Scuff on a piston skirt

[fourbarrel]

I rebuilt the engine last season of my '98 SRX,well part of it at least.Another jug and a new piston and rings was needed.Yes I stripped the entire engine down and split the cases,cleaned everything,oiled the bearings and put it all back together.So long story short I was headed out for what ended up being the last ride of the year when the mag piston seized as a result of an air leak around the reed cage.I got literally about 3 miles before it locked up and now I'm in the process of getting the crank fixed (needs connecting rod on mag end) and new pistons and rings.The centre piston ended up with a little damage as a result of the gulp of fresh air and I'm wondering just how detrimental to the integrity of the sealing of the piston to cylinder a small scuff would be to having a proper running and performing engine.The piston has without exaggeration no more than 4 miles on it and about a grand total of a half hour of run time,taking into account the initial startup and warm ups.I'd hate to replace the piston if it would still do the job of a pristine one,plus it would save me the cost of a new one.I'll be putting new rings on it anyway but if I can get away with running the scuffed piston it would save me the cost of one anyway.It may sound like I'm cheaping out,and perhaps I'm trying to a bit,but the price of OEM parts in Canada are that much more than what prices are in the US even given the difference in the money that if I could get away with buying one less part then that makes the rebuild a bit more palatable.

It might be difficult to tell from the pic but the scuff is deep enough that a nail will catch it the grooves but I'm wondering if a little sanding of the scratches to flatten them out would be ok.

 

[MrSled]

I rebuilt the engine last season of my '98 SRX,well part of it at least.Another jug and a new piston and rings was needed.Yes I stripped the entire engine down and split the cases,cleaned everything,oiled the bearings and put it all back together.So long story short I was headed out for what ended up being the last ride of the year when the mag piston seized as a result of an air leak around the reed cage.I got literally about 3 miles before it locked up and now I'm in the process of getting the crank fixed (needs connecting rod on mag end) and new pistons and rings.The centre piston ended up with a little damage as a result of the gulp of fresh air and I'm wondering just how detrimental to the integrity of the sealing of the piston to cylinder a small scuff would be to having a proper running and performing engine.The piston has without exaggeration no more than 4 miles on it and about a grand total of a half hour of run time,taking into account the initial startup and warm ups.I'd hate to replace the piston if it would still do the job of a pristine one,plus it would save me the cost of a new one.I'll be putting new rings on it anyway but if I can get away with running the scuffed piston it would save me the cost of one anyway.It may sound like I'm cheaping out,and perhaps I'm trying to a bit,but the price of OEM parts in Canada are that much more than what prices are in the US even given the difference in the money that if I could get away with buying one less part then that makes the rebuild a bit more palatable.

It might be difficult to tell from the pic but the scuff is deep enough that a nail will catch it the grooves but I'm wondering if a little sanding of the scratches to flatten them out would be ok.

This happens on occasion from snow ingestion or iced cylinders from running the sled and tossing it onto a trailer not fully up to temp and taking off down the highway. The rings are what make the seal the skirt should be smooth but they all will get scuffs depending on the type of riding and if the motor is warmed up or not. Whats the compression on that cylinder?

 

[pete_man26]

Since you have it out, I would get some 800 or 1000 grit sandpaper and try sanding it down to see how much you clean up. That will help determine if it can be reuseable or not. I have done this in the past on scuffs but they were smaller then this without any grooves.

 

[fourbarrel]

This happens on occasion from snow ingestion or iced cylinders from running the sled and tossing it onto a trailer not fully up to temp and taking off down the highway. The rings are what make the seal the skirt should be smooth but they all will get scuffs depending on the type of riding and if the motor is warmed up or not. Whats the compression on that cylinder?

I checked it before I tore the engine down and it only had 100 psi in it,but the rings are scored so at the very least it needs new rings.I did take at it with some 1200 grit sand paper and it took a lot of the rough edges out and if I can get it to where I'm comfortable with it then I'll snap new rings on it and run er.This happened because of a poor seal around a reed cage.

