Topic: First Motorcycle/ First Motorcycle Project - Cafe Racer

[GabeTheBear]

Hey Guys! This is actually my first time posting on a forum and first time building/owning a bike. But I'm really excited to be here and hope I can get some help if/when i run into any problems.

I come from an automotive/fabrication background and have always been drawn to motorcycles but never really had the opportunity to get my hands dirty. I was on craigslist one day searching for a good deal and ran into two CB750's for sale. One was a 1971 CB750 that is pretty much complete but dirty, rusty and damaged on the right side. The other was a 78' with the frame, engine, swing arm and front end. They were both $125 a piece so i met with the guy and picked them up. I'll post more pics as I'm tearing down but these these are the pictures from the ad.

[knowsnothing]

Welcome!  Looks like you have some work cut out for you    I am not sure if you are aware, but that 78 you have is an F not a K.  The F's are known to have some valve issues if not probably cared for.  Good luck!

[GabeTheBear]

Thanks knowsnothing, i did know that but I'm not entirely sure what it means. Are the parts interchangeable? Do i need to plan on dedicated to one of the motors? Is one generally better than the other? Any general comments will help. Thanks!

[knowsnothing]

Thanks knowsnothing, i did know that but I'm not entirely sure what it means. Are the parts interchangeable? Do i need to plan on dedicated to one of the motors? Is one generally better than the other? Any general comments will help. Thanks!

If it were me, i would focus my attention on the 71.  They are far more desirable than a 78 F and it looks like its more complete than the F.  Also, the engines in the 78 Fs are know to have valve issues.  Honda changed the angle to squeeze in large valves and by doing so created some problems that develop around 30k miles. 

Another heads up, K and F parts are not direct swaps and will take some work to use.  1971-1976 750Ks are all interchangeable though if you need to go part swapping.   The 1969-1970 are usable, but are crazy expensive and the 1977-1978 Ks are red-headed step children and differ from all of the other years in pretty significant ways.   I hope that helps.

[GabeTheBear]

If it were me, i would focus my attention on the 71.  They are far more desirable than a 78 F and it looks like its more complete than the F.  Also, the engines in the 78 Fs are know to have valve issues.  Honda changed the angle to squeeze in large valves and by doing so created some problems that develop around 30k miles. 

Another heads up, K and F parts are not direct swaps and will take some work to use.  1971-1976 750Ks are all interchangeable though if you need to go part swapping.   The 1969-1970 are usable, but are crazy expensive and the 1977-1978 Ks are red-headed step children and differ from all of the other years in pretty significant ways.   I hope that helps.

Thanks knowsnothing, that's the path i'm on right now. I want to use the engine and frame from the 71 for sure. I know the frame has a hole on the lower right side about the size of a quarter. Hopefully when i take out the engine that's all i have to deal with.



The engine on the other hand has fin damage to the head so i'm going to have to try and find at least the casing. Which is what i prepared for when i bought it. But still a drag.




I also discovered the fork top bridge is cracked in two places. But i definitely expected problems like that to show up.




I only paid $200 for both bikes so as long as i can get at least one of the frames and one of the motors, I'm content. But i'm sure i'll be able to salvage a lot more out of them.

I guess at this point my only question is if worst comes to worst can i use the 78 frame, which i don't want to do but if i can i'll consider it.

Other than that i'm just excited to get the Engine out this weekend so i can start tearing it down and see what the damage is going to be.



Any questions and comments are welcome! Thanks!

[knowsnothing]

Nice progress so far.  A bummer about that unicorn top triple tree.  They are hard to find and worth good money.  There is supposed to be washers in the gaps where the screws go through.  If you don't have the washers in place and  tighten them, they will break like yours.  If you do a forum search you will find more info about it and what people are doing for replacements. 

If the hole in the frame is due to rust, definitely check and recheck the rest of it to make sure it is ok.  It also looks like the bike might have been laid down on its right side (fin damage) so check to make sure the frame is still straight.  It would a shame to finish the project just to find you have a bent frame at the end (already happened to a guy on here). 

