Author Topic: 1971 CB750 Cafe Boombox!!! (Read 6724 times)

Flick · « **on:** November 26, 2011, 05:09:02 PM »

Hey guys I have a 1971 cb750 that I have had since 2004 and I am now beginning to build into a cafe racer. I've got a lot of different ideas and questions right know that I need to figure out but I though I would go ahead and start documenting progress. I'll be on the slow track due to a new baby and a lot of overtime at work but one day I'll get'er done...
One rare accessory for cafe racers that I am going to try to incorporate into my build is a AUX radio. This will only consist of a small amp to connect directly to my phone or mp3 player and a few speakers I'm still trying to figure out where they will go......

Here is what I started with:

Flick · « **Reply #1 on:** November 26, 2011, 05:12:40 PM »

Bought some fork seals to rebuild forks, then bought tubes from Franks Forks

Flick · « **Reply #2 on:** November 26, 2011, 05:55:13 PM »

Rebuilt forks and a snapshot of the bike how she sits right now, sorry for the clutter...

Roach Carver · « **Reply #3 on:** November 26, 2011, 05:59:02 PM »

almost done.

Flick · « **Reply #4 on:** November 26, 2011, 06:33:35 PM »

Haha, yep all i got to do now is finish....

bluesmoke69 · « **Reply #5 on:** November 26, 2011, 10:48:25 PM »

You got started that's good. Slow and steady wins the race. LOL

Terry in Australia · « **Reply #6 on:** November 26, 2011, 11:22:21 PM »

Looking good mate, let me know if you are gonna sell all the "take off" parts, I need a pair of fenders and a 4 into 4 exhaust system, if yours are in reasonable condition? Cheers, Terry.

WhyNot2 · « **Reply #7 on:** November 27, 2011, 05:24:21 AM »

Subscribed......................

Those forks bottoms look great, man, good job.

Once again, thanks for the PM.........

MoMo · « **Reply #8 on:** November 27, 2011, 06:03:26 AM »

Belated welcome. Your forks do look good, were the originals bent or pitted or did you just want to get rid of the top rusted area? Keep plugging away, you'll get it done...Larry

Flick · « **Reply #9 on:** November 27, 2011, 07:23:33 AM »

Thanks all... Sorry Terry but I actually have sold the rear fender, exhaust and got a guy wanting a shipping price on the front fender. Thanks yall, I'm liking how the forks turned out. Photolar, the originals were not bent but pitted and one tube was pitted in the travel area.
HELP:
I've got a couple of questions I need to figure out before I buy a ton of parts. My bike, motor, tranny, ect.. has 64,394 miles on it and the motor leaks quite a bit. I'm not a mechanic at all but it seems like it runs decent to me. What should I look at doing mechanically before all the cosmetic building? I would love to rebuild the motor but I'm afraid I don't have the skills and would not know what to look for when I get it apart!?! All advise is welcomed, Thanks

MoMo · « **Reply #10 on:** November 27, 2011, 05:21:01 PM »

Any sign that the motor had been apart? Like allen heads instead of phillips? I would do a compression check to make sure it is even across all 4 cylinders, and a leak down test if possible. Does the top end or lower end leak oil? There are more than enough people on this forum to help you get through a motor rebuild...Larry

Flick · « **Reply #11 on:** November 27, 2011, 08:05:41 PM »

Larry,
The stock phillips are still installed and seem to be in pretty decent shape, seems to be a little scuffing on a couple of them... The leaking is from the top end coming out of the fins. There is not a specific compression tester for cb750's is there just as long as the threads fit? This will be my first time to do a test, my battery is off can I just remove all four spark plugs put the tester in and kick a few times until the gauge reading is steady? My carbs are still installed and there is still oil in the motor. The gas tank is disconnected. Thanks for the help - Jacob

lucky · « **Reply #12 on:** November 28, 2011, 01:39:57 AM »

Quote from: Flick on November 27, 2011, 07:23:33 AM

Thanks all... Sorry Terry but I actually have sold the rear fender, exhaust and got a guy wanting a shipping price on the front fender. Thanks yall, I'm liking how the forks turned out. Photolar, the originals were not bent but pitted and one tube was pitted in the travel area.
HELP:
I've got a couple of questions I need to figure out before I buy a ton of parts. My bike, motor, tranny, ect.. has 64,394 miles on it and the motor leaks quite a bit. I'm not a mechanic at all but it seems like it runs decent to me. What should I look at doing mechanically before all the cosmetic building? I would love to rebuild the motor but I'm afraid I don't have the skills and would not know what to look for when I get it apart!?! All advise is welcomed, Thanks

With that many miles and that many years I would rebuild the engine.
Cycle Exchange could give you a price. Tell them what you want.
It does take a lot of tools and skills even if you know how.

