Topic: '78 750 F3 Comstar wheels on a '78 750 K8 ?

[IndianRider]

wanted to convert my CB 750 K8 front to a dual disc set up in the front and have an opportunity to get a front end from a 1978 CB750 F3 (comstar wheel,rotors, calipers,fork tubes and master cylinder) except the upper and lower triple clamps ..  is this a direct bolt on to a '78 K model  without the triple clamps .. 

also how would it look visually ? .. anyone got pics of the comstar wheels on a K model ? i hope it doesnt look too wierd with a comstar front and a spoked rear ..     but better braking with the dual setup up front would be really welcomed .. 

any pics of K series bikes with the comstar wheels would be greatly appreciated ..   

 

[martin99]

The only problem I can forsee is that the F3 - if it's the same bike as the F2 here in the UK, and I think it basically is - will have had a brake line splitter which is mounted on two studs protruding from the bottom yoke, I wouldn't have thought the K8 would have this, but I'm not sure so if it has  - sorry I spoke! Anyway,assuming it hasn't it will have implications for your brake line routing.
Cheers
Martin

[eldar]

Well if you can get a whole front end, then great! it wil swap in no problem. You will have to probably get a different master, one thats a bit larger with either a line splitter or a longer banjo to use 2 lines.  The rear should slip into the swing arm BUT you will need to mount the caliper and reservoir and that will take a bit more work.

[IndianRider]

Well if you can get a whole front end, then great! it wil swap in no problem. You will have to probably get a different master, one thats a bit larger with either a line splitter or a longer banjo to use 2 lines.  The rear should slip into the swing arm BUT you will need to mount the caliper and reservoir and that will take a bit more work.

eldar,

i am also getting the F3 master cylinder (new one) along with the front comstar wheel/both rotors/both calipers/ tubes with lowers and both lines with the bango fitting from the F3 ..  i just didnt know if i need the triple clamp as well from the F3 to fit the K8 .. 

not worried about the rear for now and i dont mind having a comstar in front and the spoked drum wheel in the rear  ..  but wi anted to see if anyone had a pic of the comstar on the K series ..

i checked the parts fiche for the K8 and the F3 ..   the fork tubes & the upper triple clamp are the same part numbers .. the lower triple clamp with the stem is NOT the same part #'s (different rake or trail ??) .. 

does this mean the means the diameter of the fork tubes are the same and the distance between the tubes is also the same (same upper triple clamp) ..  so im thinking the F3 front end should fit using the stock K8 triple clamps .. 

i still would like to know if anyone had done this yet before i bite the bullet and spend $$ .. ive hit the search button but it looks like most folks replace the front end with a Goldwing front end .. i havent seen anyone using a F3 front end ..

[eurban]

All of the SOHC 750s including the F2 and F3 use 35mm forks so the diameter of the tubes is not an issue.  The spacing between the forks should also be the same.   Honda did bring the forks tubes closer in the front to back direction to the steering stem on the 77 and 78 bikes.  Your K8 triple tree setup should have this update.  Not sure why the top clamps would have the same part number as I am pretty sure that the F2/F3 have lower risers to mount the handle bars than the K7/K8s.  Don't know for sure if there is any difference in rake built into the trees.  Basically the F2/F3 forks should slide into your stock trees just fine.   Probably a good idea to upgrade to tapered steering bearings while things are apart.  Also take a good look at the pistons for the brake calipers as they are almost always rusted to sh**.  . . . .

[upperlake04]

From the Official 1978 Honda Shop Manual -           F3                  K8

                    Caster(degrees from horizontal) --     62.5               62
                     Trail  --------------------------------------     113.5mm        115mm
 
  I have original upper and lower triples on the bike and another on the shelf - if you want measurements   or pictures, it can easily be done..

[IndianRider]

ok .. it looks like the caster and trail is different on the '78 Kk and F3 series .. but if the fork tube diameter and width between them (same upper triple) is the same, the front wheel and fork assembly from the F3 should fit the K8 with the K8's triple clamps .. 

and as eurban mentioned, i found out that the calipers for the F3 are jammed up like crazy and the selller advised using dual piston calipers from the cb900 models .. acc. to him the cb900 calipers fit the F3 lower forks with "minor" mods .. 

