Author Topic: Magpie's CB750F DOHC Project (Read 16926 times)

Magpie · « **on:** March 30, 2012, 07:13:06 PM »

I think I should keep a record of what I do to/with this free bike. While not a SOHC4 it will still be fun to work on and ride. I hope to use it as a daily rider, be able to park it without worrying too much about it and not answer so many questions when I park the K1's.
So, about 2 weeks ago my parts man called to say a guy called the shop and wanted to get rid of a bike. He didn't want money for it and had the registration papers too. Off I went to see it and the deal was done with some trepidation. I saw myself as a SOHC4 guy but it's time to broaden my horizons. All the reports said these were good bikes except for the charging system and the cam chains.
Here's some pics where it was and when I got it home. Cliff.

Magpie · « **Reply #1 on:** March 30, 2012, 07:26:33 PM »

The "bike ran when it was parked" which was sometime in 2002. I put a battery in it, hit the starter button and it turned over nicely. Happy days, it's not seized. I've had enough of seized motors. The carbs came in a plastic tote. The po had taken the bike to a local shop for a price on getting it running, they took the carbs apart, the po didn't want to spend the money on it, so he took it home and put it in his garage. He's now happily riding a 2012 Road King.
There's plenty of info about the carbs so I made sure all the pieces were there, got them organized and went to town cleaning them. Pine Sol works great on cleaning aluminium and Autosol makes it shine. I ordered a set of allen head screws for the carbs which has not arrived yet so I can't assemble and mounts the carbs to see if the damn thing runs.

grcamna2 · « **Reply #2 on:** March 30, 2012, 07:34:01 PM »

I Really like you're organized parts bins...it must save a Lot of hunting around on a dark floor for an hour

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Magpie · « **Reply #3 on:** March 30, 2012, 07:39:08 PM »

Next, the brakes. They seemed to be dragging but maybe it was just in gear! Anyway, I wanted be sure I could stop. I took apart all 3 calipers, cleaned the hell out of them, the seal was nice and pliable and the piston like new. So they just took some tls. the rear master cylinder was next. Again, it was dirty but just needed some attention. The rear brakes pumped and feel solid. The front master cylinder was another story. The resevoir was full of crap and the lever area crusty. I took the cylinder apart, cleaned things up and ordered a rebuild kit which has not arrived yet. As soon as it shows up the front brakes will be made to work.
Cliff.

Magpie · « **Reply #4 on:** March 30, 2012, 07:47:17 PM »

Next, the electrics. I didn't take many pictures because I wasn't sure about posting this build but you're all good guys so I'll take more in the future. How's that for sucking up?

The charging system is a weak point but the rotor and stator all checked out to specs. Yahoo!
Two interesting units on these bikes are the spark units. They are located under the seat just above the battery and are another weak point. They appear to have bled or melted some black goo from the back of them into the battery box! Again, another check and they came to spec as well. This is getting better all the time. I pulled them off and filled the backs with epoxy. Cliff.

Magpie · « **Reply #5 on:** March 30, 2012, 07:58:38 PM »

While all this was going on I was cleaning, cleaning and more cleaning. The bags and fairing were removed and the hunt was on for a set of stock looking pipes. We have an insurance program here that if you can get the bike to near what it was new you can qualify for a Collector license plate and have cheaper insurance. If you have several collector bikes you get one plate and can move it from bike to bike and save a ton of money on insurance. So, here's what it looks like today and a picture of the Mac 4 to 2's that I found for a good price from another vintage bike enthusiast. That's his bike in the picture.
The pictures make my bike look better than it is because they don't show the rust spots and blemishes. If it's a good runner than it will look like new when I'm done. I still haven't heard it run. The post office kills me!
To be continued.
Cliff.

Magpie · « **Reply #6 on:** March 30, 2012, 08:07:24 PM »

Quote from: grcamna2 on March 30, 2012, 07:34:01 PM

I Really like you're organized parts bins...it must save a Lot of hunting around on a dark floor for an hour .

It's great unless you drop one of the teeny tiny o rings on the floor and it rolls away to God know's where!

Cheers, Cliff.

grcamna2 · « **Reply #7 on:** March 30, 2012, 08:29:59 PM »

She's a Real Clean Machine & your giving her anything she needs..Great Job;when they're set up right they have a good kick at 6500 rpm...a DOHC rush

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The picture of the other DOHC CB750...;those are the MAC 4 into 2 exhaust ? they look just like stock & in excellent condition

. Magpie, what main jets do you have in there? Stock? or bigger for that 4 into 1 ? Those MAC may take something not much larger than Stock

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You certainly were in the Right Place at the right Time for that Sweet Deal

Magpie · « **Reply #8 on:** March 31, 2012, 07:37:45 AM »

Right place, right time - for once! I didn't look at the jet size, I guess I better and make a note of it. The exhaust on the other bike is the same as I'm buying from the owner, new, still in the box. Not sure why he has 2 sets but he's offering me a very good deal on them.
Cliff.

grcamna2 · « **Reply #9 on:** March 31, 2012, 02:00:08 PM »

Cliff,
I think those MAC will have No problem passing for Stock pipes to an unsuspecting inspection officer, they usually don't sound any louder than stock...at least New ones !
When you get you're pilot circuits fine tuned along with an excellent Tune Up it should run slow w/ a feather on the throttle.
I have a brand new (NOS) valve cover gasket along with a good incremental assortment of valve adjustment pads/shims to choose from if you want..let me know the sizes you require..I'm sure I can help.

