Honda CB750 Sandcast

FRONT FORK SUSPENSION UPGRADE

1941wld · 19 · 34140

1941wld

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I want to do an internal front fork suspension upgrade to my 1969 CB750 sandcast daily rider. Does anyone have any information on what works or has anyone done this before. I need some help in on this upgrade.
Thanks,
Conrad


Wayne

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What result are you looking for Conrad? A more "sporty" or track feel? Softer or just better all around?
I use Progressive springs my Harley's. They're awesome and really make a difference in the overall ride.

http://www.oemcycle.com/Item/product/900024449
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Steve Swan

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Ditto what Wayne said. 

I've used Progressive's in a number of non-Honda bikes and Progressive's DO make a difference.  Significantly lessens front end dive and rebound is more, well... progressive.  On BMW's i've owned, the Progressive's made the bike not feel like the same bike, that being in an obviously positive way.  I wouldn't make any other modifications than Progressive's otherwise the rear shocks won't be able to keep up with the changes.


vnz00

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Im currently building a CB750F2 Cafe Racer.  You can buy cartridge emulators for CB750's which a lot of members on the SOHC forum have installed and reported significant improvement.  It is recommended that these arent used with progressive springs however.  You can purchase heavier, non-progressive springs to suit your weight.  You can also buy pre-load tensioners which go in place of the fork nuts.  I have them but havent built up the front suspension yet, so cant report on performance so far.  This would more than likely be more expensive than the progressive springs alone, but worth a research so you know your options.  I believe they are called RaceTech Gold Valve Cartridge Emulators.  To install, you strip your fork, drill out the damper holes in the damper rods (removes their damping ability, which is replaced by the adjustable valves of the emulators).

Regards,
Steven.


1941wld

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So I email Mark McGrew at M3 racing.
Hi Mark,
I want to upgrade my front fork suspension on my CB750. I'm replacing my seals and I polished my lower legs and just did not want to put it back together with out adding some 2013 technology to the inside of it. I'm hoping you would share some of your knowledge with me.
Thanks,
Conrad

Conrad.   This is not good news S those forks are nothing more that spring retainers! Lol they have no dampening control, very poor upper bushing only', most forks now have upper and lower bushings which allows a much more complainant as the bushings reduce "sticksion" . I helped Vic World make his CR750 work as he wanted the look if the early forks from the outside. I instructed him to use the tubes and internal components from the 77-78 F2 models. And then you can run. RaceTech Gold Valves that control  compression dampening. We at M3 Racing Factory can make these mods as I don't know of any bolt in parts for these early forks . Mark
 


Steve Swan

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I wouldn't be alarmed w/ what other people do or say.  In short, everybody's got their perspective.  I am not a suspension guru, but i do know fundamentals based from my experience.  It's only natural to desire the best for our bikes.  But just because Honda built the best technology in 1969 does not mean the technology compares to 2013.  Of, course, it's dated, by 45 years.  Conrad, there really are not alot of "plug and play" options w/ our old forks.  Progressives will make a difference, you'd be happy with those.  I don't pay much attention to what guys in other clubs are doing, but emulators are also a great product.  The only concern i would have installing Emulators, is your stock rear shock might not be able to keep up with the Emulators.  The Emulators are an ingenious way of attempting to give our old fork some valving to actually control the movement of the oil rather than simply have it be pounded by the action of the aluminum slider going up and down around the steel leg.  The Emulator will not allow the front end of the bike to compress as quickly, giving it a more even rate of compression (eliminates dive) and same for rebound (eliminates the bike wanting to high side in a turn.)  If your rear shocks have not been modified to have the same compression/rebound rates as the forks, the ft/rr suspension systems will not be "balanced"  and you'll have a more ill handling motorcycle than stock.  I don't know if the sohc guys are running stock rear shocks w/ their Emulators or if they go with a set of Worxs on the rear or not....   Typically, guys will adjust the spring load tension on the rear shock to attempt matching what the Emulator's affect has done to the front.   Myself, for the sake lessening the dive, i would put in a set of Progressives and be done with it.  Dive, braking in turns, is the thing most guys notice.  If you do want to have some control over rebound, then Emulators will do that.  The lack of rigidity of the frame on the CB750, combined with the heavy weight of the engine, stresses the unit more than it can tolerate when powering and braking while doing turning work.  Any stock CB750 will dive and pogo when pushed hard in turns.  the only thing i will say which will sound 'smart' is if one has not experienced dive or pogo'ing on a CB750, then one has not braked hard into turns at the same time accelerating as much as one can thru the turn and as hard as one can out of the turn.  Progressives, Emulators, Worxs, other products are built to help reduce or eliminate these issues.  Doing anything with the stock CB750 suspension system is not going to make a world of difference.  But, it WILL make a pleasant and  rewarding differnece.  Most of us don't ride like squids any more, at least i sure don't.  Modifying stock suspension for street use can be rewarding.   Upgrading suspension to FWO race track conditions is for people with money to burn and makes for a very unenjoyable street ride.  Anyway..


