Topic: Building a Custom Exhaust: Cylinder 1-4 Orientation

[Ellz10]

I have run the same cb900 Vance and Hines 4-1 header on both a cb900 and a K2 cb750. It took a little encouraging to bolt it on but it went. Just due to the 4-1 design and the angled ports.

Don, did the CB900 Vance & Hines you put on the K2 connect successfully and without any leaks?

I'm curious about how the fitment went up at the ports.

[Ellz10]

***Update***

So I spoke with Kmb69 and asked him if the '79 & up 750 dohc and 900s will interchange at the head exhaust ports and he said:

"Zach,

I have never done it personally, but I have been told they will interchange at the head.
It might take a little "push and pull" but the headers are usually flexible enough to do that.
Might have to fab some rear brackets but they are relatively simple to make.

K****"

With that being said, I went ahead and looked into it a little more and found this set of Delkevic 4-1s for the '79-'82 CB750 K - DOHC.

Now looking at the flange area that goes into the head, it does look (I think) like it will interchange, just without the need for the joint collars that come stock on the '77/78s.

Thoughts anyone?

[Alan F.]

https://www.cb750.com/threads/anybody-put-dohc-exhaust-on-a-sohc.3899/

[PeWe]

Several 4-1 to CB750 K0-K6 have those fittings to the head.
Just remove the stock K0-K6 head spigots and mount the 4-1.
I used M8 bolts, allen head.
Below a K6, but could be older as well. Passenger footpegs as usual.

Alfa 4-1, purchased new 1983-84
Below 2014


Same 4-1, same bike from an other angle 2015.

[robvangulik]

***Update***

So I spoke with Kmb69 and asked him if the '79 & up 750 dohc and 900s will interchange at the head exhaust ports and he said:

"Zach,

I have never done it personally, but I have been told they will interchange at the head.
It might take a little "push and pull" but the headers are usually flexible enough to do that.
Might have to fab some rear brackets but they are relatively simple to make.

K****"

With that being said, I went ahead and looked into it a little more and found this set of Delkevic 4-1s for the '79-'82 CB750 K - DOHC.

Now looking at the flange area that goes into the head, it does look (I think) like it will interchange, just without the need for the joint collars that come stock on the '77/78s.

Thoughts anyone?

That is the same principal as the pic I posted in your other thread, reply #3....

[Shtonecb500]

try to design something thats not in the way of the oil drain plug, the lower frame rails so u can easily jack the bike up, and so you can take off the oil filter without having to pull the pipes.


My favorite header which is a yoshi style hand bent header pipe, is in the way of the my oil drain plug, barely allows me me to get a scissor jack under the rails, and I cant unbolt my oil filter but it doesnt have quite enough room to completely out from behind the pipes, I have been lazy before and just unscrewed it, dumped all the oil out over the pipes and put it back on lol....prolly wont do it again tho.


Oh and I stripped one of my exhaust studs...probably cause i take my pipes off for every oil change.

Enjoy.

[Tracksnblades1]

I have run the same cb900 Vance and Hines 4-1 header on both a cb900 and a K2 cb750. It took a little encouraging to bolt it on but it went. Just due to the 4-1 design and the angled ports.

Don, did the CB900 Vance & Hines you put on the K2 connect successfully and without any leaks?

I'm curious about how the fitment went up at the ports.

 If it had issues, I would not have posted about it fitting. Why not just get a header that is made for your bike?  Did they stop making them?

It’s a wet “Sump-Thing” conversion…
Standard headers rub its extended sump (oil pan) is what I’ve read.
The 900s are wet sumps and the dual overheads are a taller engine. So supposedly the header hangs down lower on a single overhead.

But you should know for sure because you tried it.  😇. I know the only difference I’ve seen between a yoshimura 4/1 for a sohc 750 F and k is where the rear bolt hole tab is welded on the pipe.  Besides neither had spigots, forcing you to use the provided studs..

[PeWe]

A 4-2 will not fit?

[Ellz10]

Thank you everyone for your helpful responses!

I went ahead and ordered the 4-1 headers from Delkevic for the '79-'82 DOHC.

Talked to a few different people whom have done this before and a couple had mentioned they only needed slight modification to the flanges to fit, so I'm pretty excited!

I'll update this thread for the final result!

A 4-2 will not fit?

I'm sure I could make it fit, but it would be a pain with the kickstand, wet sump, and the rear sets getting in the way.