[IndianRider]

upperlake  .. any differences bet. the upper F and K triple clamps ? parts # is same for both ..   part # is is different for the lower clamps / steering stem though

[upperlake04]

IR - you're asking a newb who has never seen a K upper tripletree, but I'd think they're interchangeable if the parts numbers are the same. I picked up this F3 triple on eBay a few months back for $15.US

-another somewhat related thought - assuming the difference in rake in the two models is in the distance the forks are held away from the steering axis by the lowers and not in any headtube/frame angle difference, and the uppers are the same - wouldn't the bearings be cocked off square on one of the models?  Maybe 1/2 degree is inconsequential.

[mick750F]

   I'd guess that the difference in part numbers of the lowers is due to the "F" having a splitter for the brake lines mounted on two bolts coming out the front of it. The horns are mounted there as well. I haven't looked that closely at a '77-'78K front end to be sure about it but that's what I suspect. If this is the case then you will either need the "F" lower to do your conversion or rig something up for the splitter.

   From previous discussions about the calipers here in the forum the dohc calipers are a direct bolt-on although I believe you need the mounting brackets as well as the calipers.

Mike

[IndianRider]

that must be it.. the F lower triple might be a diff part # becasue of the splitter/horns mounting ..  so it looks to me like the setup would work ..i'll keep u all posted if i do it ..

[IndianRider]

ok ..

next week i am getting the F3 front comstar wheel with rotors and the forks ( no triple clamps) and will keep you all posted if it will bolt on to my K8 ..

if it bolts on, all i need to get is the brake calipers and upgrade my master cylinder ..  im planning to go for the dual piston calipers from the 1982+ CB900F, CB750F etc. and other bigger hondas during that time frame..

will keep u all posted and hope it works out ...
 

[doobiebro]

I am interested to see how this works out also.  I have a 1977 750K with the standard spoked wheels, but I have recently purchased a set of Comstars from a 1979 750K Anniversary Edition.  I am hoping everything will line up correctly, but will be monitoring this thread to see if you have any issues that I may learn from.  Also, I am a little apprehensive about the appearance - spokes versus mags.  The spokes have such a classic look, but the mags seem to reflect more of an aspect of speed.

[IndianRider]

ok here u go ..

just got the F3 front forks with the comstar wheel and bolted right on to thestock  K8 triple clamps ... here are some pics ..  looks like it was a direct bolt on with no problems .. only issue i fore see is the dual  rotors moving freely with the dual piston calipers i am going to use with this set up ..  see next paragraph ..  also noticed the speedo gear is now on the left side instead of the right side as on the K8 .. dont know if the speedo is working yet ..will check later ..

now, instead of using the stock F3 single piston calipers, i decided to use the honda dual piston calipers from a 1982 V45 Sabre/magna .. ( other dual piston caliper bikes are 1982 Cb750 F SS, 1982 CB 900 F SS, 1982 V45 Sabre etc.  etc and maybe other honda models also) ..

BUT, for these dual piston calipers to fit on the F3 lower fork tubes, you need the caliper brackets from the 1982 CB750 F SS or the CB 900 F SS models. i was told by a member here that you CANNOT use the caliper brackets from the honda "C" custom or "cruiser" style models .. so i needed to get caliper brackets only from the "later" SS models and i found the brackets from a 1982 CB750 F SS on ebay .. the stock caliper brackets i am getting with the V45 calipers will not fit on the F3 fork lower tubes ( might fit but alignment and angle might not be right)

once again this i am still at the planning  guessing stages .. once i get these calipers from the '82 V45, i will see how they fit on the F3 lowers and update all of you ..  unti lthen enjoy the odd comstar front with the spoked rear .. am looking for a '78 Cb750 Automatic model 17 inch rear comstar "drum" wheel if this works out .. 


right side view





left side





notice speedometer gear outlet on left side just under the axle ..




closer view right side

[Terry in Australia]

Very nice mate, I've decided to tear my 1977 F2 down and transfer all the F2 components over to my spare K2 frame this year, including the engine, forks, both wheels, swingarm, electrics etc, in fact pretty much everything apart from the seat, tank and other cosmetic items.

I've been "waxing lyrical" for quite awhile about the benefits of having the classic K looks enhanced with upgraded F2 componentry, so I won't bore anyone's pants off here, suffice to say that the end result is the bike that Honda shold have built to continue the line, which I'll refer to as the "K9".

Don't forget to fit an F2/F3 fender on those forks, or maybe a later CB750/900F item as they look cool and will bolt straight up, or at least get yourself a fork brace, (no, I'm not trying to sell you one of mine) as those forks will flex mightily under the vastly improved brakes, and of course your K8 fender won't fit. Cheers, Terry.      

