Melted Piston Any Ideas

jasontaylor1974 · 01-15-2007, 12:08 PM

Ok my son was given a 1991 cr250 that needed repairs so I started checking it out and found very low compression so we pulled the head and the piston was melted on the exhaust side at the rings so I ordered a new top end kit from Namura Technologies after putting it together it started fine and I ran it about an hour and then put it up for the night. The next day we ran it for about 2 hours and then the flame arrister came off the silencer and all power was lost the silencer did not have any packing in it. I pulled the spark plug and it appears that the piston must have hit the plug just enough to close the gap so I verified that the plug in it was the wrong one. I then pulled it back apart and the new piston was melted on the same side (exhaust pipe side) but a different spot lower portion of piston melted off please see pictures 1st pic is the original piston I mixed the gas 32:1 and was running it easy for break in

tigmaster · 01-15-2007, 01:21 PM

well my first and probaly obvious question to u is: is your impelar intact and does your cooling system low freely. also if yur plug was too deep in the fuel mixture preignition definately could have happened but i guess it wouldnt be on the side of the piston. was the same plug in for both pistons? well ill think about it for a bit and ill figure it out for you. any other important details i should know?

jasontaylor1974 · 01-15-2007, 05:15 PM

I did find one of the reeds sucked in so I replaced both of them and it was the same plug but the original piston did not hit it

1bad250 · 01-15-2007, 06:04 PM

first off im suprised it ran with a reed sucked in. the engine is runing hot there is a lot of things that need checked first off did you remove & clean the power valve? a ring gasket between the exhaust port & expation chamber with springs, try to find any kind of air leakes, jeting the carb.,repack you silincer,look for a obstuction in the coolent passages,also the head could have been serfaced way to much & you need to run at least 93 pump gas. let me know how its going & give more info.

1bad250 · 01-15-2007, 06:09 PM

Oh ..detination means MELTDOWN..

jasontaylor1974 · 01-15-2007, 08:20 PM

I pulled it the rest of the way down and found that the plastic gear that drives the water pump impeller had all of the teeth striped off. The reed that was sucked in was on the first tear down the new reeds still look great. So I believe the problem was the water pump not working, however I plan on re-packing the silencer, installing the correct plug and verifying the jetting is there any thing else I should check?

tigmaster · 01-15-2007, 08:46 PM

silencer packing does not affect the temperature of your engine, however it will affect performance. that engine was destroyed, i cant believe how many things were wrong with it. good that u got it figured out though.

wr250f95 · 05-24-2007, 11:58 PM

his problem is solved but i still have something to say, On another forum a couple of the pro engine builders were saying to run engine hard for the break in, not revving the crap out of it but still letting it get into the mid rpm ranges. They claim that it provides better ring seal thus creating more horsepower.

tigmaster · 05-25-2007, 12:00 AM

yes!!!, read my how-to here

http://www.mototips.com/how-tos-perf...procedure.html

wr250f95 · 05-25-2007, 12:08 AM

well said. Ill keep an eye on you, im willing to bet youll be one of those top engine builders building engines for the pros.

01-15-2007, 01:21 PM	#2 (permalink)
tigmaster Administrator Join Date: Aug 2006 Location: Missouri, United States Posts: 7,659 iTrader: (1)	well my first and probaly obvious question to u is: is your impelar intact and does your cooling system low freely. also if yur plug was too deep in the fuel mixture preignition definately could have happened but i guess it wouldnt be on the side of the piston. was the same plug in for both pistons? well ill think about it for a bit and ill figure it out for you. any other important details i should know? __________________ --'03 CRF450r-- --FMF Pipe, Pro-Tech Revavle-- --Vortex Basket With Tusk Disks And HP Springs-- --Pro Taper Triple Clamps And Bars-- --Devol Full SP With Moose HGs-- --Renthal 13/50 With R1 Chain-- --Now It Is The End, Probably...-- --'06 CBR F4I-- --Bone Stock-- Check Our Latest How-To Here

01-15-2007, 08:46 PM	#7 (permalink)
tigmaster Administrator Join Date: Aug 2006 Location: Missouri, United States Posts: 7,659 iTrader: (1)	silencer packing does not affect the temperature of your engine, however it will affect performance. that engine was destroyed, i cant believe how many things were wrong with it. good that u got it figured out though. __________________ --'03 CRF450r-- --FMF Pipe, Pro-Tech Revavle-- --Vortex Basket With Tusk Disks And HP Springs-- --Pro Taper Triple Clamps And Bars-- --Devol Full SP With Moose HGs-- --Renthal 13/50 With R1 Chain-- --Now It Is The End, Probably...-- --'06 CBR F4I-- --Bone Stock-- Check Our Latest How-To Here

05-25-2007, 12:00 AM	#9 (permalink)
tigmaster Administrator Join Date: Aug 2006 Location: Missouri, United States Posts: 7,659 iTrader: (1)	yes!!!, read my how-to here http://www.mototips.com/how-tos-perf...procedure.html __________________ --'03 CRF450r-- --FMF Pipe, Pro-Tech Revavle-- --Vortex Basket With Tusk Disks And HP Springs-- --Pro Taper Triple Clamps And Bars-- --Devol Full SP With Moose HGs-- --Renthal 13/50 With R1 Chain-- --Now It Is The End, Probably...-- --'06 CBR F4I-- --Bone Stock-- Check Our Latest How-To Here

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01-15-2007, 05:15 PM	#3 (permalink)
jasontaylor1974 C Rider Join Date: Jan 2007 Posts: 3 iTrader: (0)	I did find one of the reeds sucked in so I replaced both of them and it was the same plug but the original piston did not hit it

01-15-2007, 06:04 PM	#4 (permalink)
1bad250 C Rider Join Date: Jan 2007 Location: illinois Posts: 9 iTrader: (0)	first off im suprised it ran with a reed sucked in. the engine is runing hot there is a lot of things that need checked first off did you remove & clean the power valve? a ring gasket between the exhaust port & expation chamber with springs, try to find any kind of air leakes, jeting the carb.,repack you silincer,look for a obstuction in the coolent passages,also the head could have been serfaced way to much & you need to run at least 93 pump gas. let me know how its going & give more info.

01-15-2007, 06:09 PM	#5 (permalink)
1bad250 C Rider Join Date: Jan 2007 Location: illinois Posts: 9 iTrader: (0)	Oh ..detination means MELTDOWN..

01-15-2007, 08:20 PM	#6 (permalink)
jasontaylor1974 C Rider Join Date: Jan 2007 Posts: 3 iTrader: (0)	I pulled it the rest of the way down and found that the plastic gear that drives the water pump impeller had all of the teeth striped off. The reed that was sucked in was on the first tear down the new reeds still look great. So I believe the problem was the water pump not working, however I plan on re-packing the silencer, installing the correct plug and verifying the jetting is there any thing else I should check?

05-24-2007, 11:58 PM	#8 (permalink)
wr250f95 Super Moderator Join Date: May 2007 Location: New Mexico Posts: 8,447 iTrader: (1)	his problem is solved but i still have something to say, On another forum a couple of the pro engine builders were saying to run engine hard for the break in, not revving the crap out of it but still letting it get into the mid rpm ranges. They claim that it provides better ring seal thus creating more horsepower.

05-25-2007, 12:08 AM	#10 (permalink)
wr250f95 Super Moderator Join Date: May 2007 Location: New Mexico Posts: 8,447 iTrader: (1)	well said. Ill keep an eye on you, im willing to bet youll be one of those top engine builders building engines for the pros.

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