I would've rather had a 4-2, that was my original plan, but in the end the headache just wasn't worth it. Perhaps I'll switch it in the future.

[Ellz10]

So after inital mock-up, it was as others had told me - modifications were needed at the flange, just a bit shaved off. I'm working on that tonight, but it looks good otherwise! Going to fab up a bracket for the elbow and I've got an 8" muffler on the way from Cone Engineering.

[Tracksnblades1]

So after inital mock-up, it was as others had told me - modifications were needed at the flange, just a bit shaved off. I'm working on that tonight, but it looks good otherwise! Going to fab up a bracket for the elbow and I've got an 8" muffler on the way from Cone Engineering.

Pictures of the shaved flange modifications please.
You can document the dohc to sohc difference for all..
Looking good.😇
 I think you’ll like the sound of a 4/1, especially with well synced carbs going through the torque curve..
I think they sound good at high rpms as well.

[newday777]

So after inital mock-up, it was as others had told me - modifications were needed at the flange, just a bit shaved off. I'm working on that tonight, but it looks good otherwise! Going to fab up a bracket for the elbow and I've got an 8" muffler on the way from Cone Engineering.

Just be very careful going over speed bumps......

[calj737]

So after inital mock-up, it was as others had told me - modifications were needed at the flange, just a bit shaved off. I'm working on that tonight, but it looks good otherwise! Going to fab up a bracket for the elbow and I've got an 8" muffler on the way from Cone Engineering.

Just be very careful going over speed bumps......

The tail of the system is currently unsupported hence the appearance of scraping the tarmac. In actuality, once completed and properly secured, it will not be an issue under normal traffic pathways.

[newday777]

So after inital mock-up, it was as others had told me - modifications were needed at the flange, just a bit shaved off. I'm working on that tonight, but it looks good otherwise! Going to fab up a bracket for the elbow and I've got an 8" muffler on the way from Cone Engineering.

Just be very careful going over speed bumps......

The tail of the system is currently unsupported hence the appearance of scraping the tarmac. In actuality, once completed and properly secured, it will not be an issue under normal traffic pathways.

But it does hang lower than the SOHC 4into1 systems.  I scrape the speedbumps with a Hooker 4into1 and a Kerker 4into1 if not careful.

[Ellz10]

So after inital mock-up, it was as others had told me - modifications were needed at the flange, just a bit shaved off. I'm working on that tonight, but it looks good otherwise! Going to fab up a bracket for the elbow and I've got an 8" muffler on the way from Cone Engineering.

Pictures of the shaved flange modifications please.
You can document the dohc to sohc difference for all..
Looking good.😇
 I think you’ll like the sound of a 4/1, especially with well synced carbs going through the torque curve..
I think they sound good at high rpms as well.

So first attached pic shows how I had to shave both sides to fit into the port. 2nd pic shows the "before" I shaved both sides to give people an idea of why it wouldn't fit - the outer ring wouldn't fit on these 4-1s. 3rd pic shows the gap between the flange and the exhaust stud at the head (I circled in red).

Now this is where I believe I'll need to either put a small spacer there (on each one) or weld said spacer to the flange itself so I don't have to worry about losing it.

At first I thought that gap was normal to leave room for tightening down the flange with the gasket in, but I believe that gap is too large for that to be true.


Also, I do believe I'm going to need to get a different set of exhaust studs, I would imagine I'll need '79-'82 studs because there's no more thread room for the nut to secure the flange all the way. You can see in the 3rd photo. However, I think if I go the spacer route, I won't need the '79-'82 studs set.

[Ellz10]

So after inital mock-up, it was as others had told me - modifications were needed at the flange, just a bit shaved off. I'm working on that tonight, but it looks good otherwise! Going to fab up a bracket for the elbow and I've got an 8" muffler on the way from Cone Engineering.

Just be very careful going over speed bumps......

The tail of the system is currently unsupported hence the appearance of scraping the tarmac. In actuality, once completed and properly secured, it will not be an issue under normal traffic pathways.

Yes sir.

[PeWe]

Russ Collins 4-1 had also not much clearance for bumps.
Here a K7 version on my K6. More upwards at rear.
16" rear wheel and 6" longer fork tubes.

[Ellz10]

Several 4-1 to CB750 K0-K6 have those fittings to the head.
Just remove the stock K0-K6 head spigots and mount the 4-1.
I used M8 bolts, allen head.
Below a K6, but could be older as well. Passenger footpegs as usual.

