200X piston to cylinder clearance

[Keith Salyer]

I am boring my 200X to 65mm 10.25-1 piston and need the recommended clearance on a fresh bore.. Can you help?

[DohcBikes]

If it is a Wiseco, I believe they call for .002 piston to cylinder clearance.

[Dirtcrasher]

10.25, probably is Wiseco. I think if I had an air cooled engine I'd add another .001 and jet it towards the fat side.

[barnett468]

Whether it is a Wiseco or not, I would run a forged piston in that cylinder between .00175” and .002”. You could run .0015" with careful break in imo.

At least some types of Wiseco pistons are "cam" ground, irregardless of this fact, simply measure the piston at its widest point below the oil ring.


OIL – I would also break it in on non synthetic oil that has ZDDP levels above 1100 ppm. An oils ZDDP level is often noted in the oils MSDS which is available on line.

It has been determined that using either synthetic blends or full synthetics for piston ring break in on 4 strokes, can delay, or even prevent, proper ring break in.

[El Camexican]

From the Wiseco Q&A page

Q 05. There is no piston to wall clearance on the box label, what is the piston to wall clearance for my application?

A. Wiseco Powersports pistons are designed for optimal piston to wall clearance for the specific bore size of your engine. For example, your 125cc dirt bike engine is 54mm bore, the Wiseco piston is designed just for that bore size, and does not require any specific adjustments to fit properly.

Some applications, such as higher stressed race engines (or nitrous injected), forced induction engines (supercharged or turbos), do require additional piston to wall clearance than Wiseco has designed into the part. These are special applications that are normally built at high performance engine shops. These builders are familiar with the needs of these engines, and can help establish the needed engine set up parameters including piston to wall clearance. As a general rule, any high stress engines that include nitrous, turbo or supercharging, up to high pressure blowers require an additional .001 to .003" clearance.

Q 10. What is the proper ring end gap for my 4-cycle engine?

A. Wiseco 4-cycle Powersports piston rings are designed with the proper end gap for most applications. Because 4-cycle engines contain two and three rings, the end gaps do require different values depending on the ring. This chart will help illustrate the minimum ring end gaps:

Top ring 2nd ring Oil rail
Most standard engines 0.004 0.005 0.015
Modified engines or Nitrous Oxide 0.005 0.0055 0.015
High performance racing 0.0055 0.0053 0.015
Racing with Nitrous / Turbo 0.006 0.0057 0.015
Blower / Forced induction 0.007 0.0063 0.015

Multiply your bore size in inches times the value on the table (to convert metric bore to inches, divide your metric bore x 25.4. For example, 77mm divided by 25.4 = 3.0314”, multiply this times the value on the chart).

Note: If your piston contains only a top ring and oil set, simply omit the second ring requirements



Oddly enough a search for Wiseco's recommended break in oil comes up blank. (FACT)

[atc007]

I stay right around the 2 in all the ones I did. If I knew the guy wouldn't break it in right or warm them up right. I would give him some extra clearance . Tighter it is,if all is well with break in,warm up,hone ,oil ,air filter etc... The better and longer she'll run/

[DohcBikes]

Excellent addition of info on the all important ring end gap El Camexican. This is just as critical as having the proper piston to cylinder clearance.

Wiseco is so confident in their forging process that they are attemting to save us the headache of measuring.
For example if i were to go in and just have my cylinder bored to exactly 65.5mm and order a 65.5mm piston from wiseco, the clearance is built in.
Still,
I usually order my piston first, measure it, then tell the machinist what I want done for that particular application.

[Dirtcrasher]

I stay right around the 2 in all the ones I did. If I knew the guy wouldn't break it in right or warm them up right. I would give him some extra clearance . Tighter it is,if all is well with break in,warm up,hone ,oil ,air filter etc... The better and longer she'll run/

Thats the thing. What percentage of engines are properly broken in. I'd rather be safe than sorry......

[atc007]

Lol, my customers were schooled pretty hard. The ones I knew wouldn't listen got the slappers

[Keith Salyer]

I bought the piston from a member and it didn't come in a box.... but the price was right Thank you for the info. I can let the motor shop know the tolerances..

[81Rmachine]

A few words i remember when setting the clearance on anything from valve guides, rods, mains, or pistons is that if the clearance is a little loose only YOU know about it but if its a little too tight EVERYONE knows about it lol!
Dirtcrasher is absolutely right, better safe than sorry of course based on the application air cooled engines can run tighter tolerances than a liquid which comes as a surprise to some people because they run hotter. In reality this is true BUT when it comes to clearance you have to look at temperature bias, while the piston warms up the jug expands more consistently as it isn't jacketed with cool water. Wiseco uses a 2618 alloy on just about everything i believe which has the highest coefficient of thermal expansion compared to any other alloy such as 4032 and especially hypereutectics. Set it right at .002 and you'll be just fine!