CB700SC engine

[84cb700scdlb]

I just bought an '84 CB700SC and the engine has been halfway torn down see my other post, new to me CB700SC for details. Any way I was wondering where I could possibly find an engine reasonable if this one ends up being beyond repair or just for a spare. Will any other engine fit say a 750 out of a later model, I've read that the 650 has different mounts due to the angle but didn't know about the 750.

[fishmeister]

Save yourself all the headaches and find an 85 or 86 700 engine.

[84cb700scdlb]

That's kinda what I was thinking, just don't know where to find one.

[fishmeister]

It's an 85 or 86, there are no new ones. Stay away from 84, they had some issues.

I don't think this forum has a rebuilt source for engines.

Just like everyone else has to do, EBAY, Craiglist, Google, bike boneyards, etc.

Then you have to trust the seller.

If you split cases and size crank bearings etc., you can make a rebuild.

If you just band-aid it up, that's what you got.

The other alternative is take the engine (85 or 86) to Honda and pay.

[84cb700scdlb]

I just checked the engine out further and one of the rods has a lot of movement on the crank. I haven't torn it down any further than taking the head and oil pan off. It appears it would need a crank and 1 rod. So if anyone knows of an engine for sale I'm in need '85 - '86 preferably. If I can't find one I will have an '84 CB700SC for sale.

[fishmeister]

The crank can be ground to meet the clearance needed with one of three sets of oversize main bearings Honda offers.

Still, i'd prefer not to spend the cash on an 84' engine.

[SmokinFast]

...So if anyone knows of an engine for sale I'm in need '85 - '86 preferably. If I can't find one I will have an '84 CB700SC for sale.

I got 2 CB700SCs off of Craigslist for cheap ($250 and $400) by putting in a 'wanted' ad. You might want to try that too. I got a 3rd bike for $250 by quickly responding to a Craigslist ad within an hour of when it was listed.

None of the bikes ran when I got them-- they needed carburetor rebuilds, electrical repair, and freeing the rings because they sat so long. I've restored 2 of them. I sold the 1st one, the 2nd I ride daily, and the 3rd one is waiting for me to install an alternator chain.

So bikes and parts are out there. Craigslist and eBay are probably your best resources.

[84cb700scdlb]

I just put a few wanted posts on craigslist, thanks for the idea. Fish I was just wondering how much different is the 84 from the 85's and 86's? Was there some changes on the engines that makes them a lot better? I'm new to these so I am just being curious, trying to learn. Thanks for any info. BTW, I found an '85 engine for $740 shipped to my door at a salvage yard, has 14,xxx miles?????

[fishmeister]

Everything is chancy. Depends on how much you can trust the seller, return policy, references etc.
$740 seems a bit pricey to me, but shipping is expensive. That's about as low miles as you'll find.
They will pop up on e-bay from time to time, depends how much of a rush you're in.
I really don't want to recommend something and find out it bombed.

There was a guy that was selling one and actualy posted a video on ebay of it running before he parted the bike out. That was good.

[SmokinFast]

I agree with fishmeister and I'd skip the salvage yard -- too pricey.  If you keep your wanted ad in for a few weeks you should get some replies.

Also, check out http://craiglook.com   You can search all Craigslist ads within a given number of miles from your city.

[Anchormarck]

Everything is chancy. Depends on how much you can trust the seller, return policy, references etc.
$740 seems a bit pricey to me, but shipping is expensive. That's about as low miles as you'll find.
They will pop up on e-bay from time to time, depends how much of a rush you're in.
I really don't want to recommend something and find out it bombed.

There was a guy that was selling one and actualy posted a video on ebay of it running before he parted the bike out. That was good.

I bought an engine off ebay from a guy that did that - maybe the same guy? Just got the engine in last weekend. Got the carbs and such in today. I've done this before and remembered what a PITA it is to re-install the carbs in the tight space. Anyway, the engine runs - but I'm not getting spark. Hmmm...

