[Hmd123]

Hello,
       Has  anyone gone for 612CC with High compression piston & COMPETITION cams ?

i am going through it. abut, my worries are will the valves hit the piston with out any of 2 / 3 mm compression plate .
and what would be the CR.

I really appreciated your answers.. 

[ace.cafe]

You will need at least the 3mm compression plate, and put a thin green half-mm gasket on top and under the bottom of the compression plate, giving 4mm of total spacing under the barrel. No less than that.
You may need more spacing than that, depending on what octane fuel you can get.
That system is VERY prone to detonation(pinging) so I would tend to use a little bit more spacer thickness to be on the safe side.

[da punds]

Hi hmd123,
I have a 612 and although I use Magnum cams instead of the usual Hitchcocks ones, I have found that 2 2mm plates and 3 base gaskets, (sandwich gasket plate gasket plate gasket), gives me a good balance and means I can avoid detonation. I would also say that ignition timing is quite critical and in my case very retarded to standard.
I have to say the torque from this setup is amazing, top gear pulling all the way from about 20 mph all the way off my clock (85 mph), and it gets there very quickly.
If you were looking for outright performance I would say avoid the long stroke crank, Ace's solution will be much faster.

[Hmd123]

Thank you ( ace.cafe  & da punds) for the fast reply.

i would do my best ,it is going to be rebuild in the end of this  month ,,,

thank you indeed

[Hmd123]

Hello ace.cafe,the OEM fluting push on my bike got totally damaged ,,

so, i fitted new bearings.but the long stroke crank could not fit easily into the bearing and before assembling the crankcase the crank was rotating  easily  but after assembling the crankcase found the crank would not spin easily just with a little force.

what could be the problem and what would be the solution if it so?


thank you   
                       

[ace.cafe]

Hello ace.cafe,the OEM fluting push on my bike got totally damaged ,,

so, i fitted new bearings.but the long stroke crank could not fit easily into the bearing and before assembling the crankcase the crank was rotating  easily  but after assembling the crankcase found the crank would not spin easily just with a little force.

what could be the problem and what would be the solution if it so?


thank you   
                       

Well of course, since I can't see it or feel it, it's hard for me to tell you what's wrong.

However, I can say that it is common for the long stroke crankshaft to have a tight fit in the crankcase, and sometimes needs to have the bottom of the internal crankcase relieved out by machining or grinding because is can rub on it there.
That might be the situation with your bike, but I don't know for sure. You would have to take it apart to see if it is rubbing there.

[AzCal Retred]

I know many folks aren't big proponents of the 103 mm stroker crank. It appears to me that a 6.5/1 forged piston driven by one of these would have about an 8/1 CR with no compression plates needed. It ought to live on pump gas just fine. It should have a usable RPM spread from maybe 2000 RPM to 4000 RPM, and the lighter piston (than the 8.5/1, 87mm) should help with vibration. Power/torque output should be hearty, maybe 28-30 BHP. If you aren't needing big power, this combo looks like it might work well for touring or just for us folks in the +200 pound category. Ace says the stroker works well for sidecar use or 2-up mountain touring. Most of the time I'm most comfortable at 50-55 anyway, the wind blast doesn't appeal to me anymore. It'd be pretty cool to have some roll on capacity on a long slope. Is there anyone running a 570 set up? If your crank dies, it's the same money and you get the good crank pin.

[Adrian II]

I just had a look at the on-line catalog, the lower compression forged pistons don't seem to be available in 87mm.

A.

[AzCal Retred]

Right you are, Adrian. I wasn't clear. I am looking at a 570 IB Bullet build - the 103mm crank & 84mm piston. Looks like it'd make a nice durable tractor motor to pull my petite self around. For me I don't see any downsides. I like to "chug" along anyway, looks like a modern crankpin would facilitate that with no oiling concerns. The 570 should have a 7.5 - 8.0 /1 CR with the forged 6.5 piston as best I can tell. That's enough for me, and it'll be way more than the stock motor for low & midrange, and should be pretty bulletproof.