Topic: Oh Boy this will be fun! (Exhaust stuff)

[babyfood1217]

So i'm in the process of rebuilding my 1976 CB750k6 still.  Things have been so, but some money just came in so i'm finally getting the project rolling.  A full engine gasket set and a new 4-1 header was ordered a few days back (KERKER off of eBay), and so I started looking at mufflers for it.  Now I love the original look of the older HONDA bikes and truly debated whether or not I should restore it to original condition, or tweak it a bit so it really fit my style.  Well, obviously style it is.  I ended up bidding on and winning an exhaust system (sans headers) off of eBay for a 2004 HONDA CBR 600RR.  For those of you who may not know, the 600RR is a supermodern sportbike with, now get this, an UNDERTAIL EXHAUST!  That's right, I am going to be retofitting an undertail exhaust onto a '76 CB750.  Now, I am quite mechanically inclined, and have access to any tool necessary to facilitate this modification to my bike, but I will be the first to admit I don't know too much about actually tuning a bike.  I was told by a friend to, once I got the exhaust installed, take it and get it dyno-ed, follow that with tuning, and getting it dyno-ed a second time to really get the most out of what I've got.  Now, I would like to get pod filters (38mm I think for my bike), and although I haven't really decided on them yet, and assuming this whole dyno thing is a worthwhile endeavour, I would want the pods on before I went in correct?  I would appreciate all comments on this matter, whether it be about the exhaust system, or about the dyno issue.  I guess I have no problem adding modern components to such a beautiful old machine, and although his bike pics have been posted on this board before, I can't help but mention Tim Shutters in regards to what I am hoping to do.  Well there you have it.  What do you guys think?

-Chris Gerber

Exhaust Link:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=4546109307&sspagename=STRK%3AMEWN%3AIT

Links to Tim Shutters bike:
http://www.robswheels.com/tims_other1.htm
http://www.vjmc.org/members/shutterst.htm

[MRieck]

 The undertail sounds cool. I think it would work better on an F model as it has the cowling behind the seat. You could use a different tailight, like from a newer GSXR or Busa, and have a nice wide one off oval exhaust tip stuffed in there. Anyway it is an interesting idea. I'd put individual filters on it and than tune it. I could have installed a front and rear end from a ZX-7 on my CB but I personally like the old look (spokes).
 It still took some machine work to fit a 78 F front end (forks and calipers) to 75 F rotors and spoked wheel. Thank god for CNC.

[MetalHead550]

 :oWow!  I found my new dream bike!  Beautiful!

[mcpuffett]

wow that's a nice bike you have there 8)can't wait to see your next one   mick.

[babyfood1217]

Just got the KERKER headers and the 2004 CBR600RR can/midpipe in this week.  I purchased these items with full knowledge that there would be some tricky modifications to be made, so here comes the first few...

- The inlet on the midpipe for the muffler is approx 1-7/8" diameter.  The outlet on the header is 2-1/2".  So there is a 5/8" difference that I need to address.  My question is are there adaptors in the aftermarket exhaust industry to correct situations such as this?  If not, I could easily weld something up, but purchasing would make things that much easier.

- A custom seat is obviously going to have to be made (in order for the can to fit underneath.)  I would still like to have a seat cover that appears genuine to this line of bikes, but with the mods/custom seat, I'm not sure if the cover will still be able to attach.  How exactly does the cover attach to the pan?  I was thinking, could a wooden seat be fabricated, sealed, foamed, stretched with the cover, and the cover then riveted onto the wooden pan?  Does anyone know about custom seat building?  Fiberglass is also an option, but I am concerned about strength and heat resilience.

- I need some good references on how to properly tune a bike.  I know that checking the state of the plugs is a good indicator, but I want this bike to get the most bang for its buck.  Also, what tuning issues might I come across when using a downsizing adaptor between the header and the midpipe? 


          - Chris Gerber

[Lumbee]

...get yourself a compression tester...this will give you an indication of overall cylinder/valve condition...should be in the neiborhood of 120-150 psi.  Anything lower and new pistons rings/gaskets/valve cleaning is in order.

[Bobby]

Wow!  Great CB Chris!!  The only thing missing is a vintage Tracing Racing Body!   


-Bobby

[Geeto67]

anybody got a way of getting in touch with Tim Shutters?

I wanna ask him about the swingarm on that bike.

[dusterdude]

where do you reckon tim got the cafe/bobtail thing.