MoMo · « **Reply #13 on:** November 28, 2011, 01:50:42 AM »

Quote from: Flick on November 27, 2011, 08:05:41 PM

Larry,
The stock phillips are still installed and seem to be in pretty decent shape, seems to be a little scuffing on a couple of them... The leaking is from the top end coming out of the fins. There is not a specific compression tester for cb750's is there just as long as the threads fit? This will be my first time to do a test, my battery is off can I just remove all four spark plugs put the tester in and kick a few times until the gauge reading is steady? My carbs are still installed and there is still oil in the motor. The gas tank is disconnected. Thanks for the help - Jacob

Jacob, no specific tester as long as it has an adapter to fit the plug thread size. Throttle wide open and kick till the needle stops rising, but it seems like the motor has never been apart and the leaking is probably from the pucks under the cam towers so at least a top end overhaul does seem to be in order-if you do it yourself you are looking at 400 to 500 minimum(gaskets, rings, honing, etc). Looking for a running donor motor with low miles is an option...Larry

Flick · « **Reply #14 on:** November 28, 2011, 07:18:41 PM »

Just so I know all of my options, what year model motors would be compatible with my bike? 1971 CB750

Roach Carver · « **Reply #15 on:** November 28, 2011, 07:42:41 PM »

69-76( or is that 75) will be the easiest.

Flick · « **Reply #16 on:** December 01, 2011, 07:25:38 PM »

Ok guys I had a buddy from college come over yesterday and take a look at the bike. He and his dad have rebuilt many car/pickup motors and they have boring/honing equipment and he thinks he can help me get the motor rebuilt. He brought his compression tester but unfortunately it had a fitting that was to large. Off hand does anyone know what size fitting will work for my bike? Also he wanted to know what compression ratio yall would suggest for 91 octane pump gas?
Thanks-Flick

Roach Carver · « **Reply #17 on:** December 02, 2011, 07:03:02 AM »

Look around the forum for cr. I have no idea. For the fitting just match it to your spark plug. I dont know the size or pitch.

MCRider · « **Reply #18 on:** December 02, 2011, 07:32:09 AM »

Quote from: Flick on December 01, 2011, 07:25:38 PM

Ok guys I had a buddy from college come over yesterday and take a look at the bike. He and his dad have rebuilt many car/pickup motors and they have boring/honing equipment and he thinks he can help me get the motor rebuilt. He brought his compression tester but unfortunately it had a fitting that was to large. Off hand does anyone know what size fitting will work for my bike? Also he wanted to know what compression ratio yall would suggest for 91 octane pump gas?
Thanks-Flick

Its a 12mm spark plug. Your friend probably has the more common 14mm size. I think the thread pitch is 1.25 but I'll check.

As to CR, as long as its tuned well, upwards of 10.5 will work. 9.0 is fine. I think there is a consensus to avoid ethanol.

Flick · « **Reply #19 on:** December 02, 2011, 07:31:51 PM »

Thanks for that info, I bought a compression tester today with the 12mm and did a test...
Results:
Cylinder 1 - 90lbs
2 - 95lbs
3 - 90lbs
4 - 90lbs
Also I took a picture of my plugs, Left to right is Cylinder 1, 2, 3, Cylinder 4 is not pictured, it looks just like #2.

Roach Carver · « **Reply #20 on:** December 03, 2011, 05:55:13 AM »

Heres my two cents. I would wash the engine well and ride it a while and recheck the compression and re-evaluate the oil leak.

Flick · « **Reply #21 on:** December 07, 2011, 03:40:28 PM »

Thanks Roach Carver, I've got a lot to purchase before my bike is ridable again (Clubman bars, Exhaust, Controls ect), but I think that is what I will do... I did just buy another cb750 yesterday and I'm going to keep that motor. The odometer only shows 19,000 miles or so. But I know this bike has just been sitting in the PO's back yard for at least 10 years probably more than that. It is a 1976 cb750 and I am going to part it out so if any of yall are interested you can hit me up in my for sale thread, there is a link at the bottom. Here are a couple of pics of the bike...

