New CMB67 Piston

[WikiWiki1]

I just bought a new piston and sleeve for my CMB green head and noticed

the piston is covered with tiny pits (metal porosity). Is this normal?

I have never replaced one before so I'm not sure it they are supposed

to be this way. My original one does not have this.

Thanks, Brent

 

[MrUnlimited]

I just bought a new piston and sleeve for my CMB green head and noticed

the piston is covered with tiny pits (metal porosity). Is this normal?

I have never replaced one before so I'm not sure it they are supposed

to be this way. My original one does not have this.

Thanks, Brent

It depends where the shop=owner stored it, if it was a moistured area it could be the cause. You can remove it with a fine grit sandpaper

 

[glenng]

I just bought a new piston and sleeve for my CMB green head and noticed

the piston is covered with tiny pits (metal porosity). Is this normal?

I have never replaced one before so I'm not sure it they are supposed

to be this way. My original one does not have this.

Thanks, Brent

Kinda looks like corrosion Brent, I don't think this is normal.

Glenn

 

[Hydro Junkie]

Definately not normal. IF you bought it locally, I'd take it back and ask for a good one as that one is definately corroded. You can sand it if you wish, just be careful not to be too agressive as it could change the shape and make the piston worthless

 

[Bob Howard]

If you try to clean it up use 0000 steel wool

Bob

 

[Hydro Junkie]

If you try to clean it up use 0000 steel wool

Bob

Maybe mixed with WD-40? What about using that Nev-R-Dul metal polishing wadding? That would probably take off the corrossion and protect it at the same time

 

[Bigbird]

I just bought a new piston and sleeve for my CMB green head and noticed

the piston is covered with tiny pits (metal porosity). Is this normal?

I have never replaced one before so I'm not sure it they are supposed

to be this way. My original one does not have this.

Thanks, Brent

If it were me, I would hate to pay out that much cash and have to sand it to make it work. Need to get a new one.

BB

 

[Tom Foley]

Guys ...relax ....the cast piston has the dull look to it and it does not look like a billet machined item . I have seen this in every Italian made motor since my first OPS back when Dinosaurs roamed ! It has the appearance of a lightly pitted surface that has been machined (OD Ground ) . I would not worry about it as it is normal , but if you like please post pictures for verification .

DONT SAND IT OR POLISH IT !

 

[Martin Hamilton]

Their is nothing wrong with that piston, Its not corrosion or anything like that or porousity that you need to worry about. What you think is small holes in the material is silicon dispersed through out the piston, This is very common in cast pistons. The pistons with a shiny surface are billet machined pistons that have a much finer dispersal of silicon and other elements through out the piston that you dont get with castings. As already said do not touch the piston with any thing abraisive to try to clean piston as its not corrosion, Or you will ruin the piston especialy if you dont know what your doing regarding useing anything on pistons and liners. Pistons and liners can have and do have abraisives used on them to lap them but not if you are inexperienced in this area. Regards Martin.

 

[SayMikey]

Their is nothing wrong with that piston, Its not corrosion or anything like that or porousity that you need to worry about. What you think is small holes in the material is silicon dispersed through out the piston, This is very common in cast pistons. The pistons with a shiny surface are billet machined pistons that have a much finer dispersal of silicon and other elements through out the piston that you dont get with castings. As already said do not touch the piston with any thing abraisive to try to clean piston as its not corrosion, Or you will ruin the piston especialy if you dont know what your doing regarding useing anything on pistons and liners. Pistons and liners can have and do have abraisives used on them to lap them but not if you are inexperienced in this area. Regards Martin.

Wipe it good with WD-40 and put it in. Whats the sleeve look like good I assume?

 

[Stuart Barr]

Brent,

I have looked at my inventory and found all the pistons look that way. I agree with Tom and Martin, don't sand or alter. Some of these are already in service and I have not heard of any problems with performance or durability.

Stu Barr

 

[WikiWiki1]

Thanks for all the info! The piston is very smooth but it just looked odd

to me. I'm going to go ahead and install it as is. You guys rock!

Brent

 

[Martin Hamilton]

Those black looking dots are just the silicon crystals vital to stop the piston expanding when hot, So just run your motor. Regards Martin.

 

[Joe Wiebelhaus]

Its your camera resolution, bet ya cant see it with the naked eye, but up close and a flash you get all the silicon reflection.

DONT touch it, run it.

see pic of another.