Reusing Solid Head Gaskets

[bezabill]

i stil cant find a solid copper one for my star twin???

[trevinoz]

Neither can I. In fact I have never seen one for the long-stroke engine.
  Trev.

[bezabill]

do you think thay are all compiset

[BSA_54A10]

Another 2p's worth here.
If you have not done so yet google webzseums and have a look at their 1950's BSA factory promo film,
Engines rolling off the line and not a calibrated tool anywhere in sight.
The actual torque figure is a bit esoteric.
If you got 100 top mechanics to torque down the head, then measured the actual foot/ pounds on each fastener then you would have 101 different values.
What is important is that ALL THE FASTENERS ARE THE SAME , so the clamping force around the cylinder is uniform
Plus or minus a couple of pounds will make no difference, none, diddly squat, nadda, nine.
The values published are usually towards the high end to compensate for poor mechanics who do not prepare the joining faces properly.
I suppose it is a philisophical difference between the older "know the theory" generation and the younger computer & calculator generation where "the actual number is important".
All alloy motors will hold back 12:1 compressions with as little as 15ft/lbs and indeed 30ft/lbs will start to tear the threads in the alloy.
Now a cast iron head on a cast iron barrel should be able to take in the order of 80ft/lbs before you start to tear out the threads but if you have to go over 30 then there was something fundamentially wrong with the assembly.
The head bolts only have to do one thing, create a uniform clamping pressure and the  excess tension on the bolts is simply there to compensate for the bolt expanding more than the head & barrel and reducing the clamping force lower than that required to seal the combustion chamber.
Exces torque will not only stretch (& potentially break ) the bolts but will cause the head gasket to extrude into every open cavity and may in fact cause the gasket to leak.
Fire proof suit on I retire to a neutral corner.
Bike Beesa
Trevor

[beezalex]

FWIW, since there are no torque specs for A10's, I've just been using the A65 figure of 32 lb-ft since they are of VERY similar design.  Now, I realize that iron heads don't have as much thermal expansion, but the above figure should work equally well when hot or cold, no?  So, I agree with Trevor, if your barrel and cylinder faces are flat and your gasket is annealed and of uniform thickness, excessive torque can only lead to distortion and potential leakage.

[RichardL]

Well, now I am duly fearful of having a distorted and leaky head gasket. My possible solace being in the fact that some others here are also using torque values at the higher end of bolt ratings. The fact is, my surfaces may not be perfect, as I had to restore them by hand following a botched skimming job. At the same time, I have to wonder if my previous 38 ft.lbs  was the cause of the previous leaks. I need to look back at the leakage paths in the old gasket to see if there are clues.At this point, I'll go ahead and mount the rocker box so I can do a compreesion test before committing to final reassembly.

Trevor, interesting point about the lack of torque wrenches at BSA. I previously posted an article talking about the first patent dates for torque wrenches in England and it was near the beginning of A10 model life. (Can't find it now while thumb-typing on the train). On the other hand, I've also seen an article where Roland Pike appears to be talking about torquing head bolts with a torque wrench. I'll post it if I remember.

OK, my hands are falling asleep and we're arriving at the station, so, bye for now.

Richard L.

[RichardL]

Update regarding 40 ft. lbs. on a well-annealed (to the extent I could do) head gasket. Apparently, no gasket distortion causing leaks. Around 162 PSI (+/- around 2 PSI) on each cylinder after a squirt of oil to take rings out of the equation. I think I'm happy.

Richard L.