Author Topic: Ill-Advised Super Sport (CB750-F0) (Read 21679 times)

Jessamine · « **on:** July 11, 2018, 08:07:16 PM »

Hi y'all!
Figured it was about time to migrate my updates from my first post ("Should I Buy This 75 CB750F?"http://forums.sohc4.net/index.php/topic,173039.0.html) into its own project thread. Exciting!

Quick backstory: I got a gut feeling on July 4th immediately upon waking that I should check craigslist motos; top of the list was this bike, posted for an asking price of $900 24 minutes prior. I called the guy immediately, still half-asleep, and asked if I could come check it out. I'd been looking for a new project bike for awhile, and I've always loved old Hondas, so I wanted to jump on it. I went and checked it out an hour later. He explained that it had died just as he was about to pull out of his driveway for the first test ride, and he hadn't been able to start it again, and he believed it was a broken cam chain.

Despite my hesitation at the non-running engine, everything I checked (besides the non-existent compression) seemed solid. He'd thrown a lot of new parts on and gotten some maintenance done recently, including new instruments, tires, seat, rebuilt shocks/forks, fresh paint, valve job, and a new head gasket too. I wasn't willing to shell out $900 for it, but I talked him down to $600 with delivery to my workshop and felt good about it.

A week later, he dropped it off at the makerspace I'm a member of, the title was signed over to me, and I'm the somewhat-ill-advised owner of a Super Sport! HERE WE GO!

jgger · « **Reply #1 on:** July 11, 2018, 08:16:34 PM »

Congrats! You know these projects ALL need to have a name? Might I suggest TOADJASO

, just for fun.

Good luck and I hope it works out well.........keep us posted!

Jessamine · « **Reply #2 on:** July 11, 2018, 08:35:19 PM »

TOADJASO does have... a ring... to it?

I tried to think something up, but couldn't come up with a clever name. Won't really know what fits til I get the build concept worked out, but right now I'm thinking a glittery purple frame would be trick.

Jessamine · « **Reply #3 on:** July 11, 2018, 08:42:29 PM »

Soooo I couldn't help myself, and I spent all evening after work tonight tearing into the bike. In four hours, I managed to pull everything off the bike to be able to drop the engine, and (with the help of a serendipitous new friend who has a 76 CB550) I even got the engine out of the frame and onto a cart!

Things I learned tonight:

I popped open a few tappet covers and confirmed that, with the electric or kickstarter, the valves are definitely immobile but the pistons move freely; this just supports the PO's hypothesis that the cam chain went.
Pulling the spark plugs and shining a light down into the cylinders, I wasn't able to see any obvious damage to the pistons from striking a valve... maybe I got really lucky and the timing was just right to avoid valve damage??
Most of the bolts on the bike are at least slightly stripped. I was just barely able to get the carb boots loosened, but I'm absolutely going to need to replace many of the small JIS bolts ASAP. Is there a good allen-head bolt kit the hive mind recommends?
The battery is an almost-new AGM, which was kept on a battery tender. Score!
Bike was obviously laid down on the right side at some point; the brake pedal has a small gouge in it and the right footpeg (and the associated engine bolt, FML) is slightly bent. I was able to gently coax the engine bolt out with a hammer and punch, and I'll probably try getting a torch on it to straighten it back out before reassembly.
There's significant thread damage on a number of engine-retaining nuts/bolts. I'll have to replace the nuts at least, and possibly the bolts too. Anyone with a good source for replacements?
The headers are actually in awesome shape under the exhaust wrap, surprisingly enough! If I want to, I bet I can polish the chrome up nicely and ditch the textile aesthetic.
My boy Keith with the CB550 recognized the seat on my new bike as being a custom piece from an eBay seller who makes a lot of "cafe" accessories; he said he'd try to track down the maker's name.
The chain on the bike was an endless style, with an obvious rivet link on it. I cut the pin heads off, and will probably just get a new master link for it (though it's pretty worn and maybe I should just get a new chain)
Why the hell would Honda put JIS bolts on the valve cover?? Sadists! My manual impact driver just arrived in the mail today (though not in time to be of use tonight), and I can already tell it's going to get pleeenty of use.

