Topic: How far can you bore a CB650???

[PrestonNB]

  I, of course, have a 1979 CB650. I planned on modifying the bike before I picked it up. Then I saw it for the first time and decided to leave it alone being it only had a little over 7000 miles on the entire bike. Now, 2000 miles later, I have changed my mind. I recently ran into some problems and I started looking into modifying it once again. I am trying to find out how far you can bore the 650 before you run into major problems. I read that you can push it as far as 800 cc but I'm not sure if it is true. I think with running that big I would need to reinforce the frame possibly or the swing arm to take the difference in torque no? Along with any opinions, I was also curious about what companies to go to for big bore kits and other parts I would need for doing such a project. I am planning on building this bike for using on the track and street, so it's power and reliability I am going for.
  If anyone has other ideas they want to share with me feel free to do so. I am trying to learn as much as I can. Thanks for reading.

[Terry in Australia]

G'Day Mate, do a search on "Paulages", Paul used a CB650 engine in his CB500 Cafe bike, and took it out to 718cc, using 61mm CB750 pistons. I don't think you can take them out much further than that without major engineering work. Cheers, Terry.

[PrestonNB]

Thank you very much Terry. I will look him up for sure.

[MickeyX]

I was just going to tell you the same thing Terry did.  Paul did an incredible job on his bike. Knowing him, he's already gone as far as one can possibly go on an engine that size. 

We have two '80 cb650s. One restored, one seems to be turning into a donor bike.  Same engine, carb, trans as the '79... body style changed though. If you do anything else, I'd say change out the carbs. "Soos" is a good source for what has been tried or may work. Check out his threads on it.

[PrestonNB]

Any recomendations on what carbs to get? I know the ones on my bike were rebuilt just before I bought it. But it spits alot. The Spark plugs are all good. So I am figuring the carbs.

  Sorry guys, I made this sound stupid earlier. So I am editing. I have checked everything that has been said. So all that is left are the jets. I am starting to think the "rebuilt" carbs aren't rebuilt after all. Which wouldn't surprise me honestly. When I have time off from work I will pull the carbs and have a look. I hope this edit makes it more clear. After reading, I can see why turboguzzi said what he said. I did sound like a kid that doesn't know anything. So I am sorry about that. Again, no sleep is a bad thing.
  One thing I ran into around Modesto is that I can't get parts for the 650 without costing me a ton of money. So far the bike has cost me $2000 for the purchase and $3000 approximately since then. Had the forks rebuilt when they decided to start leaking like crazy. I figure, I have enough money in it now that I might as well keep going.

[kslrr]

The "spitting" could also be a sign of ignition timing off, valve clearances off, or still dirty fuel/air circuits in the carbs.  Also, the CB650 was designed to run lean from the get-go which could be the issue.  Other than the jets, not much else is adjustable in these carbs.  I mixed parts from 2 different configurations of the pre '81 carbs to get the setup I needed to run pod filters with the stock 4-4 pipes on my '81/'79 hibrid.

[paulages]

on the contrary, i have room to grow!  i 'm using 64mm pistons, and the 750 liners can take 65.5mm before getting too thin, which is 752cc in a 650 engine. whenever i blow this one up, i'll go bigger. i posted this info and a link in another thread for you.

http://forums.sohc4.net/index.php?topic=40414.0

[paulages]

Any recomendations on what carbs to get? I know the ones on my bike were rebuilt just before I bought it. But it spits alot. The Spark plugs are all good. So I am figuring the carbs.

cb750 carbs drop right on. K1-6 carbs are easy to fiddle with, late (PD) carbs have accelerator pumps.

[Terry in Australia]

While not wanting to rain on Paul's parade, there's no way I'd bore stock CB750 liners to 65.5mm. The stock liners are only 70mm OD, so removing all but 4.5mm at the "thick" end, (which equals 2.25mm wall thickness) and 1.25mm wall thickness at the "waisted" (bottom) of the sleeves is asking for trouble, IMHO.