Flick · « **Reply #22 on:** December 19, 2011, 07:18:44 PM »

Alright I finally got back in the garage for a couple of minutes and took my steering shaft out and spilt my balls all over the floor. After I powder coat and Im ready to go back is there an alternative bearing system?

lucky · « **Reply #23 on:** December 19, 2011, 08:51:59 PM »

Quote from: photolar on November 28, 2011, 01:50:42 AM

Quote from: Flick on November 27, 2011, 08:05:41 PM
Larry,
The stock phillips are still installed and seem to be in pretty decent shape, seems to be a little scuffing on a couple of them... The leaking is from the top end coming out of the fins. There is not a specific compression tester for cb750's is there just as long as the threads fit? This will be my first time to do a test, my battery is off can I just remove all four spark plugs put the tester in and kick a few times until the gauge reading is steady? My carbs are still installed and there is still oil in the motor. The gas tank is disconnected. Thanks for the help - Jacob

Jacob, no specific tester as long as it has an adapter to fit the plug thread size. Throttle wide open and kick till the needle stops rising, but it seems like the motor has never been apart and the leaking is probably from the pucks under the cam towers so at least a top end overhaul does seem to be in order-if you do it yourself you are looking at 400 to 500 minimum(gaskets, rings, honing, etc). Looking for a running donor motor with low miles is an option...Larry

I think he should rebuild what he has. Take your time.
There is not any running CB750 engines out there. They are ALL 33 years old.
They need to be taken apart and have new rubber parts and bearings.
The crank journals can get clogged with old oil and bits of debris.
There are NO low mile donor engines.

bluesmoke69 · « **Reply #24 on:** December 19, 2011, 09:30:39 PM »

www.allballsracing.com/ They make good tapered bearings, and Good luck

Terry in Australia · « **Reply #25 on:** December 19, 2011, 11:12:40 PM »

Quote from: Flick on December 07, 2011, 03:40:28 PM

Thanks Roach Carver, I've got a lot to purchase before my bike is ridable again (Clubman bars, Exhaust, Controls ect), but I think that is what I will do... I did just buy another cb750 yesterday and I'm going to keep that motor. The odometer only shows 19,000 miles or so. But I know this bike has just been sitting in the PO's back yard for at least 10 years probably more than that. It is a 1976 cb750 and I am going to part it out so if any of yall are interested you can hit me up in my for sale thread, there is a link at the bottom. Here are a couple of pics of the bike...

Geez, I nearly cried when I saw that K6 mate, I can never understand why anyone could leave a nice bike like that in the weather for so long, although I suppose in Texas you don't have to worry about snow and ice? Anyway, best of luck mate, I'll be interested to watch your progress from across the pond. Cheers, Terry.

Flick · « **Reply #26 on:** December 20, 2011, 08:21:23 AM »

Lucky I agree I would love to just rebuild the motor since I will be tearing down to the frame and have the motor out anyway...

Thanks bluesmoke, I will order that kit tonight

Terry, yes it's a shame that bike was left out for so long and it only has 19,000 miles, I'm with you I just don't get it. We do get some snow and ice here in the panhandle of texas. Actually the day I picked it up it was covered with snow. Thanks and cheers...

MCRider · « **Reply #27 on:** December 20, 2011, 08:29:02 AM »

For a lot of people these bikes were just expensive toys. Motorcycling is not in their blood. Don't know if that's the case with your PO, just saying...

They were relatively inexpensive for their high profile wow factor. Anyone could buy a CB750, and it was recognizable as something special. Then once the new wears off, they got pushed into the corner. And the PO bot a jet ski or some such.

At the time they were parked they weren't even worth enough for the PO to try and sell it. And often there was just the little lingering feeling that, "someday I may want to ride it again". And some good memories.

And one by one they will be repurchased, and restored, by those who do have it in their blood.

Flick · « **Reply #28 on:** December 20, 2011, 05:29:58 PM »

Well said MCRider...

Against all the odds I managed to get back in the garage again this evening for a little while. I removed rear wheel and swing arm, then cut and ground the chain guard tabs off... Next I will get some paint stripper, then PC. I'm thinking there is probably removable bushing where the rear axel goes through the swing arm, if this is the case will I need to remove these before baking the swing arm?

On a different note something I have been pondering a great deal is the cycle x twin carb system, I really want to go with this system but I will have to do some frame mods. I called cycle x and the guy said the air filters interfere as well as the throttle cables with the backbone. I know Dyrden is going for it on his build. Has anyone tried this on a stock frame with pancake filters?

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Author Topic: 1971 CB750 Cafe Boombox!!! (Read 6724 times)