'86 CB700SC may be deep-sixed

[Zabo]

I recently procured an '86 from a friend that gave up on it due to both lack of time, and finding a sweet plum colored 650 to use instead (it was running and mostly intact when he got it.)

Short story was that the guy that owned it before him rode the bike like an ass and as a result trashed the engine from what we could tell. When he got it in his garage, he tried to start it. Hit the clutch and shifted into neutral, heard it click and engage neutral. Then he went to start it, and that's when things got weird. He had power and everything to the bike; gauges, lights, everything else worked. But when he tried to turn it over, all he got was a whirring sound like the timing chain for the cams had slipped and was just slipping like mad. That was the last time he tried to start her. He got it off the center stand, and while it was in neutral, tried to wheel it into a corner.

Didn't work. The bike's back wheel locked up and he had to lift it from the rear to move it around. When he pulled the engine to inspect the shaft and rear drive assemblies, the shaft and final gear were fine. So we know it's not the shaft. That was when he decided to tear into the engine. As of now, he has the valve covers off and the cam gears and chain 'look' fine. Of course, this was a month ago, and now the engine has been sitting with the valve cover off in a Michigan late summer/early fall. So of course the cam lobes have oxidized. Pipes are SOL too, as they've corroded beyond repair. Carbs are a mystery because we haven't torn into them yet.

So, my question is "Have any of you guys come across this problem where the Transmission/Final Drive has seemingly jammed and caused a whirring noise to sound upon startup?"

I have found a few parts engines that I could salvage a transmission off of if it comes to a gutting of the back half of the case.

Off topic though: Being an A&P trainee, Honda aircooled engines seem to be easy to slide into after having tinkered with 0-200s in an overhaul class which I am taking concurrently with this project (overhauling engines according to FAA Regulations). So I'm also considering this an after school learning hobby of mine. Fun-fun.

EDIT: I think this may have been posted in the wrong section, so if a mod wants to or could move it for me; I'd appreciate it. Thanks.

[gammer]

It sounds like you have two issues...
There are actually two chains internally on this engine. The first, which you have described, is the cam timing chain. The second, which I suspect is what you are having issues with, is the alternator chain. This chain runs from the alternator shaft/starter to the crank. I suspect that this chain is broken. I had mine brake on my Nighthawk and I had to split my engine to replace it. My chain broke because the tensioner for this chain broke and was "free floating" for a bit before the engine was shut off. I've heard of this chain braking on a few other Nighthawks too.
Anyway, when you hit the start button all I heard was the starter spinning.

Your other issue is obviously transmission related. Could be a bent shifting fork...could be gears...who knows at this point? You can't really tell until you split the engine.

If you have access to a spare engine with a good bottom end, then I'd pick it up. Split the bottom off both engines and put the good bottom end on your top end...or perhaps if the spare engine is in good enough condition, you could just use it and keep your current engine for spare parts.

I personally have had two of these engines apart and I can tell you that if you are the least bit technically inclined, and you take your time, then you should be fine with working on them.

The hardest part you will encounter is getting the engine back in the frame. Its a pain to line up the final drive spline with the cv joint, while at the same time trying to get the engine mounts lined up. Its a tight fit and definitely a two person job. I recommend doing this job with the valve cover off and the oil pan cover off to give a tad bit more space. If you leave the oil pan cover on, the definitely leave the oil drain bolt off 'till you get the engine back in. Also if you are worried about scratches on the frame, wrap some towels around it 'cause you will not be able to get the engine back in without some scratching.

[Zabo]

I had already talked to the salvage guy that had the other engine up in Lansing and he said that engine had been sixed because of a thrown crank. So this may be a matter of actually gutting both engines and putting the innards of the de-cranked engine into the one that I have out of the bike now. I have no qualms about splitting the case or anything because it's nothing I haven't dealt with before on larger engines. As for scratches, I don't care. That's what flat black spray can paint is for. I also have my friend to help me because it's living in his garage until the bike is back on it's wheels.

But I take it the crankcase is sealed with a paper gasket rather than the customary aircraft grade gasket sealer and silk thread. If not, this is going to be funny.

[gammer]

There is no proper gasket for the crank case. I sealed mine with that Honda goop that the dealer recommends just for this job. It worked great.

The bottom end comes apart very easily. I thought it would be difficult at first, but every "section" comes off on its own...and there is no reason to dismantle anything. For example: I thought the shifting mechanism had to come apart first, so I took it all apart and realized after that it didn't need to come apart. Just take things off in sections.
If you have a manual, you can use it to help plan out the process first.

[Zabo]

Yeah, good to know. I do in fact have the factory manual/overhaul manual for the bike, so this is a major plus. It's how I kinda diagnosed the problem in the first place. Also, having the torque values handy is nice as I've read through the forums and found that stripping bolts seems to be a problem.

[gammer]

Good stuff. Once you get working on it, its actually kind of fun...and you will appreciate the technology of this engine and the beauty of the "inards" when you have it apart.
Its not the kind of job you would want to do on a regular basis, but its neat to get in there and see how things are put together.
I have two spare engines, both with tranny issues, that I will be splitting this winter. So I have to look forward to this job at least one more time...

Good luck...and enjoy!