Nord lock washers on cylinder heads

[dickie]

Folks,

I'm just putting together a top end kit for my current project and can't decide whether to use nord lock washers on my cylinder head or not.

To me it's obvious that you should use them, but as I often hear people talking about heads needing to be checked I wonder why everyone isn't using them.

Is there a problem with using them that I'm not aware of?

Is it simply because not enough people have heard of them?

Interested in any information or opinions............

[coaster]

I'm not a fan personally, they are meant for situations where vibration causes nuts and bolts to loosen and work by a ratchet system that actually slackens off slightly as you reach your chosen torque. Ask yourself if you have ever heard of head nuts vibrating loose? I certainly haven't. Gaskets will settle though hence the need to check torque after a hundred miles. That's my take on it anyway

[dickie]

Interesting point coaster. You're dead right in your precis of how they work and what they're for.

Maybe I'm confusing the torquing up after settling with vibration.

[gaz_powell]

I always use a thick flat and good quality spring with a deep nut .....never had head come loose on any of my many engine builds (including vespa)

I always torque them

[dickie]

I've been persuaded.

I'll miss them off. Just ordered deep nuts (ooer missus) and thick washers from mb.

I'm trying to be a little over the top with the quality of this engine build just because I want it to be absolutely perfect.

[dscscotty]

No spring washers for me! They can splay out, Prefer a good thick flat washer and a dab of lock-tite

[Warkton Tornado No.1]

The correct tightening of assemblies such as vehicle cylinder head nuts is to a recommended torque. That torque will ensure that the fasteners are stretched by the correct amount to put them under load.

High tensile fasteners require specific load determined by torque, dependent upon their grade to function correctly & not fail.

The size of the fasteners & quantity used will be selected by the Design Engineer to serve the dual purpose of maintaining the integrity of the assembly, in this case the Lambretta SI, II & III cylinder head & cylinder assembly.

So, many years ago, Innocenti calculated that four M8 x 1.25 rolled thread studs of a particular grade (unknown to me) would function & that a tightening torque be applied to the nuts within a certain range.

So far, I doubt any reader would dispute the above.

Where things get a little vague are when people start to have things different to that intended, deliberately or not.

My own opinion is that Innocenti cylinder head nuts &/or the studs will have had a coating of some type & not been dry. A graphite coating, for instance, may have been present.

Because I prefer to use three long nuts, nominally 12 mm long, in addition to the cowling nut, my own logic dictates that each is fitted with a smear of Copaslip type grease. This is done purely with a view to consistency. Preferably, flat, plain, thick hardened washers are also utilised.

Hypothetically, the grease allows 10% less torque to be required, but for the reasons stated above (Innocenti may have had pre-lubed parts & I use longer nuts) I would just go for the lower torque figure stated, in theory.

(In actual fact, I go rather higher than 15 ft/lbs @ my own risk but wouldn’t recommend you do the same.)

The only place I use any thread retainer, such as Loctite Studlock, in this application is when the studs are screwed into the crankcase. The amount required is minute to ensure you don’t get hydraulic lock which will break your crankcase as I can testify.

I hope to have helped.

[hullygully]

in the oil & gas industry they are becoming the standard replacement for nylocs, slightly briefer than the above

[dscscotty]

Without the Jargin x2 BSM winning engines had only flat washers holding cylinder heads in place, no issues over 23 or so events.

[dickie]

in the oil & gas industry they are becoming the standard replacement for nylocs, slightly briefer than the above

Sort of correct but not quite. In many applications nylocs are better.

Vibration causes nylocs to back off enough to lose tension but never unwind beyond the point of losing tension completely. So for joints where tension is critical, like a high capacity winch mount they have reduced, but not removed the need for shear-stops. A nord-lock is less likely to lose tension but once it does it's no better than a plain washer.

They have also become a pain in the arse financially as designers often specify them without thinking about the application properly! From memory, an m50 costs about £40 each!

Also, in short fasteners, the tension reduction caused by the ramp effect that warkton mentioned can occasionally be intolerable. The ratio of the ramp height to bolt stretch in these applications can be something like 5:1.

[coaster]

...................Also, in short fasteners, the tension reduction caused by the ramp effect that warkton mentioned can occasionally be intolerable. The ratio of the ramp height to bolt stretch in these applications can be something like 5:1.

