Topic: Motor questions

[racemx51]

Hey guys, coming to you guys because you seem to know what the hell your talking about. Im in the process of building my second 73 CB 750. The first one is stock other than just a 4-1. Basically it was my trial bike.. Been racing motocross all my life and have been a Pro since '05 so I know how to work on bikes very well. But obviously these road bikes are a bit different. Especially these old ones.. This second bike Im building, I want to be pure perfection.. I want to bore the motor, which I plan on doing with the help of Wiseco (Im supported by them through my MX racing) but Id like to know what I should do with cams, etc. Im sure there are a lot of small little things you can do with these to make big differences.. I know thats the way a dirt bike is.. Obviously I dont know these little things though.. So what do you street bike experts have for tips? Dont be afraid to get technical with me. I do serious motor work to my bikes every year to be able to compete with the factory bikes..

Now, on the other hand, I dont want to go stupid crazy with it, I just want the motor fresh and faster than it is now..

[scottly]

The Wiseco 836 kit is a well proven setup. From there, a mild port job, a cam with upgraded springs, and bigger carbs will wake these old bikes up a bit. Also, a fair amount of weight can be removed. The bike in my avatar weighs close to 400 pounds, with no fuel.

[racemx51]

Yeah I cut a ton off my bike I just built. Feels so much lighter compared to before I started on it.. Thanks for the response man.

Come on guys, wheres the love? Whats the best cam, and all that stuff? Help a brother out! Its my first CB motor that Im modding out..

[mec]

check this:
http://forums.sohc4.net/index.php?topic=54803.0

mec

[wrenchmuch]

check this:
http://forums.sohc4.net/index.php?topic=54803.0

mec

You asked for it .

[turboguzzi]

check this:
http://forums.sohc4.net/index.php?topic=54803.0

mec

hei mec, i think he said "I dont want to go stupid crazy with it"....

BTW, compliments on the dry clutch build, impressive.

are you friends coming again to our last race in Franciacorta in two weeks?

Cheers
TG

[MCRider]

RaceMX, your question is too open ended. A Wiseco 836 and a ported head are the starting points IMO. And you could stop there and be very happy. "Fresh and faster than it is now".

But the "best cam" and how many other tricks you want to employ just depends on what you want to do.

There are a t least 10 cams, then there are springs, rockers, retainers, valves, crank work, rods, trans, coatings, treatments, etc things you can do each adding a step of complexity and cost, infinity.

I'd save some money for suspension upgrades to compliment the horsepower.

You want it to be "pure perfection" but not "stupid crazy". For many these are mutually exclusive. Can't have the former without the latter. Is that pure perfection show, or street, or track, or stock, or custom, etc.

Let us know what kind of riding you'll be doing. Thursday night drive ins, 400 mile day trips, weekend overnights, track days, drag days, show only.

I've employed about everything i could in my project and am now pining the things I've left out. Gotta draw the line somewhere.

[Sam Green Racing]

Come on guys, wheres the love? Whats the best cam, and all that stuff? Help a brother out! Its my first CB motor that Im modding out..

The Megacycle 125-60 is a realy good cam with the pistons you have. A little bit hotter is the 125-70, it can give over 90bhp with the right set up. I have one of the last Billet 125-75 cams going spare with only around 30 miles on it if you're interested.

Sam.

PS, it's sold.

[MCRider]

An 836, with a ported head and a cam (and a pipe I assume) is going to be needing stronger rods pretty quick. Add $1,000+. (rods, crank work, etc.)

[Jim F]

If you want to get the best out of the head to complement everything else
call Mike Rieck up in the Boston area

you can PM for more info but we all in some sort or another run his heads (Or most of us) and
he gets the most out of these old slugs

There is no one better

Jimmy

[Sam Green Racing]

And there are hundreds of members that will second that.

Take a look at his cylinders to check out his work. http://forums.sohc4.net/index.php?topic=49438.525

Sam.

[bear]

Come on guys, wheres the love? Whats the best cam, and all that stuff? Help a brother out! Its my first CB motor that Im modding out..

The Megacycle 125-60 is a realy good cam with the pistons you have. A little bit hotter is the 125-70, it can give over 90bhp with the right set up. I have one of the last Billet 125-75 cams going spare with only around 30 miles on it if you're interested.

Sam.

Only ridden on Sundays A Sammy.
PM sent

Cheers,
Brian

[racemx51]

MCrider, what I mean by perfection is a tight motor that is as brand new as I can make it.. And the looks of it to be perfect.. I run and have worked in a body shop for years so Im very hard on myself as far as the looks of something I build..

As far as motor, I want to make it faster, like with the 836cc kit. And port it, because we do all our own porting here. I guess what I was asking was what kind of options I have.. I dont want to spend stupid amounts of money, but I want it to be pretty fast.. Im going to put new valves, rod bearings, etc all in it. So Im curious to as what stock VS A/M parts cost. I guess this is all stuff I can search and over time find out on this fine world wide web but I figured Id ask some people that have done these things before and know what works and what doesnt. I know enough about bikes but not a 1973 one.. I wasnt even thought about by my parents yet when this bike was on the showroom floor..I know that a Pro Circuit valve in a 2011 RMZ 450 is said to be much stronger than a stock one but really is basically the same for twice the money.. See what Im saying? I know all the ins and out about a motocross motor so basically my mindset is, okay well it must be the same for these bikes..Might as well find out from people who know..

