Author Topic: 1974 Honda CB750 K4 Cafe Racer rebuild  (Read 49449 times)

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Offline swan

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1974 Honda CB750 K4 Cafe Racer rebuild
« on: June 03, 2009, 02:33:32 pm »
Intro
I am documenting a cafe rebuild of a 1974 Honda CB750 K4. Let’s call it a chopper rescue project. I have built many Hondas and British café bikes and frequent the forums often but have never posted a bike project from beginning to end until now, so here goes…

I will document the major portions of the build as reference for others doing the same, post problems encountered with my solutions and emphasize the non-stock custom work. Many areas of CB750 restorations are well documented on this forum need not be repeated (carb and tank cleaning, frozen brake caliper, etc).

History
Two years ago I bought a K4 and a K3 CB750 from dude out in the countryside for cheap. I had other project bikes in progress but the price was too good to pass up, so I bought them and stored the until this week.. The K4 turned over and had compression while the K3 was frozen. I spent an afternoon cleaning the carbs, tank, petcock, installing new battery, flushing the old oil and put the 4-4 exhaust from the K4 and fired her up. Tweaked it a bit and it idled and rode well, but the front brake caliper was frozen so I only rode a few miles on empty back roads to assess its condition. Solid motor, clean functional carbs, transmission crisp and smooth, crap brakes and tires and ugly as hell. A perfect candidate for a café rebuild. For the Honda purists, I am not destroying anything special, it is a Honda K4, not a Vincent, and there are thousands of these rotting away in barns, garages and backyards.

Life happened, several other bikes completed and sold, fell in love with a Norton, so I am finally making to the time to tear into this project. I have bought a mountain of new Honda OEM and aftermarket parts waiting for this bike. New rims, tires, spokes, all new cables, Fast from the Past rearsets, battery, pod filters, larger main jets etc.

Personal
I am a British bike junkie and build Honda cafes as my methadone and financial source to support my British habit. Like most everyone on this forum, I enjoy wrenching, building, restoring bikes and the pride and self-satisfaction of making something old beautiful again. It is my passion and hobby, but not my career. My day job is in the museum field and I am a trained archaeological conservator and work with high end art and priceless objects centuries and millenia old, so 30-50 year bikes are relatively easy and simple to work on. Free time is scarce for me and is spent either riding or restoring bikes to keep me sane and out of trouble. Cycle therapy.

Goals
My goal for this bike is to build a cafe racer in the true sense and spirit of the term: stripped down and fast with good handling to mimic the British track racing bikes of the 1950’s and 60’s. Appearance, though important, is secondary to function.  There is more to a café racer than a bad black paint job, rearsets and an ugly seat on an ill running bike. I do crank up rebuilds on all my motors, complete rebuilds on my wheels (new bearings, spokes, rims and tires), meticulous electrical and carb work and work methodically, without shortcuts. The 74 K4 will be based heavily on two of my previous CB400F café builds; Honda Milano red tank, Manx seat, plain black side covers, black cylinder, clubmans, rearsets, 4 into 1 exhaust, rebuilt wheels etc. A strong and powerful girl in a sexy red dress. The K3 will have a strong Norton Manx and Triton influence (black hubs, front drum brake, black fenders, Manx seat, rearsets, clip-ons 5 gallon Manx tank, Dunstall and John Tickle style goodies etc). One of these two will have a GT550 4LS shoe front brake drum just like my Triton.
CB400f cafe
recent CB400f cafe

CB750 K4 as purchased in all its 1970’s chopperesque glory.  Ugly, but got her running within an hour. A solid bike, but since it has been sitting for years I am going to build it from the crank up with all new gaskets, seals and replace the bearings as needed. Repaint cases, polish covers and rebuild carbs, paint frame, rebuild wheels etc, here we go…..

« Last Edit: June 04, 2009, 06:29:37 am by swan »
1975 CB400 F cafes, 1974 CB750 K4 Cafe, 1966/1976 Triumph/ Norton Triton Cafe and 1962 DBD34 BSA Gold Star Clubman.

CB750 build http://forums.sohc4.net/index.php?topic=52551.0

Offline swan

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #1 on: June 03, 2009, 03:23:24 pm »


Finally, made the time to start this one. 6 uninterupted hours of bike time on a Friday and 8 hours on a Saturday-heaven! Stripped her to the frame, pulled the engine and pounded knee indents in the tank, first coats of filler and sanding.

