir - would be interested to know what caused that myself
 
Looks like two I've seen before on cars.....

One was a 4cyl VW Rabbit that had been driven till it stopped with no oil in it.

One was a Blown chevy corvette drag car that had a fuelling problem & ran super lean & bang.....

Could have been either or a bit of both....

Dan :)
 
Usually, a lean mixture or timing too advanced causing preignition will burn a hole in the top center of the piston. My best guess, is no oil flow, or blocked oil supply, oil pump problem.

Earl


[quote=NATEO
any ideas what could cause the piston to melt? I have a new top end to put on, but I want to make sure its not just going to melt another piston...
 
like earl said, before you put this thing back together, check your entire oil system from screen in oil pan to the passages up into the head and the oil pump too. The PO may have gotten a piece of RTV stuck in i passage somewhere and burned up a piston.
 
first timer said:
like earl said, before you put this thing back together, check your entire oil system from screen in oil pan to the passages up into the head and the oil pump too. The PO may have gotten a piece of RTV stuck in i passage somewhere and burned up a piston.
Click to expand...

ok, I will check the passages, screen and pump before I put stuff back on...

am I going to see major issues if I just swap parts without honing and new rings? I can still see the pattern from the last time it was honed. of course I will check rings when I get the block off....
 
if the cylinders on the donor engine check good, (IE: it had a fresh rebuild or was low miles before retirement) then you should be perfectly fine.

you will need to make sure to use all 4 pistons in the same order they came from the donor engine, as well as the cylinder block.
 
focus frenzy said:
if the cylinders on the donor engine check good, (IE: it had a fresh rebuild or was low miles before retirement) then you should be perfectly fine.

you will need to make sure to use all 4 pistons in the same order they came from the donor engine, as well as the cylinder block.
Click to expand...

ok, thanks... looks like I will be digging into my engine even more tonight!
 
I would use the matching block, remove the oil pan & check the oil pickup for derbs. While your at it remove the clutch & replace the O rings on the oil pump
 
Since it was just one cylinder it doesn't seem likely that it was the oil pump (although I'd check for debris of course). That piston is clearly melted which means it got killer hot. The only thing that comes to mind is that the cylinder was running lean while the others pulled it along...straight into hell. Great paper weight by the way. :) Take the carbs apart and look for an obstruction in the main jet circuit would be my recommendation.
 
Nessism said:
Since it was just one cylinder it doesn't seem likely that it was the oil pump (although I'd check for debris of course). That piston is clearly melted which means it got killer hot. The only thing that comes to mind is that the cylinder was running lean while the others pulled it along...straight into hell. Great paper weight by the way. :) Take the carbs apart and look for an obstruction in the main jet circuit would be my recommendation.
Click to expand...

I agree. Check your plugs on all cylinders. You will get an indication as to whether it was the engine or just that cylinder that was running lean. I suspect that its just that pot. Looking at the pics, there has been some serious heat across the whole piston. The top ring has expanded that much that it laps by around 1-2 mm. Even the oil control top ring has overlapped due to excessive expansion.
If there was an oil feed problem, there should be some signs of that on the other pistons/cylinders as well. Check the condition of the wrist pin and gudgeon holes on the melted piston. These get lubrication from oil misted up from the crank/sump area during normal crankshaft rotation. If the gudgeon and pins look ok on all the other pistons, you can dismiss the lack of oil theory.
 
Last edited:
49er said:
I agree. Check your plugs on all cylinders. You will get an indication as to whether it was the engine or just that cylinder that was running lean. I suspect that its just that pot. Looking at the pics, there has been some serious heat across the whole piston. The top ring has expanded that much that it laps by around 1-2 mm. Even the oil control top ring has overlapped due to excessive expansion.
If there was an oil feed problem, there should be some signs of that on the other pistons/cylinders as well. Check the condition of the wrist pin and gudgeon holes on the melted piston. These get lubrication from oil misted up from the crank/sump area during normal crankshaft rotation. If the gudgeon and pins look ok on all the other pistons, you can dismiss the lack of oil theory.
Click to expand...

the rest of the rings look fine. There is no excessive wear or warping.. the cylinder walls look ok too. I will check plugs tonight.
 
Could there have been an exhaust leak on that cyl? Bad valve timing combined with a nasty exhast leak could cause that, maybe, but your head would probably be trashed too. Take the cams out of that head before you reinstall it and check the cam seats for scoring or worse.

I'd say it's definitely an intake or exhaust valve burn becasue if it was a general mixture problem, the piston would probably burn in the middle. What side did the piston burn, intake or exhasut?
 
Jethro said:
Could there have been an exhaust leak on that cyl? Bad valve timing combined with a nasty exhast leak could cause that, maybe, but your head would probably be trashed too. Take the cams out of that head before you reinstall it and check the cam seats for scoring or worse.

I'd say it's definitely an intake or exhaust valve burn becasue if it was a general mixture problem, the piston would probably burn in the middle. What side did the piston burn, intake or exhasut?
Click to expand...

that was on the exhaust side. the cams look ok. there is wear on them, but nothing excessive...
 
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