Maybe I should just stick to my 836cc plan and port it and call the motor good as far as 'upgrades'?

[MCRider]

racemx: That gets us closer. The 836 with your port job, a nice valve job (no need for different valves) new guides (maybe) and a few touches will be very nice. Rods not needed. Probably no bottom end work needed. (You mentioned rod bearings. Usually no need unless high mileage or abuse.)

For a really good street bike, most stock parts cost the same or more than the A/M parts. Only until you want something REALLY special will the A?M parts get more pricey. I think.

But you still didn't tell us what the bike is for. Saturdays in the twisties. High rev Friday nights with the boys. Racing for pink slips. overnight tours, etc. That will drive what extra stuff you may want to have.

And don't forget the chassis. Rework the forks (cartridge emulators), swingarm bushes and shocks. Tires. Stock suspension on a 73 is pretty wimpy when new, worse later.

[racemx51]

Well my brother and I both have CBs.. I have that first one I built which is stock just turned into a cafe (and waay lighter haha) but we are both putting 836cc kits in.. We both race motocross at a high level so my guess is we will be bombing around at a pretty good pace    Plus a lot of friends have HDs with $7000 into there motors. Which I dont need to match, but I just want to be able to keep up no problem if say, we are heading to the beach.. Like I said though, getting to the point where I need different rods and stuff, that seems maybe a bit far but depending on cost I guess Id do it.. During the week it'll be basically just cruise rides...Work and back, some rides at night with my brother, etc. I really would like to put a different front end on this thing so I can have dual disc, etc. My brother modified his hub so he can put dual disc on but Id rather just put a whole different front end. These forks are extremely simple and not much more than some springs..

So you dont think it needs rod bearings? Now wait, I forgot to mention, this motor was stuck when I got it, only one cylinder but still. I think the bike has about 27,000 on it..

[MRieck]

Put in OS intakes (33.5) with the 836 kit. You will need aftermarket springs too. Get a cam...that 125-75 is a good one. Ti retainers are a good idea. What is your experience porting older 2 valve engines? I have experience with CRF heads and definite ideas about what aftermarket valvetrain parts to use and which not use.

[biker1966]

Hey, Can anyone help me . I'm looking to build my 1974 cb750 to a 915cc. I want to put a real high lift cam in it . The highest I dare to go on the street .Now I live near Binghamton NY . Does anyone know someone that can build the motor for me and do the work. What is the right cam for it. I want it to have Balls...

[Retro Rocket]

Hey, Can anyone help me . I'm looking to build my 1974 cb750 to a 915cc. I want to put a real high lift cam in it . The highest I dare to go on the street .Now I live near Binghamton NY . Does anyone know someone that can build the motor for me and do the work. What is the right cam for it. I want it to have Balls...

Start your own thread dude, you will get plenty of answers.....

[Jim F]

 My engine was built years ago but with other peoples suggestions of what would give it  reliable power.

an 836 kit from Wisco.
mild street cam with heavy springs and Ti retainers
stock valves
bronze guides
my own porting (Before I knew Mike Rieck)
stock rods and  crank
The Honda cranks are forged and very strong.
Dyna S ignition with Dyna coils and smooth bore carbs.

I really do a lot of Tinkering on my bikes, so they don't see a lot of street time but the bike
has started every time and is a very reliable bike
with out putting thousands of dollars in to the build
but I have 10,s of thousands of dollars in my time but thats for the love of working on these old slugs
Ask Mike Rieck how much time he has in his own CB.................a trillion dollars or more Mike?

good luck
Jim

[racemx51]

Who makes the best valve springs if you guys all suggest springs?

[tweakin]

This is a good place to start....   http://www.kpmivalvetrain.com/

This is what MRieck put in my head when he did my head for my 915 build.

Who makes the best valve springs if you guys all suggest springs?

[MCRider]

KPMI definitely good stuff.

Gotta throw APE's hat in the ring. Their banner is at the top of the page and they sponsor this forum.

[tweakin]

Thanks MCRider, feel bad I left out APE.  I am using them in my 836 engine.

KPMI definitely good stuff.

Gotta throw APE's hat in the ring. Their banner is at the top of the page and they sponsor this forum.

[MCRider]

Thanks MCRider, feel bad I left out APE.  I am using them in my 836 engine.

KPMI definitely good stuff.

Gotta throw APE's hat in the ring. Their banner is at the top of the page and they sponsor this forum.

Lots of good vendors, I ry to spread out my purchases.

[racemx51]

Okay so you guys think, boring kit, cam, intake valves, springs, guides, and call it good? If that motor was stuck when I got it from sitting for so long do you guys think I should tear into the bottom end and do crank bearings and stuff too? I dont want to do all this work and have something explode in the thing.. Like I said, I dont know what goes bad on these old street bike motors..First one I really tear into.. Not all that much different than what Im used to though it seems like...Might need some help timing it, havent really looked around for marks, Im sure it has them like anything else but Im used to timing 4 stroke 250Fs and 450s..