So I'm all set up to crack open the valve cover and have a look at the cam-- possibly as early as tomorrow evening. And I went ahead and brought the carbs home with me after draining them, so I can pop the float covers and check out the jetting/flush them out. I will keep y'all updated on what I find!

scottly · « **Reply #4 on:** July 11, 2018, 09:26:10 PM »

It's possible that the bolts affixing the cam sprocket to the cam have backed out/sheared off. Waiting for the autopsy report after you remove the scull-cap...

754 · « **Reply #5 on:** July 11, 2018, 09:57:54 PM »

When the motor mount bolt is bent likecthat, take it out the other way.
May have been shortened if they changed the brake mount bracket.

Jessamine · « **Reply #6 on:** July 12, 2018, 03:12:24 AM »

Quote from: 754 on July 11, 2018, 09:57:54 PM

When the motor mount bolt is bent likecthat, take it out the other way.
May have been shortened if they changed the brake mount bracket.

How do you mean "the other way"? It had a hex bolt head at the left footpeg, and the right (pictured) was a nut and had the tip bent. Pretty sure it could only be removed from the left by pulling it all the way out..

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754 · « **Reply #7 on:** July 12, 2018, 05:25:36 AM »

It is supposed to be a nut at each end stud, it's not stock.
Driving that bent end thru, not helping things.

Jessamine · « **Reply #8 on:** July 12, 2018, 05:56:10 AM »

Quote from: 754 on July 12, 2018, 05:25:36 AM

It is supposed to be a nut at each end stud, it's not stock.
Driving that bent end thru, not helping things.

Ahhh it's all clear now. I'll look around for a stock replacement; that makes WAY more sense.

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slikwilli420 · « **Reply #9 on:** July 12, 2018, 06:26:13 AM »

If you spun the engine over and the valves didnt move, that means some stayed open so you now have a handful of bent ones more than likely. The task of making this thing a runner just got more expensive.

Jessamine · « **Reply #10 on:** July 12, 2018, 06:41:29 AM »

Quote from: slikwilli420 on July 12, 2018, 06:26:13 AM

If you spun the engine over and the valves didnt move, that means some stayed open so you now have a handful of bent ones more than likely. The task of making this thing a runner just got more expensive.

PO had already cranked away quite a bit (like a doofus), so I wasn't too concerned about making things worse.

we'll see what the sitch is soon enough.

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Jerry Rxman Griffin aka MuthaF'er · « **Reply #11 on:** July 12, 2018, 10:16:43 AM »

Quote from: 754 on July 12, 2018, 05:25:36 AM

It is supposed to be a nut at each end stud, it's not stock.
Driving that bent end thru, not helping things.

It's a BOLT Frank, not a double threaded stud. 750F stuff

calj737 · « **Reply #12 on:** July 12, 2018, 11:35:05 AM »

Quote from: Jessamine on July 11, 2018, 08:07:16 PM

He explained that it had died just as he was about to pull out of his driveway for the first test ride, and he hadn't been able to start it again, and he believed it was a broken cam chain.

The infamous, "Ran when parked" defense...

Its not the end of the world, but expect a full engine rebuild is in your future. That way, expecting the worse, you won't be surprised or pissed when you discover the extent of probable damage. It can be rebuilt; we have the technology, better, stronger, faster... Hey, its the "Lee Majors Bike!"

PeWe · « **Reply #13 on:** July 12, 2018, 12:17:59 PM »

An old CB750 engine need a full rebuild anyway. Open valve cover asap to see why valves do not open. If cam chain snap it might block the crank to rotate. (When I drop the cam chain during rebuild crank will be blocked after 1/2 turn.)

