Piston marking

[Graeme1198]

Hi guys,

I striped the top of the engine down yesterday as I’m going to get my head and cylinders cleaned up by a shop as it’s looking a little tired.

So everything’s in great condition for the age and I’ve gone over all the tolerances and measurements etc.

But, always a but.... The pistons have a lot of very light scratches on them. Although inside the bores it’s still the nice honed cylinder walls no marks or issues in there.

I’ve added a photo below of the piston, it’s the same on both sides. Both pistons.

What do you thinks caused this? I’m going to get some new pistons as peace of mind. But want to prevent this happening again unless it’s general wear over time.

Thanks

 

[650Skull]

Check out these guys.........they sell 447 and 553 pistons.........
https://www.cruzinimage.net/?s=xs650
make sure what engine you have in your bike. If it an 75B European/British bike it will most likely b a 553.........a US import will b a 447...............447 or 553 will be stamped on the conrods

Model ID here
http://www.xs650.com/threads/xs650-...workshop-manuals-and-other-information.30569/

 

[YamadudeXS650C]

Hard to tell how deep or serious your scratches are. They might be insignificant.
There are methods for measuring the depth of a scratch using a micrometer.
Google "how to measure a scratch".

e.g. :

 

[Graeme1198]

Check out these guys.........they sell 447 and 553 pistons.........
https://www.cruzinimage.net/?s=xs650
make sure what engine you have in your bike. If it an 75B European/British bike it will most likely b a 553.........a US import will b a 447...............447 or 553 will be stamped on the conrods

Model ID here
http://www.xs650.com/threads/xs650-...workshop-manuals-and-other-information.30569/

Thanks for info it’s a US import, I’ll have a look at the rods tomorrow.

 

[Graeme1198]

Hard to tell how deep or serious your scratches are. They might be insignificant.
There are methods for measuring the depth of a scratch using a micrometer.
Google "how to measure a scratch".

e.g. :

Thanks for your reply, they’re barely able to catch on my nail not that that’s a very accurate measure.
I’ll have a look into measuring them with a micrometer. Thanks

 

[YamadudeXS650C]

Thanks for your reply, they’re barely able to catch on my nail not that that’s a very accurate measure.
I’ll have a look into measuring them with a micrometer. Thanks

Actually, the "nail test" is used a good deal in garage tech.
Your scratches seem minor. You might try getting a close-up photo for us, or measuring them.

 

[Graeme1198]

Actually, the "nail test" is used a good deal in garage tech.
Your scratches seem minor. You might try getting a close-up photo for us, or measuring them.

I’ll have a look at measuring them. I’ll get some other photos also so I can share them and get some advise.

 

[5twins]

That's normal wear. The piston rocks back and forth on it's pin as the rod pushes it up and pulls it down. The front and back sides of the pistons are thrust into the cylinder walls and that scratching is the result. When new with a tight piston to cylinder clearance, very little piston rocking happens. As the parts wear and more clearance develops, more rocking and wear (scratching) happens. As mentioned, yours doesn't look too bad, but you should measure the piston anyway. If you clean the top off, you'll find a 3 digit number stamped in it. This was the fractional portion of the piston size when new, as in 74.xxx mm. The 3 digit number replaces the 3 x's .....

You measure the piston front to back about 1/2" up from the bottom on it's skirt. See what it measures now compared to what it was new.

 

[Jim]

Agree with others, the scoring doesn't look too bad at all. If everything measures good, I'd reuse 'em.

 

[kshansen]

Agree with others, the scoring doesn't look too bad at all. If everything measures good, I'd reuse 'em.

I guess it all depends on what you want from this engine. If looking to have a 100% perfect like new engine and you are planning on putting a hundred thousand miles on it over the next couple of years. Then I might be tempted to replace them.

However if this is going to be just an engine you want to run good and maybe put twenty thousand miles on it over the next five years I would just reuse them with new rings and a very good cleaning of the bores with maybe a very light hone job to give the new rings something to wear into.

Just make sure if the bores are honed that you clean them surgically clean.

I always liked to wipe down with clean detergent oil then wipe off with a clean white cloth. If the cloth is anything other than the color of the clean oil repeat and keep repeating this till the fresh white cloth stays clean.

 

[hovel]

I think that freshly machined cylinders, even after just a light hone, should be washed down well with hot, soapy detergent water. Rinse, dry, and immediately oil the walls with whatever you'll be using in the crankcase. You won't believe how fast the walls will flash-rust.

 

[Graeme1198]

Thanks for all your comments, all great info. I’ll measure them up today and see where I’m at.

 

[Tlted_Jelli]

That's normal wear. The piston rocks back and forth on it's pin as the rod pushes it up and pulls it down. The front and back sides of the pistons are thrust into the cylinder walls and that scratching is the result. When new with a tight piston to cylinder clearance, very little piston rocking happens. As the parts wear and more clearance develops, more rocking and wear (scratching) happens. As mentioned, yours doesn't look too bad, but you should measure the piston anyway. If you clean the top off, you'll find a 3 digit number stamped in it. This was the fractional portion of the piston size when new, as in 74.xxx mm. The 3 digit number replaces the 3 x's .....

View attachment 284697

You measure the piston front to back about 1/2" up from the bottom on it's skirt. See what it measures now compared to what it was new.

What does the "1" stamped on there mean?

 

[5twins]

I think it indicates the production run or lot. It doesn't have anything to do with the sizing.