I cleaned the exterior of the motor, pulled the carbs, soaked the cover screws in PB Blaster overnight and removed them with an impact driver. All but two screws came off easily. One screw on the breather cover got strippied and one on the stator was drilled and removed with a reverse easy out tool in a hand drill.

The stator and clutch covers were removed along with the carbs, clutch plates and basket, starter, oil pan and filters to lighten the motor before pulling it out of the frame. Two lifts and I got the beast out of the frame and on to a milk crate. It is still weighs more than I do.


Everything was cleaned, photographed, bagged and labeled. The frame and swing arm was an oily mess, but all that oil kept the rust at bay. Spiders were evicted.

Proper use of a self-service carwash....


Sump oil filter…. This is why I always strip my bikes down to the crank. You never know what has happened to your bike with the previous owners.

I have been waiting two years cut the rear hub out of the god awful, ugly 16’ Harley rim and fat tire.  Why people insist on hobbling their machines with fat rear tires is beyond me.  The hub will be highly polished, drilled with a few large holes with screens for ventilation, but will not have shotgun blast holes a la Carpy. I have a brand spanking new 18” DID rim, new spokes and Dunlop D404 waiting to surround the hub.


I picked up two Suzuki GT550 4LS front drum brakes recently. One, I bought a $200 parts bike to get it and the other I literally stole from someone on Craigslist who had no idea it was worth $300-400 unrestored (To thwart hate mail and possible theft charges I will not reveal the price). I collected all the necessary parts to install dual drilled front discs but I may go with the GT 4ls drum on this one.

The K4 tank was exceptionally clean and had one small dent, so I filled it, primered and painted it black. It is not pictured and I will save or sell it. For this project I used the tank from the K3. It was clean on the inside, but a Bondo queen on the outside and the tank badge holders were filled in. It was ugly and I had no problem smacking it with a hammer. I created a pattern outlining my knees, traced it on to the tank and pounded away with a rubber and plastic headed mallet. No problems, easy to do and both indents are symmetrical. The indents were filled with body filler and sanded twice. I layed down one guide coat of primer and sanded it to determine the high and low spots of the tank. I filled the lowspots, sanded again and it now has another guide coat. On more round of sanding and spot filling and then on to final prime, paint and clear.



I am busy this week and a have big pile of junk waiting for me this weekend. Frame to paint, tank to sand, prime, paint, clear and polish, motor to break down, rebuild, paint, polish...

Cannot wait, stay tuned…

« Last Edit: June 03, 2009, 06:40:55 pm by swan »
1975 CB400 F cafes, 1974 CB750 K4 Cafe, 1966/1976 Triumph/ Norton Triton Cafe and 1962 DBD34 BSA Gold Star Clubman.

CB750 build http://forums.sohc4.net/index.php?topic=52551.0

Offline andy750

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #2 on: June 03, 2009, 04:18:48 pm »
Ill be watching this one as I liked your CB400 build...are you planning on selling the 74 seat? Is it in good condition? Looks interesting...let me know if you do.

The only thing i would say so far is I agree with you about the 16` Harley rim but to be honest the bashed in tank look is so passe....its old, its boring, everyone does it.....and dosent look that great IMHO....better to go with a stretch tank ala DME (forum member) or get a CR-style gas tank...or allow dunstall tank ;-)....but they thats just me.

Anyway looking forward to the rest.

cheers
Andy
Current bikes
1. CB750K4: Long distance bike, 17 countries and counting...2001 - Trans-USA-Mexico, 2003 - European Tour, 2004 - SOHC Easy Rider Trip , 2008 - Adirondack Tour 2-up , 2013 - Tail of the Dragon Tour , 2017: 836 kit install and bottom end rebuild. And rebirth: http://forums.sohc4.net/index.php/topic,173213.msg2029836.html#msg2029836
2. CB750/810cc K2  - road racer with JMR worked head 71 hp
3. Yamaha Tenere T700 2022

Where did you go on your bike today? - http://forums.sohc4.net/index.php?topic=45183.2350

Offline swan

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #3 on: June 03, 2009, 05:40:57 pm »
Andy,
Thanks. The seat was crap, non-stock and I tossed the cover and foam. I kept the seat pan for reference when I lay up a fiberglass Manx seat.

This is the first time I have done knee indents, they are functional and I wanted to give it a go. I did for me and not because others are doing it. I want to buy or build a Manx style 5 gallon for the next CB750 project.

