questions about the exhaust

[benjixt]

hello evrybody,

this forum and website is just fantastic...

i've got a question on the website at this page

http://www.cb750sandcastonly.com/support23.htm

it's writing


     D.  Outlet Diameters
           1.  Early Type - 52mm o.d., 48.5mm i.d.
                A.  No internal baffling, essentially megaphone
           2.  Late Type - 52mm o.d., 48mm i.d.
                B.  Internal baffling present


what is O.D and I.D??
i understand the difference between the early and late exhaust type but where exactly is the 48 or 48.5 mm size??

second question i've got 2 cb750 diecast one 10131XX and the other one 10282XX
in your opinion what type of exhaust was on this bike when it was new??

unstamped or HM300

thanks to your help

Benji

[Steve Swan]

o.d. = outside diameter
i.d. = inside diameter

Someone else with more "K0" knowledge will need to share if your 131xx & 232xx bikes use the same exhaust.  I believe they do, as a 13xxx vin mfgr date should be around Dec.69 and a 23xxx vin should be around Feb.70.  The 13xxx bike will use the same exhaust as late prod.sandcast which are "no.no" with late type baffles (non- Lotus Root.)  What i am not sure about is the 23xxx vin, what exh.type was fitted at factory.  Might be same as late prod.sandcast or might be next type used on "K0" bikes, i.e., stamped "HM300" with NO relief for brake pedal.  This type of exhaust was used into early K1 production, this i know because i owned a nice 46xxx K1 with these exhaust on it.

[benjixt]

hello
thank you very much for this informations steve you're great
about the mfgr my candy blue green 1013XXX is 11/69 and my 102XXXX is from 03/70

about the exhaust i'm ok with you for the "no number" on my 1013XXX like the last sandcast and for my 03/70 i don't know hm 300 or "unstamped" that's the question...

[benjixt]

hello
anybody know from which number the exhaust change from unstamped to hm300??
regard
benji

[Steve Swan]

48/48.5mm = inside diameter of muffler outlet. 

.od = outside diameter.  id = inside diameter. 

Both your bikes would have unstamped exhaust.

[benjixt]

thank steve for this  info about the inside and outside diameter i have understand that

but my question is to know from which vin number exhaust change from unstamped to hm300

however thank you very much steve for you help

ps: it's not really easy for me towrite in english it's possibla that i do  some mistake sorry

benji

[kp]

I think we've been here before  or maybe not. In any case it will be good to get some member feedback (I'm not holding my breath though)
There are at least 3 early exhausts for the 1969 bikes that I know of but there may be more and I'm not sure there is a definitive answer to your question
Type 1 The Lotus Root type was only seen on the "sandcast" bikes. This exhaust has the large diffuser/baffle and has no stampings or indents/paragraphs (these are the pressed sections below the rear brake pedal and gear change pedal).
Type 2 The second generation type were similar to the lotus root pipes but had some differences the main being the smaller diffuser/baffle. Again, no stampings and no indents/paragraphs. Seen on sandcast bikes and at least some of the early production diecast bikes of 1969 (and maybe 70).
Type 3 The third generation type were the same as type 2 but had HM300 stamped on the pipes were we see the common HM300/HM341 stamping. There were no indents/paragraphs seen on this pipe. My VIN 11970 bike had this type pipe fitted which I believe were the original pipes.
Now the thing to remember is that there is no hard and fast rule when it comes to a number of components fitted to any Honda motorcycle and the 1969/70 CB750 is no different and some might say the rules were very unclear. I think Chris R may have some info on this subject.
I would accept that there are some (maybe many, maybe US only, maybe, maybe, maybe) bikes that came with unstamped (no HM300  stampings) all the way up to VIN 30000 or VIN 45000.
Benji, I would suggest you buy a set of Yamiya pipes, fit them to your bike, fit sunglasses, stand back and enjoy  Bling unlimited    KP

[benjixt]

thank to your reply
i'll order a yamiya set
Benji     

[als750k0]

A further question. I have 2 CB750 K0 die casts. The one that is registered with CB750 Sandcast and a barn find that I am beginning to work on. The registered bike has exhaust pipes that are not stamped and the barn has HM300. Just curious as to when the pipes began to be stamped with part numbers. Thanks Alan