company products support news



Q I have a 2 cylinder engine. Can I bore just one side?

A YES. Boring one side is virtually undetectable.

Q Will my engine be out of balance if I have one oversize piston and one stock?

A NO. Modern pistons, especially forged, are internally lightened to compensate for the larger diameter.

Q I heard my engine will not be as reliable once I bore it. Is that true?

A NO. It depends on two things:
Most important is who bores the cylinder and who finishes the cylinder.
It also matters what kind of piston is used. Many people think a piston is

a piston and they buy the cheapest one they can find.

Q Will my engine run hotter once it is bored?

A NO. Properly done it will run no hotter than stock.

Q Should I mix extra oil in the gas?

A NO. Extra oil:

can cause the piston to run hotter during breakin.
can cause excess carbon to accumulate.
can cause the cylinder walls to glaze and the rings may not seal properly if at all.

Q What is the difference between cast and forged pistons?

A A cast piston is liquid molten aluminum poured or injected into a mold. A forged piston

is made from a solid ingot and pressed or extruded into shape before machining.

Q What piston would you recommend? Why?

A A forged piston, specifically a Wiseco.

1- Cast pistons are brittle and often shatter causing catastrophic engine

     damage. Forged pistons are stronger to a much higher temperature

      than a cast piston could endure.

2- Forged pistons dissapate heat better and run cooler than cast pistons.

3- Forged pistons are a hi-silicon, low expansion aluminum alloy with

     improved cam and taper grind from computerized machining, that

     controls expansion to allow tighter pistonto wall clearances. This

     increases piston stability and maximizes horsepower.

4- A forged piston is also lighter than a cast piston because less material

    is needed to manufacture a strong and dependable forged piston.


1- Start your engine and let it idle, occasionally blipping the throttle for four to five minutes. Allow the engine to cool completely. Repeat this heat cycle process four more times.
2- Warm up the engine again and ride the bike five to seven minutes at a very easy pace. Very the rpm, and do not ride at one speed. Do not ride at more than 1/3 throttle or more than 1/3 rpm. Let the engine cool down completely and repeat the initial break in ride. Let the engine cool down.
3- Check the base and head nuts for proper torque. Check the coolant level and coolant as necessary.
4- Ride the bike for five to ten minutes at a moderate pace. Very the rpm, and do not ride at more than 3/4 throttle or more than 3/4 rpm. Then let the engine cool completely and repeat this secondary break-in twice.
5- Replace the spark with a new one. Ride the bike for five to eight minutes at a moderate pace. Vary the rpm, and shift up and down gears. Once the engine is up to operating temperature, you can make a jetting pass. Start in second gear and ride at full throttle at fourth gear, fully revving out fourth gear. With the throttle wide open in fourth hold the kill button down, pull the clutch and stop. This is called a plug chop.
6- Read the spark plug. With a pocket flashlight and a magnifying glass, look at the porcelain part of the plug only. As you view the plug from the center electrode, look down on the length of the porcelain to its base. There should be a dark chocolate colored smoke ring. There was not sufficient time to thoroughly color the whole plug, so the nose of the insulator may still be white. As long as there is a visible dark ring at the base, everything is OK. Remember, we want break-in jetting, so the plug should read rich/dark. Richen the jetting as necessary. If you are having a hard time reading the spark plug, follow the proceeding steps: Put the plug in a vice and hacksaw around the plug at the washer. Break the threads off with vise grips and the porcelain will be easy to read.
7- Complete the break-in by riding at an aggressive pace for fifteen minutes. Vary the rpm and do not cruise at part throttle. Ride hard without revving the engine too high. At the end of this final break-in session do another jetting pass/plug chop as described above. Check the spark plug for the correct dark/rich condition. Wiseco piston equipped engines will require another one or two break-in cycles. If your engine is equipped with a Wiseco piston, continue with the following steps: Ride at a s recreational pace not revving the engine hard. Full throttle should only be used for very short periods. Fifth and sixth gears should only be used to cruise. Ride one tank of gas through the engine in this manner to complete the break-in.
8- Replace the spark plug with a new one. Ride the bike aggressively for eight minutes and do a jetting pass/plug chop in fifth gear. If the porcelain is still dark/rich, lean the main jet size one at a time until the smoke ring at the base of the porcelain is light brown. If the porcelain base is white, do not run the engine and contact Bill Bune Enterprises. If the plug color looks good, continue riding at a race pace for ten minutes. Stop and let the engine cool. Check the torque on the cylinder base and head nuts.


More on jetting: If you generally run your engine flat out sixth gear, then make your jet pass/plug chop in sixth. Motocross jetting is checked in fifth gear, therefore it is not safe to run MX jetting in the desert wide open in sixth. Desert jetting is richer than MX jetting. When running an engine at full throttle for extended periods, be sure to chop the throttle decisively to slow down. Just rolling out a little can seize a well-jetted engine.

