Topic: Sleeves cracked: next best option

[The Wurst]

Ok so upon me getting my cylinder unstuck, the bottoms of my sleeves became cracked on the inside two. I have Hondaman's book, and before reading it I wanted to go big bore, but in the bore section he recommends stronger studs and helicoiling them deeper into the block. I don't want to do all of that work, and also from what I understand I will loose a redline with that as well. I want to be able to rev to the 10,500 redline it had originally, because I like the sound of a high revving motor.

So with cost being of primary importance, then high revs being second: What is the best option for me?

I was thinking about getting another jug but can't find any off of ebay. I need new pistons regardless of the decision. Big bore, Resleeve?

[Jerry Rxman Griffin aka MuthaF'er]

Depends on how big. 849 or less just find another block. 890 or above you will need to resleeve anyway.

You do not necessarily need to helicoil the block. Won't hurt but may not help anything.

[MRieck]

I would switch cost as primary importance with the non attainable 10,500RPM redline.  There is so much here unsaid that I can't even believe I responded to this post (except I'm on vacation).

[The Wurst]

I thought it was 10.5 but now that I look it more the max rpm of the red part on my tach is 9800. that's where I will set my rev limiter, the red starts at 8500, and from what I understand thats the maximum continuous, and anything between that and 9800 is a shift point for racing or hard accel

[Retro Rocket]

making  power at those revs is going to cost you a small fortune, most of the power is locked up in the heads on these bikes, so head work is a must, you'll also probably need stronger rods and probably carbs if you plan on spending a pile of time at max revs, so as Mike Rieck{resident head expert} suggested, cost is going to be your main concern...

[The Wurst]

Sorry I should explain my use. It is to be a street bike, and to be something that can handle highway speeds and slightly greater with ease, and look and sound cool doing it. I don't want the fastest bike out there, but something that is just fun to ride. I like the sound of this bike as it reaches the point he shifts, and I'd like it to go a bit higher. https://www.youtube.com/watch?v=a7TMc7PsBOI

I will probably create a project thread soon too, and I will link it when I get the chance.

[Retro Rocket]

Sorry I should explain my use. It is to be a street bike, and to be something that can handle highway speeds and slightly greater with ease, and look and sound cool doing it. I don't want the fastest bike out there, but something that is just fun to ride. I like the sound of this bike as it reaches the point he shifts, and I'd like it to go a bit higher. https://www.youtube.com/watch?v=a7TMc7PsBOI

I will probably create a project thread soon too, and I will link it when I get the chance.

A stock 750 will do highway and above speeds easily, put a 4 into 1 on it and you have the sound. That bike in the clip would be lucky to be revving at 5-6000 rpm, it will rev higher easily, there's absolutely no need to be revving these bikes to 10500 on the street ever, unless you like rebuilding blown engines or like spending a packet on a tough engine that may survive those revs. Have you ridden a good running 750...?  If the sleeves are screwed just replace them with stock sleeves and pistons, thats your cheapest option, then if you decide you want more power at a later stage, then weigh up your options, there is also a cheap 836 kit that runs stock compression but will give a bit more torque and power based on the bigger bore size. I would ask a lot of questions here before doing anything, sounds like you aren't really that experienced and there are tons of great knowledgeable guys here that can help...

[PeWe]

Several posts on this forum that state that revving over 9500rpm will not gain much except need of expensive mods like lighter crank and better con rods. Like the APE ultra crank http://cbrzone.com/cranksrods.html

I have thought about it too when driving my bike with std crank-rods + lighter alternator. No need of revving more than 9500. (even with the high rev screaming CX-7 cam) I'm fine with max 8500 rpms. Mostly change gear at ~6000 rpm when cruising around the town.
My engine is 836cc, ported head with larger inlet valves, hotter cam.
Ultra crank would be nice... but I have no plans to open the engine again.

[Bill/BentON Racing]

I would switch cost as primary importance with the non attainable 10,500RPM redline.  There is so much here unsaid that I can't even believe I responded to this post (except I'm on vacation).

Lol. I have a cylinder or two or three or....... contact me if you need a good used cylinder, Bill

[70CB750]

If I shift at 6000 it is already reckless driving in 3rd gear. 

[Garage_guy_chris]

you sound like me about a year ago. What I learned. Set your budget and then figure out what can be done with said budget.

For a first time out your best looking at a 811, 836, or 849cc engine. Also consider what its gonna cost to refresh the bottom end and transmission. stuff like:

-crank bearings
-transmission bearings
-cam chain
-cam chain tensioners
-primary chains
-primary tensioner
-clutch
-reseal gaskets and seals

[bear]

I would switch cost as primary importance with the non attainable 10,500RPM redline.  There is so much here unsaid that I can't even believe I responded to this post (except I'm on vacation).

I can't believe you did either.

Cheers,
Brian

[The Wurst]

Maybe I don't need high revs then. Haha. I will be replacing all rubber in the engine, I have a bottom end seal kit coming in, and I held off on the top end kit because I am unsure of the bore I will be going with it. My budget is going to fluxuate, and this project will take a while for me to complete.

Couple questions-
1. How hard is it to replace tranny bearings and crank bearings?
2. What are good primary chains to use, as well as cam chains?

