ET: Engine (Twin) Piston Ring Location & Head Nut Torque

[Rob H]

Quick question - is there any convention for the location of the gaps in the piston rings when replacing the barrel.
The initial thought was to gap the top ring to the rear of the barrel ant the others at 120 deg apart?

Also anyone have any recommendations for how tight the head nuts should be?

regs

 

[passenger0_0]

As I understand it the rings can slowly wander around their grove as, unlike a two stroke, there is no peg to locate their position. Staggering the groves on assembly as you describe is probably more important. I'd be interested to hear other opinions on this topic.

I'm sure you're up with the play regarding the need to lap in the cylinder liner/head sealing faces and muff/head contact faces with different grades of grinding compound?

I have always torqued the cylinder head to 30 ft-lbs when using the one piece head studs and never had a problem. This figure might even be a little high but what is clear is that the cylinder heads simply won't take any more without serious negative consequences. I've not yet had the pleasure of tightening the early two piece system as my Old Series B Rapide just keeps on going (a good thing). Thinking to the future however I would welcome any advice on the torque required for both the cylinder head tube nuts and inner stud nuts for early motors.

 

[vibrac]

Head nuts Lots of referrals to this on the forum
OIL LEAK FROM COMET HEAD WHEN COLD is a good example
as I said there, my take is 32ft lbs it's about the only time I use a torque wrench on a Vincent

 

[greg brillus]

It is all to common to find pistons who's ring gaps are in alignment. I set them up with the gaps set just aft of the center-line of the gudgeon pin and alternating left and right, or as close to 180 degrees apart as you can. Head torque as mentioned 30 to 32 Ft Lib's, make sure you lubricate the threads with grease or anti-seize as some of the newer stainless head nuts can tend to grab on the studs and give a false reading. After the bike has been for a good run around the block and allowed to cool overnight, retorque the heads........ One at a time,.back off each head nut and use a good "Rolling torque" bringing the nut fully down to the correct figure, use a spring scale and an open end spanner to do this. Or else use the spanner on it's own and pull each nut down by an amount not quite as much as from 12 o'clock to one o'clock on a clock face. This with a single paper cylinder base gasket used under the barrel. Recheck the tappets, and nip up the pushrod tube gland nuts, plus the exhaust pipe finned nuts, and you should be good to go. Remember to retighten the cylinder head bracket nuts and lock nuts as well. These need to be backed off so there is free movement to adjust the cylinder head nuts on their own. Cheers.....................Greg.

 

[roy the mechanic]

I would go along Greg's route, just make sure you don't have any ring gaps on the thrust side (that is where the oil hole lies) or you may have a "smoker"