A lot is said about bolts 'stretching' but the amount they are able to stretch depends on the material being clamped by the bolt. Where aluminium or soft steels are concerned, the component being clamped will compress/deform long before the bolt/stud has got anywhere near it's designed 'stretch'. That is why I would never use Nordlocks on the head bolts, ally head plus ally barrel = loads of compression potential, Exhaust studs in an iron barrel might be a different matter but that 'ramp effect' mentions means that compressible gaskets will be squeezed and then have the tension lessened a smidge which can't be good can it?

[Warkton Tornado No.1]

The fasteners used for securing the aluminium alloy head, cast iron cylinder & gaskets to the crankcase of Innocenti Lambretta products were almost certainly originally specified of a quality & grade to take a determined pre-load such that they would serve their function in maintaining the integrity of the assembly.

In other words, the recommended torque would ensure that the cylinder head nuts would not loosen by virtue of the fact that the studs were stretched.

Although the studs would be stretched, they would return to their original length when the cylinder head nuts were loosened in the instance of disassembly.

Most fasteners in general engineering use have a recommended torque to ensure that any joint they provide remains stable, & the fundamental way they achieve this is by being loaded via that torque to stretch them.

This procedure is not at all like current automotive practice where Torque-to-Yield (TTY) studs or bolts are utilised & are designed to stretch beyond their elastic limit (yield point) into the ‘plastic region’ meaning they are only suitable for use once & should not be re-used.

Finally (I hope) the following information is based upon a small amount of research on sites that I believe to be trustworthy from an engineering aspect. You can only make your own decision & any hilarious quips based upon your own beliefs. I would hate that somebody wrecks an engine because they decide to ignore established engineering principles. Personally, I would always use plain, thick, hardened washers particularly in the example this thread commenced with, namely the aluminium alloy cylinder head.

From what I have been able to ascertain, if washers are to be used, they should be plain, flat & hardened. ‘Lock’ washers should not be used with a plain washer & are in general not recommended.

[gaz_powell]

I find these threads interesting with different opinion - generally based on peoples own experience

To note

PX parts manual indicate flat and spring

SR lambretta exploded diagrams indicate a wavy washer (Innocenti and SIL ?)

as my formative years were based on the p range thats what i have stuck with and no adverse issues on Vespa or Lambretta with cast or ali barrels

Something else to note

Vespa service manual quotes PX head torque settings 12-16 ft lbs - without head gasket
(I was advised to go 19 on my ali barrel by the tuner which i did)

TS1 head torque setting at 23 ft.lbs - with a head gasket

The studs to all purpose are the same in both P2 vespa and lambretta

I stick to the above

Gaz

[Warkton Tornado No.1]

Many years ago, I too would use spring & plain washers but I now reason that the fasteners (studs) being stretched are what prevents the nuts loosening, especially as I use an anti-seize compound & they have never come loose.

All that I have been attempting to get across, is that good engineering principles are often disregarded, or not even fully understood, when it comes to certain self builds by enthusiastic owners of Lambrettas, yet we rely on the same principles to keep the wheels on our cars.

Undoubtedly, you are best to stick with what you trust as it is inconceivable that fresh, good quality spring washers would in any way cause harm. ‘Lock’ washers on the other hand is the term given to the ‘wedge–lock’ type & their derivatives.

Interestingly enough, the variance you quote for ‘with gasket’ or ‘without gasket’ are what I would have expected. That said, I have seen head gaskets fail & still avoid their use @ all costs.

[coaster]

Just to add even more uncertainty, a Google search revealed that there is a massive difference in recommended torque for given bolt/stud sizes dependent on the grade of steel used to make it. I guess we just have to trust that non Innocenti studs are all made of the same grade steel

[dickie]

Just to add even more uncertainty, a Google search revealed that there is a massive difference in recommended torque for given bolt/stud sizes dependent on the grade of steel used to make it. I guess we just have to trust that non Innocenti studs are all made of the same grade steel

Put some threadlock on it and the coefficient of friction can be less than half! And halving the friction = double the bolt tension!

None of us will sleep tonight.

[coaster]

Just to add even more uncertainty, a Google search revealed that there is a massive difference in recommended torque for given bolt/stud sizes dependent on the grade of steel used to make it. I guess we just have to trust that non Innocenti studs are all made of the same grade steel

Put some threadlock on it and the coefficient of friction can be less than half! And halving the friction = double the bolt tension!

None of us will sleep tonight.