Can you run a scratchy piston

[Noobi06]

A lot of people say you should replace the piston when its scratchy.
Others say as long as the piston ring is in good shape, you can run a very scrathy piston.
What is right? I know the more hours on a piston, the more risk of it cracking or breaking cause other stuff to get destroyed such as the cylinder.
Also, if number 2 is correct, doesnt that mean I can run the same piston for hundreds of hours and just replace the ring every now and then.

[SS109]

There is no way in hell I would run any piston that is scuffed/scratched up! Just not worth it, IMO, to risk it.

As for the rest, cast pistons start to weaken after so many cycles. I won't run a cast over 100 hours so not even worth thinking about just replacing the rings. Now, a good forged piston, as long as it's not messed up, I'll run them until the compression starts getting low and then swap the piston and rings. Again, not really worth doing just the rings on any 200cc or larger bike IMO/IME.

These are just my opinions based on my experiences wrenching on 2T motorcycles since the 1980's and what brings me peace of mind. YMMV!

[Noobi06]

How long do you recon I should run a Wiseco forged piston (200dollars) before changing? Having in mind that compression isnt shit
I mean replacing a piston is way cheaper than a cylinder which I cant afford, at the same time you can save a lot of money by doing few piston changes

[SS109]

I know forged can go a really long time but it all depends on how you ride. Harder you ride the faster things need replaced.

That said, I have one bike, a KDX220, that has about 300 hours with a Wiseco in it. Compression is just now getting to the low end do I'll go ahead and swap it out.

[Soderberg]

The way most of us replace pistons today, is the modern way of being stupid. The only thing we do is to feed the manufacturers bank account. 95%ISH of the wear is taken care of the piston rings. If the piston has the right meassure, just go with the rings. Before the 70ies, even race teams welded scored pistons and put them up in a lathe to get them back to right specs. As said above, I wouldnt recommend this for MX (only for enduro). The more you rev, the more the piston gets beaten up.

Another thing that is kinda hysterical is air filter replacement, and for that sake ALL filters. How many of you change the filter after every practise? Probably most of you. The right thing to do is to meassure air flow and let the numbers tell you when to change it. OR oilflow if we talk about oil filters. As this is difficult on a bike I do like this. When training I change when the filter starts to look terrible, normally 5-15 hours depending on where I drive (sand, dirt etc). I dont care if the bike starts running bad at the end of a daily training. The only thing that will happen is that the filter is too dirty and the engine looses performance, idle etc. It will never run lean, only fat. Before a competition I always change filter, as I cant afford the bike to run bad.

Why do I say this?
I have worked arround filter experts my entire grown up life and Im 55. At an industry a filter can cost from $10000 up to infinity. The dirtier a filter is, the better it cleans the medium. To a point where it reduces the performance of the ment function. This is just a tip for all who hates the job with cleaning and changing air filter. And as I said, remember that the dirtier the better to a point.
Cheers

[Noobi06]

By the sound of it, I shall only replace rings and not piston if piston has minor scrathes. If they are more scratches that could damage, I shall replace for the good sake

[Zman]

Why is the piston scratched? Do you have a air leak in the carb boot or is the air filter not sealing well? Getting debris in the engine is the mostly likely way to get a scratched piston.

[Noobi06]

My piston is not scratchy. This was just thing i was thinking about