Stay tuned for more...
« Last Edit: June 04, 2009, 04:30:17 am by swan »
1975 CB400 F cafes, 1974 CB750 K4 Cafe, 1966/1976 Triumph/ Norton Triton Cafe and 1962 DBD34 BSA Gold Star Clubman.

CB750 build http://forums.sohc4.net/index.php?topic=52551.0

Offline Sheik Yerbouti

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #4 on: June 03, 2009, 05:52:18 pm »
Good stuff. Good to see people who know what they're doing, and then there are asshats like me who fumble aimlessly. Excited to see progress.

Do0ki3 PWNS

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #5 on: June 03, 2009, 05:55:28 pm »
cool.

Offline swan

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #6 on: June 08, 2009, 07:39:35 pm »
Busy week, out of town with little time to touch the project. I managed to sand and polish the fork lowers, front hub, primary covers and dissembled rear hub as well as picked up new bearings front and rear.

You know the drill: paint stripper, clean, 400, 600, 800, 1000, 1500 grit sandpaper wet and dry and polish with black, brown and white polishing compound with lacquer thinner clean between all.

I will have a full day off on Thursday dedicated to working on bikes and have another pile of new parts ready to go.



« Last Edit: November 25, 2012, 12:13:04 pm by swan »
1975 CB400 F cafes, 1974 CB750 K4 Cafe, 1966/1976 Triumph/ Norton Triton Cafe and 1962 DBD34 BSA Gold Star Clubman.

CB750 build http://forums.sohc4.net/index.php?topic=52551.0

Offline swan

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #7 on: June 13, 2009, 08:31:16 pm »
It was a beautiful weekend and I spent most of it working on bikes. The Norton got new exhaust headers and I put  200 miles of curving, empty backroads on her.

Several hours were spent cleaning, preparing, sanding and blasting the CB750 frame, swing arm, stands and trees. I spray primed everything with a two part catalyzed primer and painted with single-stage gloss black and flat black for yokes. Everything was wet sanded with 1500 grit to knock off the orange peel and followed by hand and machine poishing with 3M rubbing compound, swirl remover and final polish. I love my Dewalt 849 polisher! Everything looks great and it is a shame though most of the frame will be covered.


I laced up the polished front hub with new spokes into a new DID rim, new bearings, trued it, and wrapped it in new rimstrip, tube and new Dunlop 100/90/19 D404 tire. Looks like it is doing 100 mph when standing still. Truing wheels takes time and patience but is one of favorite parts of any bike build. Something very zen about getting the axial and radial rotation perfect. Here is a very easy to follow tutorial on trueing from Dan Jones here on the SOHC forum: http://forums.sohc4.net/index.php?topic=368.0


The rear hub was cleaned, stripped and I started to sand it. It takes ages to polish these hubs to perfection.

Dissembled, cleaned, polished the front forks and rebuilt with new seals. Still need to drill and paint the front rotor and then the front end will go together.


One more round of guide coat sanding and spot filling on the tank was done and I repaired the side covers with MEK and ABS plastic. I found some Legos at a rummage sale, mixed them with MEK to create a glue to fix and seal the cracks on the covers. It works and I read about it here http://forums.sohc4.net/index.php?topic=49736.0

I have a busy work week ahead with limited free time but am looking forward to building the rolling chassis, finishing the tank and covers. Stay tuned...
1975 CB400 F cafes, 1974 CB750 K4 Cafe, 1966/1976 Triumph/ Norton Triton Cafe and 1962 DBD34 BSA Gold Star Clubman.

CB750 build http://forums.sohc4.net/index.php?topic=52551.0

Offline JAG

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #8 on: July 26, 2009, 01:43:49 pm »
Great work! I'll be watching!!
Cafe Racing is mainly a matter of taste. It is an atavistic mentality, a peculiar mix of low style, high speed, pure dumbness, and overweening commitment to the Cafe Life and all its dangerous pleasures. I am a Cafe Racer myself, on some days - and it is one of my finest addictions. ~H. S. Thompson~

Offline NPHLYT

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #9 on: July 29, 2009, 05:08:01 am »
I can't wait to see how this ends.....
NPHLYT
1970 CB750 Mutt
1962 Sears Allstate Puch

Offline swan

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #10 on: August 04, 2009, 11:37:27 am »
Sorry for the delay, but life happens, valve spring broke on the Triton, sold the Norton and am in title hell with this bike. Stayed tuned I'll be working on her this weekend.
1975 CB400 F cafes, 1974 CB750 K4 Cafe, 1966/1976 Triumph/ Norton Triton Cafe and 1962 DBD34 BSA Gold Star Clubman.