 

[MrSled]

I checked it before I tore the engine down and it only had 100 psi in it,but the rings are scored so at the very least it needs new rings.I did take at it with some 1200 grit sand paper and it took a lot of the rough edges out and if I can get it to where I'm comfortable with it then I'll snap new rings on it and run er.This happened because of a poor seal around a reed cage.

Sounds like a great plan!!

 

[roudyroy1]

so the mag cylinder leaned out and you also noticed the center piston was damaged? Those 2 cylinders have their own separate carb, reed and exhaust system. so i do not think your mag cylinder leaning out would cause the damage found on the center cylinder since they do not share an induction system,unless you had another air leak on the center cylinder as well. Assuming the center cylinder did not have an air leak; usually if it was lean you would see the effect of the heat on the piston crown and exhaust side of the piston, not the intake. intake side seizure like that is commonly found due to water (snow) ingestion washing off the oil film off the skirt.

As for the scuffing this is what Yamaha recommends in their manual to deal with piston scuffing. The skirt does not have much to do with cylinder sealing but more with keeping the piston stable in the bore, be mindful that this is the THRUST side of the piston so it is subjected to higher forces. i would see how it responds to the following procedure and go from there. its hard to say without having it in my hand but you more than likely will be okay. i have seen a lot worse run for years.

 

[MrSled]

so the mag cylinder leaned out and you also noticed the center piston was damaged? Those 2 cylinders have their own separate carb, reed and exhaust system. so i do not think your mag cylinder leaning out would cause the damage found on the center cylinder since they do not share an induction system,unless you had another air leak on the center cylinder as well. Assuming the center cylinder did not have an air leak; usually if it was lean you would see the effect of the heat on the piston crown and exhaust side of the piston, not the intake. intake side seizure like that is commonly found due to water (snow) ingestion washing off the oil film off the skirt.

As for the scuffing this is what Yamaha recommends in their manual to deal with piston scuffing. The skirt does not have much to do with cylinder sealing but more with keeping the piston stable in the bore, be mindful that this is the THRUST side of the piston so it is subjected to higher forces. i would see how it responds to the following procedure and go from there. its hard to say without having it in my hand but you more than likely will be okay. i have seen a lot worse run for years.
View attachment 63467

Awesome info!!

 

[Srx007]

That piston doesnt seem too bad, if it measures well, why not. My opinion I would replace it and only re-ring the others, but thats just me AND YOU FEEL COMFORTABLE AFTER TAKING SOME MEASUREMENTS and Ya I hear ya about the price of OEM SRX pistons in Canada, they are definitely pricey, like the 223$ before tax (JUST FOR PISTON) quote that I received from the dealer. I have heard good things about PRO-X pistons which come with Piston, Rings, Circlips, Pin and Needle bearing at a quote of 123$ before tax, so you might also want to inquire about those pistons since you have the engine apart. Wanted to throw that out there and hope it helps CANT WAIT FOR SNOWWWW

 

[YAMMIEGOD3:16]

great info right from the book. 3:16x (yammie tony)

 

[fourbarrel]

so the mag cylinder leaned out and you also noticed the center piston was damaged? Those 2 cylinders have their own separate carb, reed and exhaust system. so i do not think your mag cylinder leaning out would cause the damage found on the center cylinder since they do not share an induction system,unless you had another air leak on the center cylinder as well. Assuming the center cylinder did not have an air leak; usually if it was lean you would see the effect of the heat on the piston crown and exhaust side of the piston, not the intake. intake side seizure like that is commonly found due to water (snow) ingestion washing off the oil film off the skirt.

As for the scuffing this is what Yamaha recommends in their manual to deal with piston scuffing. The skirt does not have much to do with cylinder sealing but more with keeping the piston stable in the bore, be mindful that this is the THRUST side of the piston so it is subjected to higher forces. i would see how it responds to the following procedure and go from there. its hard to say without having it in my hand but you more than likely will be okay. i have seen a lot worse run for years.
View attachment 63467

The centre reed cage also had a small gap in the reed cage seal which accounted for the small scuff.