[Jerry Rxman Griffin aka MuthaF'er]

you sound like me about a year ago. What I learned. Set your budget and then figure out what can be done with said budget.

For a first time out your best looking at a 811, 836, or 849cc engine. Also consider what its gonna cost to refresh the bottom end and transmission. stuff like:

-crank bearings
-transmission bearings
-cam chain
-cam chain tensioners
-primary chains
-primary tensioner
-clutch
-reseal gaskets and seals

Just ordered from Yamiya in Japan from Chris' list and got some smoking prices. If you were to skip the clutch and the tranny bearings you are looking at $400+. Order from the States, add another $100. Plus Yamiya may be the only place to find a primary tensioner now. $72.54. You can get by with Honda primary chains. Yamiya $52. US $100 or more. Couple 'heavy duty' primaries out there $250+ but it's overkill mostly unless you're only gonna be running WFO on the strip often IMO. It's insurance however. Crank bearing $10 - $12 per half shell so you need 10. Rod bearing $8 - $10 X 8. Tsubaki cam chain heavy duty $30 shipped from Amazon. Other reputable sites are selling for $70. Tranny bearing rarely get replaced but you could consider that. Good bearing are not cheap and not all may be available.

Choose your poison wisely. Theory is overkill in most instances. You're not going to put 100,000 miles on it.

[754]

80 % of CB 750 motors can reuse most of those parts and would be fine up to 836 cc.
 If you plan on racing it at the drags a few times, and riding street..probably. Be fine..

[PeWe]

All chains and tensioners to be replaced when engine is opened.

If the crank bearings look good without scratches or not too much scuff marks they can be reused.
I replaced mine just for sure at last rebuild despite I had ran the bike only about max 30.000 kms since last replacement together with ALL bearings at 65.000 km's back in the 80's. They are not that expenisive.

I did not check the rod bearings. Did not touched those bolts when rods felt ok without any play and knowledge they were checked at my local tuner for 30.000kms ago.

I replaced the primary chains too when engine was open. Additional Euro HD chains from Germany (Classic Cycle City). These are a little bit tighter than I remember the OEM chains were, less rattling sound in engine if I remember correctly.
The service limit of 70mm was not reached yet, just 67.5mm measured according to the manual. New chains are about 65mm measured from oil sump gasket to the tensioner. The reinforced were a little bit less than 65mm.

I guess the old std chain could have been sitting for another 20.000kms or so.  I do not know how quick the chains becomes longer when they have started to extend themselves. I have used the bike mostly for touring during the driven 30.000kms.

I do not know the service limit for all ball and needle bearings in engine. If engine has 100.000kms it might be time to replace them all?  I replaced all at 65.000km's.

[The Wurst]

Ok, so I remember where I got the 10,500 redline from. its from a parts bike i was looking at getting, and now have! its a 77 or 78 f model! Are the f models rare? Did not come with title. Sorry for the poor picture. Has dual discs on front and two on the rear. I'm kind of let down that I do not have two swappable engines due to the F model differences, but this one turns over and has 2300 miles on it.

[seanbarney41]

F3 motor bolts right in to any cb750, in a k0-k6 you will only need either a 10mm offset rear sprocket as available from CycleX or the sprocket carrier and spacers from a k7/8.

[Jerry Rxman Griffin aka MuthaF'er]

Rare is relative.

F0 = 15,054 built in the first 4 months of F's
F1 = ~30,000
F2/F3 - don't know for sure

I wouldn't recommend to attempt spinning a stock engine to 10,500. Good HP builds rarely will see that. No real sense as the HP is dropping off so it's time to shift before 10-5. Now if you build it RIGHT and dyno it and it's still producing top power at 10-5 then go for it. First missed shift T 10-5 and it's toast.

[The Wurst]

Yea, I wont ever spin it up to that, I just wanted to explain that that's where I saw it

[The Wurst]

And also, are all the parts swappable between frames? I would want to use the rims and discs as well.

[seanbarney41]

If you want the front rim and brakes, the whole frontend bolts right on.  For the rear, I think the easiest way is to use the whole swingarm, but I am not sure.  Member 70cb750 is using these F3 parts on a K3, he has a build thread for it.  Pm him for details.

[Old Scrambler]

WURST..............your in West Bend..........I'm near Cascade.  I have a few K models and some F2-3 models in my garage. Plan a trip some day and I'll show you a few things............such as...........yes, the black F motor will bolt into the K frame but its harder to install because of the deeper oil-pan fins. Yes, the swingarm will fit......BUT its wider and requires the top shock studs to have lengthened shoulders for alignment. The swingarm is also longer so if the wheel is not fully forward, the tire may touch the K fender.......depending on tire size and shock compression.......or how large your passenger may be .

I have spare sleeves and many other parts. 

[The Wurst]

@Old Scrambler, this is going to be a cafe racer, so the minor changes won't be an issue. I'd love to take a ride up when it gets warmer!

[Old Scrambler]

Give me a shout..........AM is best...............My calendar gets pretty busy when the weather warms........

For a cafe............consider using an alloy swing-arm from an early Ninja. Same diameter bolt and axle. Just a thin shim-washer to center in the stock frame. Remove the mono-shock 'junk' and weld-on small blocks for twin-shock mounts.