Questions about 146mm rear pillion bolts used on first 1221 bikes

[markb]

I understand that the early bolts are 146mm long and the later ones are 148mm.  I would assume that the thread length is probably the same and the unthreaded portion is what is 2mm different.  In that case a later bolt could be used to make a replica early bolt by shortening it by 2mm and chasing 2mm more thread.  Anyone ever do this?  Are the heads the same on early and later bolts (hex size, "8's")?  Anyone have one of each that they could compare?
Thanks,
Mark

[hondasan]

Pictures attached (hopefully!) of original bolt from #302 and a NOS "020" one. Head size is the same, and is plain - no "8" on either. length is shorter as you already know. Chamfers more pronounced on early one. as you say, appears to be possible  to modify late into early type.

Cheers - Chris R.

[markb]

That is excactly what I was hoping to see.  I think I can do that.  I see what you mean about the chamfers.  Looks to be close to 30 degrees instead of 45.  Don't know what that would be in metric (just kidding).    Chris, would it be possible for you to give me accurate dimensions of the early bolt.  I should start scrounging for later bolts.  I need two pairs but once I'm set up to do them I should do as many as I can.
Mark

[hondasan]

No probs - I'll get you the dimensions this week.

I did not re-use the correct shorter bolts on #302 as it is fitted with HM300 pipes (+ longer bolts) right now. The plan was to ride it occasionally, but two years on from finishing the resto I still have not! I do have a et of Yamiya "lotus roots" for it, but not sure if they are accurate in the detail of the pillion fottrest mount. Anyone else know?

Cheers - Chris R.

[Steve Swan]

Hi Mark & Chris,

I have a set of the later bolts, lock & flat washers with nuts, if you need/want them, Mark.  Either nos or used.

Chris, i used the early shorter bolts which came with 232, they were still present, holding HM341's in place with nuts and lock washers only.  (Still amazes me how much of 232's original small parts were still with 232, considering it had gone through 2 engine changes after leaving the assembly line.....)   Using these early shorter bolts with lock and flat washer and nut tightened on Yamiya LR's, i have about 3mm of the bolt protruding.  When i took receipt of my Yamiya LR's in 2006, I remember measuring the mounts, i cannot remember the width of each mount nor the combined width of both mounts..........  Nor, did i write down the width of the mount.....

What i can say, as a FACT, is what i photographed and recorded in the "Technical/Restoration Support" section of the website - http://www.cb750sandcastonly.com/support23.htm

The photos and measurements i took from a set of 3 original production LR's and 1 original production "no.no" exhaust i owned 3-4 yrs.ago.  The measurement of the muffler mount hole on the LR muffler = 55mm.  "no.no" = 58mm.  Hence, obviously the reason the early LR style exhaust use a shorter bolt, and "no.no" exh.use the longer bolt.  

I am going to assume because (on 232) i have approx. 3mm of the early bolt protruding beyond the face of the nut, the Yamiya LR's muffler mounts are the earlier 55mm thickness.......  I DO have a set of unmounted HM300's, dedicated to 2157, if Mark measures his LR mount thickness, i can measure the thickness on these HM300's.

[hondasan]

I did try to fit the HM300's to #302 with the early bolt, but would of needed to leave out one of the washers as Steve says, hence fitted the longer bolts so it at least looks right wrt the bolts.

Bolt measurements (originals from #302)

Head = 17mm A/F, 7mm thick
Plain shank = 14mm diameter x 117.5mm long to START of "mid" chamfer
Mid chamfer = 22° from axis of bolt x 3.5mm length
Thread = M12 x 14mm long
End chamfer = 22° from axis of bolt x 2.5mm long

Gives a TOTAL bolt length of 144.5mm (checked and confirmed by measuring overall length to make sure the above all "add up").

Lengths of chamfer and thread are measured as near as possible as deciding where the intersect between thread and chamfer starts ios not exact due to helical nature of thread.

If you need any more Mark, just ask.

Cheers Chris R

PS, turns out looking through my stock of silencer mounting bolts that I have THREE distinctly different lengths. The longest one is likely from a K7, which I will probably shorten as Matrk suggests to suit one of my earlier bikes.

[markb]

Chris,
Thank you very much!   Just to make sure, you are including the thickness of the head in the length?  I usually go by the convention of measuring the length under the head (except for flat heads) but no worries.  I'll post back with my results.  I'm assuming the originals also had the earlier, duller finish zinc?  Of course after machining they should get replated.
Thanks again,
Mark

Actually, looking back at your pictures, they both look quite shiny.

[hondasan]

Yes, the overall length of 144.5mm does include the thickness of the head (I agree that usual convention, here in the UK too, is for the quoted length of the bolt to be taken from the underside of the head). Using normal convention then , the bolt length is really 137.5mm.

They are shiny because they were re-zinc'd along with all the other fasteners, the original finish having grayed over the preceeding 40 years.

Cheers - Chris R.

[Steve Swan]

Mark, like i said, if you need bolts/wshrs/nuts, lemme know.  i can measure them to make sure they are what you can modify for use.

[markb]

Steve,
Do you have some later bolts that you would sell?  I'm not sure if they're available anymore but a search on ebay come up empty.  Although Yamiya has them for $28 a piece.  Ouch.  Their picture is not too good but it looks like the later style. 

[Wayne]

Mark
I believe 90146-300-020 is a good number from Honda for the low low price of 21.49 ea.  There's an ebay listing for a whole kit including the later pillion bolts.

http://cgi.ebay.com/ebaymotors/NEW-EXHAUST-HARDWARE-BOLT-KIT-HONDA-CB750-1969-76-P41-/270695372253

[markb]

I guess $66 for the kit isn't too bad if the bolts are $43 of that, but still.  I know the part number in the listing is for the later bolt but doesn't it look in the picture like it has the lower-angle chamfer like the early bolt?

[markb]

I'm confused.  Here's some pics of some bolts.  The top one is off of 5383 (although no way of knowing if it's original.  The bottom one came out of an unopened bag with part #901146-300-020.  Both should be the later bolts.  Notice the top one has the chamfers like the early bolts but it is the longer of the two, 142mm (under the head).  The -020 bolt is 140.5mm.  Also the 5383 bolt has a center drill in the end of it.  So here's my questions:
Is it possible the 5383 bolt is a fake?
Is the later bolt 3mm longer than the early bolt?

[hondasan]

Never seen a bolt with that centre drill in the end! I do sometimes wonder whether items like this (especially if NOS spares which may have been manufactured later) will have some detail variations as you observe.
Yes, the later bolt is slightly longer that the early type (pre 1001222) - about 3mm sounds right.

Cheers - Chris

[kmb69]

Mark, I believe the bolt with the center drilled end was machined from a longer bolt. The "torn/rough" finish on the long bevel and the "torn/rough" finish in the threads indicates that it was either machined on a less than ridgid lathe setup or machined at too slow of speed. It is highly unlikely (IMO) that original Honda parts would exhibit those specific conditions.

Keith