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Just a FYI - you can't skim much more than .025-.030" off a 650 head, they are not like a 900/1000 head where you can take a lot off. You can skim some off the barrel but it needs to be done on the bottom so the liners need to be out of it (the pistons sits down in the hole pretty far) don't take anything off the top of the barrel as the liner lip is where a lot of the ring seal happens. There is a lot of room for the piston crown to come up into the combustion chamber on a 650 head, even with aftermarket pistons.

Roger that understood, the best I've seen is 10.25 to one pistons, I think 12:1 or 13:1 for the 750 from Dynoman.

577nitro-

577nitro wrote:

Roger that understood, the best I've seen is 10.25 to one pistons, I think 12:1 or 13:1 for the 750 from Dynoman.

577nitro-





 

I looked at that page, the high compression pistons are for a 4 valve water cooled engine (picture of the gasket has cam chain on end) at 71/73/75mm diameter (too big for a air cooled 750 barrel)

If you need maximum compression for your altitude keep the combustion chamber as small as possible (do not big valve it) remove some deck and run the stock cams. As soon as you run cams with more duration you will end up loosing some compression. Your looking for as high a cranking compression as you can get (190-210 PSI) static CR numbers don't mean squat, you can make a 10.25:1 CR piston behave like a 12:1 piston by squeezing up on the dome. A Bondo cast will confirm this.

You will also need to upgrade the starter motor to a 4 brush unit from a GPZ750 as it will be a lot harder to start.
 

Yeah..I must have gotten that confused with the zx7.

577nitro.

Just got my 700cc big bore with a bored set cylinders...fleabay special.    Very nice quality pistons, the cylinder block has some sort of half baked paint job on it that will need to be vapor blasted, along with the other bits.  

Not sure about which cam to go with but want to go with something to get a bit more out of it, I'm at 5500' so I'm already down 20% in power.  
577nitro

 

Well this ain't good...pulled the cam cover and cams last night to start the 700CC big bore swap and found three of the lobes with damage both ex and in.   I don't know anymore than this but I'm defiantly doing a full tear down now.  Which also means a full on resto-mod.   Just for sh**s and giggles what do ya'll think of a possible engine swap with a H2 750 two stroke?  I have three of them, they came with my 72 H2.   That would be a wild ass ride, and probably handle better too...just a thought.

Back to the 650/700 engine though, anybody have any experience with hotter cams for this engine, whats a good combo?   

Thanks
577Nitro-

577nitro wrote:

Well this ain't good...pulled the cam cover and cams last night to start the 700CC big bore swap and found three of the lobes with damage both ex and in.   I don't know anymore than this but I'm defiantly doing a full tear down now.  Which also means a full on resto-mod.   Just for sh**s and giggles what do ya'll think of a possible engine swap with a H2 750 two stroke?  I have three of them, they came with my 72 H2.   That would be a wild ass ride, and probably handle better too...just a thought.

Back to the 650/700 engine though, anybody have any experience with hotter cams for this engine, whats a good combo?   

Thanks
577Nitro-

Just my personal opinion but I think the H2 motor would look lost in a 650 "roller" and how does the header spacing compare with the with of the frame front tubes ?? now how about the H2 motor in a CB350 or early VF750 frame for something Harris/Spondon looking 
 

Well, the plot thickens...I have stripped the engine top end and covers, to remove the engine from the frame, and while examining the cylinder's found that somebody has already done a big bore conversion.  However, its not the 700cc but a bigger one.   The pistons measure 64.87mm, not 64 as on my 700cc kit.  WTF Over?   No brand name other than a "w" on the bottom.  They also have a larger skirt.  No sign of blow by either, looks like a 10.1 CR as well.   The barrels are the 650 ones, so it's not a 750 set.  

From the shape of these I'm thinking the low compression is from the head and valves they look worn and in need of a full overhaul.  Really carboned up a well. 

I'll upload some photos latter today.

577nitro
 

A 65 mm piston gives 720 cc, "W" is Wiseco, the liners will be on the thin side unless someone put sleeves in it (rare)

Injected wrote:

A 65 mm piston gives 720 cc, "W" is Wiseco, the liners will be on the thin side unless someone put sleeves in it (rare)

 yeah they are pretty thin, definitely the original sleeves.  They seem fine no galling or ringing.  Didn’t know wiseco made a 720.

 Not sure what I’m going to do here..I have two big bore kits. 

577 nitro

They discontinued the 720 kit over 20 years ago maybe more. You can still get rings for them but I don't think Wiseco sell the rings.

That kit bore has about the same liner thickness as boring a 750 to 810 cc.

I have a NOS 720 kit I bought a few years back, and have a barrel bored for it sitting on the shelf till I use it. I will be running a oil cooler on my engine as it will have a few other go fast goodies attached.




 

Injected wrote:

They discontinued the 720 kit over 20 years ago maybe more. You can still get rings for them but I don't think Wiseco sell the rings.

That kit bore has about the same liner thickness as boring a 750 to 810 cc.

I have a NOS 720 kit I bought a few years back, and have a barrel bored for it sitting on the shelf till I use it. I will be running a oil cooler on my engine as it will have a few other go fast goodies attached.

 

Yup that's it, those are the pistons.

Thanks
577nitro