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Author Topic: Head Nut Torque  (Read 402 times)

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motoguzzibill

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on: July 31, 2018, 07:22:00 am
I have replaced the head gasket on my 06' AVL, along with a little port cleaning, and am wondering about the "correct" head torque specification. My manual states both 33 and 24 NM in different places. Does one just split the difference?

While working on the head I found several joint areas, carb, exhaust, and valve seat areas where restrictions or significant edges existed. These were removed and the ports smoothed. The engine feels like it breaths quicker and has improved throttle response. Total power is the same as the piston is still stock, but the delivery has improved.

So what is the magic number for the head nuts?
Bill


ace.cafe

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Reply #1 on: July 31, 2018, 09:37:05 am
20 ft-lbs on the head stud nuts.

It saves the threads in the engine case from pulling out.


Adrian II

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Reply #2 on: July 31, 2018, 10:55:09 am
Torque wrench? Just a normal socket wrench with a long-series socket (don't know why the main studs are over-length), nipped up "nice and tight" by hand has always worked for me.

I found that the OEM M8 flange nuts are quick-rust items, (except the two inside the rocker box), good candidates for stainless steel replacements, grab another couple for the exhaust flange while you're about it.

The exhaust ports on all the Electra heads I have seen are terrible, with a lot less to do on the inlet (and very tempting to take it out to 36mm at the flange, I have yielded on several occasions).

However, the worst feature seems to be where the inner parts of the underside of the valve seats actually stick out into the ports, there's still enough metal in the casting to support them, but it just seems all wrong, and I can't see it helping performance any.  The answer is probably one of Ace's re-worked heads if you have the $$$.

A.
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Mick Bailey

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Reply #3 on: August 01, 2018, 06:01:40 am
I also use 20 ft-lbs. These studs pull out of the crankcase very easily and I found out the hard way - I ended up helicoiling my crankcase. Before tightening the head make sure the studs are screwed down into the crankcase. With my bike they weren't. I noticed the excessive length of stud projecting above the nuts before removing the head but never though anything more until the first stud pulled out. It tuned out that they weren't screwed in enough on my bike (YMMV) I screwed them down but it was too late for that one and it pulled out again. The studs were extremely slack anyhow so I decided to helicoil them with D3 inserts.

Be especially careful if you use a click-stop torque wrench. I find I get more feel for whats going on by using a beam-type and torquing in three stages. It gives you a better early-warning. Just the same if you use a regular socket wrench - you can feel what's happening.

I did my wife's bike last week. Like my own bike, the head was way off being flat and I spend some time with a surface plate, files, scrapers and engineer's blue. It always leaked oil from the pushrod tunnels and now it seals just nicely. A flat surface means that you don't need to pull down the head over-tight to get a seal.  After a few miles though I checked the tappets and they'd gone a tight due to the head settling slightly.
   


Superchuck

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Reply #4 on: August 01, 2018, 09:22:03 am
Amateur follow-up question:

I've read on these forums that some people recommend torquing the head bolts in 'steps' instead of going straight to the final 20 ft-lb, with the reasoning that this will give you a better, flatter seal on the head gasket, and will not risk damaging anything.  I figure if I'm taking the time to do it, why not take 5 extra minutes and do it in steps... can't hurt I suppose.

But, I am confused as to how one does a stepped torquing.  Do I tighten all bolts in a star pattern to:

7 torque on first pass
14 torque on second pass
20 torque on final pass

That makes sense to me, but I read an old post which muddied the waters and got me all mixed up.

Thanks in advance!
Chuck


Adrian II

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Reply #5 on: August 01, 2018, 09:23:56 am
Quote
the head was way off being flat

Must have been from the same batch...

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


Mick Bailey

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Reply #6 on: August 02, 2018, 02:04:05 am
That's exactly how ours were - rough as hell. The service manual gives the flatness service limit as 0.05mm.......

To answer Supechuck, that's how I do it with composite gaskets. The reason is that if you tighten the first nut down to full torque it can cause excessive pressure on a small area of the gasket and crush it - especially if it has sealing rings built in. Torquing in steps is supposed to maintain an even pressure and reduce this possibility. The other reason is that with some engines this is necessary to reduce the chances of the head warping. I doubt that this would be the case with the Enfield.


tooseevee

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Reply #7 on: August 02, 2018, 06:54:37 am
         My head came nice and flat with a few minutes on glass with a piece of emery. That flash in the lower part isn't really a gouge like it looks. Just a product of a flash angle or something.

         Torqued it down 20 pounds incrementally nice and easy with new washers. Retorqued after a couple heat cycles and two or three trips down the road. Over a 1,000 miles now no leaks no problems, runs like a Swiss watch.   

           Thanks, Ace. I can never pay you back.
« Last Edit: August 02, 2018, 07:01:28 am by tooseevee »
2008 AVL Classic.Extensive head work by Ace.Ace canister/TM32/Ace manifold.Small open bottle/hot tube removed.Pertronix Coil.Bobber seat.Fed mandates removed.Battery in right side case.Decomp&all doodads removed.'30s Lucas taillight/7" headlight.


Mick Bailey

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Reply #8 on: August 02, 2018, 01:19:07 pm
Advice to anyone is to make sure your glass is flat! A lot isn't and I gave up looking through the sheets I have and reverted to a surface plate. Tempered glass is the worst - the process seems to cause it to bow.


Arizoni

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Reply #9 on: August 02, 2018, 05:33:57 pm
As a side note for the curious, 20 lb/ft of torque applied to one of the 5/16" or 8mm studs or bolts will create a compressive force of around 3,840 pounds.

With 6 of them working together there is about 23,040 pounds of force holding the head on. :o
« Last Edit: August 02, 2018, 05:38:24 pm by Arizoni »
Jim
2011 G5 Deluxe
1999 Miata 10th Anniversary


Adrian II

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Reply #10 on: August 03, 2018, 12:08:43 pm
Advice to anyone is to make sure your glass is flat! A lot isn't and I gave up looking through the sheets I have and reverted to a surface plate. Tempered glass is the worst - the process seems to cause it to bow.

My piece of plate glass is an old and quite thick oval display stand top from my late father's shoe shop, must be 1950's or even earlier... Plenty large enough to take a sheet of wet and dry and reface cylinder head joint faces. Trying to get a replacement as flat as this could be difficult.

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...