Honda-SOHC

SOHC.co.uk Forums => CB750 => Topic started by: El__burro on September 01, 2016, 07:23:13 PM

Title: K2 4 into 2 exhaust (DIY)
Post by: El__burro on September 01, 2016, 07:23:13 PM: i am going crazy with the idea of "transforming" the 4-1 in the pics below to a 4-2.
I am trying to see whether or not anyone has attempted this and with what result?
Eventually i would need a 2 into 1 and a couple of muffler too.

I would consider part exchange

Regards
el__burro
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: Johnwebley on September 01, 2016, 08:29:10 PM: I would suggest a 4-2 system should be cylinders 1-4 and 2-3 on paired pipes,
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: El__burro on September 01, 2016, 10:20:51 PM: so its almost impossible as 1&4 wouldn't end up on the same side as they are short.
What about 1-2 and 3-4.
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: matthewmosse on September 01, 2016, 11:20:31 PM: I have a set of cb550 4 into 2 pipes, not yet got around to fitting them, I could possibly dig them out to photograph to give you an idea how it has been done though it will not get fitted for a while and the 550 isnt reallly the same in any case..... I think its made to do 1&2, 3&4 as pairs.
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: El__burro on September 01, 2016, 11:26:07 PM: That may be helpful.
Thanks
El__burro
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: Chris400F on September 02, 2016, 09:07:59 AM: Here's a thought ....
Where does the collector box for your system sit relative to the centreline of the bike i.e. is it about in the middle or offset to one side?
If it is roughly central would it be possible to modify the collector box to add another outlet pipe on the other side to the existing one?
This would give you a 4-1-2 system which could then be fitted with the twin silencers (or mufflers) you presumably desire.
From the pic of a collection of parts it is difficult to visualise how the complete system would look when fitted to the bike.
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: El__burro on September 02, 2016, 10:20:06 AM: Good thinking Chris.
I guess it's time to fit it and see.
El__burro
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: Rob.b (Rob Birkett - RIP) on September 02, 2016, 01:19:50 PM: HI,

It's a pound to a penny bet that your collector is going to exit on the right hand side of your bike. I think it is going to be really difficult to adapt the collector so that it can accommodate a 4 into 2 system. However, having looked at the collector it seems to have a wide and roughly symmetrical layout for receiving the 'down pipes', so for what its worth here is my suggestion; Don't bother with the collector and cobble up something using your set of 'downpipes' and off the self parts, I have added a photograph of what I managed to make at home using my own 'downpipes' and parts from:

http://www.classicbikeshop.co.uk/

It took quite a bit of head scratching but I'm happy with the result. Not Cheap though I spent about Â£225 on it.

here is my 500

[attachimg=1]

Rob
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: El__burro on September 02, 2016, 09:58:57 PM: most probably you are right about the collector being located on the centre-right of the bike, I am trying to see if the downpipes I have can be diverted to 2 per side without much struggle.
Your bike looks great and this is exactly what I am trying to achieve. (4-4) Just thought it will be easier getting to a 4-2.
Thanks for your suggestions,
please keep them coming.

el__burro
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: matthewmosse on September 03, 2016, 09:49:17 AM: I think 4 into 4 would actually be easier but cost more - 4 silencers not 2. I would think probably the 2 left pipes would need cutting and welding, or bending ( probably with heat ) to point over the other way, and I'd anticipate them having a bit of extra length needing trimming off that side as the'd no longer cross the bike. Then there is the issue of getting it chromed or painting or avoiding chrome dammage when bending. Not inpossible - I think I would start by trying to clamp the engine end of the right hand pipes in a massively strong vise using substancial and shaped to suit soft jaws made of a hardwood like oak then inserting a tight fitting bar or pipe with plenty of length and swinging on it . This was something I had thought about doing in the past and I might well revist over winter or spring if I embark on a cb500 project. My starting point would be a motad 4 into 1 system with a rotten silencer. The 'fun' bit will be measureing the length of all the downpipes and angles when on the bike to see how much bending or cutting and welding is needed.
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: Chris400F on September 03, 2016, 10:06:01 AM: The downpipes in the pic all look to be about the same length and the collector exit pipe has quite a bend in it, which is what suggested to me that the collector may be located centrally(ish) under the engine and that it may be possible to add another exit pipe and a second silencer. You still have the issue of fabricating suitable changes to the collector box and bending an exit pipe, but not impossible and working with what you have.

If you want to go down the 4 pipe route DK have listed in their online spares shop something described as 'Honda CB750 CB 750 SOHC 4x Finned Exhaust Collars & Header Exhaust Inserts ', see http://www.dkmotorcycles.com/used-spares/headers,_manifolds_and_studs_1/243128/. The accompanying picture shows a set of downpipes; if these are for a four pipe system then that would seem to be a good starting point for a 4-2 or 4-4 system.
Title: K2 4 into 2 exhaust (DIY)
Post by: El__burro on September 08, 2016, 09:56:46 PM: Today I've managed to set the 4 pipes to see if this "job" can be done.
To this stage I am concerned with how little floor clearance there is.
Is that ok?
By looking at other set up I think its too low.

