How Do I . . . Build a Big BORE Motor? (86mm or larger)


Expertise Required, Planning, Estimated Time, Parts Needed, Tools Needed, Step-By-Step, Break-In Procedures


Topic:                          What does it take to build a big bore motor? It takes the following:

      • Proper Planning - parts, machining, consumables, etc.
      • Fairly decent technical skills
      • A good machine shop you trust
      • Basic (metric) hand tools
      • Patience . . . lots of patience
      • Money . . . if your planning says you need $1000.000 - plan on having $2000 available.

Expertise Required:      Better than average level. Besides the ability to disassemble and reassemble an engine, you'll need to have the ability to do the following:

      • Use the proper tools to be able to measure the port timing for your motor
      • Setup and use a Degree Wheel properly
      • Accurately measure the ports on your motor (width and height)
      • Accurately measure the piston you are using - and - the NEW BIG BORE PISTONS you plan to use

Planning:                     You will need to plan the following correctly:

      • How much power do want to make?
      • How much money do you want to spend?
      • What octane of fuel do you want to run?
      • Are you capable of doing this project . . . seriously?
      • Do you have a machine shop that you can trust to bore and deck block?
      • Do you have a machine shop that can modify your cylinder head properly?
      • Oversize pistons - Are you gonna use off-of-the-shelf Wiseco or Tohatsu pistons? Are you sure they're still available in the size you want?
      • Head Gasket - You gonna have a stock one modified, or have a custom one made? If custom, will you with fiber or copper (copper requires much better block/head surface preparation and very rigid installation procedures.
      • Crankshaft Rebuild - Plan on having the guys tig weld the pins and weld in a plug in the lower wheel

Estimated Time:            My experience has shown that the time needed is as follows:

      • Planning the parts needed, sourcing the parts and getting them ordered (4 hours)
      • Removing cylinder head, setting-up Degree Wheel (1 hour)
      • Measuring the port timings for all of the ports (1 hour)
      • Measuring deck height for both cylinders (about 5 minutes)
      • Disassembling motor, cleaning bores, and doing a port tracing (about an hour)
      • Putting all of the information gathered into a spreadsheet style of format (1 hour)
      • Accurately measuring new pistons (squish band, dome height, pin height, pin boss width, etc) (30 min)
      • Getting crankshaft cleaned and boxed up with new parts to send off to Northern Crankshafts (1 hr)
      • Initial block cleaning after coming back from machine shop (1 hour)
      • Porting - basic cleaning to get aluminum to match liner (1 hour). If having to raise/modify ports, plan on a minimum of (4 hours)
      • Polishing Cylinder Head Domes (about 1 hour)
      • Prepping block for paint (1 hour)
      • Painting block and head (including primer) (2 hours)
      • Measuring and correcting ring end gap (30 min.)
      • Trial assembly (without rings) to verify proper deck height and port timing (1 to 2 hours)
      • Final Assembly of Short Block (1 hour)
      • Trial fit of head (measuring squish with solder) (aboug 1/2 hour)
      • Cylinder head installation (about 30 min.)

Parts Needed:               Plan on the following minimum parts list:

      • Crankshaft parts - rods, lower bearings, lower pins, all bearings and center seal
      • Pistons - New Wiseco or Tohatsu pistons
      • Piston Pins - New Suzuki pins (the thin-walled shiny ones)
      • C-clips - New Wiseco, Suzuki, or Tohatsu ones. Never re-use old clips
      • Seals - New Suzuki Upper, Lower, and Crankshaft seals
      • Gaskets - New Suzuki Magneto Housing Gasket, Carburetor Gaskets, Fuel Pump Gasket, and Air Box Gaskets
      • Head Gasket - Use a modified Suzuki 60hp gasket or custom-made one of your choosing. Note: You will need to be dead-nuts sure of the gasket's thickness (when torqued) in order to know how much to machine the block and/or head.
      • Cylinder Head - Modified properly to achieve the proper squish band - AND - the proper volume.

Tools Needed:               Besides the standard metric hand tools, you will need the following:

      • Degree Wheel
      • Digital Dial Indicator that's long enough to reach down in the bores to the piston top at BDC
      • Caliper or equivalent that will help you measure the port shapes
      • Dykem Blue (or equivalent) to mark ports for adjustment/correction
      • Porting (cleanup only)- Dremel with right-angle attachment,beaucoup grinding stones for steel, various burrs for aluminum. 3M style buffing stars for polishing.
      • Porting (real deal) - Flexible shaft porting tool with long shanks and tons of attachments (lots of mooluh)
      • Consumables - WD40, Aerosol Brake Cleaner or Berryman's B-12 (carb cleaner), White Cotton Rags
      • Hand-Impact Driver - for countersunk magneto base screws and magneto screws

Step-By-Step:               Perform and record all measurements first (during teardown). Then you can do the following:

      • Crankshaft - box it up with all of the new parts and send it off to Northern Crankshafts
      • Once you have recorded all port timings, you can then decide what changes need to be made (decking block, porting, squish band changes, etc)
      • Pistons - once you have yours in your hand (and have measured them correctly), you will know if you need to deck the block (and how much), you will know if you need to adjust port timings, and you will know how much you need to modify the cylinder head.
      • Perform all of your porting cleanup and/or modifications prior to having the block machined
      • Degrease the block and head and get them cleaned-up and ready for machine shop
      • Get your machining instructions together and take parts to the machine shop
      • While you're waiting to get the block/heads back, take the time to degrease, debur, and clean up all of the fasteners. I don't recommend bead-blasting them, but a rotary tumbler works pretty good.
      • When block gets back, prep it good - and immediately oil down the cylinders
      • Piston Rings - Set the end gap properly (a ring end gap grinder works great)
      • First Trial Fit - Assemble pistons onto rods, throw a couple of o-rings on the pistons and drop the crank in (carefully) and button up the bottom end with a few bolts. Don't tighten them down over a couple of ft lbs - just enough to make sure the crank is held in place firmly. Rotate engine around and measure all of the port heights (from the deck) to make sure they're where you want them.
      • More Port work - If you need to make some adjustments at this point, be vewwy careful not to nick the cylinder anywhere with the porting tool. Also be aware that a full de-greasing/wash will be necessary when you are done.
      • Final Assembly - Carefully install the rings, install the 2 new seals in the lower seal housing, grease-up the lower main seal and get your 1211 ready.
      • Carefully lower pistons into bore and set crankshaft bearings down into the saddles. Be careful to get get center seal lip oriented correctly - and - make sure the bearing alignment pins are in their correct spot. Note: On 88mm motors you need to be extra careful when sliding into their bores because the sharp edge of the cylinder sleeves are exposed (if you counter bored the bottom correctly). Sometimes a little screwdriver helps here - but be careful not to snap a ring off.
      • Slide a couple of pieces of wood under block so that pistons won't hit table and spin motor to make sure it turns freely. Tilt up bottom end of the crank and install main seal.
      • Slide on the lower seal holder - make sure you get the little tang on the correct side. Look and the mating surface of the engine housing and you'll see which side it should go on
      • Apply 1211 (case sealer) put the lower engine half on and torque down properly (per service manual)
      • Roll motor over and put a little oil (either 2-stroke oil or 2-stroke engine fogging oil) on the cylinder walls
      • Clean both the block surface and the cylinder head surface thoroughly, install the head gasket and torque down (per the service manual)
      • Prep it for paint - and paint it
      • Run a tap through all mounting holes if they were painted over (coil mount, fuel pump, starter bracket, etc.
      • Install new seal into magneto cover, fill it with waterproof grease, grab a new gasket and install flywheel cover using a hand-impact to set the countersunk screws correctly.

 


Break In Procedures:     Opinions vary but here's the method I've used sucessfully:

      • Fuel - double-up on the oil mixture for the first 5 gallons
      • Jetting - if you've built a Hogzilla, then you need to be conservative on the jetting until you get it dialled in. I like to start at either 165 or 162.5 jets for break in.
      • Timing - for break in I like to have the mark in the middle of the hole.
      • First Start - I like to fire it up on the trailer and run it for about 30 seconds or so until I feel some heat building in the block/head. Shut it down and let garage clear out the HUGE SMOKE CLOUD
      • After block cools back to room temperature, I like to do that one more time.
      • Once I get to the lake, I like to run the motor on the trailer for about 2 or 3 minutes until it feels like there's pretty good heat in the motor. Shut it down and let it cool back down for about 5 minutes.
      • Off the trailer and ready for the first ride. It is extremely important to let motor warm up properly before putting any kind of load on it.
      • Idle out from the boat ramp for about 2 or 3 minutes until the motor is starting to get some heat in it. Now, add about half throttle to get the bike moving pretty good - but do not come up onto plane. Keep it there for about 15 seconds, then let it drop back down to idle speed. I do this about 3 or 4 more times on BIG BORE motors with FORGED pistons.
      • Now I roll the throttle on (not full throttle) to get bike up on plane and slow motor back down just enough to stay on plane. After about 30 seconds, I drop back to idle (for cooldown). I'll do this barely-on-plane procedure about 5 or 6 more times - with additional idle around time too. Head to the beack and let it cool down completely (ending first major heat cycle)
      • Out for another ride - after proper warmup again. Same thing on getting up to plane except I increase the speed to about 1/2 throttle (or around 4000 rpm I think). At this time I determine whether the carbs need to be sync'd. If the motor will idle way down without dropping a cylinder, then they're spot on. After about 20 minutes or so of riding, I let things cool down again.
      • Final break in rides - I continue with the long warmups (proper warmups) and constantly vary the speed of the motor. Eventually I do a couple of full-throttle bursts - holding it wide open for about 5 seconds - then slowing back down to an idle. I'll do about 5 or 6 more WOT bursts and then drop down to idle for a half minute or so.
      • Once I've burned about 4 1/2 gallons, then I'll try going WOT for 10 or 15 seconds - then back down to idling around for cool off.
      • Once 5 gallons of the double-oil is done, I'll drop 5 gallons of 91 or 92 octane with 50:1 mixture in there and continue with the short WOT bursts. After burning about a gallon, I'll pull the plugs and see what they look like. Usually I like to burn this additional 5 gallons before doing any jetting changes.

 

Simple eh? 

 

 09/12/2017

Copyright 2012 Capt'n Obveeus

Joomla templates by a4joomla
+