Head gasket blown

Hi,

Just got my head back from the shop after having new valves put in and the head cleaned.
I used a new composite head gasket and tightened the head down, torqing the 4 bolts I could get to and guessing for the other 6.

The bike started and ran quite well so I went for a run around the block and tuned the carbs a bit. On a second run there was a big bang and a saw a piece of the head gasket hanging out near my knee.
The engine stopped so I pulling in the cluch and coasted to a halt.

Was it a simple torquing problem. I will take the head off and see if there is any other damage.

What did I do wrong to cause such as catastofic gasket failure. ? Should I consider using a Copper gasket ?

Regards,
Sean

There should be no problems holding a composite gasket if the head and barrel is flat. Retorquing several times is needed but it sounds like yours didn't last long enough to get to the retorquing stage. So it was either not torqued right or it was not flat. A copper gasket will not cure either of those problems. Jim

For what it's worth you can get a torque wrench onto the front three recessed bolts by putting a long box spanner onto them and using a socket on the top of that.

This is how I torque those three bolts.

pommie john said:

For what it's worth you can get a torque wrench onto the front three recessed bolts by putting a long box spanner onto them and using a socket on the top of that.

This is how I torque those three bolts.

Click to expand...

For those who don't know this already, check out CNW website, Matt sells a kit of lovely ARP 12 pointed fixings for the head, and also one for the base studs. With this head kit, its really nice to be able to use proper sockets and a proper torque wrench and not have to faff around with box spanners. Well worth considering IMHO.
And the base studs are also far more sensible... you can fit the nuts AFTER the barrel is seated on the cases. Can anyone tell me why the OEM nuts and studs are so long? Its like they were designed to be a pain in the ass, but I'm assuming I'm missing something here!?

Fast Eddie said:

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And the base studs are also far more sensible... you can fit the nuts AFTER the barrel is seated on the cases. Can anyone tell me why the OEM nuts and studs are so long? Its like they were designed to be a pain in the ass, but I'm assuming I'm missing something here!?

Click to expand...

If you wind the nuts off up to the top of the studs you can break the gasket and lift the barrels . Saves whacking them with a soft hammer.

I had the exact same problem a few years ago after replacing head and barrel.
Turned out that the cylinder head was perfectly flat but the barrel wasn't (750 cast iron). Had it skimmed and never had the problem again.

Hi,

I had the head checked for flatness when the valves were changed. The flatness of the barrel is unknown.

i will put a straight edge on it when I get the head off again.

I think I will just have to try a new gasket and be very careful with torquing next time.

Thanks,
Sean

What you might consider is removing the 3 studs in the barrel and running a new flat file over the stud holes.
My head leaked at the front until I did that. They were raised a bit. Then I smeared a little bit of silicone on the gasket, both sides, around the push rod tunnels and drain hole. Not a leak in 3 years so far.
As for torquing goes. On initial start up you should only get it to operating temp and not ride it, let it cool over night and retorque it.
Ride it easy for 50 miles and retorque the next day.
I retorqued it 5 times, once before each ride.
Seems to be fine and worth the effort.
Of course being flat is where it's at if you know what I'm sayin'

Whilst I fully intend to follow the program stated here: running the bike without riding, leaving overnight before re-torque, ride 50 miles and re-torque, ride 100 miles and re-torque, etc, etc... what I struggle to understand is how the factory managed?
There is obviously no-way any factory could productionise such a routine, yet it wasn't standard practice for all Commandos to blow a gasket leaving the showroom.
So, what did the factory do?
And why can't we just do the same? Why do we have to do something so different and complex?

From the factory the parts were brand new and flat.
Were they ever started and run in first? I don't know but I bet they were and retorqued and then required them to be retorqued by the dealership after a set amount of miles.
I'm just speculating.

Did the bikes come from factory with a composite or copper gasket?
Copper does not require retorquing so it would solve that problem for the factory, tho I could not get copper to hold, while the composite has been fine.

