Topic: Best engine mods

[nitrofish1]

Lets say that I've changed my mind, once again, sort of, about how much to spend on modifying my 750's engine.

If I spend 1200 or so, not including the cost of gaskets, what would be the best way to extract power out of that engine? A mild port, big bore with upped compression, new valve train combo?

Or should I just purchase the APE 836 kit which includes all of this except the head porting? Also mind that with a bigger bore comes the cost of boring and new sleeves.

[nitrofish1]

I'm probably only going to have this bike's motor apart once, unless something breaks, and it is going to be my cafe racer, so I'd may as well make it perform. I don't think it will be my last cafe bike but for a bike that I'm building to represent myself, I'd just like it to be fast.

[Schnell]

Add nitro?

[70CB750]

or fish?

[nitrofish1]

HA! so really what is the best? 

[70CB750]

The best way  is to buy Mark Paris's book:

http://www.lulu.com/us/en/shop/mark-paris/my-cb750-book-hardcover-edition/hardcover/product-16107855.html

He talks about cheap and not so cheap alternations to the motor for power gains - besides a wealth of information on maintenance and technical details.

[strynboen]

why not just run it..as it is,,, for 1 seson

[nitrofish1]

why not just run it..as it is,,, for 1 seson

Book is a bit pricey...... 

Is there a sport to be had in running it stock? I was just considering a hotter cam and valve springs upgrade but I was thinking of going a little further, hence the question on post 1.

[BobbyR]

I think you should contact MReick. He dies head work and has a motor he built for himself puts out close to 100 Hp

[setdog]

Buy another motorcycle...best mod ever!!

[nitrofish1]

I think you should contact MReick. He dies head work and has a motor he built for himself puts out close to 100 Hp

Already got a price list from him for porting the heads.

[PeWe]

836 + cam, + ported head with valves, springs and retainers  + lightened alternator (cost not much), APE HD cyl studs.
Valve guides, seats might be an additional cost.
Check with MRieck on this forum about ported head.

Fresh bore and decked cylinders + head is probably needed anyway independent of bore size.

4-1 pipe. I have Yamiya's Yoshi replica on my list. This one has low short design that allow use of OEM passenger foot pegs.

What about the engine overall status?
Clutch OK?
Internal chains might need replacement together with the tensioners that have rubber wheels, today bakelite.
Primary chains + cam chain
So whith the crank cases opened you might find the crank bearings bad....

I know, I have just done this again.... this time better primary chains, reinforced almost 270 euro.
Tsubaki Camellia HD cam chain is cheap about $30-35US.

[Toxic]

What do you want out of this project?  Your $1200 will wake it up some but fast is a relative term.  It's not going to be fast by current standards and it is plenty fast to have fun on as is.

BTW --- Mark's book is going to be the cheapest accessory you will ever buy for this bike.
If you plan on keeping the bike it will pay for itself many times over

[PeWe]

inspiration cont.

[nitrofish1]

At the minimum I was going to do new valve springs and the #41 webcam to liven it up.

Just looking for something that would at least be a noticeable amount faster than stock and I figured that a cam and springs would at least achieve that.

Was already going to purchase new cam chain, the primary chains look good, and so far of what I have seen of the main bearings they are in good shape as well. Staring at the bottom end I have not seen anything glaring at me as a major problem, all the components look good.

[Duke McDukiedook]

Any mods of this sort will have you changing out all the gaskets and o-rings at the minimum. Include that in your costs.

[bollingball]

why not just run it..as it is,,, for 1 seson

Book is a bit pricey...... 

Is there a sport to be had in running it stock? I was just considering a hotter cam and valve springs upgrade but I was thinking of going a little further, hence the question on post 1.

I think you should contact MReick. He dies head work and has a motor he built for himself puts out close to 100 Hp

Get both and a fatter wallet. If you want to go faster you got to pay Once you open it up it just snowballs from there. If you are going to change this then you really need to change that. Decide how much HP you want then what it will take $$$ and save till you can do it all at once.

[nitrofish1]

Any mods of this sort will have you changing out all the gaskets and o-rings at the minimum. Include that in your costs.

Already planned on that. I've fully disassembled the engine, I'm not the type of person to reuse 38 year old gaskets.... maybe I'll just stick to the cam and springs.

[PeWe]

I modified my engine and some bike parts for same amount of cash I could buy a brand new Kawasaki 1000J back in that time 1983-1984. I had very fun with my bike then and still have it, spending a lot again.. :-) An old CB750 has its charm...
Most of the km's I have used my bike was before tuning it. 79-83 just cafe racing by act.

If starting from the beginning today.... maybe a 5-10 years old, low miles Yamaha XJR1300 with inlet mods increasing the HP from 106 to over 120... Kawasaki Zephyr 1100 look good too but less hp, some models look like the old Z1 900/1000.

