Engine Top End

As I mentioned in the last posting, I plan to work on the reliability piece with the engine. Again, its no powerhouse, but it is known for its reliability, especially when compared to 450 moto bikes. There are, however, 2 known issues when the engine is worked hard at high sustained revs. The camchain on pre-2002 bikes can slip due to a poor automatic camchain design. In the middle of the summer, I replaced mine with a manual camchain by APE. Sorted.

The second known issue is a bit more involved. The valves are weaker 2-piece design, and can come apart after lots of abuse. Again, for piece of mind, I have decided to get proper race valves installed, along with better quality springs. When I send the head down to Eddie Sinceros of Sinceros Speed Works, he will also shim the valves to whatever cams I have... and since I already have the cams out... I'll be sending down a pair of stage 1 hotcams for him to put into spec.

Again, the urge do go overboard is still quite strong, but I need to hold off for awhile and continue to develop the bike. Power is nothing without Control...! The big bore will have to wait.

I did take the cylinder itself off as well, and everything appeared to be in good condition. The cylinder will get a quick hone with a ball hone -- the cross-hatch marks could be seen, but there were a few streaks of increased wear in a few spots. Nothing major. I did check and the piston ring end-gap was well within specs -- not sure if it was the original piston or not inside. The piston is marked ART, which is an aftermarket supplier. However, sometimes when these companies grow they become OEM suppliers as well.

I did get in the necessary supplies to properly rebuild the top end. New base and head gasket, a piston circlip (got a couple extra while I was at it), an new set of rings (ouch!), and that's about it. I decided to get the thinner "E" base gasket, which will increase compression somewhat. Might add 1/2 a hp -- but I always put premium fuel in the bike at all times, so pinging won't be an issue. Haven't sent off the heads yet, as I am still waiting on the cams to arrive. Perhaps I can time the assembly for when Dad or brother Tim show up -- an extra hand threading the timing chain through the head would be helpful!

As promised, I bought the "rights" to the digital photos that Rob Bye took at the track. Again, a pretty weak angle of lean, but I am exiting turn 5 in this shot... I know I had the machine heeled over much farther than this! As well, I've spent a total of about 8 minutes on the bike on a track... excuses, excuses!

Lastly, I'm doing some research as to the "ideal" exhaust header length as I want to get a header fabricated out of stainless by my friends at Cycleboyz. I found an online header length calculator, and after doing some research, came up with the following specs...

Exhaust open BBDC: 65

Exhaust close ATDC: 29

Engine RPM: 7250

cc of 1 cylinder: 434

Results: 26" tuned length from valve head

Primary ID: 1.625"

Tailpipe Length: 22.967" (this is the muffler)

So, the figures above are for an E cam, which is similar to the hotcams. The RPM figure is based on where the HP peaks on these engines. The 434cc is anticipating a bigbore (eventually). The ID of the header works out to roughly 1 5/8" -- smaller than the 1 3/4" I currently use. And of course, the header length is quite short!

The final design might look something like this (quite popular on the showroom floor!)

But, I really don't want to creat a situation like this... even though it is a racebike, and I'm a MotoGPwanna-B... will continue to do some research. I'll see what the cycleboyz guys say. Right now, I'm leaning towards 1 3/4" tubing, and shortening up the whole assembly, although I don't think I can fit a 26" header and exhaust under the engine -- it'll be a bit longer, and attach to the right peg. This saves me monkeying with the rear seat subframe -- the muffler attaches to the peg assembly like on the Gixxer above. I think I can also shorten the TwoBros muffler I have to suit... and by shortening it in the right place, I can cut out the area that was damaged in the previous owner's crash. As always, stay tuned. The frame and swingarm should be back from the painter's in a couple of days.