MPS-PG-650 build

[JimL]

Carbs will fit, and still have room under the tank.

JimL

[JimL]

Handlebars will be mounted lower after the fairing is fitted and steering stops in place.  This is a pretty little thing, despite the strange pushrod engine!

[Old Scrambler]

Very creative build.............Certainly looks to be a challenger in the 650 class.

[JimL]

We hope so, it will be running against the record Dan set this year.  This is the same engine, but a little more serious power upgrades, plus chain drive instead of shaft.  This bike will also be a "bolt-in" candidate for my "half-a-680" 340cc single (my 680cc gave us a couple of 159+ miles, this year).  That little motor will have to wait for future years, and lower gears (poetry).

Regards, and happy Holidays!
JimL

[wobblywalrus]

Jim, this is in response to your saying there are problems with getting power at over 10,000 rpm.  Most of my experience is with British stuff and 10,000 rpm means an exploding motor.  I never thought about how to get power at those engine speeds.  The following are some things I read about or heard during discussions.

The engine math we use is based on average values, for the most part.  The actual things happening in the engine vary above and below that average.  The calculations might show the average mach numbers at the valves to be slightly below sonic.  In reality there might be some places where it is sonic and this will hurt power.

Proper fuel atomization can be a problem with some delivery systems at high engine speeds.

Flame front speed is dependent on the properties of combustion and not rpm.  Possibly at high rpm the peak pressure spike in the combustion chamber is occurring too late in the cycle.  The piston is too far beyond TDC.  Some additional spark advance might help.

This is about all I know. 

[JimL]

That's what I'm thinking.  I've been pretty conservative with the timing, but I know I'm getting late, now that I'm starting to burn and distort exhaust valves.  I'll have to step up a little on fuel, and burn earlier, and hope I can "climb out of the hole" on 4th-5th gear upshift.  That's catching about 140mph, now, and I'm just about falling off the cam on the shift.  Funny how the power band gets so narrow as the speed creeps up (it's mostly just plain "lack off cubic inches" in my little engines.)  Perhaps someday I can build a skinnier bike.

Regards, JimL

[55chevr]

Running smaller displacement engines and a narrow power band means gearing is critical.  The great white dyno will keep you out of the power band in high gear if you miss the gearing by one tooth in the rear.

[JimL]

I missed it by two, this year, due to my old eyes reading the numbers on the sprocket wrong, and my befuddled brain thinking, "...why am I cutting so much out of this chain?" 

"Left the money laying on the table", as they say.  I sure hope I've got this new bike figured about right; I don't have as many gearing choices available due to the shorter chassis creating a "close" spot at the swing arm sliders.
Regards, JimL

[wobblywalrus]

Those Honda race bikes from a long time ago all used reverse cone meggas, as I recall.  That might be what you need to widen the power band.

[thefrenchowl]

JimL: now that I'm starting to burn and distort exhaust valves

I suppose your engine is still water cooled??? If so, the usual cause for valve failure in such engines is cooling water flashing out as steam in the proximity of the combustion chamber.

Usually caused by having not enough pressure in the system to prevent the water flashing. The practical remedy is to make the outlet water pipes on top of your heads a much smaller diameter to create a back pressure that will increase the temperature at which water will flash. Restrict by inserting a reducer.

Check how small the outlets are on this Miller supercharged engine:



Patrick

[Koncretekid]

I missed it by two, this year, due to my old eyes reading the numbers on the sprocket wrong, and my befuddled brain thinking, "...why am I cutting so much out of this chain?"  

"Left the money laying on the table", as they say.  I sure hope I've got this new bike figured about right; I don't have as many gearing choices available due to the shorter chassis creating a "close" spot at the swing arm sliders.
Regards, JimL

Jim,
This is what I did to help me choose the correct sprocket. Red is the fastest (smallest), orange is next, etc.  Easier to remember what color to use than try to remember the number.

As to your problem of burnt exhaust valves, I would re-visit your decision to flow the cooling water in the reverse of normal (thru the heads first).  I think it is possible that some areas high in the heads may be starved for cooling water.

Tom

[JimL]

Interesting and good thinking.  I did have some air trapped last year (learned recently that I have to suspend the bike vertically to get it all out).  I found no evidence of water getting through the head gasket, but steam is really a gas and I don't think I would have noticed that after wrestling off the heads.

 I can easily go back to stock water flow (that's how I originally ran it, in 2010).  I'll figure that out next summer; everything is packaged up to store, now, and I won't have access until about July.

Thanks for all the help and support, folks.  It seems like I've learned more on this forum than all the schools in my life!

JimL

[JimL]

It has been a while since I could work on this, but we are trying for Speedweek since my APS bike is ready and loaded.  The first pic may not seem very interesting, but it is a real lesson in reading the rule book correctly AND looking at the manufacturers parts closely. 

I had lengthened the swing arm early in the project, adding just over 5 inches to the stock 55.3" wheelbase.  Sounds logical, but that is wrong.  The rule book reads MAXIMUM wheelbase can be 10% over spec.  Well, it turns out spec is with the axle slid all the way forward.  This means you can only add 10% MINUS the maximum adjustment range in the swing arm.  Today I took the extra wheelbase out, to bring me back to 60.8" maximum wheelbase.  I took out enough to put the back of the window one-half axle width behind the max wheelbase.

When I reassembled and adjusted the axle all the way back, I could only get to 60.2" max wheelbase.  I have now learned that the window in the swingarm is longer than available travel of the chain adjustors.  It seems there is a little arrow, in the adjuster casting, on each side.  Honda makes the window long enough to see the indicator when the axle adjusters bottom against the end caps.  I'm guessing they want you to see that there is no chain adjustment left when the arrows hit the end of the window....not the axle.  I hope this helps someone else figure out how to avoid my chain of mistakes.

The second photo shows our water cooling tank, since we dont have enough room ahead of the engine for a radiator..  Much more to do, but at least it is moving forward.

Regards, JimL

[wobblywalrus]

It looks like you have a handle to move the trailer with the orange bike on it around the shop.  A good idea.

[JimL]

Actually, that is a bumper to protect the back of the bike, and it is pulled out of the receiver and installed sideways (to the left) with the "gloved hand" on the ground.  It then serves as a stabilizer when I hoist the bike off the trailer and swing it over the left fender.  The bike has a pair of heavy tabs under the front of the frame, which bolt it to the trailer (no tie downs needed). 

This MPS bike now has a pair of bolt down tabs for the same purpose.  I will post a pick when I finish the mount and have the bike bolted to the stand.  I had it bolted to my flatbed when I brought it from Colorado last month.  It was the only part of my load that didnt need constant attention on that long run.