On a two stroke dirt bike, what is a new top end?

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On a two stroke dirt bike, what is a new top end?
If you ask different people on Craigslist, news paper ads, and other selling formats, you will get many different answers.
But, lets be clear, a new piston and ring set is not a new top end.
A new piston and ring will need to be done on a two stroke bike every few races or every few seasons.
This is considered normal and required maintenance.
So, what is a new top end?
Well, let's take a look at the parts is a two stroke top end.
Head, cylinder, exhaust valve assembly, piston, ring, wrist pin, cir clips, piston bearing, and gaskets.
Head.
A head has many functions and is often times overlooked when a top end rebuild is done.
A head can affect average riding temperatures, power, compression, economy, and a host of other things.
If your head is re-combustioned correctly you can have more power, cooler running temps, and better economy.
You see, over time a head will wear.
That's right, the combustion chamber will actually wear even though at times they appear to be in excellent condition.
Also, the head needs to be flat.
Of course you can just slap a decent looking head on and if it's flat enough it will run but you won't be getting the most out of your rebuild.
So, when you want to do a complete top end, send your head in and have it surfaced and re-combustioned.
You might also want to have your squish angle changed depending on your model.
Cylinder.
Most modern cylinders are Nickasil plated.
This plating is not bumper chrome and it's not industrial chrome as you would find on a Hydraulic cylinder.
It is a special blend of compounds that if done correctly provide extremely good combustion sealing as well as longevity.
Even the best plating job wears over time.
You can check out the chrome and it may look good but unless careful measurements are taken from around the bore you may have an egg shaped bore which will loose you power and wear even faster with a new set of rings.
Any scratches that can be felt with your fingernail are loosing you power.
Basically there are two choices.
You can have your cylinder re-plated or you can sleeve it.
Sleeveing allows you to bore the cylinder out larger than stock (As long as pistons are available) a few times before it will need to be re-sleeved.
The disadvantage is it requires a longer warm up time and some say they are slightly down on power do to a lower lubricity factor then Nickasil and they will wear out faster between bores then Nickasil.
Exhaust valves
These are often over looked when top end work is done.
At a minimum, the exhaust valve assembly should be disassembled, throughly cleaned, and carefully inspected.
The manual should be consulted and all specs verified.
Are there any bearings or seals?
REPLACE THEM!
Look for any slop in the linkage and replace anything that is worn.
A sloppy linkage setup will change when and how much the exhaust valves open and close.
This can have a dramatic effect on power delivery.
Piston
What piston you choose is up to you.
I like the Wiseco forged pistons but others have equally good success with other brands.
The problem that we have run into is that piston sets do not include a new wrist pin bearing.
If the customer forgets to order a new one, they will often re-used the old bearing.
This should never be done but if they are selling the bike anyway, they will not care.
So, when considering buying a bike that is advertised with a new top end, here is some questions that you may want to ask.
1. Do you have all the receipts?
This will show you what all has been replaced with no doubts.
No receipts? Buyer beware.
It has been our experience that some people will say whatever they think you want to hear just so they can sell it.
2. Who did the work?
If the seller took it to a reputable shop, then you can rest easy that it was done right.
If the seller did the work themselves, ask if they have the Service manual.
If they don't, where did they get all the specs?

I hope you find this information helpful.
Questions or comments?
Feel free to post.
Thanks!
SB