[84cb700scdlb]

I found an '85 engine for $350 but second gear is out. I watched the video on here and feel like I could perform the work. I could use the transmission parts out of the '84 engine I have or there are some on E-bay for sale. Is this a good deal or do I keep lookin?

[fishmeister]

I'd wait. How do you know how good your trans parts are? There were some changes between the 84 and 85/86's. Not sure how that would work out.

Be nice to find a runner to pop right in. (they usually come off the crashed bikes)

[cz75fan]

I'm wondering if the crank and rods would fit from the later generation of Nighthawks. Might be worth looking into plus it would give you the full 750cc's like the original 700's were everywhere in the world except the US of A.

[fishmeister]

The way to determine that is called cross-referencing......everyone should try it.

[cz75fan]

Doing a little checking around, if for nothing else my own curiosity, but sadly the later model 750 Nighthawks crank won't work in the 700 engine. Bummer:(

[84cb700scdlb]

I bought an '86 engine, I'm in the process of installing it and have a couple of questions. The '86 engine has a vent tube in the rear valve cover that the '84 engine didn't have, it's on the right rear of the engine. Does anyone know where this hooks up to? Also the exhaust studs on the '86 are a little larger than the '84 so I had to drill the header flanges out to fit which was no problem but I want to make sure I get the right size nuts since I didn't get them with the engine, so does anyone know what size these are? I picked up some 7m x 1.0 but haven't had a chance to check them yet probably be this weekend before I get to go work on it again.

[real_psyence]

Hey - I'm in the process of doing the same thing. Laid my '86 down, found a nice '84 rolling chassis and am (hopefully) finishing the swap tonight.

The tube you're talking about goes to a little breather box that mounts to the frame on the right side, right above the airbox boots. I think it's just labeled "tank, breather" in the airbox parts fiche. 17350-MJ1-000
 
At least, that's the one that looks right. I'll take a photo and verify tonight.

[gammer]

Doing a little checking around, if for nothing else my own curiosity, but sadly the later model 750 Nighthawks crank won't work in the 700 engine. Bummer:(

The cranks from the Cdn 84-85 CB750SC will fit the 700 engine though...
And I might now of a certain Canuck who has a spare crank  

[fishmeister]

I could use the American and Canadian part #'s for those cranks, if you know them.

[84cb700scdlb]

It would appear that the '84 doesn't have this breather tank since it didn't have a place on the old engine for the tube and the breather tank isn't called out on the parts fische. So can I just run a hose and connect a small breather to the end of it, like an aftermarket valve cover breather from a car?

[real_psyence]

Not sure re: the auto breather. It does seem kinda redundant on the '86, though I think it's part of emissions. The manual only shows it on two pages really, 1-15 and 1-16 IIRC. I took a photo of the piece itself on the bike. It basically connects the vent tube coming out of the valve cover with the one coming out of the crankcase and the drain box on the bottom of the airbox.


man, that flash picks up *all* the dirt :-)

If you ended up getting one you'd need to get two new hoses for crankcase=>breather and breather=>drainbox. On the '84 these are just connected directly. I think the idea is to get vapors collected and burnt by the engine...

The '86 studs are 7mm on the nut end - not sure of the pitch. 90304-MJ0-920

[gammer]

I could use the American and Canadian part #'s for those cranks, if you know them.

Hey Fishy...
I can't find the parts numbers online as anything online is US.
The next time I'm at the Honda dealer, if they aren't busy I will get them to look up the part number.

[fishmeister]

Thanks Ghammer, all the Canadian years of the 750 sc.

[84cb700scdlb]

I wonder if I can just tee the upper crankcase vent into the lower one since my bike doesn't have the breather tank. I'm sure they added it to later years to help cut down on oils leaks, let all the air vent out instead of blowing gaskets out. Thanks on the bolts too, they are M7 x 1.0 on the outer threads.