Thanks
el__burro
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: Rob.b (Rob Birkett - RIP) on September 09, 2016, 05:23:02 PM: Afternoon,

Yes they look too low, they are going to ground. I reckon that it's going to be far too much hassle to make them work. Best bet is to follow the advice of Chris400f and buy a set of standard four into four down pipes to use as a basis. You can sell your four into one setup to offset the cost.

Go for it.

Rob
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: El__burro on September 10, 2016, 09:34:18 AM: Yeah, I thought so.
rather than spending over Â£100 for the pipes, I am thinking of trying to make them myself.
I found some material on ebay and some tutorials on YouTube.
I have worked out that (if successful) I will be spending less than Â£100,
learn something new in the process and eventually make some more to sell later on.
Has anyone ever tried to do this?
Thanks
el__burro
https://youtu.be/utkQf454ibQ
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: royhall on September 10, 2016, 09:56:56 AM: That guys a real expert. I have tried that technique a few times (not exhaust pipes though) and it takes expertise to not have the pipe necking down and making it oval. For what I was doing the ovality wasn't important, but it would look a mess on a bike. If you can find a local company with a mandrel bender, that's the way to go.
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: Chris400F on September 10, 2016, 05:29:53 PM: From what I have seen and read making exhausts is pretty specialised stuff.
Not only do you need to bend the pipes, making a matching set for a multi-pipe system, but also make flanges or similar on the ends for mounting the pipes to the head. You can't just bend this stuff over your knee.
Even Motad with all their experience don't seem to be able to get the bends quite right in their 400/4 replica system for the pipes to align perfectly.
I remember watching the Guy Martin programme when he was building a bike to do the Pike's Peak race.
The guy making the exhaust had a piece of kit that cost lots of thousands of pounds but he still couldn't make the pipes for Guy's bike as the curve radius was too small so they ended up welding short sections together to get tight enough bends.
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: matthewmosse on September 11, 2016, 08:53:37 AM: Thin wall thickness of the material means it kinks or goes oval very easily. You can try packing it with sand and plugging up the ends to bend it ( putting a spring inside is a plumbers method for bending copper but would be unlikely to work on metal pipe, you'l still end up with a kinked pipe, just with a kinked spring stuck inside! there are other methods) and a mandrel bender is going to do better than one of the Â£100 machine mart style benders. Somewhere I have a custom bike magazine detailing how to build a diy mandrel bender for exhaust bending from a scrap brake hub and drum for this kind of job. or buy lots of ready made bends but I found that was looking likely to add up to quite a bit of cash just to get 8 bends for the downpipes. Then there are lots of welds. I'll report back when I have time to weld up my current batch of repaired exhausts using a few sections of stainless like you show to repair my cb250s pipes that have rotted their balance pipe out on two sets of pipes now, ditto a ca125. It worked out very cheap as a way to get pipe to sleeve over the rotted area and re make a balance pipe, so far I am very inpressed with the look of the pipe, quality of the swage to sleeve it over itself and the service of the supplier but I have yet to try to get bends made. I reacon a Â£100 bending machine such as I have would be fine to tweak a bend by say 15Â° or so in 1 mm pipe, but from expirience using mine, these benders sub 2mm pipe just collapses its wall too easily and ends up with kinks and horrid flats at about 45Â° when you need about 95Â° bends for the headers. For my stationary engines I have resorted to cutting and welding pipe at 45Â° in a few places to get an approximate of the bend I want, and also just cutting up mild steel exhausts for cars. It works out cheap enough and works for a stationary engine, but getting those 8 bends with 4 that match top, and bottom could prove a pain. Might be worth asking about a reduction in price from the supplier of ready made pipes and bends to do say 2 sets of exhausts worth of 90Â° bends, then alter the ammount of bend a bit at home and weld up.
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: El__burro on September 20, 2016, 12:02:53 PM: one last question before I give up on this..
Can i fit cb500 k 1972 on my cb750 k2?
thanks
el__burro
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: Trigger on September 20, 2016, 01:06:24 PM: No
Title: Re: K2 4 into 2 exhaust (DIY)
Post by: Rob.b (Rob Birkett - RIP) on September 20, 2016, 08:19:28 PM: Quote from: El__burro on September 20, 2016, 12:02:53 PM
one last question before I give up on this..
Can i fit cb500 k 1972 on my cb750 k2?
thanks
el__burro

Hi Donk,

Have you got down pipes for a CB500 K? if so I'm interested if they are in nice nick.

Have look at this thread if you've not already seen it.

http://www.sohc.co.uk/index.php/topic,10142.msg81379/topicseen.html#new

Rob