Where to buy higher compression pistons for cb750F
- Thread starter Finnigan
- Start date
Finnigan said:
I've seen more than a few people switch to early K top ends with wiseco 836 pistons, that might be because a while back they didn't even make big bore pistons for the F.
They require different pistons because the combustion chamber is shaped differently, and K piston actually drop compression when paired with an F head.
From what I remember, there's something about the valve angle on the F's that cause the valve guide wear.
surffly
Over 1,000 Posts
It's not as simple as swapping heads as some of the oil passages are different.
But yes a K head on an F motor will drop the CR.
77-78 F heads had larger valves and a different angle to increase the power in the sohc motors to slightly less then they started with in '69.
Valve guides and seals wear out very fast and smoking is a very known issue.
There is not "mods to the f head"
Maintenance is what it is and will need to be done so that cost is lost.
I'm saying that the $500-700 spent on pistons and boring a sohc may sound good and translate will to others at the bar or reading the FS add, but that same money spent on porting the head and changing cam will yield a better street engine and more useable power.
There is a guy named mike in the boston area that is an expert on porting sohc engines.
Don't forget that you can't just change one thing and done.
-will need 3-5 complete sets of jets to tune the engine (dyno time is better)
-quality air filter....not pods of any kind
-good exhaust to make use of the motor....not short cut offs or a Mac
-basic maintenance will need to be up to date or the improvements to the engine will break other things
-ect ect
Very few individual parts or systems on a motorcycles.
Have to look at the big picture.
Is the motor really where you want to start? Do you have the funds to see it through?
Maybe the $5-700 is better spent on shocks and forks?
But yes a K head on an F motor will drop the CR.
77-78 F heads had larger valves and a different angle to increase the power in the sohc motors to slightly less then they started with in '69.
Valve guides and seals wear out very fast and smoking is a very known issue.
There is not "mods to the f head"
Maintenance is what it is and will need to be done so that cost is lost.
I'm saying that the $500-700 spent on pistons and boring a sohc may sound good and translate will to others at the bar or reading the FS add, but that same money spent on porting the head and changing cam will yield a better street engine and more useable power.
There is a guy named mike in the boston area that is an expert on porting sohc engines.
Don't forget that you can't just change one thing and done.
-will need 3-5 complete sets of jets to tune the engine (dyno time is better)
-quality air filter....not pods of any kind
-good exhaust to make use of the motor....not short cut offs or a Mac
-basic maintenance will need to be up to date or the improvements to the engine will break other things
-ect ect
Very few individual parts or systems on a motorcycles.
Have to look at the big picture.
Is the motor really where you want to start? Do you have the funds to see it through?
Maybe the $5-700 is better spent on shocks and forks?
Finnigan
Over 1,000 Posts
The F motor is where I want to start, I have the funds to see this through and I'm not looking for a maintenance free bike. I want something I can consistently improve and maintain, but if there is a known issue and fix then I'd like to start there
Please understand that i want to do this the RIGHT way. I just split the cases on a seized motor and want to take care of whatever i need to before its in the frame
I dont need to spend money on more displacement and I would rather keep the motor as stock and reliable as possible without changing anything unnecessary. The big bore was an idea but not the real goal.
This is going to be my bike for a long time, not just a project to sell later
Lets start with a basic question: Will keeping everything stock with maintenance and quality parts be enough to have a fun and reliable motor? Or should I consider changing/modifying for reliability and longevity?
Please understand that i want to do this the RIGHT way. I just split the cases on a seized motor and want to take care of whatever i need to before its in the frame
I dont need to spend money on more displacement and I would rather keep the motor as stock and reliable as possible without changing anything unnecessary. The big bore was an idea but not the real goal.
This is going to be my bike for a long time, not just a project to sell later
Lets start with a basic question: Will keeping everything stock with maintenance and quality parts be enough to have a fun and reliable motor? Or should I consider changing/modifying for reliability and longevity?
surffly
Over 1,000 Posts
How can you know that the modifications you are doing are improving they bike if you don't start with the bike 100% stock?
I had a 78f for a bit 100% stock.
There were many other things that needed upgrading before the motor.
Are you a member of the sohc4 forum? If you aren't you should be.
Seek out some writings by "hondaman"
I have a write up over there for a nice bolt on caliper upgrade using OEM parts. I go by "jaguar" there.
Few upgrades you really should look into.
-Gl1000 fork swap. 37mm and lighter.
-the caliper swap I talked about. If you use the right Gl forks you can have the best of both worlds.
-good rear shocks one inch longer then stock. Hagon, yss, progressive
-rebuild the swing arm pivot.
-quality tires.
-tappered head bearings.
Keep the fenders, air box, bars and seat stock.
Stock motor should be fun.
There isn't really that much HP to be found in these motors, so unless you are racing against another sohc you will still be slow...ish...lol
I had a 78f for a bit 100% stock.
There were many other things that needed upgrading before the motor.
Are you a member of the sohc4 forum? If you aren't you should be.
Seek out some writings by "hondaman"
I have a write up over there for a nice bolt on caliper upgrade using OEM parts. I go by "jaguar" there.
Few upgrades you really should look into.
-Gl1000 fork swap. 37mm and lighter.
-the caliper swap I talked about. If you use the right Gl forks you can have the best of both worlds.
-good rear shocks one inch longer then stock. Hagon, yss, progressive
-rebuild the swing arm pivot.
-quality tires.
-tappered head bearings.
Keep the fenders, air box, bars and seat stock.
Stock motor should be fun.
There isn't really that much HP to be found in these motors, so unless you are racing against another sohc you will still be slow...ish...lol
Finnigan
Over 1,000 Posts
I'm going to be doing the wrench work myself, like my last build...
But having some insight from people who have done this before is always a good place to start. I think you seriously misunderstood my question. For example I didn't know that the 360 engine had oiling issues until someone here pointed me to resources to learn about it. We're all learning here
But having some insight from people who have done this before is always a good place to start. I think you seriously misunderstood my question. For example I didn't know that the 360 engine had oiling issues until someone here pointed me to resources to learn about it. We're all learning here
Valve angle is identical to the K's....the F2 valves were sunk to make room for the larger valves. The F2 port is much better than any K as it starts out 2mm larger in regard to cross section. The long side...especially behind the guide.... is much, much better. I have had 5mm valves made for the F2 for an LSR engine but they are still heavy if you stick with the stock tulip. I am sure F2 5mm conversion valves will be available in the future with a different tulip.mlinder said:
