question about boring..

R

racemx51

New Member
Just took my motor apart from the bike I bought with a locked up motor. Came loose pretty easily but one cylinder is a bit rougher than I would like...I was thinking of maybe just having it bored out and having a bigger displacement...Its on a 73 CB 750. Any of you guys done this before? Where is a well known place to bore these things and were can I get oversized pistons?
I mean, I could just try to clean it up the best I can and just run it but Id like to make sure the thing is in tip top shape..

Thanks guys..
 
racemx51 said:
Just took my motor apart from the bike I bought with a locked up motor. Came loose pretty easily but one cylinder is a bit rougher than I would like...I was thinking of maybe just having it bored out and having a bigger displacement...Its on a 73 CB 750. Any of you guys done this before? Where is a well known place to bore these things and were can I get oversized pistons?
I mean, I could just try to clean it up the best I can and just run it but Id like to make sure the thing is in tip top shape..

Thanks guys..
Click to expand...

836 kits are cheap and easy for that motor, cyclexchange has an 850 kit that looks promising too, you can probably get out of it for under $500 machining and all
 
theres something called searching... look at the top of the page.
 
I can research all day long but Im not stupid. Ive been involved in motorsports all my life racing motocross and you can look up ten different boring companies within five minutes but I can tell you eight of those ten wont do as well as the two others.

An example,
A crank for a dirt bike...'search' online. You'll find, Pro X, Hot Rods, Wiseco for example. Pro X explode, Hot Rods crank cheeks break apart and ruin your motor 95% of the time, and Wiseco is getting to be fairly decent. Stock is still best although way more expensive. Its worth it...Instead of blowing up your motor and doing everything all over again, you dont, you just spend an extra $100 on a good OEM crank.

You cant research that online...Sure, you can read 'reviews' but those are just a bunch of blow hards that could have just sucked dirt through there air filter and blamed it on the crank...

So, my point is, why bother replying to be if your gonna be a jackass about it?

But thanks everyone else...I'll check into doing this and see the cost compared to just rebuilding it stock...Thanks guys..
 
836 uses CB350 pistons, common mod.
Should be able to get a load of CB350 pistons cheap around here
 
crazypj said:
836 uses CB350 pistons, common mod.
Should be able to get a load of CB350 pistons cheap around here
Click to expand...

I know I have 2 if you need them. Sounds like the 836 route would be the most cost effective. Shit I may even have 4. I'll have to look. They'll all need new rings of course.
 
racemx51 said:
So, my point is, why bother replying to be if your gonna be a jackass about it?
Click to expand...
sorry for the threadjack, but i really wanted to give you some support on this... i look at the title of a thread and if it looks interesting, or like something i might be able to help with i read it. if i can't help or it's boring i move on... simple. why throw stones?
i pretty much gave up on caferacer.net because of the pointless pejorative comments tossed at new members there. i hope we can be kinder here...
there's no harm in asking a question and a lot of times you'll get an excellent answer from someone who knows your specific situation, rather than trying to assemble a bunch of bits from threads shown by the search function.
my 2¢
 
overdraft said:
sorry for the threadjack, but i really wanted to give you some support on this... i look at the title of a thread and if it looks interesting, or like something i might be able to help with i read it. if i can't help or it's boring i move on... simple. why throw stones?
i pretty much gave up on caferacer.net because of the pointless pejorative comments tossed at new members there. i hope we can be kinder here...
there's no harm in asking a question and a lot of times you'll get an excellent answer from someone who knows your specific situation, rather than trying to assemble a bunch of bits from threads shown by the search function.
my 2¢
Click to expand...

I completely agree. And just ignore Rocan, everyone else does.
 
djelliott said:
I know I have 2 if you need them. Sounds like the 836 route would be the most cost effective. Shit I may even have 4. I'll have to look. They'll all need new rings of course.
Click to expand...

i also have two in stock size good condition if you need them.

Ethanol said:
I completely agree. And just ignore Rocan, everyone else does.
Click to expand...

agreed. on second thought, maybe you dont want my pistons? :D
 
So all I would have to do is buy CB 350 pistons for a '73?

I called a guy from around here thats a master of Honda motors and asked him who to talk to about boring and he pointed me towards a guy from Mass thats really good at boring motors I guess...So I should just call him and ask him if he can bore the 750 into a 836?

Sorry for all the dumb questions guys but like Ive said, I know all things moto not so much on the street side. On a dirt bike you have certain boring options you can do and thats it. Like a 167 for 125 and things like that..I know the company to go too and the size they will do so its a lot easier for me..Street bikes, Im def learning things about ::)

Let me know guys...Thanks..
 
get a set of cb350 pistons.

go to a reputable machine shop that can bore a motor that size.

give them the pistons, the motor, and tell them to bore the motor to fit those pistons. as for clearances... id have to check. if you bring it to a honda specialist, theyll know right off the bat what you want.
 
The clearance on mine was .002 but that was on a CL350. Not sure with the 750. Everything else Rocan mention was correct. You want to bring THE pistons and rings you will be using.
 
I think the stock clearance is around 0.0008"~0.0012" for a CB350, check in service manual.
Personally, I've done hundreds of 'big bore' conversions over the years and use 0.0015" ~ 0.0017" for just about everything Japanese without any problems (Harley's need more, but that's a much bigger piston)
Basically, use about 0.0005" bigger than stock clearance
 
crazypj said:
I think the stock clearance is around 0.0008"~0.0012" for a CB350, check in service manual.
Personally, I've done hundreds of 'big bore' conversions over the years and use 0.0015" ~ 0.0017" for just about everything Japanese without any problems (Harley's need more, but that's a much bigger piston)
Basically, use about 0.0005" bigger than stock clearance
Click to expand...

wouldnt a larger piston need less clearance as there is more material to be heated/ piston acts as a better heat sink?
 
rocan, look up thermal expansion of aluminum alloys, bigger piston gets bigger
 
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