Topic: Supersport 4 into 1 exhaust too short for a CB 750 K

[aminemed]

Hi everyone,

I'm sorry if this subject was discussed before, but i've searched without finding an answer.

I bought a 750 F1 4 into 1 exhaust to replace my K2 4 into 4 exhaust, polished it, painted it, but now that i'm installing it into the cylinder head, i've an issue: the exhaust is somehow not strongly attached. It seems to me that it is not the right size, maybe the head is too short: i tried to tighten the clamps and collar to their max but the exhaust keeps shaking when i move it.

What can i do for that ? (except buying a brand new 4 into 1)

[Ridem32]

Seems like your crush washers are still in your head. Did you install new ones?  You might have to look very hard to the the old ones in your head.


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[ekpent]

 Did you replace the 4 exhaust crush gaskets also ? That might help tighten the pipe to head. Ha ha looks like Ridem and I tied making a post ^^

[754]

 Spacers or washers under the nuts ..  The studs may be wrong length or installed backwards .

[madmtnmotors]

Did the F1 exhaust use spigots or did it use the split collars and outer clamping ring on studs? If the split collars are inserted backwards they won't clamp down properly.

Can you post picts? Properly installed they should work fine.

[ekpent]

Did the F1 exhaust use spigots or did it use the split collars and outer clamping ring on studs? If the split collars are inserted backwards they won't clamp down properly.

Can you post picts? Properly installed they should work fine.

Split collars on those.

[aminemed]

I have split collars

[madmtnmotors]

I have split collars

The "double lip" goes towards the outside. The long, thinner portion of the collar goes towards the head. Is this how you have them oriented?

[aminemed]

This is the schematic of both exhaust. The flange of the K seems to be longer than the collar of the F. Any thoughts ?

[flybox1]

I have an aftermarket exhaust I used on K engine, and it is now being used on an F engine.
You need to check the items covered in previous posts.

-New copper crush washers.
-Exhaust studs installed correctly...the longer threaded end goes in the head, first
-Exhaust flange/split collars oriented correctly. 


Bandaid Fix - add 2 washers under each nut on the studs.

[madmtnmotors]

From my post six years ago:

http://forums.sohc4.net/index.php/topic,94787.msg1058895.html#msg1058895

Okay, took a little longer than expected to get the comparison pictures but here they are. On the left is the late model split collar with clamping collar, while on the right is the earlier model spigot. The late model is a shorter assembly but is designed to include the thickness of the flange on the end of the head pipe. Pictures titled "Offset 2" and "Offset 4" show the late model split collar with an approx .215" plywood shim.

The dimensions referenced in picture "Collars 2A" that represent the working height of each from the underside of the flange to the bottom of the assembly.

The "XX" dimension for the late model split collar is: .885 in

and the "YY" dimension of the spigot is: 1.025 in

for a difference of .140 in. So if the header flange is less than .140 in then there may not be enough compression on the gasket to hold a good seal. If this were the case then a thicker gasket would be in order.

The outer collar of the later model clamping assembly may be bottoming out on the screw bosses in the head since the later model clamping assembly is indeed shorter. Dry fit one of the half moon and clamping ring assemblies in the head without the pipe and without any gasket installed. Any slack in the inner half moons? If so, how much? I think the screw bosses for the exhaust spigots in the early head might be a couple mm longer than the screw bosses for the studs in the later heads. No amount of washers under the nut will compensate for that. I think the clamping force might be coming up short as a result. A couple of options might be:

>Stack two exhaust gaskets (least effective IMHO)
>Grind a couple mm off the inside of the outer clamping rings
>Grind a couple mm off the screw bosses in the head
>Punt    (rarely an option for me    )

[aminemed]

Well, thanks a lot for those explanations. Pictures say it all.

What would be my best shot ? grind a couple of mm off the inside of the outer clamping rings ? that would make both collars have the same height.

[madmtnmotors]

Well, thanks a lot for those explanations. Pictures say it all.

What would be my best shot ? grind a couple of mm off the inside of the outer clamping rings ? that would make both collars have the same height.

I knew I had made this comparison, I just hadn't realized it was so long ago. I would dry fit one without the pipe nor gasket and see what you get. You could also measure the distance from the gasket surface to the outer face of the screw boss and compare it to the working height of the half moon clamping assembly first. If the measured height of the outer face of the screw boss is less than the height of the half moon clamping assembly then something else would be causing the problem, although I can't imagine what else it could be.

[aminemed]

FYI i do own both exhausts, with their respective flangers, collars etc..I do not know if this can be helpful for a sort of conversion

[aminemed]

Do you know if there is any flange adaptor that can make a CB 750F exhaust fit a 750k cylinder head. I went through what is mentioned above without success. Exhausts pipe still are not strongly tightened, too short..

[754]

Yeah ..washers..
Maybe you endedvupvwith some aftermarket 1/2 moons.. Some are shorter..

[madmtnmotors]

Pictures?

I went through what is mentioned above without success. Exhausts pipe still are not strongly tightened, too short..

Can you please post some pictures. My money is on the fact that the later half moon clamping assembly is shorter than the original spigot assembly and the later half moon clamping assembly is bottoming out either on the screw bosses in the head or you are running out of threads on the studs. Or are you using bolts? If so, are the bolts too long?

Figure out where the half moon clamping assembly is bottoming out and we can advise you more knowledgeably. Have you measured the height of the outer face of the screw boss from the gasket seat? If so, what was that measurement? You're sitting there looking at it, but without pictures we can't see what you see...

[aminemed]

I'm sorry I can't provide pictures right now (I'm at the airport for a business trip), but meanwhile, I can't move on to something else, I've been building the bike for more than a year and really frustrated to discover this when I thought that the bike was complete.

Anyways, you're completely right: the later half moon clamping assembly is shorter than the original spigot assembly and the later half moon clamping assembly is bottoming out on the screw bosses in the head.

That's why, I'm wondering if there are any adaptative aftermarket half moons or if I can maybe take my half moons to the local machinist and ask him to make them longer by a few mm

[754]

Sure spend 50 bux or more to not use 3 bux worth of washers or spacers.. Your money..
 

[aminemed]

putting 3 spacers or 2 spacers next to each other is not in my opinion the best..can they resist to the heat?

[Don R]

 In my experience the F0 or F1 4-1 exhaust doesn't fit a k frame due to the brake pedal on the k hitting the header. I have used the F2 header on a K though.

[aminemed]

must be an F2 exhaust then..I know for sure it came from a 750, F1 or F2 can't tell, the bike from which we removed it was in such bad condition that it was hard to know its year or specific model..I'm right now just starting to regret that choice, maybe aftermarket exhausts were a better option..

[754]

 Are you kidding ? I used washer and lockwasher on  mine..
Get your machinist to make 8 4mm long washers if it makes you feel better, can use aluminum.
 F1 and F2 use diifferent rear masters and brackets , should be real easy to tell, or look at frame numbers.

[aminemed]

spent all the day reading all the topics on flanges, spigots etc.. 754 I came across an old post where u say that u have mounted an F exhaust on a 73 motor (which is exactly my case)
http://forums.sohc4.net/index.php?topic=28953.0

one last question: can you please tell me if my 4 into 1 stock pipes spigots will fit with the F pipes? same diameter ?

[754]

It was a non stock pipe that had its own flanges.
 No F used spigots..

These pipes..

[PetesPonies]

I just put an early K style, aftermarket, exhaust on my '77 F and no problems with fitting the head. I had to add the spigots, etc. I'm still trying to sell the complete F exhaust assembly.