some camshaft questions

vr3506

vr3506
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Hi everyone,

I now there is a difference between the unstamped XS1 cam and the later 447 cam.

Tonight I found out, I have a cam stamped "1", and a cam stamped "2".
Can anyone tell me something about these?

regards Jan
 
I guess I could take a stab at this.

Of the pics that I've seen of 256 cans, the embossed numbers appear rough-textured, as though they were part of the forging process, like casting numbers. Possibly a way to track the forging operations, or to indicate a change to the raw forging.

The follow-up machining process is independent, and can have its own variations.

The 256 cam appears to have possibly 10 variations, since it started with part number suffix -00 with the '70 XS1 to early '71 XS1B. The suffix was bumped to -01 with the mid-year XS1B, possibly to correct a grinding error. The final suffix is -09, to be used as replacements for all 256 '70-'73 engines, making a possible total of 10 variations. The variations could be simply improvements in the grinding process and tolerances, and/or supplier changes, similar to what I witnessed on Hondas. I haven't seen suffix numbers stamped on the cams, and have seen only one document about a 256 cam change, to cover that grinding error.

I've had my suspicions about secret/undocumented cam profile changes, similar to the different cams used on the Honda CB350 vs CL350. Very subtle timing differences to move the torque peak high on the CB, and mid on the CL, and to match the different exhausts.

This *was* done when the cams were changed to the 447 version.

Honda kept the parts and service departments informed of this, but not well revealed to the general public. Back then, Yamaha's documentation and parts revisions were not up to the same level as Honda, so these cam markings may simply remain as mysteries.

Edit: In addition to the mid-year '71 XS1B camshaft suffix number change, 2 other changes concerning the camshaft occurred.
- Change from internal roller bearing to bushing, for the advancer shaft.
- Change the 40x25mm end seals.
It is unknown if all 3 changes occurred simultaneously...
 
Last edited:
Goodmorning 2M,

They both have bushings, don’t know when Yamaha started to use bushings instead of neadlebearings.
Can you say anything about this?

Regards Jan
 
'Morning, Jan.

I don't have a specific date or engine serial number when the camshaft internal needle bearing was changed to bushing. Closest I can determine is somewhere mid '71, during the XS1B/XS1F production. That's when the camshaft suffix number went from -00 to -01.

So, a bushed 256 camshaft could be XS1B/F, XS2, or TX650.

From what I've been able to gather, I posted an engine change chronology for the 70-71 engines in post #7.

http://www.xs650.com/threads/yamaha...ins-service-data-brochures.31022/#post-436609
 
That's a very odd Numbered frame.......Usually all model no's start with a ***101 number. There is a Euro 74 TX frame no mentioned, (That i have never been able to confirm) that starts as 476 - 200101.

Nothing corresponds with just a single digit on the end of the ID 6 numbers..............What do the rear foot peg mounts look like........

ID Chart01.jpg Country ID and Colour Chart World wide  Jpeg 1.jpg
 
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