kmb69

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Conrad.   This is not good news S those forks are nothing more that spring retainers! Lol they have no dampening control, very poor upper bushing only', most forks now have upper and lower bushings which allows a much more complainant as the bushings reduce "sticksion" . I helped Vic World make his CR750 work as he wanted the look if the early forks from the outside. I instructed him to use the tubes and internal components from the 77-78 F2 models. And then you can run. RaceTech Gold Valves that control  compression dampening. We at M3 Racing Factory can make these mods as I don't know of any bolt in parts for these early forks . Mark

Typical McGrew, usually negative and ALWAYS HAWKING A BUCK. Emulators for a serious Cafe or Road Racer.

Ditto on Steve and Wayne. The Progressives are really nice in a daily rider. Real hard to beat for $60 plus shipping.

Keith


kp

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As Swannie says, tuning a 69 four to handle is akin to performance tuning a sack of spuds. Sure it can be done and Rickman was a good example of how to sort a Honda or Kawasaki. Back in the good ol days when I could ride a bike (at least in my mind I could ride a bike probably because I was stupid and more stupid) I owned a Bridgestone 350 GTR and I could outrun my mates on their K1's, Bonnies and Kwakas 500's in the twisty stuff no F'n problems. In my day British bikes were supreme and I can remember that they did handle fairly well but the Honda four was the king of grunt, four cylinders, disc brake and those pipes, BUT if memory serves the Norton Commando was the king of frame design and a dream through the twists and turns and was streets in front of anything else from anywhere for handling. Alas it's 750 engine was still not a match for the Honda and the rest is history. The triumphs and BSAs were sorry pieces of junk and tried catch up with their pathetic attempts at a 750cc engine. Mobile oil leaks we called them. Them days the helmet doubled up as an oil catcher when one parked their BSA or Trumphy (let's not forget the Harley's either .... Ay Wayne ;D ) The British bikes never needed an oil change cos they got one every 500 miles by just topping up what was lost  :P :P :P
Sorry to steal your thread Conrad but I suppose we should ask why did Honda change the fork outers to the more robust looking K1 design. I would probably agree only going with the progressive springs but then despite not having a clue about this techo talk, I wouldn't deviate from stock to start with. Hmmmm! My anal streak coming out again Mark  :D
Yabba Dabba KP


1941wld

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Looks like we are having a great de-cuss'ion going on. ;D
Mark mentioned the CB750 F2 front end (1977 or 78).
Is that the Super-Sport model or what?
The front end mods Mark is talking about are under 400 bucks and are internal (plus an F2 donor front end).
I also understand from Steve that the rear shocks would need to be upgraded to some modern ones to match the front end changes.
I'm not looking to do laps at Barber, just want to improve the ride for my bad back and neck so I can keep riding.
The comment Mark made about the spring holder was all they had in 1969.
Most of ya'll say replace the springs only. I may try that and some different fork oil. I'm 240lbs., what weight oil should I use?
Thanks,
Conrad



kmb69

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Conrad, I cannot help but believe that McGrew's suspension is much stiffer than what I think you are looking for. Probably not so good for your back. It is designed for road racing to be more resistent to diving during hard braking in the corners as well as resistent to lift when acccelerating. He is talking about beefing up the 77-78 Super Sport front end. I think you can use and do the same thing with the early CBX front ends also. It is a very good solution for what he designed it for but probably will not provide the street ride you are looking for. As far as weight of fork oil, you are probably going to have to experiment to see what feels good to you. The same goes for how much pretension you put on the springs. I use automatic transmission fluid in mine but it may be too light weight for you but I am a trim 215. ;D ::) The ATF also helps to keep the fork seals from leaking. Keith


Steve Swan

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Ditto what Keith says.

Try a set of Progressive's in your stock forks and see how that works for you.  Experiment with different weights of oil.  Try one mod at a time and if you still are not satisfied with the ride, then spend the big bucks on a completely different suspension setup.  

