Hi,
As you will probably know I wrench on engines once in a while, and things that are obvious for me, aren't apparently logical to others (and probably the other way around).
This is also the case with re-torque the cylinder head cap nuts.
The reason of blowing gaskets, just after a rebuild, could be due to not re-torquing the head.
After assembly of the head the bolts should be put to the specified torque. After the first cycle (a short ride, cold, warm, cold) the head should be re-torqued.
It seems to be a lot of work (it is !), but it is absolutely necessary.
I re-torque the head twice, once as described above, and again after 200 - 500 miles or so (after the first long highway ride).
I've never experienced a blown head gasket (with CB72 / 77 's) but I don't know if this is due to the method I describe.
(I assemble the head nuts with a mixture of copper grease, graphite and a few drops of oil, and before re torque I lose the nut a bit (no more then 1/8 turn), and then set to the specified torque, this is done in the same sequence as described in the manuals, thus a cross pattern from the inner to the outer cap nuts),
Jensen
re-torque head (cap nuts)
re-torque head (cap nuts)
Last edited by jensen on Thu Sep 23, 2010 7:21 am, edited 1 time in total.
assembly of Japanese motorcycles requires great peace of mind (Pirsig)
Indeed Steve,
BTW, an error has occurred in the info about the torque specifications. When lubricate the cap nuts, the torque values should be between 10 to 20 less then the specified torque. The specified torque is specified as dry (not lubricated), I messed up becuase I "translated" the specified torque already to lubricated torque, Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
head torque and re-torqueSo if I understand you two correctly, after say 500 break in miles, the engine should be removed again and a re-torque of the head bolts is necessary correct?
Any one else wanna step up with their opinion? This is a good subject as I just put back on the road today my CL after a complete tear down and top end rebuild. Thanks, Mike
Hi,
Most important is the re-torque after the first cold - warm - cold cycle (re-torque when the engine is cold). When running the engine for the first time, everything "sets" and therefore re-torque is necessary. I'm sure the engine is not to be removed, as all cap nuts are accessible (don't forget the nuts below the spark plugs, For your convenience, just don't add grease to the nuts, because Honda always stated "dry" torque values. With re-torque add an extra 10 % on the specified torque (only once, not twice). Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
Just a personal note......but my (own) procedure, nowadays, would be to raise the motor into a rolling chassis -- I don't have a bench motor steady -- and nip up the mounting bolts; provide a fuel supply (obviously!) and run it for 5-10mins with a desk-fan blowing from the front.
Leave it overnight then, next day, drop the motor and torque the nuts again. I prefer to use a 'click-click' torque wrench (as opposed to a torque meter, with the scale & pointer) and I feel, when it comes down to it, the second and then the final (500mile) torquing, the head 'n' barrels M8 studs benefit from a "click-plus-half-a-flat" method on the correct wrench setting; a tad over is better than a smidgeon under. For the M6 studs, under the plugs, I use a 10mm socket on a short ¼"-drive 'rodent's dropping' and tighten them as much as I dare. When the top end heats up for the first time the components expand, causing the gaskets compress a little more; then when the top end cools, the components contract leaving the gaskets at a new, microscopically reduced thickness. Necessary? Perhaps. More work, yes. But worth it? Maybe. Better than oil leaks? Deffo! The peace of mind to know I did all I could is worth the extra effort.
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