Back to Tech Tips

To assure maximum results from your big-bore kit, it is recommended you have a competent local shop which is proficient in small engine boring work complete the necessary work. Satisfactory engine performance demands precision machining.

Your Powroll kit is engineered to install without additional modification. However, problems can arise due to variations in OEM parts, possible worn parts, or use of other aftermarket parts. For this reason, it is imperative to perform the basic engine checks which follow.

These instructions are directed towards knowledgeable mechanics who have access to the proper equipment. They are not intended as a complete guide to all machining and installation procedures. 

Failure to read and follow these instructions may result in shortened engine life.

CLEANLINESS

Pay particular attention to installation cleanliness. Wash all parts in solvent, then hot soapy water before assembly. A tiny particle of grit can cause huge amounts of grief!

ENGINE DISASSEMBLY

After complete disassembly, remove all gasket material and dowel pins. Carefully clean all mating surfaces. If your kit contains a new cylinder sleeve, refer to step 2 for installation procedure. If your kit bores into the stock sleeve, proceed to step 5. In any event, make certain your cylinder is in good condition, without cracks or other flaws before proceeding.

BORING CYLINDERS FOR OVERSIZE SLEEVES

1. Press out old sleeve (Cast-in sleeves must be bored out).

2. Clean the crankcase and cylinder block. Inspect mating surfaces.

3. Boring bar set-up should index to the lower machined surface (crankcase side) of the cylinder block.

4. Center on the existing cylinder bore. Double-check for accurate bar alignment. There should be no more than .001" variation from top to bottom of cylinder.

5. Carefully clean the oversize cylinder sleeve and gauge its outside diameter. The cylinder block bore should be .005" undersize to allow for honing. Final sleeve-to-cylinder interference fit is .001" FOR EACH INCH OF SLEEVE DIAMETER.

6. The sleeve in most Powroll kits will fit the original cylinder flange counterbore. To ensure correct fit, cylinder counterbore measurement should be .005" to .010" larger than the sleeve flange.

7. Counterbore depth should be at least .oo5" less than sleeve flange thickness to allow for final surfacing.

8. Debur top of cylinder after boring.

Some oversize sleeves may require case enlargement. In an existing machined bore, use the original bore to center, and enlarge to a diameter .040""greater than the spigot of the new sleeve. Do not exceed original depth.

1. Cylinder bore should be honed to arrive at interference fit of .001" for each inch of sleeve diameter. For multi-cylinder engines, measure and fit each sleeve separately. All parts should be at room temperature for accurate measurements.

2. Thoroughly re-clean all mating parts before installing sleeves (solvent and hot, soapy water).

3. Place cylinder in 350* oven. Heat for at least 30 minutes or more.

4. Place sleeves in freezer for an equal amount of time.

5. Heated cylinder should be supported to permit passage of sleeve spigots beyond bottom of the cylinder. Insert chilled sleeves into their respective bores. Make sure sleeve flanges seat into the cylinder. Allow the cylinder and sleeve assembly to return to room temperature before proceeding.

6. Cylinder may contract away from the flange of the sleeve as it cools. To completely seat sleeve, it should be pressed down with several tons pressure. Use a pusher with the same diameter as the sleeve flange.

7. Surface top of sleeves down to cylinder deck height. Lap or blanch for final finish.

8. Bore and hone sleeved cylinder as outlined in #5.

BORING THE CYLINDER

1. Index the boring bar to the BOTTOM of the cylinder.

2. Find the required piston to cylinder wall clearance specifications at the bottom of this page. WARNING – Powroll pistons are designed with taper and cam engineered into them, and are NOT round. Take diameter readings to determine the widest cross-section of the piston (may be at the bottom of the skirt, or the middle, depending on piston design), use the widest reading to determine bore size. Powroll has determined correct clearance for your bore kit, not following the recommended clearance can cause decreased engine life.

3. Underbore sufficiently to allow honing to remove all machining marks (using 320 to 360 grit) before arriving at final clearance. Test your progress: It’s better to hone cautiously, making several fitting tests, than to suddenly discover the hole is too large.

4. Re-check piston-to-cylinder clearance.

5. Clean cylinder, piston, pin, clips (or Teflon Pin retainers) and rings. First in solvent, then blow dry, then wash in hot, soapy water. Blow dry. Take special care with Teflon Pin Retainers, any grit left on the retainer can scratch the cylinder.

6. Complete cleaning of cylinder using a clean, white, lint-free towel and a small amount of engine oil. Keep using a clean area of the towel, wiping until the towel comes away with no residue.

CHECK PISTON PIN END PLAY

Fit the piston pin supplied with your Powroll kit by oiling the pin liberally. Before installing onto rod, test for correct piston pin end clearance.  Set Teflon pin retainers or circlips in place.  Slip piston/piston pin assembly into cylinder.  Lateral pin movement shouldn’t exceed .040".

