Exhaust gaskets at the head reusable?

[GS1000G Shopper]

It occurred to me I can figure this out with what I have. I did some measuring today using the flanges from the pipes and one of the 8mm bolts. The flange is about 26mm thick. The bolt when inserted into the flange sticks through about 16mm. The hole in the head is deeper than this which is why the Advance Auto studs were too short. EDIT, I measured them and they are 20/8/22 with a 4mm hex extension, see below for what these numbers mean. I added a nut and lock washer to the top of the bolt to simulate it installed and got 35mm. Putting 35mm together with 16mm, I got 51mm, hence my original number.

Studs are sold either fully threaded, equally threaded, or unequally threaded. Our ideal stud would have a 16mm threaded side along with say a 20mm side, with the rest being unthreaded.

I checked McMaster, who give tech drawings for almost everything they sell. The closest one I saw was a 50mm broken down as 12mm and 20mm threaded, which left 18mm unthreaded (looking from the head, it's 12/18/20). It's part # 93210A030 and sells for $2.41 each. There was an equal length 50mm one with 20mm threaded on each end, but when it was scaled out in a diagram (attached) it was also too short.

I also looked at the next size up equal length, 65mm (20/25/20), and it stuck out too far from the head. The next size up unequal length, 60mm (10/28/22), either had less in the head (10mm) or did not leave enough threads past the flange when the 22mm side was put into the head.

Like most things in life, it's a tradeoff. The unequal length stud sticks out far enough to engage the nut is not as deep in the head, while the equal length one goes into the head further but does not stick far enough out to engage the nut.

Hope this helps.

EDIT #2
I re-checked the 50mm studs from 034 motorsports ($3.75 ea). They are listed as 16/10/21 with a 4mm hex, for 50mm overall. I scaled them in my diagram and if you use the BMW nuts (no lockwasher) they should be very close to a perfect fit for the GS (thread still not fully engaged). They have the benefit of the hex to install them, but cost a little more than the McMaster ones.

The AP Tuning studs and nuts ($16 plus shipping) look like the best fit and value when you factor in shipping cheaper nuts. They are stated as being .5/.25/1.25 for 2" OA length. In metrics, this is 12.85, 6.4, and 32.1. I've updated the diagram.

[Nessism]

Sorry to say but I don't think you are analyzing this correctly because the bolt holes are not in plane with the exhaust port exits. Plus, you have the thickness of the exhaust gaskets to consider.

Do you have any old exhaust bolts left? If so, measure the overall length, including the head on the bolt, add another 10mm and that should be the length you need. Am I missing something?

[GS1000G Shopper]

Good point about the gaskets. I did use one of the old bolts to measure past the flange, and I think your math should put it within range.

If anything, the studs could stand to be on the long side since my diagram shows the Advance Auto studs sticking out slightly. When I installed them (note: with gaskets in place), they were flush. This means the only ones that would work properly are the McMaster 50mm unequal or the AP Tuning ones. Possible fits due to this include the McMaster 60mm unequal length, which puts 22mm into the head (I don't have a head to measure for thread depth).

EDIT
Found this on my earlier post in this thread:
For reference, the OEM bolt is 8mm x 1.25 pitch x about 50mm long (with the head)

Adding 10mm gives us 60mm. The most secure fit would be the McMaster 60mm unequal length studs, assuming they fit all the way into the hole w/o bottoming.

[GS1000G Shopper]

I ordered both 45mm and 50mm studs from Allen's Fasteners (prices with shipping were good and shipping was quick), plus some flange and locking nuts (8 each, I was shorted 4 of the 45mm studs). These studs will go 10mm into the head.

I'm attaching a side-by-side photo of them with the Advance Auto Parts 56mm stud. I tried cutting some more bottom threads on one of the 50mm studs but only got another 1.3mm according to my caliper.

I should find out the status of my cylinder head this Friday, so I'll have more info soon.

[GS1000G Shopper]

The head is home, a $45 repair. Only problem is he drilled & tapped the hole for a 7mm thread (I was sure I said I'd do this, hence the low price). Repair looks good, and after test-fitting the 45 & 50mm studs with pipe, retainers, and packing, the 50mm is the one to use. I'd like to have more than 10mm of thread into the head, but am hopeful they will do the job.

[Roostabunny]

Alleluia, praise be, and thank you for this thread!!!