CB750 build http://forums.sohc4.net/index.php?topic=52551.0

Offline NPHLYT

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #11 on: August 04, 2009, 11:02:46 pm »
Sorry for the delay, but life happens, valve spring broke on the Triton, sold the Norton and am in title hell with this bike. Stayed tuned I'll be working on her this weekend.

I used a mob in Nevada for my Puch, cost me $80 and I now have the title. I will see if I can find the name, but I am out of town.
NPHLYT
1970 CB750 Mutt
1962 Sears Allstate Puch

chnclr

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #12 on: October 28, 2009, 05:09:56 pm »
Nice work. I'm currently building a cafe cb750k5. I was thinking about using a drum for the front hub. I know it doesn't stop like a disc, but I don't plan on tearing up the streets. I just like the more vintage look of a drum. Problem is... I'm not sure what drums/axles will fit the front end of a cb750k. Will I also need a different rim, given that the spoke angles will be different from a larger diameter hub? Any direction you could offer would be appreciated.

Thx,
Ken

Offline bucky katt

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #13 on: October 28, 2009, 10:27:15 pm »
any idea if stock off the shelf spokes will work for that front (whatever bike they might be for) or will youhave to get custom spokes made? i too have a 4ls front drum and i think if i dont put it onto my suzuki titan i might like the look it gives on my k4 750.
Of all God's creatures there is only one that cannot be made the slave of the lash. That one is the cat. If man could be crossed with the cat it would improve man, but it would deteriorate the cat.
Mark Twain - Notebook, 1894

Offline greenjeans

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #14 on: October 29, 2009, 06:40:08 am »
I think I saw the drum brake on ebay you were talking about.  I was going to bid on it and completely forgot...lucky you.
I keep looking for one of those brakes off the GT750 but keep missing them - can bring myself to bid over $400 for one.

Nice progress, look forward to seeing the finished product.
Yep, I'm the kid that figured out how to put things back together...eventually.

traveler

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #15 on: December 25, 2009, 05:22:57 pm »
How about an update?

:D

~Joe

Offline swan

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #16 on: November 25, 2012, 12:10:17 pm »
Well, time to dust off this project and get started again. Cold weather is here, snow is coming and time to work in my cozy shop all winter. I will have several restored bikes this spring. With this CB750K4, I want to put her on a diet, shed much of the unneccessary stock components, add a British cafe racer elements of style and produce a fast, well-handling and reliable motorcycle that looks like it could have come from the factory.

For the first time ever, I had problem titling this non-titled bike in Minnesota. I have successfully obtained titles for 7 other bikes with Bills of Sales and sellers' statements but since this bike came from Wisconsin I had problems titling in it Minnesota. I will come up with an alternative method to get it titled by this spring (title service, forum member titling in another state and "selling" the bike back to me, etc) While this project has been in storage (3 years) I have moved house, rented a proper workspace (with a lift, tools and refrigerator full of beer, etc) bought, restored and sold or kept several other motorcycles (several CB400f's, 1966 Triumph Bonneville, 1959 BSA A10, 1974 Norton Commando, a few more CB750 parts bikes and my beloved 1962 BSA Gold Star restoration). I have nearly all the parts I need, the bike frame has been painted gloss black, wheel hubs painted, new bearings pressed in, trued spokes, rims, new tires etc. She is a rolling chassis and time to get back to work.

I lugged the motor over to the Winona Riders' workshop yesterday so I could break it down to the crankshaft, access its condition, clean, paint and heat cure the engine cases, cylinder, head and covers, new gaskets, seal and anything else it needs to be new again. I did run and ride this bike when I first bought it and it had good, even compression in all four cylinders and rode well. Here we go:

Several hundred pounds of grease, oil, dirt and anodized alloy-yuck.


Upper valve train looks really good and clearances were all correct.


No problems removing the valve cover or cylinder head other than one marred screw from my impact driver. The pistons were evenly carbon coated and the bores look good, no damage.



All four cylinders are even and well within factory specified standard wear. No trauma or drama, confirming what I suspected; this is a common Midwest bike that suffered lack of use rather than abuse. Hopefully when I dig into the lower end tonight there are no problems. Regardless, I will strip it to the crank, measure all the tolerances, rebuild with new gaskets and seals and fix or replace anything bad. Stay tuned...
1975 CB400 F cafes, 1974 CB750 K4 Cafe, 1966/1976 Triumph/ Norton Triton Cafe and 1962 DBD34 BSA Gold Star Clubman.

