Exhaust bolt torque

[bill_face]

THE ANSWER IS 19Nm or 1.93kg/m IS TOO MUCH. I wouldn't recommend going above 1.6kg/m or 11.5ft/lb or 15Nm

Hello. I have a '79 GS550. I threaded one of the exhaust manifold bolt holes, so having heli-coiled it, have done them all up pretty gingerly since. The trouble is there are quite a lot of fumes coming out from the manifold outlets. (I'm not sure if manifold is the right word, but i mean the bit where the exhaust connects to the engine).

I had a look through the torque specs and couldn't see any for these bolts, and went with the generic bolt diameter torque.

Just incase I'm missing a part/seal of some sortI have: circular metal bits (seals of some sort?) (they were new ones with an engine rebuild kit) that sit in the engine ports, then the exhaust goes into the ports, then there are the brackets that tighten the exhaust onto the engine, using a lip on the exhaust. These lips don't touch the engine. I'll attach a photo.

I'm guessing more torque might squash up the internal metal bits such that the lips would touch the engine. But I don't want to threat any more holes as I've got the engine back in the bike and the frame would prevent some heli-coiling.

Any advice???

I hope it all makes some sense.

 

[bill_face]

Here is a pic of the internal bits I was mentioning:


I noticed on ebay they sell fibre seals. Is that what I'm missing?

 

[BigD_83]

It looks like the collar is sitting at a jaunty angle, top to bottom, and the top is not pushing on the shim.

What happens if you flip the bracket (collar) around 180 degrees? Will it still line up with the bolt holes?


I seem to recall something funky about the ones that came with an exhaust off a 650GL that didn't properly match up to my 650G.

 

[Guest]

The clamp doesn't need to sit snug against the head. But you do need sufficient torque on the exhaust bolts to compress the gasket and form a seal. If you can't find a torque specification, and they're still leaking, I would tighten the bolts a little more - just 1 lb/ft maybe. Test and repeat until you have all four sealed.

 

[standswithabeer]

there is sometimes a balancing act between getting the exhaust collar flat against the cyl, whilst having the exhaust muffler mounting bolts line up. maybe focus first on getting the collar flush with the cylinder while making sure the "gasket" is centered. it's been my experience that some shuffling of the entire assembly may be needed to have the rear mounting holes line up while the collar is flat against the the cyl. there is some play where the headers meet the exhaust can, just under the footpegs. i'd start by having the collar flush with the nuts snugged a little, with the middle joint and rear mounting bolts loose. then start tightening from front to back.

if the seal doesn't compress sufficiently while you're attempting to correct misalignment as shown, you can easily pull the stud from the aluminum cyl.

it's possible someone in the last 40 years has installed the system not perfectly lined up.

 

[Steve]

Before installing the new gaskets, did you verify that any old gaskets had been removed? :-k

It's easy to miss the old gasket, it simply looks like a mounting ledge for the new gasket.

.

 

[bill_face]

Thanks for the replies. I'm going to try refitting it. When I first got it running I remember it smoking from the front end, but then it seemed to go away. But maybe it just reduced. You can't really see the fumes in daylight, but you can smell them. At night you can really see them coming over the headlight.

I did remove the old gaskets when I rebuilt the engine, but some of them were really stuck in, and I had to use a chisel to split them to get two out. Hopefully I haven't done more harm than good.

StandsWithBeer I'm sure the answer is in your post, but I'm not entirely sure I understand it. I think this is because my exhaust doesn't seem the same as what you are describing. I only have one mounting point under the muffler. I'll attach a pic, maybe someone could shed some light on what exhaust I've got.

 

[standswithabeer]

didn't realize you have aftermarket exhaust, is there any any adjustability where the individual headers meet the collector?

 

[Nessism]

Before tightening up the head bolts you need to loosen the muffler hanger in the back so the entire system can slide backwards and crush those donut seals. The fact that the flange is sitting at an angle is evidence that there is uneven alignment of that pipe into the head so that needs to be corrected.

 

[Guest]

It's a Motad system. The downpipes are seperate from the silencer, so theoretically there is the possibility of adjustment. In practice, every one I've seen is corroded in that area, and you would most likely damage it if you tried to dismantle it. Go with what Ed said - loosen the rear mount, ensure a good flush fit at the head, and tighten from there.

 

[Nessism]

Those flanges will not sit flush with the head. They always stand proud a ways and that's okay. They should have an even gap all around though, that's the part that needs to be addressed.

 

[bill_face]

Thanks for the help guys. I've fixed it now. I started by giving the bolts a bit more of a crank, and discovered that the bolt holes start threading at 19Nm or 1.93kg/m or 168 inch/lbs.

So I then took it all off heli-coiled the stripped holes and propped the exhaust up on some brick rather than attaching the mounting bolt. I then torqued it up to 11Nm and it has stopped leaking.

 

[Grimly]

maybe someone could shed some light on what exhaust I've got.


View attachment 56837

That's a Motad.