Been searching and searching for an authoritative thread concerning exhaust flange studs... specs, how to calculate what I need, where to buy... Woohoo! And the dang links still work! Double woohoo!

GS1000G Shopper, you're my new hero.

[Roostabunny]

Hey as long as I'm riding the wave of all your research, measurement, and documentation, any of you guys know if these same measurements might apply to an '81 GS850? Is your exhaust stock?

Thanks again!

[GS1000G Shopper]

Thanks. Donations can be sent to...

I like to write tech threads so guys like you can come along months/years down the road and get some help.


The one thing that really upsets me when I have a vehicle problem is to find a posting of someone having the same problem & then posting "Hey, I fixed it." with no solution offered.

/ soapbox

I'd look at an online parts listing for the 850 & 1000 to see if the same part # is used for both bolts (presuming they're still available). If so, it's a fairly safe bet the above would work.

[afholderman]

So after reading this thread I checked out allen's fasteners, and they have a 65mm stud available. In your previous post you lamented that you would like more than 10mm of thread available, so would you in turn suggest the 65mm over the 50mm?

[Roostabunny]

OK, here's the scoop -

GS850GX Stock flange bolt -
1807056 (465651-001)

GS1000GX Stock flange bolt -
1019880 (465653-001)

So the bolts are not the same, I think the number in parentheses is the Suzuki part#. However, does anyone read Suzuki Partnumber-ese? Could these be a 51mm vs a 53mm bolt?

Meanwhile, for what it's worth, the exhaust gaskets ARE the same.

GS850GX Stock exhaust gasket -
1052343 (484407-001)

GS1000GX Stock exhaust gasket -
1052343 (484407-001)

And a side question - the purpose of the copper nuts is... because they're locking? Single-use, deforming, like a crush washer?

[afholderman]

And a side question - the purpose of the copper nuts is... because they're locking? Single-use, deforming, like a crush washer?

Self locking and being that they have different expansion rates than ferrous metal and are corrosion resistant they won't seize.

[GS1000G Shopper]

So after reading this thread I checked out allen's fasteners, and they have a 65mm stud available. In your previous post you lamented that you would like more than 10mm of thread available, so would you in turn suggest the 65mm over the 50mm?

I'm neck deep in 25 year old Honda gauges now, so I had to re-read my post & look at my original diagram, and then look at what Allen's has. They list the 65mm as an M8x1.25 x 22 and M8x1.25 x 10, so the threaded parts are no different. The length is made up in the unthreaded portion. Reversing the 65mm stud on my diagram so you could run it another 6mm into the head, and you'd have no threads to attach the nut to. The 65mm also would not work since it would be too long, as I recall there is a clearance issue due to the down tubes on the frame.

I've had zero issues with the Allen's 50mm so far, and use the bike at least once a week.

OK, here's the scoop -

GS850GX Stock flange bolt -
1807056 (465651-001)

GS1000GX Stock flange bolt -
1019880 (465653-001)

So the bolts are not the same, I think the number in parentheses is the Suzuki part#. However, does anyone read Suzuki Partnumber-ese? Could these be a 51mm vs a 53mm bolt?

I looked at my Suzuki parts place & got this for the bolts into the head (they're in the muffler section):
'80 & '81 1000G:
BOLT
01500-08453 (replaces 01107-08458)

'80 & '81 850G:
BOLT
01500-0835B (replaces 01107-08358)

I looked at an '81 650G as well:
BOLT
01500-0840A (replaces 01107-08408)

My guess would be it is a slightly shorter length. I don't get the part number system at all. Honda sometimes gives dimensions, and yet labels identical parts w/ different numbers- i.e. the sender gasket on my Sabre is 39 x 5mm, which is the same as the newer VFR800. The parts listings show identical dimensions & the senders bolt up exactly the same w/ the same pattern, yet the gaskets carry different part numbers.

Allen's fasteners are dirt cheap- I'd suggest buying a set of both 45 & 50mm like I did & using whichever one fits best.

[5azzmonkey]

For reference, the OEM bolt is 8mm x 1.25 pitch x about 50mm long (with the head). The hex is 12mm, and the lock washer under it is about 14mm.

Results:

Set of 16 BMW studs (unknown thread size & length) and copper nuts, $35. Studs have internal 3mm hex for installation.

I just called turnermotorsport.com and they said the studs were M6x40 so they will not work on our GS's