Alfa 4-1, purchased new 1983-84
Below 2014


Same 4-1, same bike from an other angle 2015.

Hey PeWe, did those flanges require any kind of spacers or modifications? Was there any gap of some sort close to what I posted above, like 3mm or so of a gap?

[PeWe]

It fitted direct.
Bolted to head with M8 bolts, stock type copper seals.

[Ellz10]

It fitted direct.
Bolted to head with M8 bolts, stock type copper seals.

I believe I'm going to go the M8 bolt route as opposed to getting later model studs or having some made. I'm going to need spacers there though, bout 3mm wide, in order to have that snug fit. The trick is finding the correct size spacer to put there so that the gasket gets pressed enough to whatever the torque spec is. It's going to be a slippery slope.




What is the torque spec for the exhaust ports there?

[PeWe]

You'll feel when it stops, a little bit more for copper seal to form.
Tighten all very loose to start with so all pipes will alugn correctly.
Tighten in  steps  until all are tight. Tighten each brackets 2 bolts so it will go on parallel.

You'll need to retighten after a ride or 2 when copper seals sets as usual.

I use alu paste on those threads.  Withstands +1100C.
I use it on plug threads too, just a little.

Below my old Alfa 4-1 made for K0-K6.


#
The stainless Hindle 4-2-1 has stainless spigots that are bolted to head like stock K0-K6.
Pipes goes on section by section by ease if properly aligned and secured with springs. Take pipes off the opposite way, release springs on each section and final bolt at rear.

[Stev-o]

It fitted direct.
Bolted to head with M8 bolts, stock type copper seals.

I believe I'm going to go the M8 bolt route...

I had a Kerker on my K5 and also used SS bolts, worked fine.

[calj737]

Proper torque for M8 bolts is 16-18 ft/lbs. the purpose of the copper O-ring is to act as a crush seal. Coat the bolts with copper antisieze. It’s designed for high heat applications.

I’m a bit confused: I thought you were using a spigot style exhaust flange? If so, the port side of that flange should fit neatly into the head and have a flat or routed surface to crush the copper O-ring. Securing that flange to the head with bolts or studs (doesn’t matter which, either are widely available) then allow you to slip the tube onto the spigot and secure with spring clamps (per Pete’s picture on the Hindle system).

[Ellz10]

You'll feel when it stops, a little bit more for copper seal to form.
Tighten all very loose to start with so all pipes will alugn correctly.
Tighten in  steps  until all are tight. Tighten each brackets 2 bolts so it will go on parallel.

You'll need to retighten after a ride or 2 when copper seals sets as usual.

I use alu paste on those threads.  Withstands +1100C.
I use it on plug threads too, just a little.

Below my old Alfa 4-1 made for K0-K6.


#
The stainless Hindle 4-2-1 has stainless spigots that are bolted to head like stock K0-K6.
Pipes goes on section by section by ease if properly aligned and secured with springs. Take pipes off the opposite way, release springs on each section and final bolt at rear.

Perfect information, thanks Pete!

Question for you though: attached is a zoomed in screenshot of the last pic you posted showing the area between the flange and the head and there's a gap there. Is that okay to leave that gap there?? That's what I was referring to in my last couple posts.

[Ellz10]

Proper torque for M8 bolts is 16-18 ft/lbs. the purpose of the copper O-ring is to act as a crush seal. Coat the bolts with copper antisieze. It’s designed for high heat applications.

I’m a bit confused: I thought you were using a spigot style exhaust flange? If so, the port side of that flange should fit neatly into the head and have a flat or routed surface to crush the copper O-ring. Securing that flange to the head with bolts or studs (doesn’t matter which, either are widely available) then allow you to slip the tube onto the spigot and secure with spring clamps (per Pete’s picture on the Hindle system).

16-18, thank you! I'll pick up some copper antisize today after work, the only kind I have it the aluminum antisieze.

Sorry to confuse, not my intention! So to clear up the confusion (hopefully), my exhaust is exactly like Pewe's, with the only exception being that my headers dont have a spring with a hole to attach to on the flange.

And as I mentioned in my most immediate reply above, you can see that what I was referring to and confused about was the need for a spacer in that gap that I circled. I thought I needed a spacer there to fill the gap so as not to bend the flange when it's being tightened at both ends.