Even if cam has snapped as it has done in some threads due to blocked oil transport to one side of the cam, some valves should move.
If both cam bolts have came loose, they might be broken when colliding with the cam chain tunnel in the head, sprocket will then move free not moving cam at all.
All parts are worth more than $900

Jessamine · « **Reply #14 on:** July 12, 2018, 12:51:47 PM »

Well would you look at that... Some doofus didn't torque the cam sprocket bolts correctly.

Jessamine · « **Reply #15 on:** July 12, 2018, 01:16:43 PM »

The good:
-there is no visible damage
-the cam and adjacent case is coated lightly and evenly in oil
-the oil passages appear clear
-one of the sprocket bolts was hanging out right in the open
-cam chain rotates freely with crank

The bad:
-only one of the sprocket bolts could be located
-head gasket is split at one point
-valves are a little inconsistent; #1 Exhaust and #4 Intake rockers are looser than they should be with the cam in this position.

754 · « **Reply #16 on:** July 12, 2018, 01:28:34 PM »

The bent bolt, is it front or lowercrear ?
78 F are longer than the older ones, i think they were double threaded... could maybe be wrong.?

PeWe · « **Reply #17 on:** July 12, 2018, 02:03:25 PM »

Good news! The other bolt might be found in the oil pan.
You'll see if it has any marks when finding it. No specific marks, probably no problems.
Those bolts must be locked with Loctite medium and tightened rather hard. Threads cleaned with acetone first.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #18 on:** July 12, 2018, 02:23:54 PM »

Hoping the threads in the cam are still good. So the VALVE COVER gasket is broken. Easy cheap fix. With a little luck................

Jessamine · « **Reply #19 on:** July 12, 2018, 02:34:36 PM »

Quote from: Jerry Rxman Griffin aka MuthaF'er on July 12, 2018, 02:23:54 PM

Hoping the threads in the cam are still good. So the VALVE COVER gasket is broken. Easy cheap fix. With a little luck................

Threads in the cam sprocket bolt holes? They look spotless, actually. Metal is the nice and even with the expected brownish tint of old oil residue.

My cam chain tensioner rollers even look good.

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Jessamine · « **Reply #20 on:** July 12, 2018, 06:20:57 PM »

Anyone have a good source for cam sprocket bolts? Or if they're a common size, know what that is? The one I found still in the head was too damaged to check reliably, and I want to get some quickly so I can evaluate the engine further.

cjespersen · « **Reply #21 on:** July 12, 2018, 08:33:26 PM »

Also when searching for the cam chain sprocket bolts they are often called "knock bolts"

scottly · « **Reply #22 on:** July 12, 2018, 09:55:02 PM »

Quote from: Jessamine on July 12, 2018, 06:20:57 PM

Anyone have a good source for cam sprocket bolts?

Ask Mike; I believe he has some flange head bolts that are better than stock:
http://forums.sohc4.net/index.php?action=profile;u=49

PeWe · « **Reply #23 on:** July 12, 2018, 09:56:34 PM »

Cam bolts have special thread size, M7. I guess most CB750 parts sellers have them.
Honda stock work fine with non slotted sprockets. Yamaha or Suzuki bolts are popular with slotted sprockets. Slotted when using a hotter cam that need to be fine tuned. Possible with stock cams too, advancing it a few degrees. My modified engine has Suzuki bolts with wider heads.
http://forums.sohc4.net/index.php/topic,157585.msg1805937.html#msg1805937

Jessamine · « **Reply #24 on:** July 13, 2018, 10:58:29 AM »

Alright, I've got an NOS tensioner gasket, Athena valve cover gasket, NOS knock bolts, SS allen head engine cover bolts, and a 530 master link on the way. Should be in by next weekend at the latest.

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Author Topic: Ill-Advised Super Sport (CB750-F0) (Read 21679 times)