Resto-Mod F1 Build...kinda cafe, kinda superbike style

jpdevol

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The leaves are turning and a chill is in the air; not much riding season left, but it's time for another build. Straightened-up the shop over the weekend to start a new mess - just a raggedy CB750F1 and a pile of parts.
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jpdevol

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Motor started out - then wedged itself in a jam - too nice a day for this.......gone ridin'.
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A little more success the next day....
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Up on the stand, ready for a top-end (at least) and some Cerakote.
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And the frame stripped for eventual mods and some chrome powder (maybe?).
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jpdevol

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Never a bad idea to take some pics before disassembly (just in case):
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dirtdigger

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The original head gaskets all eventually leak. People never retorqued the head gaskets because you have to pull the engine. The cylinder studs are weak stock and stretch over time, why I always use heavy duty studs in all rebuilds and machine the cylinder block and head for use with MLS head gaskets.
 

jpdevol

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I've been a bit lazy lately: enjoying the nice riding weather while it lasts. But, some progress has been made.....

Head and cylinder vapor blasted and Cerakoted. Crankcase degreased and rattle-can PJ1 Satin Case paint. Valve cover a bit of polish (side cases yet to do).

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jpdevol

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I had this motor running when purchased last year and no issues were noted (other than gummed carbs) with 18K on the clock, so no bottom end work is planned. Top-end checked out good on wear items; old rings gapped to .014" and pistons cleared at .0026": so I'll clean and run the old pistons. The new rings gap at .011". Wrist pins and rods are good.
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jpdevol

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The cam chain was likely good, but I'll replace it as good practice, along with a new tensioner and guide. Honda folks aren't used to cutting cam chains and riveting a new one in place, but I'm an old Yamaha guy so I'm practiced at it. As I'm only doing a top-end, it's the better choice than leaving the old one in. A genuine D.I.D. chain and master link is available for those not needing to remove the crankshaft.

Grinding an old riveted pin flush
Driving the old pin out with a special tool​
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Measuring the special master link pin before assembly
...and measuring it again to ensure a proper mushroom and side plate play after assembly using the riveter tooling​
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jpdevol

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Motor is looking sharp and I like the direction this is going with the inverted forks and mono shock rear. I’ll be interested in seeing some detail shots of the rear suspension linkage. 👍🏻
Yeah, still pondering the mono shock; ya don't see too many of those done on this frame . The main frame cradle extends back to the seat/r. fender rails (as opposed to some looping back up to the backbone). I don't want to hack that (though seen it done :yikes:). I'm hoping a rather simple ladder affair welded up to the stock swingarm (got an extra) results in adequate travel. I've not yet considered a vertical shock with cantilever linkage. If it doesn't work-out, I have a set of vintage Koni shocks that'll bolt right up 🐔:)

Better lace-up a rear wheel before I start cuttin'
 
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dirtdigger

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While I admire your vision I am never a fan when people try to re engineer an almost 50 year old frame. People never take into account the forces that are present on a monoshock rear suspension and the forces you are introducing into the old frame that was never designed to handle it. Much more reinforcing and strengthening need to be brought into the build. The frame itself is very flexy and road races did work on them to stiffen them up.The swingarm for one is 100% inadequate, just take a look at a modern motocross bike or sport bike swingarm and see how much stronger it has to be to deal with the stress of a single shock. The dragracers back in the day make stronger swingarms because the stock stamped 750 arm was weak and very flexy when adding power and racing...and that was with the stock twin shock setup. There are just large amounts of force involved in single shock rear suspensions. With that said, where you have your shock right now and the general angle is very very close to how Honda did it on the cbr600F2 model of bike. Would be worth a look for you to see how the linkage is designed on that bike and what will be involved with your shock angle. Again not trying to stifle and ideas just think of the forces involved, the 50 year old frame technology you are trying to adapt to and the safety aspect of having weak parts break while riding.
 

jpdevol

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While I admire your vision I am never a fan when people try to re engineer an almost 50 year old frame. People never take into account the forces that are present on a monoshock rear suspension and the forces you are introducing into the old frame that was never designed to handle it. Much more reinforcing and strengthening need to be brought into the build.
I certainly agree that force and points of stress need consideration. The HMC CR750 race kits supplied a bunch of parts including updated forks and shocks - but, interestingly not a swingarm. The monoshock design I'm contemplating would include a a "ladder" that would stiffen the swingarm considerably and also add plate and gusseting at the top mount in the neighborhood of the rear tank mount. I've done similar mods in the past without calamity:

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Anyway, I did get the wheels laced-up and temporarily mounted the vintage Konis (a restoration in themselves). I'm not sure I like the stance as it sits with the R1 forks. So, the monoshock is still under consideration. I do have an extra swingarm, some 1.25" x 0.065" Carbon Steel Square Tube and 3/16" plate, so perhaps I'll get one welded-up to see before any frame hacking commences;)
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