➊The history of exhaust muffler
The history of CB750Four Genuine exhaust muffler
Why does CB750Four use 4-pipes exhaust muffler?
Based on the four-cylinder, four-cab, four-muffler design synonymous with Honda GP machines of the time, the four-muffler is said to have been adopted to evoke the multi-cylinder technology developed in World Grand Prix racing and to be instantly recognisable as a four-cylinder.
➋About NO NUMBER EXHAUST MUFFLER
The history of Honda genuine 4-pipes exhaust muffler
CB750Four genuine exhaust muffler has a history.
The history of exhaust muffler began from The No-Number (unmarked) exhaust muffler. It was installed on 1969 CB750K0 early model. There was no part number for it, so that's why it was called "No-Number (unmarked)".
But, each part had to be assigned a part number. Therefore the exhaust muffler stamped "HM300" was produced. The HM300 exhaust muffler started with a commonly known as the “square 3”. The font of number 3 was used this font "3", it looks angular so that's why it called "square 3". After that, the HM300 exhaust muffler was changed a commonly known as the “rounded 3”. The font of number 3 looks rounded.
Square３
Rounded３
HM300 exhaust muffler was used from K0 to K1. Afterwards, HM300 was produced again as a repair part. It had a stamp of "USA CANADA CAUTION", so it is commonly known as the “Canada Caucon".
A stamp of "USA CANADA CAUTION"
The exhaust muffler was changed "HM341" from K2.
Unlike the HM300, the diffuser pipe of HM341 has changed only a lid to prevent noise.
HM300 Diffuser pipe
HM341 Diffuser pipe
As you know, there are several kinds of genuine exhaust muffler.
Among them, YAMIYA reproduced and sell "No-number" exhaust muffler.
Type of No-number exhaust muffler
As for the No-number exhaust muffler, there are two type CB750K0 early model and later model.
For early model were fitted ※1 a baffle with numerous holes like a lotus root, so it is commonly known as the "Lotus Root exhaust muffler". The later model had ※2 a thicker baffle than HM300, so it is commonly known as "thick-core muffler" in Japan..
※1 the baffle installed to a lotus root exhaust muffler.
HM300
No-number exhaust muffler (later model)
Compare HM300 and No-number exhaust muffler (later model)
The differences between Lotus Root exhaust muffler and a later model No-number exhaust muffler
The end of the exhaust muffler is fitted with a metal "baffle" and "diffuser pipe" through which the exhaust gases pass. The way these two parts are fitted is the main difference between a Lotus Root exhaust muffler and a later model No-number exhaust muffler. As for a Lotus Root exhaust muffler, the diffuser pipe is fitted into the baffle and attached to the end of the exhaust muffler. On the other hand about a later model No-number exhaust muffler, it has the baffle welded into the exhaust muffler as an integral part, so only ※3 the diffuser pipe with glass wool is fitted.
※3
Why did this change happen?
The baffle of the Lotus Root exhaust muffler at the time, it was installed with one bolt. That bolt loosened due to vibration while driving, so there was a risk of baffles falling out. As a solution for this issue, "thick-core muffler" was born that it has the baffle welded into the exhaust muffler as an integral part.
➌The features of YAMIYA's "No-number exhaust muffler"
①Complete reproduction of the original muffler
We dare to reproduce the appearance as if it were manufactured with the technology of the time, even in areas that could be beautifully processed with modern technology.
※4
I heard that someone called the welded part ※4 “Godzilla's bone plate.
※4 This is an original
※5 The surface of the drainage hole has not been graded, and is reproduced as it was at the time.
※5 This is an original
②Double structure
※6 Original muffler was manufactured with double structure.
We also reproduced such trivial details. There are several purposes for the double structure. The typical effect is to prevent seizure. Although it takes time and effort due to one more production process, double construction is essential for complete reproduction.
③ Fits 1970-1976 CB750K series motorcycle as well
The mufflers of the time only have a small space between them and the oil filter, which invariably interferes when removing them. YAMIYA's mufflers are manufactured with fine-tuned angles to allow for the removal of other parts.
Therefore, it is possible to change the oil and filter as it is installed. We also wanted all people to the sound and detailing of the No-number exhaust muffler. That's why this exhaust pipe fits 1970-1976 CB750K series motorcycle as well. This is YAMIYA original best quality reprodction parts. Enjoy the great sound and perfect shapes!
➍Related parts
CB750K0
CB750K
CB750K
CB750K0
CB750K
CB750K