My 836cc race engine is bored to 65mm and it worries me to see how thin my sleeves now are, (particularly in an engine that will happily rev to 11,000 RPM and beyond) and I wouldn't go any thinner in a fit. The "fix" for CB750 engines is to bore the cylinder block to take bigger sleeves which allows you to take the capacity to 1060cc or more, (up to 1200cc if you use the DOHC cranks to "stroke" it) but from memory, (from reading Paul's build thread) the CB750 sleeves are as big as the little CB650 cylinder block (itself an overbored CB500/550 design) will allow. Cheers, Terry.  

[turboguzzi]

Any recomendations on what carbs to get? I know the ones on my bike were rebuilt just before I bought it. But it spits alot. The Spark plugs are all good. So I am figuring the carbs.

Preston, you sound like a good fellow, willing to learn, all good, but considering your very basic questions and the fact that you are struggling with making the bike run well with stock setting, are you sure that the biggest bore possible in a 650 is your real concern? Unless you have rebuilt a few engines from the ground up in your 21 years, there's a lot of other stuff you could do to make the bike quicker ro run well with stock carbs in the first place.

My 0.02

TG

PS, where did you read about 800cc 650's BTW? 

[paulages]

While not wanting to rain on Paul's parade, there's no way I'd bore stock CB750 liners to 65.5mm. The stock liners are only 70mm OD, so removing all but 4.5mm at the "thick" end, (which equals 2.25mm wall thickness) and 1.25mm wall thickness at the "waisted" (bottom) of the sleeves is asking for trouble, IMHO.

My 836cc race engine is bored to 65mm and it worries me to see how thin my sleeves now are, (particularly in an engine that will happily rev to 11,000 RPM and beyond) and I wouldn't go any thinner in a fit. The "fix" for CB750 engines is to bore the cylinder block to take bigger sleeves which allows you to take the capacity to 1060cc or more, (up to 1200cc if you use the DOHC cranks to "stroke" it) but from memory, (from reading Paul's build thread) the CB750 sleeves are as big as the little CB650 cylinder block (itself an overbored CB500/550 design) will allow. Cheers, Terry.  

terry-

i've installed several of cyclex's 850cc kits, and yes the sleeves get thin. due to cooling time between passes, it takes longer to bore them to ensure that there isn't warpage. i can't vouch for the longevity of the sleeves at this bore, but there are plenty of people out there running these kits.

[paulages]

G'Day Mate, do a search on "Paulages", Paul used a CB650 engine in his CB500 Cafe bike, and took it out to 718cc, using 61mm CB750 pistons. I don't think you can take them out much further than that without major engineering work. Cheers, Terry.

oh yeah, and it's 64mm pistons that make 718cc, just to not confuse the boy.

[Terry in Australia]

i can't vouch for the longevity of the sleeves at this bore,

Me either Paul, that's why I wouldn't advise it. Cheers, Terry.

[paulages]

i can't vouch for the longevity of the sleeves at this bore,

Me either Paul, that's why I wouldn't advise it. Cheers, Terry.

i wouldn't run an endurance race on them or anything, but with an oil cooler and normal street/fun riding conditions, i doubt they'd heat up enough to distort, but i suppose caution is always a good idea. if you've got a worn out 836 it's a pretty cheap option though.

[Terry in Australia]

i can't vouch for the longevity of the sleeves at this bore,

Me either Paul, that's why I wouldn't advise it. Cheers, Terry.

i wouldn't run an endurance race on them or anything, but with an oil cooler and normal street/fun riding conditions, i doubt they'd heat up enough to distort, but i suppose caution is always a good idea. if you've got a worn out 836 it's a pretty cheap option though.

Yeah, that's true Paul, boring is so expensive (especially "big bore" jobs) that if you wear out an 836cc cylinder the 850 kit is probably your cheapest option, but it reminds me of a lot of stuff that was around in the 1970's that we wouldn't touch nowadays with a 10 foot pole. Personally, if I wanted to continue with the "performance" route, I'd spend a bit more and buy a 900 or 1000 kit. Cheers, Terry.  