CB750 build http://forums.sohc4.net/index.php?topic=52551.0

Offline greenjeans

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #17 on: November 27, 2012, 06:58:13 am »
On your 4LS brake....  Are you still going to use it ?  They are monsterous yet beautiful.
I have one that I'm using on my current build. (same as a GT750 - my first ever bike)   I haven't even seen one of those pop up on ebay in a while.   There is plenty of stopping power.    However, I did have to machine a few millimeters off the plates so that I could center it in the forks.    I can't remember if I used the GT axle or modified a CB axle - been a while since I did the machining on it.

Love that Milano red - Honda, pure Honda.  Keep it going.
Yep, I'm the kid that figured out how to put things back together...eventually.

Offline iron_worker

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #18 on: November 27, 2012, 07:10:32 am »
Wow. I have a feeling this will be a great build. You are very meticulous and thorough it seems.

IW

Offline swan

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #19 on: November 28, 2012, 11:26:43 am »
Thanks guys! I sold the GT750 drum a while ago. I still have one on my Triton and once set correctly, it is great, particularly for a much lighter bike than it was designed to stop.

One step forward, several steps back....

I dug into the valves, springs and guides. So far, so good. The valves and seats look good but I am going to meet with my machinist neighbor next week to use his small bore internal micrometer and other high end valve tools to measure the guides and go from there. For now, I wanted to take the head apart and get it clean.



bagged and tagged.



I disassembled the lower end last night and was shocked to find a big gaping HOLE in both the top and bottom cases! @#%$!!! The DPO threw a chain, cracked the cases and "fixed" it with a crappy JB weld and thin aluminum plate. No wonder the motor was so heavily covered with oil and dirt near the drive sprocket. Originally, I suspected a bad seal was leaking oil. I often see chain damage on British vertical twin cases. Since they are vertically split, the damage is to only one half of the motor, but with horizontally split Honda cases, the chain blew out both halves of the motor.  My friend Pat is a master welder and can work miracles with heli-arc/TIG and I will meet with him this week to access the damage and devise a solution. If the cases cannot be saved, there is another CB750 K4 parts motor in the Winona Riders' shop I may have to use. I would rather repair the original motor since all crank, rods, bearings, gears etc are in excellent shape. Hmmmmm.... Stay tuned...


« Last Edit: November 28, 2012, 12:44:39 pm by swan »
1975 CB400 F cafes, 1974 CB750 K4 Cafe, 1966/1976 Triumph/ Norton Triton Cafe and 1962 DBD34 BSA Gold Star Clubman.

CB750 build http://forums.sohc4.net/index.php?topic=52551.0

Offline iron_worker

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #20 on: November 28, 2012, 12:18:24 pm »
Ouch! That's a pretty nasty void you got there. I think it's a fairly common problem to have though. If your friend is truly a master TIG artist then it will be salvageable. The trick will be getting all the oil out of the porous aluminium ... you make need to bake the cases or something?

IW

Offline swan

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #21 on: November 28, 2012, 12:53:38 pm »
Thanks IW, a quick search shows this is not the first time it has happened. My welder did my BSA Gold Star fin repair as seen here http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=362776&page=1

We will clean the area thoroughly, heat and I assume he will want to remove some of the cracked areas and grind a channel for a bead to grab on to. I will post photos of the process once it is done.
1975 CB400 F cafes, 1974 CB750 K4 Cafe, 1966/1976 Triumph/ Norton Triton Cafe and 1962 DBD34 BSA Gold Star Clubman.

CB750 build http://forums.sohc4.net/index.php?topic=52551.0

Offline iron_worker

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #22 on: November 28, 2012, 02:05:52 pm »
Some nice flat copper bar stock might also be useful so you can build up the area  and have a nice flat surface once you remove it. Welding access might not be great once you had it in place though.

That or just build it up higher and then have it machined down or hand file it down carefully.

I checked out your gold star fin repair... looks like if you can tackle that then this should be no problem. ha

IW

Offline bwaller

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #23 on: November 28, 2012, 02:15:46 pm »
No wonder people get into trouble when you see the condition of that sprocket.

Offline Mugen_Stumpo

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Re: 1974 Honda CB750 K4 Cafe Racer rebuild
« Reply #24 on: November 28, 2012, 02:37:11 pm »
do you biult two almost identical 400f?!

why??