Remember, the best top-end overhaul, done by the most qualified mechanic,

is only as good as your break-in procedure. Good luck!



2)   Cold seizure ( insufficient warm-up)
3)   Failure to properly wash and prelube piston and cylinder prior to assembly.
4)   Insufficient air speed through fins on air cooled engines.
5)   Improper ignition timing.
6)   Carburetor jetting to lean.
7)   Carburetor jetting too rich.
8)   Gas and Oil not thoroughly mixed.
9)   Excessive load on or lugging of the engine.
10) Worn out or improperly installed crank seals.
11) Blown head gasket.
12) Head gasket improperly installed.
13) Engine speed too high during break-in period.
14) Alteration of intake or exhaust system without rejetting.
15) Insufficient ring end gap.
16) Too much ring end gap.
17) Improper ring style or type.
18) Insufficient oil in gas.
19) Too much oil in gas.
20) Poor quality, cheap or wrong oil.
21) Too much compression.
22) Bad or old gas.
23) Gas with too low of an octane rating.
24) Addition of the wrong gasoline antifreeze in mixed gas.
25) Fuel additives improperly mixed or used.
26) Improper spark plug.
27) Insufficient piston to wall clearance.
28) Too much piston wall clearance.
29) Use of badly worn or distorted piston in fresh bore.
30) Pre-ignition.
31) Detonation.
32) Insufficient piston to squish band clearance.
33) Plugged or restricted exhaust system.
34) Air leaks around intake manifold, base gasket or center gasket.
35) Use of a piston other than the one the cylinder was originally sized to.
36) Honing too course.
37) No honing at all.
38) Head bolts overtorqued.
39) Faulty or stuck thermostat.
40) Thermostat removed from system.
41) Bad oil pump.
42) Bad water pump.
43) Improper cooling: low water level, fins clogged with mud.
44) Use of oxygenate gas without rejetting.
45) Carburetors not synchronized.
46) Loose fitting sleeve.
47) Cracked sleeve.
48) Ice in oil line.
49) Ice in fuel line.
50) Clogged, pinched or leaking fuel or oil line.
51) Cooling system not properly bled.
52) Oil injection system not properly bled.
53) Improperly installed fan shrouds.
54) Plugged jets.
55) Loose or broken fan belt.
56) Water in float bowl.
57) Dirt in float bowl.
58) Loose or missing drain plug.
59) Anti-freeze in combustion chamber; faulty head gasket or cracks.
60) Insufficient fuel; may need two fuel pumps.
61) Leaking, loose or plugged fuel pump pulse line.
62) Bad fuel pump.
63) Loose, leaking or plugged pulse line.
64) Poor quality piston.
65) Clutch not properly set up.
66) Cracked fuel line in tank.
67) No snow on heat exchanger.
68) Diesel fuel in gas tank.
69) Improperly installed piston return spring.
70) Too much alcohol in driver.
71) By far the most common cause of piston and engine failure comes from the loose nut that sits on

       the seat and over revs the engine instead of shifting it and generally doesn’t have an

       understanding of what really makes it work or how to keep it serviced.


1- Wash with Soap & Water
2- Oil
3- Ring End Gap
4- Timing
5- Jetting



Re-sleeving worn or seized motorcycle, snowmobile and watercraft cylinders,

continue to provide economical and available solutions to Riders and Racers everywhere.


Cylinders sleeved with chrome-moly iron alloy sleeves can now be bored to fit the many

over-sized pistons available on the market today. Pistons available in oversize up to 2.50mm

provide the owner with a substantial economic incentive to re-sleeve a worn cylinder. The cost

of a bore job today is usually 10% of the cost of a new cylinder. Combine that with the original

expense to re-sleeve a cylinder, usually about $200.00 (or 30% to 40% lower than new cylinders),

the owner realizes an overall savings that brings smiles to his or her riding budget.


Two stroke tuners and porting specialists find that when race porting a sleeved cylinder they do not

have to contend with flaking or peeling that they might with an aluminum plated bore. Our 2.5mm thick

spun cast-sleeves are made from an iron alloy of nickel, silicon and hardened carbon chrome of which no plating process can compare. To take it one step further Moly-2000 is added for a slick anti-resistance to friction. This special ingredient reduces ring drag to increase piston speed down the slick walls, giving you great RPM. Racers and engine rebuilders have relied on these features for fifty years.




Please email us for any inquiries:



Copyright ©2007. All Rights Reserved. Site Designed and Maintained by JTWorldwide Publishing.

No pictures or information may be reproduced without our express written consent

Home | Sitemap | Mobile Link | Useful Links