[nitrofish1]

I modified my engine and some bike parts for same amount of cash I could buy a brand new Kawasaki 1000J back in that time 1983-1984. I had very fun with my bike then and still have it, spending a lot again.. :-) An old CB750 has its charm...
Most of the km's I have used my bike was before tuning it. 79-83 just cafe racing by act.

If starting from the beginning today.... maybe a 5-10 years old, low miles Yamaha XJR1300 with inlet mods increasing the HP from 106 to over 120... Kawasaki Zephyr 1100 look good too but less hp, some models look like the old Z1 900/1000.

Right now I'm not really looking for another bike, just like to do this one, unless one presents itself at an insanely cheap price, which I have seen before. If not an XS1100 then I'd like to get a hold of a CB350 or 360, I've ridden cafe racers of these and they've been very loud, small, and actually pretty quick. Probably what made them so much fun.

[iron_worker]

One of the larger restrictions of these engines is the head. If you can afford go with a good port job. A hotter cam and stiffer valve springs will really complement the port and allow it work in the higher rev ranges.

The next step would probably be to go to a big bore and this is where it starts getting expensive. You can get the cheap ebay kits (and I've heard most people have had pretty good success with them for mild builds). You will still have the machining costs of having the cylinders bored and honed to size.

If you're not going big bore you should at least re-ring your exsting engine to bring the compression back up closer to where it should be. If your piston clearance is up around .003" or over you will really start to burn oil and really should be going with fresh bores.

Big bores builds with more hp should definitely have HD studs and stronger rods wouldn't be a bad idea either.

Once you open up the top end you really should replace the chain sliders/tensioner. If you want to go one step further and split the cases then you could change the cam chain... and then there is the primary chains and tensioner. And then if the cases are open you might as well check the bearing clearances... etc etc.

And as you can see... the snowball effect has really taken place here. I'd say considering your budget I would have the head gone through with a mild port (oversize valves if you can afford it), re-ring it, all new gaskets up top, hotter cam & valve springs to suit, HD studs if you can afford it.

If there is anything (there probably won't be $$$ lol) left then a good 4-1 exhaust will save you weight and probably add some HP too if tuned accordingly.

IW

[Nic]

Back in the day when the Z900s came out the Honda dudes were blown away with the Z's power, the Z900 and later incarnations  were  death traps though handling wise. Kawasaki didn't learn much from the MachIII did they.
A Yoshi 812 kit and a 4 into1 allowed you to keep up with the stock Z900's and then lose em on the corners. That was a pretty impressive power gain from just a slightly bigger bore. No sub for cubes.
If you don't want to put a big bore kit in you should at least go 1st oversize to re round the bores n get it going right. My basket case 750 K2 only has 30,000Ks on it but the bores are forked as are the valves. I've got the cycleX 1st over kit ( cast pistons but still should hold up to my coot riding these days) and the #41 cam, still plan to get new springs, new valves and guides and smooth the flow in the head. It never ends though, once you open it up you just know you can't stop without doing it all if you want it to last. My machine shop is wanting $250 to do the bores, not cheap but wadiyado, dunno yep how much to do the guides.
The fact that you have to pull the motor to do anything to these things is why I'll do it all n hope I never have to again. Pretty sure the bike will outlast me this time around.

[Retro Rocket]

Nic, the head has more power locked up in it that any other part of the engine, NOTHING else will result in as bigger power gain than a well sorted head, my 776cc drag bike engine ran in the 10's on methanol, small bore size with hugely ported head with bigger valves, springs , titanium retainers and a good cam and 31mm CR's. The heads are very restrictive on these bikes...

[Nic]

Thanks mate, I do intend opening the ports up a tad. I need new valves as well, if I go for bigger valves do I need to put bigger seats in or just get the machinist to reseat the bigger valves. Where does one procure these bigger valves, are the oversize valves at cycleX worth looking at?

[Retro Rocket]

Thanks mate, I do intend opening the ports up a tad. I need new valves as well, if I go for bigger valves do I need to put bigger seats in or just get the machinist to reseat the bigger valves. Where does one procure these bigger valves, are the oversize valves at cycleX worth looking at?

As mentioned earlier, talk to member MRieck, he is the resident head guru {the best}and is a mate of Kens at CycleX anyway, I am going with the 5mm {stem size} Kibblewhite oversized valves, and yes, new seats need to be fitted, the other option is stock size valves in better quality along with better springs and port work, valves deshrouded etc etc..... All depends on how much moolah you wish to spend....

[Nic]

Cheers mate, moolah is as usual, scarce. The Cycle X standard size ex valves are out of stock but should be available in a few weeks, I'm thinking to just put them in with new springs for a good solid result. Not wanting super performance but going for reliability with a tad better zip.

[Retro Rocket]

Cheers mate, moolah is as usual, scarce. The Cycle X standard size ex valves are out of stock but should be available in a few weeks, I'm thinking to just put them in with new springs for a good solid result. Not wanting super performance but going for reliability with a tad better zip.

