Topic: Rear Lower Engine Bolt

[Ellz10]

I have scoured the interweb and I cannot seem to find the rear lower engine bolt - part # 90155-392-000.

It's for my '77 CB750 K. I understand it's used across many other years.

I'm curious if anyone knows if I'm able to interchange other earlier models K0-K6 with their bolts with threads on both sides or if those are too long/short.

[RAFster122s]

Partzilla can be used to figure out the other models where that bolt's part number was used...
You may need to have a machinist make you a new bolt as most bolt houses simply won't make any long enough in that size. Ran into that with a bike I own and the corrosion was enough on the stock bolt to need another. The rod stock was threaded and then a chunk of steel welded to the other end and then cut to the proper hex shape and end dressed.
A good machinist can whip one up in about an hour if he also welds...
You need the specs of the total length, threaded length, length from underside of hex to start of threads. Thread pitch and size of course...

[Ellz10]

Partzilla can be used to figure out the other models where that bolt's part number was used...
You may need to have a machinist make you a new bolt as most bolt houses simply won't make any long enough in that size. Ran into that with a bike I own and the corrosion was enough on the stock bolt to need another. The rod stock was threaded and then a chunk of steel welded to the other end and then cut to the proper hex shape and end dressed.
A good machinist can whip one up in about an hour if he also welds...
You need the specs of the total length, threaded length, length from underside of hex to start of threads. Thread pitch and size of course...

Dang. Well I'm hoping that's a last resort and someone has one off a parts bike 🤣

[bryanj]

You could cheat and use threaded bar with a nut at each end, only you will know

[newday777]

You could cheat and use threaded bar with a nut at each end, only you will know

Threaded rod is pretty soft metal, not much strength to it.

[MauiK3]

None at Yamiya?
Also, if you look, there is higher grade threaded rod.

[Stev-o]

I might have one, do you know the dimensions?

[MauiK3]

try this

https://www.yamiya750.com/index.php?main_page=index&cPath=246_251_185_114

[Jerry Rxman Griffin aka MuthaF'er]

The -392 in the part number indicates this is a 75/76 CB750F part which could also be used on the 77/78 CB750F. If I was at home, I could check my parts cave for you. Reach out to the F community also.

[BenelliSEI]

I’ve got a box full of them. Post the diameter and grip length (outside frame face to outside frame face) you need and I’ll check. John D.

[Ellz10]

I might have one, do you know the dimensions?

I’ve got a box full of them. Post the diameter and grip length (outside frame face to outside frame face) you need and I’ll check. John D.

14" long
19mm (3/4") socket head
12mm stock diameter
Thread length is 19mm long

[BenelliSEI]

It’s so darn cold here I might not get to the shop for a couple of days. Dimensions noted, will check.

[Stev-o]

I might have one, do you know the dimensions?

I’ve got a box full of them. Post the diameter and grip length (outside frame face to outside frame face) you need and I’ll check. John D.

14" long
19mm (3/4") socket head
12mm stock diameter
Thread length is 19mm long

Sorry. I dont have that one.

[scunny]

In a pinch, I would use threaded rod, it clamps the motor, not a stress carrier.

[Ellz10]

It’s so darn cold here I might not get to the shop for a couple of days. Dimensions noted, will check.

Okay, thank you!

I might have one, do you know the dimensions?

I’ve got a box full of them. Post the diameter and grip length (outside frame face to outside frame face) you need and I’ll check. John D.

14" long
19mm (3/4") socket head
12mm stock diameter
Thread length is 19mm long

Sorry. I dont have that one.

No worries Stev-o! Thanks for looking!

In a pinch, I would use threaded rod, it clamps the motor, not a stress carrier.

Last resort I'll probably do it this way. But not if I can find the oem bolt.

[BenelliSEI]

I’ll look today.

[seanbarney41]

I remember one time I was trying to concoct some home brewed rearsets for my 76k.  Somewhere on here, someone posted that you can use an F lower motor mount bolt to help hold rearset mounting plates as it is longer.  So I bought one from an F being parted.  Nope, functionally the same as the 76k.  No idea if I was sent an incorrect part, or if that is just untrue.  It may be possible that all 750 lower mount bolts are functionally the same and Honda changed the part number for some other nebulous reason, perhaps plating type?

[MauiK3]

If you run out of options here is some threaded rod. I notice they have a lot of grades including 10.9, high strength.

[MauiK3]

Oops, forgot to put the link in!

https://www.grainger.com/search/fasteners/threaded-rods-studs/fully-threaded-rods-studs?attrs=System+of+Measurement%7CMetric~~Thread+Size%7CM12-1.25%7CM12-1.75&filters=attrs&searchQuery=trapezoidal+threaded+rod&sst=4&tv_optin=true

[69cb750]

I remember one time I was trying to concoct some home brewed rearsets for my 76k.  Somewhere on here, someone posted that you can use an F lower motor mount bolt to help hold rearset mounting plates as it is longer.  So I bought one from an F being parted.  Nope, functionally the same as the 76k.  No idea if I was sent an incorrect part, or if that is just untrue.  It may be possible that all 750 lower mount bolts are functionally the same and Honda changed the part number for some other nebulous reason, perhaps plating type?

I was trying to avoid going into the cold garage to investigate this matter ...
On the 77F there are aluminum brackets which hold the rear foot pegs, brackets look 1" thick, guessing 77F bolt is 2" longer.

[BenelliSEI]

I found one in my bin. 12 mm diameter, both the bolt head and nut take a 19 mm wrench. 14” OA length. Threads are good, but the threaded end has a slight bend.
Easy to straighten with a press or a BFH.

[seanbarney41]

I remember one time I was trying to concoct some home brewed rearsets for my 76k.  Somewhere on here, someone posted that you can use an F lower motor mount bolt to help hold rearset mounting plates as it is longer.  So I bought one from an F being parted.  Nope, functionally the same as the 76k.  No idea if I was sent an incorrect part, or if that is just untrue.  It may be possible that all 750 lower mount bolts are functionally the same and Honda changed the part number for some other nebulous reason, perhaps plating type?

I was trying to avoid going into the cold garage to investigate this matter ...
On the 77F there are aluminum brackets which hold the rear foot pegs, brackets look 1" thick, guessing 77F bolt is 2" longer.

yeah, but don't forget that on earlier bjkes that bolt holds the chunky footpeg brackets which are at least 3/4"

[scottly]

I might have one; if I do, I could ship it with the frame kit?

[JohnnyL]

I would use grade 8 threaded rod and be done.

My.02

[Ellz10]

I found one in my bin. 12 mm diameter, both the bolt head and nut take a 19 mm wrench. 14” OA length. Threads are good, but the threaded end has a slight bend.
Easy to straighten with a press or a BFH.

Thanks so much for going out to look! The bend on yours is much more minimal than the one on mine! If Scott ends up having one that isn't bent at all, I'll probably just ask him to ship it with the frame kit I'm snagging from him.

I might have one; if I do, I could ship it with the frame kit?

On that note: Absolutely Scott - if you do have one and it's not bent at all, I'd be very interested and happy to snag it from you when you send the frame kit. Speaking of which, I never got a reply to the DM I sent ya! Or maybe I did, it just didn't show up. I'll have to go look.