Over the years I have been told by more than once you were on the last bore you could go over bore or as some call big bore, their are a few options one is to go to a 435cc Stoneman has done this read more here http://www.pilotodyssey.com/435cc.htm the other option is to bore it to accept the CR450 pistons.

Afastcar sent me a Pilot cylinder on the last bore and a stock bore CR450 piston so I bored the cylinder out to acceppt the CR450 piston, a few things happen when you do this first all the port openings change for example the exhaust port gets smaller and lower, smaller because its slightly tapered and down because its angled slightly down.

The rear boost port is angled up so as you go bigger that port is lowered.

The transfers because of the way they are angled get wider as you increase the bore size.

The cylinder was getting hoserized anyways so its not a big deal to adjust the ports, the exhaust port will be wider and raised, the rear boost port will be raised and enlarged, the transfers will get the usual treatment.

Afastcar is going to run a Speedchaser Pilot Cool Head with this setup so a new dome will need to be designed to work with the increased displacement and bore size, I think I have a damaged dome that I have been saving for just a occasion it was beat up during one of my Pilot Engine crank bearing failures, if I am going to machine down a dome might as well cut the material off a damaged dome save the new undamaged dome for future use.

Some cylinder pics.

I like the sound of this...
Thanks for the posting...

It`s amazing how thin you can go with the sleeve.
I once fitted a big bore kit to a Honda Z50 and the sleeve was paper thin, thought the thing would seize with heat being air cooled BUT ran perfectly

with the cr450 piston are you going to have to run a thick base plate to space the cylinder up or does the wrist pin hole line up with the pilot piston? this is pretty freaking cool idea

Will need a spacer, left is CR500 middle CR450 right is Pilot piston

Looks like it is going to oncover the exhaust port a TDC (Top Dead Center)

Cool i couldnt tell from the other pics if the heigth were the same. this is gonna be awsome cant wait to hear how this thing performs

This is what most likly "H" will do to determine the base plate spacer allowing for gaskets as a starting point. Cowboy is correct, the difference will allow the exhasut port to open at TDC (Top Dead Center) due to the piston position. This will also or should put the crown above the top of the cylinder if no space plate is used. Not to mentin to port tiiming. Does anybody have rod lenght and stroke for the CR 450.

Ok I did a quick and dirty measurement for the spacer plate by installing the piston and cylinder on my Pilot bottom end with no gaskets then putting the piston at TDC (Top Dead Center) (Top Dead Center) the outside edge of the piston is about .210 higher than the deck (top of the cylinder)

Cylinder gasket is about .020 thick.

The bottom of the top ring groove is flush with the top of the cylinder with no gasket or spacer.

I took 3 sets of feeler gauges and set them to .210 and put between the cylinder and the crank case spacing it up the required .210 I installed the cylinder nuts and tighten them thumb tight to keep the cylinder in place.

Longer cylinder studs will be required with the spacer.

Raising the cylinder the .210 now puts the outer edge of the piston flush with the top of the cylinder.

Looks like the makings of a pretty sweet big bore mod...without the bottom case mods :) I have a question...has anyone ever tried getting a piston company to make a run of spec'd pistons...eliminating the base spacer? Just curious. And how about Nikasil? Anyone ever plate a pilot cyl?

With the .cylinder raised .210 and the piston at BDC (Bottom Dead Center) the top of the piston is real close to being flush with the bottom of the transfer ports and the center of the exhaust port.

With the cylinder spaced up .210 and the piston at TDC (Top Dead Center) the bottom of the exhaust port is still covered when I remove the piston and cylinder again I will look inside and see how close it is to not covering the exhaust port.

What am I missing?

adnoh what measurements/data do you need for the head data, can just take your Pilot data and increase the bore size to the CR450?

i have a duncan 465 kit, the spacer plate that came with it is 4.61mm thick, it also came with a duncan cool head and a 49cc dome....can post pics of the cylinder if you want Hoser?????

Yes post pics please.
What piston does the Duncan kit use?

here some pics of the cylinder......duncan uses the same cr450 piston ....whats the part number of your piston Hoser??? you could have a CR480 piston... i know the 480 had a different con rod, can't remember if it is longer or shorter now but that would put the piston pin in a different position......

Number on the box I have here is 13101-KA5-000 cant really read yours but is it the same?

