Honda CB750 Sandcast

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

markb · 26 · 8814

markb

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Good observations.  After a much closer inspection I see now that the entire length of the longer bolt is machined.  That's why the center in the end.  I can also see sprial machining marks on the head.  I think it was machined out of hex stock.  The guy must have had an early bolt that he was copying to match the angles.  Overall not too bad a job.  I guess I'll swap them for the ones on the diecast so that 5383 has the correct bolts.  Thanks guys.   
Mark B
1969 CB750 sandcast #97 restored - Sold Restoration thread link
1969 CB750 sandcaxt #576 - Sold
1969 CB750 sandcast #1553 - Sold
1969 CB750 sandcast #1990 - Sold
1969 CB750 sandcast #5383 restored - Sold Restoration thread link
1970 CB750 K0 restored - Sold
2010 H-D Tri Glide Ultra Classic (Huh?)


bojje

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Hi! I have one bike #1462 that came with short bolts. This bike also had no number original exhaust so I presume these short bolts are original. What I mean is: at least up to #1462 was short bolts used. Total lenght of the bolts is 145 mm. Regards, Bo.


Steve Swan

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Below info from website "Prod.Models." 

I'm pretty certain below info came from in later parts books.  (not the length, BUT the pn's)

Bolt, pillion step
  1 - 1221
 90146-300-010
Bolt length  146mm
 
 Bolt, pillion step
  1222 - 7414
  90146-300-020
Bolt length 148mm
 


markb

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OK, I'm confused again (sometimes not hard to do).  I think we all agree that the overall length of the later bolt (including the 7mm thick head) is 148mm.  Maybe I'm being nit picky but I thought we decided that the early bolt was 3mm shorter or 145mm (144.5 by some measurements) including the head.  I personally would go with the 145mm nominal dimension (instead of 144.5mm) because I've never seen a Honda bolt called out to a length in .5mm increments and the later bolts that I measured varied from 147.5 to 148 (typical manufacturing variation).  As long as I'm picking nits here, the correct way to specify the length of a hex head bolt is the measurement under the head.  So the correct length of these bolts should be 138mm (early) and 141mm (late) to avoid confusion.  ::)  ;)
Mark
Mark B
1969 CB750 sandcast #97 restored - Sold Restoration thread link
1969 CB750 sandcaxt #576 - Sold
1969 CB750 sandcast #1553 - Sold
1969 CB750 sandcast #1990 - Sold
1969 CB750 sandcast #5383 restored - Sold Restoration thread link
1970 CB750 K0 restored - Sold
2010 H-D Tri Glide Ultra Classic (Huh?)


Steve Swan

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I've always understood, to determine "length of bolt," the measurement is of actual shaft length; taking measurment from under the head.  (not including bolt head thickness.)  This is how i have always measured bolt lengths.  Generally, the shank is considered the "working distance" of a bolt and length of bolt is determined by shank length.

On another note, just last week, Chris and i were discussing concern for losing the thought processing how we induce, deduce, come up with conclusions for what we believe most accurate about sandcast details; simple case in point, pillion bolt length.

I can't remember where the 146/148mm measurements came from i listed in this thread from "Prod.Models."  

I know in the past, when i was restoring 232, i measured early and late bolts, i wrote it down "somehwere" and now the only place i can find the measurement is in the website.  

I know Chris and i had conversations about these lengths.  I know Chris has measured these bolts.  The parts books acknowledge different pn's ending at 1221 and beginning at 1222.  When the data listed in "Prod.Models was loaded, i loaded engine info, Chris loaded chassis info.  So, as far as length, without puling a bolt from 232 and puling a bolt from 4363, i think that's about all i can offer.  I am guessing i took the 146/148 meaurements from the Prod.Models when i was putting "88 Distinctions" together.

If i took those 146/148 measurements, they were taken starting under the bolt head, NOT including bolt head.

I guess the bottom line here is that topics such as length of pillion bolt has been discussed and we've lost the info which created confusion or having to "reinvent the wheel."  

What concerns me is losing this info, Chris says it best in his email ato me a few days ago, "Between us all, I am sure we have pondered in great detail so many of these anomalies – I still worry that our reasoning’s may gradually be lost over time. I suspect it ALL needs to be recorded somehow, and web sites are not necessarily the best way to do that given that if enthusiasm to maintain such resources wanes, or without others prepared to continue the work, they can simply be switched off and lost at some point."

I've not seen seen a center drill mark in a pilion bolt, other than Mark's and i've seen a fair number of pillion bolts.

Bo, it's probably just as difficult to explain your first hand observation of why 1462 has short bolts as it is my very distinct memory 4779 having a smooth round oil cover.  Maybe some of these differences were not as "hard and fast" as parts books say.