Glen

Player 3, if others of well known fame have not had similar events then the reflex opinion you'll get here will be "it was you own damn fault". My Trixie Combat blew a composite, aka - Flamering, out the oil drain weak spot in 15 miles on legal commute to work and almost jetted through fuel line. I had good success with prior flamering on Peel but they were made much better than the one that blew. Good flamerings had dense composite with a powdery silver adhesion coating both sides and almost solid metal rings. The weak one was more brownish and not as dense composite and only foil thick folded over metal ring instead of more substantial metal. I am not timid to max out head fastener torque so lack of clamp force was not the issue or fault of my own but was a bad item gotten from Anover. I've went back to copper with is harder to keep sealed as too timid to try the spare flamering still in bag with label on shed wall. I'm in process of resealing Trixie from air boot cracks grit making ring blow by so will try a flamering again before swearing off and at suppliers.

You don't want to over torque the head bolts as the torque increases considerable when at operation temps due to the expansion of the alloy.
I build stroker VW engines as a hobby and the head torque is 23lbs.
When at temp the head torque is around 60 lbs due to expansion.
Hobot is right about the quality of the composite these days.
2 flat planes and a tiny smear of silicone around the holes is what has kept mine right for the past few years.
Just keep the silicone away from the holes edges so it doesn't ooze out into the holes.

Care should be taken when fastening the head to begin with. Bringing the fasteners up evenly and gradually is key, particularly with the soft composite gaskets. If you get a little off kilter, one side will over squish and will never be even. This also applies with a fresh soft annealed copper gaskets.

Being able to get to all fasteners is imperative. Get the proper sockets and extension.

Fast Eddie said:

Whilst I fully intend to follow the program stated here: running the bike without riding, leaving overnight before re-torque, ride 50 miles and re-torque, ride 100 miles and re-torque, etc, etc...

Click to expand...

That's what I do.

But I do not have the definitive answer about cleaning the threads, should they be lubricated?, back off and then retorque? etc etc

If the gasket is faulty such as too weak construction or copper not soft enough it don't matter how well you torque and re-torque so leaks and blow outs will make you and others think your not up to working on a real man's motorcycle. Of course surfaces must be fairly flat faced to each other to begin with. Also if ring sealing not up to snuff that will also tend to over come the best torque attendance too. Its good practice to run the fasteners in and out to chase threads and I like anti-seize so most the torque goes into bolt stretch not bolt twist, plus its just the torque clamp force that hold these fasteners tight not thread glue as crush down of gasket and metal strain relief can occur w/o any fastener twist occurring and when time to open up again [ugh] i worry more about shearing off head corners or bolt shaft as i've had happen in other air cooled engines the bolts got rusted in place. Short of pulling out threads too loose fasteners in engines cause more damage than exceeding Norton torque values a little bit.

pommie john said:

For what it's worth you can get a torque wrench onto the front three recessed bolts by putting a long box spanner onto them and using a socket on the top of that.

This is how I torque those three bolts.

Click to expand...

I appreciate the picture, but what are the two parts, and where is the source of these parts?

I MUST BE LUCKY.I have never had the misfortune of using a gasket like described. Nor have I ever blown a gasket [ apart from something stupid going wrong at home ]. When I blew my pistons on my 850, I quickly stripped it an ordered new ones. But I forgot to order a new head gasket. Didn't have time to stuff around so applied an appropriate amount of silicone on both sides of the gasket and refitted the head .[ according to Norton specs. ] I am a mechanic [ and just like Evil Knevil or whatever he called himself, DONT TRY THIS AT HOME ] I am not going to tell you how little of the silicon I used. Someone might have a smart comment to make. I even discovered the 2 studs under the exhaust ports are pulling out [ lost both nuts ]. Fitted new nuts and found this problem, so drilled holes in them , refitted them and wired them to the fins to stop loosing them again,..
The point I am making is use the right materials and do things the right way, and all will be well.
I don't retorque used gaskets though.
I've been to 3 rallies [ bugger missed one though ] since then and no problem with engine oil leaks where I have done work on the enginge. Havn't split the cases on this one so have to admit, there is a weep from the crankcase halves.

have a nice day

plumbers crack? Only 1st one is mine & can't find my blow out photo but others seem to had similar.

I THINK I WOULD THROW MYSELF AT THE GROUND IF I FOUND THIS IN MY BIKE. LOOKS LIKE CRAP GASKETS.