Think these are the numbers for all OEM sizes
13101-KA5-000 PISTON (STD)
13102-KA5-000 PISTON (OS 0.25)
13103-KA5-000 PISTON (OS 0.50)

RING SET (STD) 130A1-KA5-003
RING SET (OS) (0.25) 130A2-KA5-003
RING SET (OS) (0.50) 130A3-KA5-003

PIN, PISTON 13111-KA5-000
ROD, CONNECTING 13201-KA5-300
///////////////////////////////////////////////////////////////////////////////////////////////////
CR480 part numbers have no idea if any of these would ever work I would have to see the the parts, probably too much info but I thought while I had the page loaded I would copy it here for future reference, note the day I looked up these numbers non of the following parts showed discontinued until you got to the connecting rod its discontined.

RING SET (OS) (0.25) 13012-ML3-305
RING SET (OS) (0.50) 130A3-KA5-770
RING SET (OS) (0.25) 130A2-KA5-770
Replaced by 13011-ML3-305 (below) 130A1-KA5-770
RING SET (STD) 13011-ML3-305
RING SET (OS) (0.50) 13013-ML3-305
Replaced by 13102-MAC-680 (below) 13102-KA5-680
PISTON (OS) (0.25) 13102-MAC-680
PISTON 13101-MAC-680
PISTON (STD) 13101-KA5-770
PISTON (OS) (0.50) 13103-KA5-770
PISTON (OS) (0.50) 13103-MAC-680
Replaced by 13102-MAC-680 (below) 13102-KA5-770
PISTON (OS) (0.25) 13102-MAC-680
PIN, PISTON 13111-KA5-770
PIN, PISTON 13111-ML3-680
ROD, CONNECTING 13201-KA5-770 Discontinued

Yep the same piston......

Will let adnoh explain to us how they get 465cc out of the 450 piston.

To get displacment you need bore and stroke the combonation of the two determines Displacment. The only varible is Guedon pin offset and rod lenghts. As a rule bore and stoke will get you close enough. If the GUedon pin ( wrist pin) is offset and the rod is shorter or longer than the stroke is altered invertical motion and effects volume. Minor but matters. What I'm refeing to is rod ratio and the time spent at a given duration or crank postion. As a rule metric bikes round up the CC displacment fo there bikes very ralery do they round down. Take the pilot 400 Stock displacment is 397 it is stamped right on the jug. This is why on a two stoke we have swept volume, uncorrected and corrected. Uncorrected is used to calculate displacment or full sweep of thecyliner according to stroke and corrected volume is used to calculate CR ( compression ratio)volume of the cylinder after the exhaust port is closed off by the piston and rings. See pic. VTDC= volume at Top Dead Center. This is the compressed volume of the the piston at TDC (Top Dead Center). If you take the corrected volume is it squished into a tighter space as the piston raises to TDC (Top Dead Center). This is why corrected volume is so important for teh target RPM is will effect the MSV ( max squish velocity) and lead to detonation. If ok a lower RPM and your raise the RPMs it may push you into detonation and you will be required to lower corrected compression raio for that rpm. See the delima. If you raise the ex port it lowers MSV by altering the CR but the rpms also increse. So the squish band need to be altered and the dome cc's incresed to operate at that rpm. Raising the head will lower CR but it also comes with isues. It alteres the squish the distance between piston crown and head. If to large teh cc'sin teh dome are at a lower density and you loose power and increse heat load and the additional heat load leaches out into the piston crown adn with the altered squish there is not enough end gases to cool and causes the pipe to go into over rev.

This is where the spacer plate thickness comes in to play if you alter the spacer plate thickness you alter the swept volume and the head design, port time and area's ect.

"H" I would look at the dome next and the height above the cylinder compared to the 400. There may need to an additional correction factor for the dome height and angle. While your at it mark the piston at the bottom of the exhaust port then measure that and log as max correction factor.

You can enter this formula into a speed sheet or do hand math with a calc.

=((3.1416*(bore^2)*Stroke)/4000)*cylinders

For bore, stoke and cylinde enter a cell # than you can just change those cell numbers and it will give you your ansawer.

Where do I enter, you forget to attach a spread sheet?

Edit
Bore is 85.5mm
Stroke is 79mm
Rod is 143.5mm
Currently the distance from top of the exhaust port to the top of the cylinder is 1.834" or 46.59mm
Target RPM is 8000?

Wonder if speedchaser can make a spacer for the cylinder, going to use a gasket on both sides of the spacer?

Hot setup would be to use O rings on both sides of the spacer but bot sure if it would be cost effective.