84 Nighthawk Vance&Hines

[Uvea]

I just got this nice 84 Nighthawk, I think it’s the CB750S? Either way I was looking at putting a nice 4-1 system on it this winter.

I’m leaning toward the V&H 14001P Pro Pipe, anyone used it before? Tips? Or maybe a better 4-1 system, I’m going for a cafe/scrambler look. I got it looking pretty Mad Max right now and I’m loving it.

 

[amc49]

Sure it's not a 700 instead? That's right about the time Harley had the over 700cc. restriction put in place.

Look the cylinder block (not head) over good, they always cast the cc. size of the engine somewhere on it.

Oops, you are in Canada, that likely did not apply.


That pipe will not fit, the '84 is different engine, it only fits first design DOHC '79-'83. I have one, it is a drag pipe and you cannot drive it on the street as the right side will hit if you even think about leaning the bike, it almost hits when mounted up.

 

[Uvea]

Thanks! I didn’t realize it was a drag pipe

 

[amc49]

They used to emphasize that but now seem to be getting vague on purpose to unload the last of them quick. Thinking they are no longer making early DOHC pipes. Nobody drags them any more and never did much in the heyday of them, the engines blew up too easy and did not make power to match other brands. Too expensive to race them too.

The Nighthawk S will likely be a b-tch to find a pipe for unless it is a MAC which are crap. They did not make enough of them to support a parts market.

 

[amc49]

Maybe I'm full of crap...............

https://www.ebay.com/b/Exhaust-Systems-for-Honda-Nighthawk-700S/177996/bn_51126384

Your key there should be the 700 cc. number, which is what US models were. Same bike and pipes should bolt right on. Make sure the year model fits as a double check.

They ARE expensive as they are rare.

 

[Uvea]

That’s awesome! The link you posted was right around the price range I was expecting for the exhaust.

I didn’t know if the 700cc was a different fit so I didn’t even look. I’m also looking for a speedometer cable so hopefully that info could help me find one!

I know it’s not about exhaust but, you wouldn’t happen to know if previous model years had the same cable would you? I actually found an 82’ cable but I’m worried they connect differently.

 

[amc49]

I'd be surprised if it fit, they pretty much change that stuff with every major model change.

Hang on a bit, I may be coming with a free service manual link.

 

[amc49]

https://www.manualslib.com/download/1437980/Honda-Nighthawk-Cb750sc-1984.html

Go down to 'I'm not a robot' and then click, then fill out the capcha there to play the little puzzle. Then choose 'get manual'.

Go down on next page to 'download as pdf' and right click and choose 'save target or link as' and save the file to your computer. 15 MB filesize. That manual is for the 750 version of the engine.

I found both the '84 700 and 750 manuals and compared the engine specs to find the difference in the engines is .150" in the stroke. That has the possibility of making the engine cylinder blocks potentially taller on the 750 model, or the difference may be made up in the rod length or the piston height and swallowed internally. The problem is similar to the one on the early DOHC '79-'83, as the 900 and larger engines had taller cylinder blocks for the same reason but it was more distance there than the '84 model, about .250" or so. It shows up on those early ones as an engine about a 1/4 inch taller, the 900 and up have an extra cylinder block fin in that distance. It shows as well on exhaust systems, most will often fit either one but if somebody closely fits the header to a 750 then it would sometimes not fit correctly on the 900 because it hits the pan too hard. Some people removed a cooling fin off the pans to help with fit. Other exhausts were made deep enough under the engine so that they fit easily on either the taller or shorter engines with no problems.

Being the difference is less on the '84s it may or may not be a problem, I'd think that since the world knew there were two 'different but the same' '84s they would make exhaust pipes that fit either, it could save them a hell of a lot of money doing so and pump up pipe sales for literally no cost. But businesses doing what they do I'd say be on the lookout for it as a possible issue. I don't think it will be a make or break issue on those, you can likely adjust in some slight way for a good fit.

 

[amc49]

BTW...........go to the partzilla website and plug in your bike and say an '82 model CB750SC Nighthawk and look up both parts diagrams to compare the speedo cables, if the parts numbers are wildly different they will NOT interchange.

 

[Boosh63]

Funny I just bought a 1984 Nighthawk 750 s which came with a 4 into 1 and I would rather have the 4 into 2