CR500 Engine Build Pictorial Part 5
This segment will deal with cylinder prep, piston selection and prep, and
The stock CR500 cylinder is unique in that it uses an unplated steel
This is what the cylinder looks like right out of the box. Note the sprayed on
plastic protective coating.
Since this engine is being built for MX racing, I decided to have it ported and
machined specifically for that purpose. The port work is designed to up the
power but smooth the "hit" making the bike faster but easier to ride.
Even though the cylinder is brand new, it was bored .001 over to ensure a
perfectly concentric bore. In addition to the port work, the base was
machined to lower the ports (alter the timing) and the intake inlet and
exhaust outlet were matched to the VForce and exhaust flange respectively.
Inlet on a stock cylinder
Reworked exhaust ports
Exhaust ports on stock cylinder.
Matched and "smoothed" Exhaust port
Matched and "smoothed" intake.
The base of the cylinder head was also machined to raise compression and a projected
nose spark plug is used.
Comparrison of BR8EV (non-projected) on left to BP8EV (projected nose).
Piston selection is critical on a 500. The increased power and vibration take
a toll on the stock cast pistons. I like to use a forged Wiseco for this
application. This piston is very strong and comes with a nice slick coating
Wiseco calls Armorglide. The piston feature reliefs and lightening holes
to keep the weight down.
It's a good idea to thoroughly clean the freshly machined cylinder and head
to ensure that all debris has been removed. Next, wipe the bore down with
ATF and a clean cloth repeatedly until the cloth contains only clean ATF.
Now coat the bore with clean two stroke oil, it's ready to install.
Prep the threads of the cylinder studs with loctite on the bottom and anti
seize near the top of the threads and install with the rounded end of the
stud facing up using a stud installer or a pair of flange nuts. Torque to 25
Coat the "small end" bearing with clean two stroke oil and install
Install a new pin in the left side of the piston leaving the gap in the middle
clear. Place the piston over the rod and push the pin through. Install a
circlip into the groove on either side with the gap at the 12:00 or 6:00
position. Make sure the circlip is fully seated.
I'll finish the engine in the next segment.
Last edited by dogger315; 01-12-2011 at 09:44 PM.
Nice .... it's interesting that you chose to smooth the intake port... I understand the matching and cleaning up the casting, but why smooth it out? Tumbling the air I thought breaks it up hence the point of some of the new products for carbs and such.
Some of the best motors we've ever had built were stock with the exception of opening up the intake and cleaning up all the casting imperfections, some of them it turned into real rockets.
Very interesting piston choice... I've read a bunch of piston debates on the 'net for the 500's and most of them end up with the Pro-X piston being the "chosen one".
Maybe you had the "one" over done to match the bore size to the proper clearance for the forged wiseco?
Very, very nicely done. I am still a fan of the plated aluminum sleeves though. In answer to smoothing the intake, the transfers seem to have a very nice texture. The actual intake area, IMO, isnt as important when it comes to the finish. Very nice! That exhaust port will really liven the beast up. Tdub
or tumble the intake charge. The conventional wisdom here is
"smoothing" the tracts (they're not polished) will speed airflow in
and out of a reed valved engine.
something stronger than a casting for this application.
go with a plated Aluminum sleeve for the CR100. He likes the heat transfer
ability of the Aluminum over Steel especially with the sleeve down. The
plan is to modify the crank to accept a larger pin so we can use late model
CR125 rods, a RM85 overbore piston (50mm) with some serious mid and up
port work on the cylinder. He is also welding up the dome on the FMF
porcupine head and reshaping it for 100cc. The engine should be a little
Last edited by dogger315; 01-12-2011 at 09:49 PM.
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