To achieve a metal to metal airtight seal is quite remarkable, and a credit to the exhaust pipe manufacturer whom created the flange, and got the angle absolutely spot on, Furness and Searle were pretty good, having the benefit of the original factory equipment I presume (now owned and used by Bob Culver) but even with their expertise I considered it necessary to use an exhaust pipe to cylinder head seal of some description.
ET: Engine (Twin) Exhaust Washers
- Thread starter Rixon
- Start date
These gaskets and flanges can be trouble, depending on perfect fits and alignment. Maybe better try some small glass fibre stove/chimney rope . No gasket at front of ex pipe, just wrap some rope under the pipe flange and screw the ex nut onto this rope. It should spread and squeeze into all free space for tight ex pipe.
Vic
stove rope 5 mm
Vic
stove rope 5 mm
I learned something ! Thank You !!
That
I think getting a metal to metal seal is more than remarkable… closer to a minor miracle. Even if the pipe manufacturer can provide consistent accuracy, all the other variables come into play. I doubt any two engines are the same. Taking an existing set of pipes, or making some with the flanges aligned is a bit of a task.
I was exchanging pleasantries with an engineer who specializes in exhaust systems. They were developing one for a V twin and long story short… they had the engine on a dyno and were using a strobe light. The cylinders were moving so much that his first thought was to flee.
Hard to say what will work better, a copper seal or something, or the glass fibre wrap around the pipe and all tightened up for practically no fretting space left. The standard nut will sit on whatever is the proudest spot on the hammered flange, so this will be one place for fretting and wear. So not a precise fit of nut on the flange. Yes, with flange sitting on recess in alu head same story , will eat into it in case when some fretting is not prevented by glass fibre. A steel shim could be added for protection instead of soft copper seal. But then, when the flange has formed a shape into the head recess it will sit quite well, plus glass fibres compressed it might last centuries. Only a test will show what´s the easiest way to fix the pipes on head with minimal troubles . I am thinking about the BMW chamfered rings for fixing pipes, worked great for more than 50 years on my 69 S . The finned ex nut could get the job as one of the rings, a 45 chamfer turned on the front face, so then only the corresponding slotted chamfer ring is required to clamp the pipe onto the head, sealing was always sufficient on BMs , so worth a try. No need to hammer a flange onto a new pipe, you will never achieve good alignment for head recess or ex nut face. So instead I would try softer material that squeezes as needed into all free space until quite solid joint - or so I guess . . .
Vic
Vic
Using the exhaust nut (with 45 chamfer) is a good idea. There isn’t much meat there so over tightening might spread the end of the flange? Not sure if that would be a concern. I think the pipe would need to be almost perfectly square to the head for it to work… certainly not much room for error.
When first try is without any flange on pipe the one chamfered ring would sit onto the end face of the recess in the head and could be made wide enough for a safe grip on the pipe, squareness not the main concern then. Just the fit will be a bit short on the pipe for looking safe. Right now I am considering having the ex nut thread a bit shorter than standard, to go with two chamfered rings, will do my own in next days. On the BMW with the alu finned nuts (lube is super critical on alu head!!) I only do them up by hand, no spanner used. Good thing is , with no copper seals not much preload is necessary on the BMs so maybe on the Vincent a bit less thread on nuts is no drama, when the chamfered design works OK with hand force only. Anyway, a good topic for discussion here, I never liked the copper seals a lot, if only for the higher preload and thread loads with them, lots of defects in that kind of threads in consequence. With BMWs you get lots of defects as well, but this is a typical case of no lube from copper grease or MoS2 paste on all alu threads, not from high torque at all. So sometimes there is a choice for you . . .
Vic
Vic
What ever method you use for the head joint, the one thing about the short stub and a sprung pipe solution (and boy can you get to the timing gears easily) is that its a long time before you have to touch it again.
Then again below that picture is an even more radical solution
Then again below that picture is an even more radical solution