Author Topic: Exhaust bolt length for CB750 (Read 6371 times)

eelliiss · « **on:** November 16, 2012, 07:14:05 AM »

Hey, I managed to misplace my original phillips head bolts/screws for the exaust into the heads. Planning on moving to a hex. Does anyone know the exact length? 8M x 1.25 x

Thanks in advance.

MattFreeman · « **Reply #1 on:** November 16, 2012, 07:17:31 AM »

So you mean the exhaust studs?

eelliiss · « **Reply #2 on:** November 16, 2012, 07:18:50 AM »

Sure. Whatever bolts the exhaust into the heads.

eelliiss · « **Reply #3 on:** November 16, 2012, 07:24:16 AM »

Acutally, upon further review, I think that the original studs were removed in favor of an alternative. What would the length need to be for a bolt if the original exhaust stud was removed?

markb · « **Reply #4 on:** November 16, 2012, 07:24:27 AM »

On early CB750s the screw that goes into the head is an M8 x 1.25 flat head. The length is 22mm. I don't think you'd want to use a hex head on a countersunk hole and I'm not sure there would be enough room for the clamp.

eelliiss · « **Reply #5 on:** November 16, 2012, 07:27:55 AM »

Quote from: markb on November 16, 2012, 07:24:27 AM

On early CB750s the screw that goes into the head is an M8 x 1.25 flat head. The length is 22mm. I don't think you'd want to use a hex head on a countersunk hole and I'm not sure there would be enough room for the clamp.

I'm running Carpy's exhaust, so there is no countersunk hole or clamp...unless I'm misinterpreting what you are saying.

markb · « **Reply #6 on:** November 16, 2012, 07:58:08 AM »

Quote from: eelliiss on November 16, 2012, 07:27:55 AM

I'm running Carpy's exhaust

Then never mind

Mo · « **Reply #7 on:** November 16, 2012, 08:20:30 AM »

Some pictures would be helpful? Also, just a general comment, but if you at all can, use studs. They'll keep the threads in the head from wearing down over time.

eelliiss · « **Reply #8 on:** November 16, 2012, 08:28:30 AM »

Quote from: malkaysi on November 16, 2012, 08:20:30 AM

Some pictures would be helpful? Also, just a general comment, but if you at all can, use studs. They'll keep the threads in the head from wearing down over time.

No pictures at the moment, but good advice. I could've sworn that someone once wrote that the length was 35mm, so that's what I got. When I got them, they looked much longer than what I remember the original screws being. Last night, I hand tightened one of the new bolts in, and they bottomed out quite abit before the end of the bolt.

MCRider · « **Reply #9 on:** November 16, 2012, 08:32:20 AM »

Here's how it goes: The early pre-K2 or so CB750s used a flange that was held into the head with 2 flat head (taper tops) screws. The pipe then slid onto the spigot of the flange and was clamped in place with a large finned clamp.

later 75os used 2 studs out of the head and the exhaust pipe had a flange on it. The pipe was inserted into the head, the flange was drawn towards the head with nuts on the studs.

Often the early style is converted to the later style to accept an aftermarket exhaust pipe.

On the later style, bolts can be used instead of the stud/nut affair.

eelliiss · « **Reply #10 on:** November 16, 2012, 08:46:44 AM »

Thanks for the reply. I guess I'll try the 22mm and see how that works.

markb · « **Reply #11 on:** November 16, 2012, 08:58:31 AM »

Quote from: eelliiss on November 16, 2012, 08:28:30 AM

Last night, I hand tightened one of the new bolts in, and they bottomed out quite abit before the end of the bolt.

Then measure the gap under the head, and a mm or two and subtract that from 35mm. That will get you real close.

eelliiss · « **Reply #12 on:** November 16, 2012, 09:11:37 AM »

Quote from: markb on November 16, 2012, 08:58:31 AM

Quote from: eelliiss on November 16, 2012, 08:28:30 AM
Last night, I hand tightened one of the new bolts in, and they bottomed out quite abit before the end of the bolt.
Then measure the gap under the head, and a mm or two and subtract that from 35mm. That will get you real close.

That would make way too much sense.

MattFreeman · « **Reply #13 on:** November 16, 2012, 11:35:10 AM »

For my 76 F I'm using 60mm allens with a nut between the flange and the bolt head to tighten the header to the head. Sounds like mine might use a longer bolt but the principal could be used anyhow and would put less stress on the head.

kmb69 · « **Reply #14 on:** November 16, 2012, 11:56:55 AM »

They are available in socket head countersink for the spigot type exhaust. Example:

http://www.ebay.com/itm/HONDA-CB750-EXHAUST-BOLTS-NEW-STAINLESS-CB-750-CAFE-8-/370620058683

Probably available for less money from a standard fastener source.

eelliiss · « **Reply #15 on:** November 16, 2012, 12:09:24 PM »

Thanks for being such a helpful bunch! Among the best guys of any forum I've been on. Be prepared for more silly questions in the future, dudes.

Thanks-a-million!

nobody · « **Reply #16 on:** October 11, 2016, 10:35:11 AM »

Why would using countersunk bolt heads be a bad idea?

I'm looking to run Cycle X exhaust and far as I can tell I need bolts 1/2 inch longer than stock.

flybox1 · « **Reply #17 on:** October 11, 2016, 10:42:23 AM »

Quote from: eelliiss on November 16, 2012, 07:27:55 AM

Quote from: markb on November 16, 2012, 07:24:27 AM
On early CB750s the screw that goes into the head is an M8 x 1.25 flat head. The length is 22mm. I don't think you'd want to use a hex head on a countersunk hole and I'm not sure there would be enough room for the clamp.

I'm running Carpy's exhaust, so there is no countersunk hole or clamp...unless I'm misinterpreting what you are saying.

Convert to studs, and draw the exhaust to the head with washers and flange nuts.
Less of a chance stripping the bolt holes with repeated exh removals for oil changes

754 · « **Reply #18 on:** October 11, 2016, 11:01:31 AM »

Or leave flanges on and have 3minute removal for the whole header.

flybox1 · « **Reply #19 on:** October 11, 2016, 11:10:15 AM »

Quote from: 754 on October 11, 2016, 11:01:31 AM

Or leave flanges on and have 3minute removal for the whole header.

I think he's running carpys yosh replica, Frank. But yeah, thats an easy removal.

70CB750 · « **Reply #20 on:** October 11, 2016, 11:13:37 AM »

+1 on studs. Steel stud in the engine eliminates repeated loosening/tightening steel - Aluminum.

754 · « **Reply #21 on:** October 11, 2016, 11:03:09 PM »

So does the spigot, it never gets loosened.

pjlogue · « **Reply #22 on:** October 12, 2016, 03:48:47 AM »

I used these: https://www.nutty.com/search.asp?keyword=XMFSC825

Use antiseize on the threads. Length was a little longer than the original bolts but had plenty of leeway in the hole.

This company is a great source of stainless hardware and price is very low compared to your neighborhood hardware store for metric stainless.

-P,

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Author Topic: Exhaust bolt length for CB750 (Read 6371 times)