RING END GAP

If Powroll bored your cylinder, our technicians have already gapped your rings, proceed to the next step.

Powroll rings are purposely oversize to enable re-ringing of cylinders which have worn within acceptable limits. Ring ends must usually be filed down before installation, see below for ring gap specifications. If end gap is not listed, gap using this formula: .0035" x Bore Size (in inches).

1. Compression & Scraper Rings, and One Piece Oil Rings: Position each ring squarely in the cylinder (use the piston to push the rings into the cylinder). Using a thickness gauge, measure the gap. File rings to the end gap listed below. Excess gap is not critical – insufficient gap can be ruinous.

2. Three Piece Oil Rings: Center (corrugated) piece will not need to be gapped. Check and file rails in the same manner as the compression and scraper rings.

1. Install rings according to orientation diagram below:

2. 

3. Place Oil Ring Expander (wavy shaped ring segment) into the oil ring groove with the butted tips of the expander facing the exhaust side of the piston. Be sure tips of the expander are visible and properly butted (see fig d). Overlap of Oil Ring Expander tips will cause severe smoking and possible engine damage.

4. 

5. Thin Rail Rings can be installed with either side up. One rail ring below oil expander ring and one above. Rail end gaps are to be located according to diagram above.

6. Once rail rings are installed, be sure the expander tips are still butted and not overlapped.

7. Installation of middle (scraper) ring: Middle ring can be either silver or black. Install ring with markings facing up.

8. Installation of top (Compression) ring. Top ring is usually silver faced. Install with markings facing up. If no markings are evident, ring can be installed with either side facing up.

PISTON INSTALLATION

Pistons have one of the following markings on the top of the piston indicating direction of installation:

       Faces exhaust

IN                     Faces Intake

No Marking      Install with larger pocket towards intake (Only if no other markings are visible)

Assemble piston in cylinder. Rotate crank until piston arrives at TDC. Piston deck area should not protrude above top of cylinder. Make sure piston also clears the crankshaft at BDC.

GASKET INSTALLATION

Some kits include a copper head gasket. For proper sealing, it is important to follow the instructions.

If a gasket is not included with your kit, use an OEM gasket, making sure to check that the piston will clear the gasket.

COMPLETE ENGINE ASSEMBLY

1. For high compression pistons, or if you are installing components from various manufacturers, it is HIGHLY RECOMMENDED to check clearance by claying the top of the piston. MINIMUM valve to piston clearances are .040" - .060" Intake, and .060" - .080" Exhaust. Minimum piston to head clearance is .040".

2. Torque head bolts to OEM specs. Do not over-torque. Re-check head bolt torque after several hours.

3. Before attempting to start the engine, slowly rotate crank by hand through a complete firing cycle. Carefully listen and feel for any interference.

PRE-FLIGHT CHECK LIST

1. First, double check to be certain all timing, valve and cam chain adjustments are correct. Then begin break-in as outlined:

2. Fill crankcase to correct level with oil. We recommend using Racing 40 wt. Oil for break-in. After break-in, use good quality non-synthetic motorcycle oil. We have not seen good results from standard automotive or synthetic oils.

3. Install oversize carburetor jets. For initial operation, install a main jet at least three to four sizes larger than stock. Move the clip down one position on the needle (richer).

4. Remove valve adjustment cap or cover. Rotate the engine by hand until oil is seen reaching the rocker assembly. DO NOT START ENGINE UNTIL OIL IS OBSERVED FLOWING INTO THE HEAD.

5. Fuel. Premium pump fuel can be used on engines up to 10.75:1 compression. 11:1 – 12:1 compression engines need ½ premium pump fuel, and ½ race fuel (NOT AVIATION GAS!). Compression higher than 12:1 requires straight race gas, at least 108 octane. These octane rating requirements must be met at all times, not just during engine break-in.

1. Start bike and hold engine at a fast idle. Run through the gears, accelerating slowly. Do not over-rev or lug the engine. Ride for about 20 minutes.

2. Stop and allow the engine to cool. Re-torque head bolts and check all other fasteners.

3. Complete step "a" again, this time running engine off and on for an hour. Stop and allow engine to cool. Change the oil and filter. Fill the engine with your regular oil. Re-check valve lash settings, timing, etc.

4. Run the engine at least 1 ½ hours before jetting for power.

1. For break in, the engine should be run slightly rich causing the engine to blubber, sputter or miss and lose power at higher RPM.

2. AFTER break-in, drop back one jet size at a time, until the engine runs smoothly in third gear with throttle wide open.

3. If engine feels sluggish from ¼ to ¾ throttle, you may need to move the needle clip.

4. Some owners try to double-check carburetion with a spark plug reading. Today’s extended-range plugs and fuel additives make this difficult to judge. We no longer recommend this test.

IF YOU LOSE THROTTLE RESPONSE: Always be alert to any loss of power, sluggishness, popping through the carburetor, or overheating. These are sure signs of improper tuning – stop immediately to avoid engine damage.