Last bit of advise, make sure to take lots of photos and bag and tag everything.  Its a little more work, but it makes all the difference in the world. 

[MCRider]

Nice progress so far.  A bummer about that unicorn top triple tree.  They are hard to find and worth good money.  There is supposed to be washers in the gaps where the screws go through.  If you don't have the washers in place and  tighten them, they will break like yours.  If you do a forum search you will find more info about it and what people are doing for replacements. 
SNIP

Yes the spacers. They are a special size and shape. Neither the bridge nor the spacers are available from Honda. You may want to convert to a later top bridge. The "unicorn" bridge like yours is expensive. New are not available. Good used goes for $100 to $300+. NOS I've seen at $395+.  Depends on the auction and demand that day/week.  The sellers often don't include the spacers.

If you stay with the Unicorn, I posted a thread on how to make the spacers. I'll direct you if it comes to that.

[GabeTheBear]

Nice progress so far.  A bummer about that unicorn top triple tree.  They are hard to find and worth good money.  There is supposed to be washers in the gaps where the screws go through.  If you don't have the washers in place and  tighten them, they will break like yours.  If you do a forum search you will find more info about it and what people are doing for replacements. 

If the hole in the frame is due to rust, definitely check and recheck the rest of it to make sure it is ok.  It also looks like the bike might have been laid down on its right side (fin damage) so check to make sure the frame is still straight.  It would a shame to finish the project just to find you have a bent frame at the end (already happened to a guy on here). 

Last bit of advise, make sure to take lots of photos and bag and tag everything.  Its a little more work, but it makes all the difference in the world.

Wow, I had no idea. Luckily i didn't get my heart set on using them before I realized they were broken. Really interesting motorcycle part though. Maybe i'll run across one but by the way it sounds, probably not.

I agree about the frame and fins. It definitely looks like it was laid down. The tank is pretty messed up as well. But I am already talking to a local shop here who specializes in classic bikes and they said if i bring in the frame they can look at it. So while i'm working on the engine i'm going to send it to them and see what they can do.

I'm thinking it's better to get it sand blasted first so there isn't any doubt about more rust and holes. Plus if they need to weld they will have a clean surface.

Thanks for the advice about bagging and tagging!

[GabeTheBear]

If you stay with the Unicorn, I posted a thread on how to make the spacers. I'll direct you if it comes to that.

Thanks MCRider, I'll let you know what I decide when i get to it.

[Stev-o]

+1 - concentrate on the 71 model.  I saw the ad on CL for those bikes, but no titles and I have too many projects already!

I have a triple top (not unicorn) that I will give you as a welcome gift!

[GabeTheBear]

Definately Stev-o. I've already pretty much committed to the 71'.

But yeah that would be awesome about the triple tree top! Thanks!

[knowsnothing]

+1 - concentrate on the 71 model.  I saw the ad on CL for those bikes, but no titles and I have too many projects already!

I have a triple top (not unicorn) that I will give you as a welcome gift!

Hey Steve-0, where was my welcome gift ?! 

[GabeTheBear]

Alright so I didn't get as much done this weekend as i would have liked but i did make a really interesting discovery when i was trying to take off the oil lines.


Almost got bit by a Black Widow. No biggie.

[knowsnothing]

yowza, i am glad we don't have those things up here.  Watch yourself.

[Stev-o]

A little Black Widow? Nothing to be scared about, it's the tarantulas that catch my eye around here!

Gabe - I work in Austin, are you available during the day? I could drop off the triple.

Knowsnotta - where's your build thread? I'll donate to the cause!

[GabeTheBear]

I live down south but i work downtown and i'm pretty much only available during lunch time. I can message you my number or something and you can give a call whenever your free. My lunch is pretty flexible.
Just let me know or we can think of something else.

[Trounce]

Hey Gabe, what kind of condition are the 78 rims in...my current build is a 74/76/78 and im looking for 78ss running gear...wheels brake parts ect....