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That's good to know. I was more wondering why the CBR300R mid pipe I linked wouldn't fit.
I think it could fit, but without the gasket. If 42mm is an external measure (O.D.), and the wall thickness is 1.5mm, then I think it is possible to close a I.D. 39mm tube on a O.D. 38mm tube and it will be fine. There is a certain element of uncertainty here. it is what it is. Big Cahuna says it worked out fine for him, so if it's the same part then it probably worked out similarly for you.
 

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So correct me if I'm wrong but with an OD of 38mm + gasket with OD of 44mm, putting a "normal" cbr250r mid pipe with an ID of 40mm would mean it would crush the gasket 4mm.

The CBR300r mid pipe has 42 ID meaning it would crush 2mm instead of 4mm creating a "looser sealing" correct? Would this even be an issue?

Also @BigCahuna what did you use as sealant on the gasket? I saw some people use silicone sealant?

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Discussion Starter · #64 ·
So correct me if I'm wrong but with an OD of 38mm + gasket with OD of 44mm, putting a "normal" cbr250r mid pipe with an ID of 40mm would mean it would crush the gasket 4mm.

The CBR300r mid pipe has 42 ID meaning it would crush 2mm instead of 4mm creating a "looser sealing" correct? Would this even be an issue?

Also @BigCahuna what did you use as sealant on the gasket? I saw some people use silicone sealant?

View attachment 45913
View attachment 45912
I have no gasket.

The stock gasket came out with the stock muffler. The cross-pipe is metal on metal contact and clamped down on one side, and spring fit on the slip-on. as far as I can tell, I don't have an exhaust leak. I did look for a thin gasket because it seems to be the proper thing to do, but I couldn't find an appropriate size and it seems OK.
 

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Oh I see, perphaps a gasket from a smaller bike would do the trick, 50cc or 125cc gasket? As long as ID is 38. Ill look around.
So having a 40mm mid pipe on a 38 OD inner pipe doesn't cause a leak? Im surprised. Im guessing for a cbr300r its probably safer to actually find a gasket
 

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Discussion Starter · #66 ·
Oh I see, perphaps a gasket from a smaller bike would do the trick, 50cc or 125cc gasket? As long as ID is 38. Ill look around.
So having a 40mm mid pipe on a 38 OD inner pipe doesn't cause a leak? Im surprised. Im guessing for a cbr300r its probably safer to actually find a gasket
It wasn't so much the diameter of the gasket, it was how thin it was. Most of the gaskets were like 10mm thickness if I remember and I needed just a few mm.
 

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So correct me if I'm wrong but with an OD of 38mm + gasket with OD of 44mm, putting a "normal" cbr250r mid pipe with an ID of 40mm would mean it would crush the gasket 4mm.
NO. It is "crushing" the OD 4mm, there for crush the thickness 2mm (from a thickness of 3 to thickness of 1)...
BUT this will never happen, because this gasket does not have that flexibility. I don't think you will be able to insert the mid pipe on it.
The CBR300r mid pipe has 42 ID meaning it would crush 2mm instead of 4mm creating a "looser sealing" correct? Would this even be an issue?
You're right, the OEM gasket crushes, it doesn't have much flexibility.
The idea with this gasket, in my opinion, is:
  • To overcome the changes in the length of the pipes as a result of their heating.
  • And perhaps also to allow adjustment to the muffler due to other tolerance considerations (If the two pipes are not parallel).
With slip-on exhausts, the tolerance system is different, because the connection is with springs and not with a clamp.
 

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Also @BigCahuna what did you use as sealant on the gasket? I saw some people use silicone sealant?
Silicone sealant? RTVs are not resistant to boiling exhaust temperatures.

In the picture below is a sealant that is suitable for sealing exhausts. I bought it over ten years ago, and still haven't used it. Maybe it has already expired?
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When I had a hole in the exhaust I fixed it with arc welding. And I don't recommend you to use such a sealant either. It might be good if you took the pipe off the exhaust manifold and you don't have a new gasket, and you don't have time to order a new gasket because you're in a hurry...so in that case it's good to have this thing. But I always make sure to have such gaskets in stock:
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Thank you for all the feeback.

I suppose in that case the ID for the OEM exhaust must be bigger if these mid pipes don't fit with the original gasket.

Yeah I agree with you for the purpose of the gasket and that's the reason why Ideally I'd want to put the mid pipe with a gasket in between. Since with either one there will be a 2mm-4mm clearance that "should" ideally be sealed.
Edit: 2mm is actually not that bad but in case of a cbr300r mid pipe 4mm might be...


I just saw a video where a branded manufacturer included a silicone sealant, and wasn't sure if it was 100% needed. But I suppose maybe not then.

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I suppose in that case the ID for the OEM exhaust must be bigger if these mid pipes don't fit with the original gasket.
YES. Not bigger, almost the same (44mm),
Yeah I agree with you for the purpose of the gasket and that's the reason why Ideally I'd want to put the mid pipe with a gasket in between
With the mid pipe, there is no need a gasket for heat differences and tolerances, because on the other side there is a flexible flip-on connection.
I just saw a video where a branded manufacturer included a silicone sealant,
It is not a sealant. It is silicon grease. The grease is to make it easier to slide the mid pipe into its place, and also to prevent adhesion between the two pipes. I use copper grease for a similar purpose.
 

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Ok, in that case ideally Id need a 38 ID 42 OD gasket and BigCahuna a 38 ID 40 OD gasket.
But maybe it's the same dimensions ID40 and OD42, because the pipe wall thickness is 1mm. You don't know what the pipe wall thickness.
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And BigCahuna already told you that it worked for him without a gasket. BigCahuna had a problem with the clamp that came oversized.
 
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