Although Mark McGrew's setup is using old forks with skinny 35mm fork tubes, his mods are for vintage racing and the vintage racer guys ride these bike WFO, just like racers running new 43mm forks and single rear shocks.  The old forks, set up for vintage racing have to function as well as they can and are subjected to the same conditions as any other modern day suspension operating under the extreme forces of braking, acceleration, lean angles and high operating temperatures, all happening very rapidly at the same time most of the time.

A racing setup like McGrew is talking about WILL be a "stiff" ride and you WILL feel every bump in the road.

McGrew's set up is not for comfort nor for aching backs and necks.  (i could be wrong, but i'll stick with believing i'm right until proven otherwise..)

Questions to ask, "What do i want the suspension to do?"  "What is the current suspension setup doing or not doing now?"  What are the modifications which can help achieve what i want the suspension to do?"  "What changes in ride and handling will result from the proposed modifications?"  "Will these changes from modifications result in what i want to achieve?"

At the worst, if you don't like the Progressive's, you're only out $60 and someone will buy them without much delay.   (I'd like a set in 2137.)

BTW....  I'd LOVE to find a decent GTR 350 !!!!!!  imho, the sexiest 2-stroke ever built.  KP, you've got good taste !


kp

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BTW....  I'd LOVE to find a decent GTR 350 !!!!!!  imho, the sexiest 2-stroke ever built.  KP, you've got good taste !
Nar, not good taste Mr Swan as my tastes are in my arse (just ask my wife); it was cheap ;D
Yabba Dabba KP


Erling

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Apparently I was not quite wrong when the Sand Cast motor and parts else needed were transferred into a Seeley frame in 1978. With a Frontfork of newer date too. Erling.


1941wld

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Thanks Steve,
I've ordered some Progressive Springs.
Now the next question.
What do you think about change the steering bearings?
Will this help the handleing of the bike?

See below:

All Balls Steering Stem Bearing Kits include all bearings and seals necessary for replacement.
*Direct replacement for OEM tapered bearings
*Upgrade replacement for all ball style bearings
*Heavy duty tapered roller bearings


Steve Swan

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I've never ridden a CB750 w/ tapered bearings.  My contemporary bikes have tapered bearings, which, as i understand it have more load bearing area and better steering feedback.  Would be good to hear from anyone who has ride experience using tapered bearings.  
 
Another consideration for improving handling would be identifying tire options, brand/model matched front/rear setups available to the CB750.  Tires are generally overlooked as part of the suspension system, but are a critical component of suspension, directly affecting suspension characteristics and handling.  Don't know how many tire options there are for the CB750, but different tires have different compounds, designed for long wear straight line touring (harder compound) then there are performance (cornering) tires shorter wear(softer compound) and then dual compound tires w/ hard compund down center and soft compound on sidewalls.  Sidewall construction's another consideration, which at the moment does not come to mind.  Think most are steel belted, no longer nylon or otherwise.  The question to ask would be does the tire have a stiff sidewall or an soft sidewall.  A stiff sidewall will give more road input aka firm ride, a soft sidewall less input and a softer ride.  I don't know if Bridgestone still makes the Accolades, they are a combination sport/touring tire.  I guess i would read the DB's at sohc4 and see what those guys are using.  Or call a dealer who knows his tires and tell them what type of riding you do and what type of ride is youe want to achieve.

After you've ridden the Progressives a while, perhaps another consideration would be rear shocks upgrade.  Modern shocks would probably go a long way in meeting your goals for your desired ride needs; generally not limited to only compression adjustments.  Worx makes quality shocks for the CB750 and if i recall correctly there may different levels of shocks available for the CB750.  I believe Worx can supply different weight springs in their shocks for rider weights, riding styles, comfort vs sport.   I'm not sure if i remember correctly, but i believe you can control control rebound as well as compression w/ the Worx shocks.  I'd suggest some internet research to see what options may be available w/ Worx or any other shock brand out there.  Worx sales or a knowledgeable dealer should be able to give you good advice to make your decision if you decide to upgrade from stock.  As mentioned earlier, match your rear suspension to what you've done to the front.
 
Emulators are a good thing, from the standpoint of controlling oil flow and controlling rebound but i don't know if there is an Emulator for the 69-76 CB750 forks....?  I know, when setting up forks w/ Emulators, there are simple modifications which can be done to the stock fork parts to control quicker or slower oil flow speeds.  I've set up several different forks installing Emulators, but these bikes were all 80's - 90's era bikes.  Like Keith said, the Emulators will give a stiffer ride, designed for sport use.  Not for comfort.
 
After you get the Progressives in, i'd experiment w/ different oil types.