[IndianRider]

thanks for the fender tip terry . . i actually did not get a F3 front fender with the set up and did not know that the K8 fender wont fit .. didnt try it yet .. 

i was thinking of one of those generic fiber glass fenders to keep it light and compensate for the additional weight from the second disc and caliper ..

hmm.. whats the details on the fork brace .. ? i might be interested  in the next 2 months once spring comes along ...

[Terry in Australia]

No worries mate, here's a pic of one I did earlier........................ 

[mick750F]

No worries mate, here's a pic of one I did earlier........................ 

   Nice corporate logo Terry!

   Also, are you sure about the dohc fenders fitting up to the F3 forks? I tried to mount what I believed to be a fender from a dohc 750F to my bike and it was a no go. The fender was on the tire before the mounting holes would line up. Now I've got to say that the only reason I believed the fender was from a dohc 750F is that it was listed that way on the mighty ebay. We all know that ebay sellers are the most knowledgeable people in the world.

Mike

[IndianRider]

the fork brace is looking good terry ..what is is going to cost us $$$

[eldar]

That brace was made jsut for me, ok well not the brace just the logo!

So you used a whole F3 front end minus the calipers and mounts? Thats nice to know, I can work with that. Now does the 78Auto rear wheel match the F3 front? I have never seen them side by side.

I think I know my next project! Hope that manual has helped you out some too.

[IndianRider]

yeah eldar .. this is what i used from the 1978 CB750 F3: 

the whole front comstar wheel set up which includes:
1: comstar wheel
2: 2 rotors
3: axle
4: spacers
5: front fork tubes including the black lower tubes

keep in mind i am still using the stock K8 upper and lower triple clamps ..

i cant wait for the 1982 CB750F SS caliper mounts and the 1982 Honda V 45 Sabre dual piston calipers to come in ( includes brake lines and master cylinder from same bike) ...

the '78 CB750 Automatic rear comstar drum wheel is a 17 incher like the K8 wheel .. i think u can also get a rear comstar drum in 16inch which came on other bikes such as the Honda CX500 or early 80's bikes.. im not sure and i need to check into this ... i never seen the A model rear drum wheel in person so i dont know if its black or silver .. doesnt matter as long as it fits and works .. 

[Terry in Australia]

No worries mate, here's a pic of one I did earlier........................ 

   Nice corporate logo Terry!

   Also, are you sure about the dohc fenders fitting up to the F3 forks? I tried to mount what I believed to be a fender from a dohc 750F to my bike and it was a no go. The fender was on the tire before the mounting holes would line up. Now I've got to say that the only reason I believed the fender was from a dohc 750F is that it was listed that way on the mighty ebay. We all know that ebay sellers are the most knowledgeable people in the world.

Mike

G'Day Mike, well my memory might be fading faster than I'd like, but I've got a 900F fender on it's way to me as we speak, so as soon as it does, I'll let you know mate! Cheers, Terry.

[scondon]

No worries mate, here's a pic of one I did earlier........................ 

   Nice corporate logo Terry!

   Also, are you sure about the dohc fenders fitting up to the F3 forks? I tried to mount what I believed to be a fender from a dohc 750F to my bike and it was a no go. The fender was on the tire before the mounting holes would line up. Now I've got to say that the only reason I believed the fender was from a dohc 750F is that it was listed that way on the mighty ebay. We all know that ebay sellers are the most knowledgeable people in the world.

Mike

G'Day Mike, well my memory might be fading faster than I'd like, but I've got a 900F fender on it's way to me as we speak, so as soon as it does, I'll let you know mate! Cheers, Terry.

  The 900F fender in my avatar doesn't fit the F2/3 forks without rubbing the tire as Mick points out. I'm using forks from a 1980 DOHC bike. The tubes are a inch longer so I have slipped them up in the trees. Also, I think the spacing on the DOHC triple trees might be juuuust a bit wider as I had to shave about 1/8" of plastic off the mounts in order to squeeze the 900F fender in place.

[Terry in Australia]

Thanks Sean, the fender I bought is for an earlier incarnation of the 900F (1979, I guess?) as it doesn't have the "scoop" thingy, and I think from memory that it's metal, but I don't know what differences there were between the two models, if any. Cheers, Terry.

[mick750F]

   I don't remember what year mine is for sure but I think it was claimed to be a '79. No "scoop" thingy on mine either and it's plastic not metal. When I got it I checked the spacing of the holes but neglected to check the mounting height. It seemed like it was going to work so I gave it a spiffy paint job only to find out it didn't fit up. One of these days I'll get ambitious and mount the fender on the brace section of an F2/3 fender.

Mike