[Geeto67]

where do you reckon tim got the cafe/bobtail thing.

That looks like stock bodywork for a 77-78 supersport (the seat looks a little shaved in the front though).

[MotoDave]

BTW, compression should be more like 170psi for a motor in good condition.

[Geeto67]

That looks pretty good, though the CF isn't my thing. Along these lines, how hard would it be to put in a fatter tire on the rear end like on Shutters's bike? Or swap in a newer front end, for that matter?

My understanding of it (from the chopper guys at honda chopper) is that the 1977-1978 bikes have enough room (due to longer countershaft) to put a 180 rear tire in the back, but you would need a bigger rim and swingarm (possibly frame) to accomidate it. I don't have the specs on shutter's bike so I can't tell you what he is running but off hand i'd say a 160 on a cbr f2 or f3 rim. Chain line would be up to you but I know a lot of guys with SOHC and DOHCs that have had a lot of success swapping in f2 and f3 cbr rims.

As for front ends it all depends on the bike and the front end. A 1975-77 gl1000 front end is a direct bolt on (using the proper timken bearings) but that is really just for the vintage dual disc front brake look. I put an fzr600 front on a kawasaki triple and I can tell you the easiest way I have found is to take the stem from the SOHC and weld it into the lower clamp of the donor front end. There was a guy on this site who did it the same way with an f3 front end and a 76 supersport 750. Shutter's bike looks to have an f3 front done the same way but I don't have the specs so once again I am not sure.

Anyway, does anybody have specs on Tim Shutter's bike, I really want to know if that is a custom made swingarm (like from jmc) or if he adapted it from a cbr f2 and the work involved.

[Geeto67]

I would really like to know, as well. I'm going to do a bit more research based on your post, but I think I am going to look into putting an F2 or F3 rear end on there so I can use a big fat rear tire.

I don't want the big front tire as much, though. I wonder what kind of front end I can find with a similarly-sized tire but improved brakes...

The best R&D is to take measurements. if you have access to a cbr f2 or f3 and a cb750 that is the best way. Here is a link to canyon runners site where he did the cbr wheel swap: http://home.earthlink.net/~canyonrunr/index.html

The least expensive way to put a fat tire on the back is to just have your stock rear honda hub relaced with a wider wire rim. The best looking way, in my opinion, is to swap in the cbr rear end and front end. I would recommend doing both the cbr rear wheel and front end since both suspensions components are designed to work with each other (albeit on another frame but still it should get you close).

There are several ways in which you can get a cbr wheel on the back:

1) have a custom made swingarm - JMC (www.swingarm.com) will mak one specially to fit
The Good: everything becomes bolt on in the rear
the bad: this can be really expensive, espically when the swingarm alone starts at $500

2) you can adapt the wheel to your swingarm
The good: keeps costs down by reusing a lot of parts you have
The bad: will only work with an f2 wheel and a 150 tire and you have to make custom made brake mounts and wheels spacers (hope you have a good machine shop).

3) you can fit a cbr rear end to the bike
The good: beefier swingarm without the cost of JMC
The bad: a lot of machine work to make the pivot smaller, Need to weld shock mounts.

anyway good luck.

[capnspif]

Hi,

First time posting to the forums, great site here. I've also been looking closely at Tim Shutter's bike and it seems pretty clear in the pics where the bike is still black that he used the stock CB750 swingarm. From the pics where the bike is orange w/ black wheels, it looks like a custom caliper bracket. Not sure how the stock master cyclinder handles the newer caliper, assume it would be ok. Really hard to tell but I'd guess that's a 160-170 tire on a 5" rim? There are some later pics I ran across where the wheels are polished and it looks like he may have adapted a newer swingarm at that point, but the pics weren't clear enough to be sure.

The front definitely appears to be from a '93-'97 CBR900RR, which would have a 16" wheel. The brakes/wheel look to be from the same bike. Given the size differences between these and the stock wheels, I wonder how well it actually handled?

I'm doing a frame up rebuild of the same bike, a '78SS and have been looking for some styling inspiration. This definitely hits the mark for me.

As to the original post, I had a 600RR for awhile and also installed an underseat exhaust kit to my VFR, for a brief time. Heat management is going to be a key and something to definitely consider.

Good luck.

Mike

[SteveD CB500F]

As to the original post, I had a 600RR for awhile and also installed an underseat exhaust kit to my VFR, for a brief time. Heat management is going to be a key and something to definitely consider.

So it's a hot a@!e problem