Topic: Mac Exhaust question

[3motodon]

Hi all - first post. 

I bought a '78 750k model last January.  It was basically a rolling frame with an engine.  Everything else was in boxes.  I've since got the bike running after 20 years of sitting.  In the purchase was a new in box Mac 4 into 2 exhaust system. 

My question is header install.  I've read on this forum other Mac questions and I noticed that many Mac headers are flared to fit over the stock flange.
 Mine are straight piped with a small lip.  Included in a box is 4 pieces of what look like adapters.  Its basically about 2 inches of pipe that has splits. 

Obviously I have no instruction and my research isn't giving me a solid path. 

[bryanj]

Those ate designed for the later style, you need later finned clamps with two studs in the head where the cointersunk screws are after you remove them and the spigots

[ekpent]

 Be happy if you mount it that it came with those four proper split collars. Bryan pointed out that you need the proper flange to mount.

[bryanj]

Ebay item 334129254114 or similar then a lenght of appropriate studding plus nuts

[Stev-o]

Ebay item 334129254114...

Hey Bryan....couldnt find it. Is it on UK eBay?

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=334129254114&_sacat=0

Doesnt he need to take off the exhaust pipe flange so the header will sit flush against the head?
[mounted my Kerker this way]

[bryanj]

Yes sorry, i looked on ebay.com but thats what was shown.
If you cant find any where you are you can buy those and have them sent to me and i will pass on at post cost for you

[xhevi]

Can I jump in and ask a quick question?
What is the OD of the collectors?

 Looking to find out what other mufflers will work with these headers.
Thanks.

[3motodon]

First off, Thank all of you for the replies.  Exhaust is an area that is not my expertise.  Okay, I'm not an expert at anything, but I can usually make old things run.

So, here's how I understand it thus far:  Please correct me on thinking errors!

The Spigots/header flange is the piece that is attached to the head with 2 screws per.  Those need to be removed so the lip of the Mac can sit flush against the head.  That would make sense to me as otherwise, they are the same diameter and that would be weird.

Studs need to replace those screws used for the spigots. 

There is also a style of flange that I need to purchase and the eBay link didn't work for me either, so I'm not 100% on what that item is.  I have two styles of hardware in my second pic next to those split collars.  One is a collar style that would use studs and one clamp style that would I assume use the spigots.   

Also, those 4 split collars - where/how do those get fitted?  I'm assuming outside of the header pipe at the head. 

Thank you all again.  It took me a bit to figure out the left hand side of the exhaust and how the kickstand goes in-between the pipe.  But I managed to figure that out with research on here. 

[3motodon]

Can I jump in and ask a quick question?
What is the OD of the collectors?

 Looking to find out what other mufflers will work with these headers.
Thanks.

OD is 55.83mm
ID is 53.22 mm

These collectors are designed to slip inside not outside, if that matters.  Hope this helps.

[xhevi]

Can I jump in and ask a quick question?
What is the OD of the collectors?

 Looking to find out what other mufflers will work with these headers.
Thanks.

OD is 55.83mm
ID is 53.22 mm

These collectors are designed to slip inside not outside, if that matters.  Hope this helps.

Much appreciated!!

[bryanj]

Try this number 294471254693 it is in the US. What you fit after removing spigot is studs in threaded holes, new exhaust gasket into hole in head where spigot came out, exhaust pipe( having slid finned flanges over the pipes) two spit collets per pipe then slide the finned flange up to the studs whichtraps the split collets between finned flange and plain flange on pipe and pulls pipe into the head.
It sounds way more complicated than it actualy is
 

[3motodon]

Okay, I signed on to Ebay UK and saw the link BryanJ refers to.  I think I do have those:)

Now to go get some studs and see if I can figure out the right steps. 

Other than my split collar fitment question, this is coming together in my head. 

Oh - is there an exhaust gasket to be used in the mix here?  I have a pic of what has to be 4 gaskets.

[3motodon]

Try this number 294471254693 it is in the US. What you fit after removing spigot is studs in threaded holes, new exhaust gasket into hole in head where spigot came out, exhaust pipe( having slid finned flanges over the pipes) two spit collets per pipe then slide the finned flange up to the studs whichtraps the split collets between finned flange and plain flange on pipe and pulls pipe into the head.
It sounds way more complicated than it actually is

Bam - the answer posted as I was typing questions.  So much appreciated.  I think I've finally got a firm handle on this part of the project. 

[RAFster122s]

The tubular ring gaskets go inside the exhaust ports and seal against the end of the pipe. Often the old ones which are usually soot covered can be crushed in the port and look like part of the head. A bit of light digging at the edges get them out. There are green stacked paper versions out there as well as the hollow copper rings that crush to form the seal.
The pipe pulls up into the opening crushing the gasket forming the seal for the port.

[Stev-o]

Oh - is there an exhaust gasket to be used in the mix here?  I have a pic of what has to be 4 gaskets.

Yes, the exhaust gasket goes against the head. Be sure to dig the old ones out, use a dental pick or similar tool.  I prefer the copper gaskets, use a dab of grease when installing to hold them in place at the head.

The stud you need is Honda part number 92700-08050-0E

https://www.partzilla.com/product/honda/92700-08050-0E?ref=c759947ac871d5f5a02c47adf62c49060d67b820

Bookmark this parts fiche, it is very helpful when assembling parts and for getting part numbers when you need to order parts...

https://www.partzilla.com/catalog/honda/motorcycle/1978/cb750k-a-750-four-k

[ekpent]

 The flange goes on the pipe first then the split collar with the wide lip facing toward the flange. There should be a groove if I remember correctly inside the flange the split collar fits in a little and as it is tightened pushes the collar agaist the lip of the pipe forcing it into the crush gasket. 
  Sometimes getting all 8 of those Phillip head screws out of the old spigots can be a little tough.Heat, penetrating oil and a good fitting quality bit on an impact driver can be your friend.

[3motodon]

This exhaust is DONE!

Thank you all So Very Much for taking the time to help. 

I'm letting her cool down a bit before I head back in to install Dyna S electronic ignition, matching coil set (5 ohm) and plug wires.  Before I spent that coin - I've cleaned the gunkiest carbs I've ever seen and rebuilt putting it back to stock tune.  Airbox installed - new filter.  New boots and stacks.  I've also sync'd carbs (knowing full well I'll have to do it again) - but I needed her to run right enough to feel comfortable putting dollars into her.  I've been busy and this forum has been my go to for research.  Also for those interested - 3@120 and 1@128 on compression - low-ish but she's been sitting for no less than 18 years, so I take those numbers with a grain of salt.  After I get her rideable, I re-check.  If same, I'll add a touch of oil in the cylinder to see if it's rings or valves. 

Been busy, but I wanted to save her.  Thanks again!

[Stev-o]

3@120 and 1@128 on compression - low-ish but she's been sitting for no less than 18 years, so I take those numbers with a grain of salt. 

Yes, take those numbers with a MARGARITA and a grain of salt! 

Them being within 10% of each other is more important than the number.

[xhevi]

Now that it's done, could you post a few pictures of the headers from a couple angles?

[3motodon]

Here you go.  Slip on's are not mounted correctly yet, but I was trying to channel what I would want to see in clearances. 

[xhevi]

Looking great.

Thanks.