Moolah is tight here as well, i'm going for balls out everything, I know, its a disease....   Talk to Mike about the valves as well, he may take a couple of days to answer but he will, he has one of my heads ATM, tell him i sent you...

Just thinking, ask Mike about stock size Manley valves....

[Schnell]

Cheers mate, moolah is as usual, scarce. The Cycle X standard size ex valves are out of stock but should be available in a few weeks, I'm thinking to just put them in with new springs for a good solid result. Not wanting super performance but going for reliability with a tad better zip.

Get new piston rings too, to completely seal up the combustion chamber, to go along with those new valves.

[Nic]

Cheers mate, moolah is as usual, scarce. The Cycle X standard size ex valves are out of stock but should be available in a few weeks, I'm thinking to just put them in with new springs for a good solid result. Not wanting super performance but going for reliability with a tad better zip.

Get new piston rings too, to max compression and min blow by, to go along with those new valves.

No worries, I've got 1st oversize pistons to go in. My original point about the 812 kit was that it's probably the cheapest way to get a good boost in HP, all this head work is way more expensive.

[nitrofish1]

I can clean up around the valves and new rings are not an issue, but once I buy a cam and springs that's 400 tied up in it already. A good mild port is another 400. Hence why I was looking at just a cam and springs.

I have yet to take measurements around the bearing surfaces, but so far there's no real noticeable play in them. Usually on the types of things I have to overhaul for work it's reached the trash point when there's a good amount of play between the mating surfaces.

The motor at this point is entirely apart, its going to be getting some fresh paint and fasteners. Lots of galvanic corrosion was present taking it apart, so all the fastener threads will be cleaned for a smooth reassembly.


Honestly, yes it's a 750 (736cc....), but I keep having this tiny little voice in the back of my head that says "Oh yeah, porting would make it go faster.... and so would this, and that, and this, and that..... its only another 200 dollars...." when the other side of my brain knows very well that it will be more than what I like to think of as "fast enough". Unfortunately my brain keeps drifting between the two extremes, when as like you all, moolah is scarce. Maybe I'll let that other side of my brain go wild when I purchase a big bore kit for something above 1000cc. I also realize that it's not going to be faster than its modern counterparts, but that does not bother me, nor cross my mind one bit, even as I was purchasing a non-running corroded pile of bike. My gf could not see the logic behind this decision, but I knew full well what the bike was, and it excited me. Yes, I'd rather buy something from 1975 that I have to put a year of work into rather than the newest sportbike. The PITA factor excites me, and it's much more satisfying. I'm creating a bike that is custom tailored to me, and how I would express myself if I were to build a bike. I'm no noob to building engines but I also need to show some restraint, especially when I know that the payoff for spending thousands of dollars is comparable to a bike from the same era that I could go purchase for a thousand dollars, right now. Now I just need to stop that other side of my brain from speaking lol.


Another question, is that Cycle X 4-2-1 exhaust system really way too loud to where I'd get in trouble for noise ordinances, or should I just go for it lol

[nitrofish1]

I'm asking the exhaust question because I'd like it to be loud but not ruin the mid range power curve by going with an open header.

[Retro Rocket]

I have no experience with Cyclex's exhaust but i imagine you could wrap the baffle with fiberglass matt and quieten it down a bit more. And by the way, i gave in to the voices years ago....

[Nic]

This is my first 750 since 79, in the good ol days I tinkered with big bores, cams and alloy rods and the faster the better. These days I'm thinkin a stock 750 will be plenty fast but, as I pull this down and that down I just keep finding things that need doing, so now I pull out the valves and I find that some clown before me has re-faced all the valves past their limits ( the guy I bought the bike off said the top end had been re, er, built? not by a long shot)  you could shave with the edges of the exhaust valves, shaking head now, so I need to buy all new valves,  do I spend a bit more and put in some bronze guides, the ones in there feel decent but why not the voice says, I can not block it out
The thing's 40 years old so it's no surprise that a lot of stuff is worn out, I just wish I spent what I had saved on the motor FIRST, I went and bought all the crap rubber stuff n all the things that I could have got one at a time when I should have spent on the motor first up. Now when I get into the motor I don't have the dough.

[Retro Rocket]

My opinion is , if you are changing valves then do the guides as well, won't cost much more and it saves a future pull down to do it anyway....    You know, better to be safe than sorry...

[nitrofish1]

I have no experience with Cyclex's exhaust but i imagine you could wrap the baffle with fiberglass matt and quieten it down a bit more. And by the way, i gave in to the voices years ago....

Well, for now I need to resist the voices, and ride with a few upgrades.

[Nic]

My opinion is , if you are changing valves then do the guides as well, won't cost much more and it saves a future pull down to do it anyway....    You know, better to be safe than sorry...

Yeah, that's what I keep hearing in my head