Magpie · « **Reply #10 on:** March 31, 2012, 06:44:24 PM »

Thanks for that! If I have to get into the engine and need the gasket and shims I'll give you a shout. Cheers, Cliff.

w1sa · « **Reply #11 on:** April 01, 2012, 01:38:26 AM »

If you acquire an early DOHC and intend to use it, (expecting some degree of reliability and performance)......make sure you do the complete service checks.... especially the valve clearances ....which most likely, have been neglected most of its life............... Ensure the clearances are set on the high side of the clearance range (even a thou or two over) for safety and performance .....don't dismiss or ignore the importance of this service requirement, hoping everything will be OK.

Magpie · « **Reply #12 on:** April 01, 2012, 08:05:14 AM »

Well I was kind of hoping they would be ok but..............................I will check them.

Cheers, Cliff.

Magpie · « **Reply #13 on:** April 01, 2012, 09:36:07 AM »

I've just been reading about valve adjustment on the DOHC forum and there seems to be quite a bit of controversy over valve clearance specs, how to set them and where to measure (at TDC or by the manual), these guys get to some serious name calling.
I have downloaded a manual and this method from the CB1100 F site http://www.cb1100f.net/Other/valvechart/papalukervalveadjust.pdf I'm still waiting on carb parts to see if the motor even runs without serious noises coming out of it before diving into the valve train. I'm holding back (trying anyway) from spending too much on it yet. If it's a good runner then it will be next in line for serious attention to detail. This bike is starting to grow on me but SOHC4's are my first loves.

grcamna2 · « **Reply #14 on:** April 01, 2012, 09:41:18 AM »

Good to hear you've uploaded the manual..going by the book is hard to beat.

somesuch · « **Reply #15 on:** April 02, 2012, 10:31:48 AM »

Do not set the valves to the (initial) lower "factory" recommended value of .002" as you will burn them eventually. I believe there was a revision later on to that value, but now I am not certain where I had seen it. Setting the valves to the largest (.005") value like that pdf from 1100f.net describes is what I finally settled on after burning a few valves when using the lower clearance (.002"-.003") myself. Have never had an issue again in 10 years of using the .005".

Magpie · « **Reply #16 on:** April 02, 2012, 11:08:00 AM »

Thanks for that, good to know! Cliff.

Magpie · « **Reply #17 on:** April 02, 2012, 05:58:01 PM »

It runs! Fired right up. Yay! Cliff.

It's Alive Too!

grcamna2 · « **Reply #18 on:** April 02, 2012, 07:26:42 PM »

Good to get her fired up ! I Like those new tires..what brand ?

Magpie · « **Reply #19 on:** April 02, 2012, 10:48:41 PM »

Those are Yokahama Tour Stars but not new, they were on the bike when I got it and are at least 10 years old. The bike was kept in a dark garage, I wonder if I can still use them? Cliff.

grcamna2 · « **Reply #20 on:** April 03, 2012, 05:21:50 AM »

They sure look nice to me...will the rubber indent with you're fingernail ? if so I'd use them.

Magpie · « **Reply #21 on:** April 05, 2012, 12:32:55 PM »

Put the gas tank on and discovered the fuel tap leaks gas like crazy and it's a rivetted one. So drill out the rivets, drill 2.5 mm holes and tap for 3mm screws, flip the 4 holed gasket over because it's good on the other side, clean the crap out of the tap and put it back together. It works, no leaky. However gas is pissing out of number 2 overflow, smack the bowl, no luck. Plus the other bowls are weeping a bit. So, need to pull the carbs, check the float levels and sticky floats, repolish the needle seats, use a bit of Hondabond on the bowl mating surface and try again. Lots of clutch rattle like the SOHC4's too.
Cheers, Cliff.

Magpie · « **Reply #22 on:** April 05, 2012, 08:45:05 PM »

Got it done. Tap rebuilt, pulled the carbs, polished the needle seats with Brasso, used some RTV on the float bowl edges, installed the carbs - everything is dry. Fired right up and idled nicely. Brakes are spongy even after rebuilding the master cylinder. I think the lines are flexing after over 30 years of age.
Now-what to do with it - a down to the frame restore?
Cliff.

grcamna2 · « **Reply #23 on:** April 05, 2012, 09:44:25 PM »

Would you just ride it as is for the season ?

Magpie · « **Reply #24 on:** April 06, 2012, 08:41:52 AM »

Just ride it for the season? I'm not sure. It will look a lot better when the rusty 4 into 1 system is replaced with a new chrome 4 into 2 system. However, riding it was the point of getting it running. Funds are a bit tight right now and the first bike to be insured will be the Goldwing. I seem to feel better when I have a bike to tinker with so riding the F and puttering with the Benly may be the way to go. At least thet will keep away from the TV and red wine.

Cliff.

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Author Topic: Magpie's CB750F DOHC Project (Read 16926 times)