CB750 Engine DOHC/SOHC swap & Model frame changes

[Frankenfe]

I am beginning to explore otions for a cb750 build. I am wondering a couple things regarding CB750 model changes.

Will a Chain drive CB750 DOHC Engine Bolt into a SOHC Frame?, With Modification? If so, What?
For Example a 1982 engine in a 1972 frame?

Did the Frame evolve for the most part like other models to a lower seat height more "Touring" frame?
Did this occur in 1979? with the DOHC Engine? (Like a 70's CB400 to a 80's CM400)

What significant changest occured in what year to the CB750 frame itself? Not Shock or fork improvements, but the frame design itself. Did the Swing arm widen for wider wheels in the '92 for example.

 

[my-79-750-k]

I know for one, the 79+ models had a removable section on the lower right side of the frame so you could actually get that dual cam lump out of the frame. Other than engine mounts, the change from a flat seat area frame to a dipped frame and the removable frame section, I'm not sure what else was changed in the frame. But that'll get you started.

 

[Frankenfe]

I have gathered Tank Below and Complete 1998 CBR600F3 Front End (Brakes,Trips, Forks, WheeL) and Rear End (Swingarm and Mono Shock, Brakes and Wheel)

I am invisioning an early "Flat Back Bone" Reinforced Frame with a Un-Painted DOHC, With a CBR600 Front End & Rear Disc Brakes. Either by Modified Stock Swing Arm or Graft of the CBR600 Rear End Complete.

 

[surffly]

No a DOHC motor will not bolt in to a SOHC frame

Why even think about the swap? neither are that hard to find....and DOHC went to 1100cc

the only difference in frame for the SOHC bikes are some are K and others are F 77 and 78 of both is alittle different.

for the DOHC bikes they had F C K
F is by far the best in terms of performance
others are cruisers

 

[Frankenfe]

Looks like a 900f may be the ticket, just so happens there is 1982 CB900F for sale local. May have to check it out.

 

[CB350f Cafe]

How much are they asking for it? Is it running?

 

[surffly]

82 and up has the better brakes

 

[Frankenfe]

How much are they asking for it? Is it running?

Asking $1,200, Running with Title, Unknown mileage at this time (Not in ad) I have emailed/called.

 

[surplus 6]

if you are thinking about tuning the 900f have a read of this, it's a cut n paste from http://www.cb1100f.net

the first line of the reply to the question made me smile

Q
i need all tuning tips for this engine :
i know wiesco do a big bore kit for these but what cams are best along with carbs etc., and wht bhp can be realistically achieved without being on the edge of reliability.

A
Turning on the key on a stock 900 is at the edge of reliabilty.

This engine is the most fragile of the bunch due to the long stroke and 15 mm wrist pin plus the shape of the conrod is entirely wrong. Basically the conrod is tapered and thinnest right under the wrist pin.

900 cams are not bad but better redegreed to 100LC intake and 105 LC exhaust. The 1100 cams are better yet 100I/105E timing.

If you are even considering making one of these run you buy an 1100 or 1000C shaft drive for the parts. The best combination is 900 crankshaft/primary drive with 1100 conrods that use the 17mm wrist pin. The 1000C was acually made this way. The reason is the 1100 has a really wide/heavy primary chain and they cut away the crank cheek to make room for it. This made the crank weak so the heavy chain would distort it at revs which would then take out the #3

 

[Frankenfe]

Thanks Surplus 6.

 

[hillsy]

I remember seeing a DOHC motor in an SOHC chassis in a custom bike mag some years ago. The details escape me but I think the transplant was quite involved - and in the end just an exercise in form as the handling was reported to be worse than either original bike.


And I've seen more CB900 in the wreckers than still on the road compared to GSX's and KZ's.


Just sayin' :

 

[surplus 6]

the cut and paste was from a web site dedicated to the cb's, I have cut n paste it to inform, not to ruffle you feathers, and as you say the 15mm wrist pins become an issue with big bores and rev's. the revs at least may be an issue if tuning is/was the goal so now everyone knows. :-*
the coils can be replaced by cbr600f2 items, for a much improved spark also a stem swap see's the triple trees/forks from said 600 pressed into service. gives a nice 41mm fork and 17" rubber 8)

 

[surplus 6]

ps. the rest of the thread on http://www.cb1100f.net/ was talking about carb swaps, reprofiling cams etc, so yes my cut n paste was taken out of context, but there is a problem if any seriours engine mods are planned. I am in no way knocking cb900F's, I have one in boxes that will have the said engine mods in before being built back up, as I do enjoy visiting the end of the twrist grip travel alot. but that will be a while yet as I have one or three projects to do before I dig out the cb

 

[Frankenfe]

Well guys I think I may have struck a deal for the CB900F, (a Kel-Tec PLR-16, 150 rds of ammo, and $200 cash. That is = to about $700 -$750 my cost. If everything checks out when I go see it this evening (Clear Title, Running, In "Good" to "Very Good" Condition) I may be coming home with it. I almost afraid it is going to be in too good of condition like like my '71 CB750 waswhen I bought it, Cuz then I won't want to molest it. I am worried the tank may not work on the late frame since it was made for an early frame. Oh well good excuse to buy one more........

I appreciate all the opinions and don't want it turn into a pissing match. All info is good, even if it is possibly biased on ones personal experiences and may not be a norm. I can then research further and draw my own conclusions. Thanks

 

[ponycarman]

Awesome! I love kel tecs. I have a pf9 and my dad has a p11. I like the pf9 when it work lol. Got to send it back to them for some work. Good luck with your deal


Totally miss read that. I thought it was someone trading the gun for your bike. Read it again and saw it was the other way around. Good luck with the deal

 

[Frankenfe]

The PLR is a nasty gun, but kinda all bad ass show with no real application and too expensive to shoot. I like my Sub2k/Glock 22 better and it has common mags with my G22 up to a 15 rd.

 

[ponycarman]

Yeah thats true. I've never shot a glock. I'm still relatively new to guns. I'm planning on getting another pistol this weekend. I hope

Sent from my LS670 using Tapatalk

 

[Mantree]

I have a interesting spin on this, what about a sohc 750 enging in a dohc 900 frame I want the kickstart with the subtransmition for a sidcar build I am already mocking up a subframe based on the forward control brackets made for the 750 engine

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[J-Rod10]

Yeah, so what do you want for all of the F3 bits?