[paulages]

i can't vouch for the longevity of the sleeves at this bore,

Me either Paul, that's why I wouldn't advise it. Cheers, Terry.

i wouldn't run an endurance race on them or anything, but with an oil cooler and normal street/fun riding conditions, i doubt they'd heat up enough to distort, but i suppose caution is always a good idea. if you've got a worn out 836 it's a pretty cheap option though.

Yeah, that's true Paul, boring is so expensive (especially "big bore" jobs) that if you wear out an 836cc cylinder the 850 kit is probably your cheapest option, but it reminds me of a lot of stuff that was around in the 1970's that we wouldn't touch nowadays with a 10 foot pole. Personally, if I wanted to continue with the "performance" route, I'd spend a bit more and buy a 900 or 1000 kit. Cheers, Terry.  

you say that now that jay has made them available again! i know, i know... you already have one. 

one thing i didn't measure when i built the 550/650 beast, was bore centers. easy to check, as any 500, 550, or 650 have the same, but that will ultimately tell how much room there is for bigger sleeves with the 650. i have a mysterious oil leak between cylinders 2 and 3 as is, and i suspect they may be due to the large bore in the cylinder hitting porous casting, kinda like the 1000cc cb750 kits would do in stock blocks.

the flanges overlap considerably on top using stock liners... the walls in the block between them in the barrels must be thin.

[PrestonNB]

Thanks for all the input guys. It's helping a lot. To turboguzzi, thank you for your concern. I know I am young and all, but I do know how to work on bikes and cars and pretty much anything else with a motor. Don't take my saying that as being rude. I just don't want my age to make people think I can't work on something. The basic questions come because of 4 hours of sleep in 3 days. Sorry for sounding stupid or anything. Now with that 800cc thing, I was looking through google. Some page popped up of a guy talking about all the kits that were available. I can't remember what it was called though. sorry. I think boring it out that much is kind of a waste honestly. It just makes it less reliable. My question about how far you could bore a 650 out came from that guy saying 800. Plus, I want to make this bike my project. Seeing as I have gone through 4 old pre 75 trucks and 3 pre 75 Camaro's, I need to stick with something for a while. haha turboguzzi, again, thank you, and please don't take anything I said wrong. If you have any ideas or anything else to say, I would love to hear anything. I joined this forum to learn from others and to show my progress on the bike. Again, thank you all. I will be checking some more to see what others have to say.

[turboguzzi]

honest answer, get some sleep and good on ya building camaros! at your age all the 4-wheels I could afford to run was a 1967 850cc mini minor (had three, one running, other two for parts) and a 1969 1300cc Triumph Herald convertible. Small cool cars that broke down all the time.

In any case, much of what you know from big V-8's might not be necessarily applicable to sohc's with miniature 160 cc pistons, so take your time.

but main point was that you could get quite a bit more form your 650 if setup right , without spitting for instance...

If your serious about hitting the track, then common knowledge is that the CB650 frame with its 27.5 degree of rake is not the most sporty handing thing out there.  You might want to find a 500/550 frame if you are serious about hitting the track or twisties. You might out run every body out there with your 800cc 650 on the straights  but people will eat you alive in the turns 

TG

 

[PrestonNB]

turboguzzi, thank you for your reply. I actually did try getting a 550....the guy sold it an hour before I went to get it. The only thing I could find was a 650. I like the classic styling. Here in California nobody has these bikes. When they do, it is rare. At least in my area of California anyways. Oh, I had the day off, my carbs are bad. They weren't rebuilt. So I am in trouble now. Any ideas on where to find good carbs at? I have tried every single shop close by and NONE can get parts for my bike. So I am thinking online is my only choice right about now. Oh and the 800cc thing is out. It's a waste. It would ruin the engine. I am looking more towards a 750 bore if anything. I understand what you were meaning about getting more from the engine in stock form. It's just that stock parts are hard to get ahold of. Oh and from v-8's...the only thing useful from them is working on carbs. Also helping my father build his ancient Goldwings helped to. Again, thank you, and I'll be looking to see what you have for ideas on finding parts.