I just measured the bolts i am using for 2157, which i believe to be late bolts.  The shank length, measured under bolt head is 142mm.  The total length, including (7mm) thickness of bolt head is 149mm.  I took these measurements three times.

I can't remember how thick an early bolt head is.  I can't remember how long an early shank is.  Nor can i remember the difference in length between early and late bolts......  2mm ?  3mm ?  I went through all this a few years ago, and now it's seemingly lost to the ages.   (should have started that old fashioned notebook i thought of starting several years ago.)



markb

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If i took those 146/148 measurements, they were taken starting under the bolt head, NOT including bolt head.
I just measured the bolts i am using for 2157, which i believe to be late bolts.  The shank length, measured under bolt head is 142mm.  The total length, including (7mm) thickness of bolt head is 149mm.  I took these measurements three times.
No disrespect intended here but aren't you saying two different things here?  Not quibbling about the 1mm difference (I'd call 148 or 149 close enough to the same) but first you say 148mm not including head and then you say 149mm including the head.  I think the head is 7mm thick for both.
Mark B
1969 CB750 sandcast #97 restored - Sold Restoration thread link
1969 CB750 sandcaxt #576 - Sold
1969 CB750 sandcast #1553 - Sold
1969 CB750 sandcast #1990 - Sold
1969 CB750 sandcast #5383 restored - Sold Restoration thread link
1970 CB750 K0 restored - Sold
2010 H-D Tri Glide Ultra Classic (Huh?)


Steve Swan

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No disrespect taken  :)  Like i said, "i believe i've written mostly drivel confusing things more."

To try to clarify how i took the measurement:  I measured head thickness the same; 7mm.  142 = shank length +7mm head thickness = 149mm total bolt length.

"Eyeballing" the length of entire bolt with mm scale beside (parallel to) bolt, appears just a hair over 148mm. 

Laying another scale on top of (transverse to) the threaded end of bolt, with this scale (going across bolt's threaded end) to the scale measuring length of bolt, I measure 149mm.

Hope this makes sense. 





markb

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I scored on two pairs of the short pillion bolts, 90146-300-010.  You can see in the pictures that they measure almost exactly the same as Chris’s measurement of 144.5 (including the head).  The chamfer on the end isn’t quite as pronounced as the one in Chris’s picture but it is right on in every other detail including the finish.  It looks like the more dull zinc and they look like they’ve been sitting around for a while.  It definitely is not the long bolt.




Here’s a link to where I bought them if you are interested.
http://www.hondarestoration.com/nosResults.asp?models=CB750K%2CCB750K-750+Four-1969

There are three groups of parts.  Scroll all the way to the bottom of the third group.  It says he has 17 available but that’s what it said before I bought my four so who knows how many he really has.  I was tempted to buy more and try to sell them but decided to pass along the lead instead.  I bought them with Paypal and got an email confirmation right away and they arrived in less than a week even though it says they’re coming from a different supplier and may take a couple of weeks.  I don’t know much else about the seller so take it for what it’s worth.  At $14.35 each I didn’t think it was a bad price.  He also has the -020 bolt for $21.49 and has some other unavailable parts too.  I picked up a couple of the Bolt A front engine mounting bolts while I was at it.  I don’t know where he is getting his parts but this may be a good site to check from time to time.

By the way I prefer to call out the length of the bolt under the head.  Mine were closer to 145mm (including the head) so I call the -010 one 138mm long and the -020 one 141mm long.

If you’re interested, good luck.
Mark B
1969 CB750 sandcast #97 restored - Sold Restoration thread link
1969 CB750 sandcaxt #576 - Sold
1969 CB750 sandcast #1553 - Sold
1969 CB750 sandcast #1990 - Sold
1969 CB750 sandcast #5383 restored - Sold Restoration thread link
1970 CB750 K0 restored - Sold
2010 H-D Tri Glide Ultra Classic (Huh?)


kp

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Great heads up Mark and thanks. Seems someone read your post and beat us all to the stash and got the remaining 13 bolts. I suspect we'll see them on eBay soon enough.
Yabba Dabba KP


markb

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 :o  ???  :-[ Well that didn't work out the way I thought it would.  I figured there would be plenty for everyone that needed them.  I guess next time I'll just buy them all.
Mark B
1969 CB750 sandcast #97 restored - Sold Restoration thread link
1969 CB750 sandcaxt #576 - Sold
1969 CB750 sandcast #1553 - Sold
1969 CB750 sandcast #1990 - Sold
1969 CB750 sandcast #5383 restored - Sold Restoration thread link
1970 CB750 K0 restored - Sold
2010 H-D Tri Glide Ultra Classic (Huh?)