[paulages]

turboguzzi, thank you for your reply. I actually did try getting a 550....the guy sold it an hour before I went to get it. The only thing I could find was a 650. I like the classic styling. Here in California nobody has these bikes. When they do, it is rare. At least in my area of California anyways. Oh, I had the day off, my carbs are bad. They weren't rebuilt. So I am in trouble now. Any ideas on where to find good carbs at? I have tried every single shop close by and NONE can get parts for my bike. So I am thinking online is my only choice right about now. Oh and the 800cc thing is out. It's a waste. It would ruin the engine. I am looking more towards a 750 bore if anything. I understand what you were meaning about getting more from the engine in stock form. It's just that stock parts are hard to get ahold of. Oh and from v-8's...the only thing useful from them is working on carbs. Also helping my father build his ancient Goldwings helped to. Again, thank you, and I'll be looking to see what you have for ideas on finding parts.

unless your carbs are absolutely trashed, there's no need to junk them. clean them well and they'll work fine. ... and believe me, you'll have a harder time finding and adapting pistons for a big bore than you will finding replacement OEM parts.

[PrestonNB]

They semmed pretty well gone. I wont be junking them ever though. Any parts I take off the bike that were stock I keep. Such as the original handlebars, etc. Do you know anywhere here in the US that has good parts paul? I know California is just a horrible place to find anything really. If it comes down to it I'll just be doing alot of other work on the bike to make it into a full on Cafe racer. Most likely getting down as far as another engine....which I would rather not do. But if I have to I have to.

[paulages]

They semmed pretty well gone. I wont be junking them ever though. Any parts I take off the bike that were stock I keep. Such as the original handlebars, etc. Do you know anywhere here in the US that has good parts paul? I know California is just a horrible place to find anything really. If it comes down to it I'll just be doing alot of other work on the bike to make it into a full on Cafe racer. Most likely getting down as far as another engine....which I would rather not do. But if I have to I have to.

describe "pretty far gone..." reddish gluelike substance everywhere? white powder eating the metal surfaces? physical damage? i've seen very few carbs not salvageable that weren't damaged by human hands (pilot screws broken off in the carb, etc.). you'd be surprised what can clean up.

use the net... parts are out there. FAQ on this site has some good references.

[MickeyX]

I found carb rebuild kits at motorcyclecarbs.com for $27.95 each. That's about $10 cheaper per set than other places. It took just under 2 weeks to get here.

We have a few decent places around the PDX area for cycle salvage. I know western cycle salvage has some but they won't do business unless in person. No, they won't go look for them and then ship them. No. I'm sure a few people on here have some sources you could check out. Ebay always has some but you can never know what kind of shape they are truly in until they are in your hands and they are usually 'as is'. I'm with Paul on this one though, why replace them? If you felt the guy was being honest about them being rebuilt, at a glance, then what makes you think they are total trash? Just curious. 

[turboguzzi]

Do you know anywhere here in the US that has good parts paul? I know California is just a horrible place to find anything really.

? 

SF is sohc city as far I am concerned, ohanlon's got tons of stuff. Ask for Scott and tell him the italian racing guy sent you.

Wish I had that kind of shop near to me in milan

TG

[Soos]

G'Day Mate, do a search on "Paulages", Paul used a CB650 engine in his CB500 Cafe bike, and took it out to 718cc, using 61mm CB750 pistons. I don't think you can take them out much further than that without major engineering work. Cheers, Terry.

oh yeah, and it's 64mm pistons that make 718cc, just to not confuse the boy.

True, but 66mm pistons make a 763cc bike....
And cb900 DOHC liners(should) work good, being 64.5mm to begin with.

Oil passages become a problem though. But thats easily overcome.






l8r