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Electra cylinder head machining

Submitted by nicholas_clarke on Thu, 21/03/2024
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Light Twins

Having got my Electra heads back from vapour blasting a close inspection reveals a potentially serious issue with the way the face of the right head is machined either at manufacture or by someone skimming the head in the past.  The attached photos show that the left hand head still has most of the lands round the combustion chamber and the push rod tunnels.   However, the righ hand head has been machined almost completely flush to the fins removing the lands around the push rod tunnels.   A careful check with a steel rule shows the face is flat and even so there is no sign of warping.

Previous owners report that the engine has always suffered from oil leak round the front of the head gasket, particularly on the right hand head, born out by personal experience and witness marks of burnt oil.   There has been plenty of correspondence on this forum about the weakness in the head design and the need to optimise the clamping force, particularly round the push rod tunnels and my right hand head seems to a good example of this problem!

I remember reading Peter Holland's account of him carefully filing down the area between the combustion chamber and the push road tube lands to optimise the clamping force which along with the use of original composite and copper head gaskets and a meticulous head re-torquing solved the leaking problems.   Sadly this would probably be impossible with my right hand head because it would mean filing away metal from the fin area which I suspect is impractical.

Predicatbly the NOC shop has 7 left hand heads in stock but no right hand heads!   Interestingly the example picture shows similar level of maching to my left hand head.   Is this an indication that because of differences between left and righ hand head castings there was less metal to machine them to allow for the change to no spigoted barrels and heads circa 1964 so all the right hand heads have been sold over the years to solve this problem?   

Has anyone experienced this problem with right hand or even left hand Electra heads and if so have you come up with a solution? 

If I have to replace the right hand head has anyone got a servicable one that doesnt have this problem they are prepared to sell me?   Norvil aren't advertising any and I have rarely seen them come up on Ebay.   I am happy to match the £50 the club is charging for the left hand head.

If I can't find a replacement Electra head I know all Leightweigh valves are the same size and the Navigator and Electra inlet manifolds are the same part number so there is commonality.   I am guessing that although the part numbers are different the basic head castings are the same and they were machined the same way when the change to non spiggotted barrels and heads occured.   Can I use a non spigot Navigator head on my Electra?   If so has anyone got a serviceable one they are willing to sell me?

Sorry for another long ramble but any advice or experience of this problem would be greatfully received - all part of the joy of Norton Leightweight ownership and my quest to get the Electra back on the road in time for the good weather..........!

Nick 

Attachments
Left hand Electra head.jpg
Right hand Electra head.jpg

Submitted by john_crocker on Thu, 21/03/2024

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Hi Nick.

Have you checked the heads are the same?  That is to say compare the depth of combustion chamber and overall height of the heads.

If they are the same then surely all okay? 

Submitted by nicholas_clarke on Thu, 21/03/2024

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Hi John, I have checked the combustion chamber dimensions as accurately as I can and they are the same so I’m not concerned about that.    

My worry is that with the way the right hand head is machined I will not be able to get a decent clamping force to achieve an oil tight seal with the head gasket on the right hand head.   Particularly as the bike has a history of this problem.    Nick

Submitted by david_cooper on Thu, 21/03/2024

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The clamping force depends entirely on the tension in the head bolts.  The pressure is force divided by area.  And the area is fixed by the shape of the head gaskets.  So it should not be a problem.

Submitted by nicholas_clarke on Thu, 21/03/2024

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The trouble is the area of the head gasket contact has been significantly increased by the way the right hand head has been machined David.   With a normally machined head like my left hand head the head gasket only contacts the head and barrels around the raised lands around the  combustion chamber and the two raised areas round the push rod tunnels.   With my right hand head the whole head gasket is in contact with the barrel.   I strongly suspect the reduced clamping force is what leads to the oil leaks.   Nick

Submitted by peter_holland1 on Thu, 21/03/2024

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Hi Nick, 

The checks John suggested seem to show all is well with head geometry. 

David is not quite correct in saying the pressure is dictated by the head gasket area and the stud loads. 

Originally the lightweight head had raised areas that pressed against the larger head gasket. So the contact pressure was determined by the raised areas and the stud loads. See early cylinder head in photo.

When the Navigator spigotless head and Electra spigotless head appeared, the cylinders got 2mm taller (height of the old spigot.) Downside was that an extra 2 mm had to be machined off the cylinder head face.

Suddenly the area of head gasket that got squeezed was much greater, reducing the pressure that holds in oil and combustion. 

On my Electra heads I have taken about 20 thou off my heads, by file, to remove the extra clamp area between push rod holes and combustion chamber. See shaded area on photo.

My Electra heads were somewhere between your right and left hand heads in "flat feature".

Castings would have varied, and yours show a small difference in fin positions. 

I'm with John. Nothing untoward. But my recommendation is to get back to the clamping pressures of the early spigotted head by reducing the wasted clamping area.

Hope this is clear. 

Peter

Attachments
IMG_20240321_144750.jpg

Submitted by john_crocker on Thu, 21/03/2024

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I would be cautious of removing metal from the head.   Removing metal will reduce the stiffness of the structure, that is to say it will be more likely to deflect.  Removing metal where indicated will better distribute the available force to where its needed.  Six of one half a dozen of the other comes to mind here.

 

Submitted by paul_griffiths on Fri, 22/03/2024

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Synopsis.

If the heads are  comparable in combustion area  and are both flat, the inlet manifold fits well all should be good to go.

Fit a composite gasket and torque it down, in this case about three times after gentle low revving running in allowing the engine to warm up gradually.

It's all about aftercare practices, taking the time to do what is required when it it is required.

It doesn't surprise me to be told that these engines have more than a tendency to leak oil when you realise the bolt hole spacing distances across the whole structure looks enormous with puny sized holding down bolts allowing low torque values to be applied. The sphere of influence of these fixings is not adequate enough it would seem.

Having followed the regime as suggested above you will not have had to splash out on more expenditure and stand a reasonable chance of success. If it does go according to plan you will have gained experience by biting the bullet and following your new gained knowledge from amongst the sages of the NOC.

 

Submitted by andy_sochanik on Mon, 08/04/2024

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Heres a picture of mine - removed a couple of years ago - for comparison.

As you can see, there are basically no lands between the pushrod holes & cylinder.

If you are happy that the head squish volume (depth) is the same for both, then use them again.

But are you certain they are dead flat? Biggest cause of cylinder head leaks is distortion when tightening the heads down. As somebody wrote, there is a lot of space between the studs. Also, do not be tempted to exceed the recommended 15 ft/lbs torque on the heads.

AND, tighten them down 2 or 3 times after a rebuild - once at 50 miles, then 250? and finally around 1,000miles - depends on your usage really, and how many 'cycles' the engine does.... Cold to Hot & back again.

Just out of interest  (on anotherr post here) the plugs used on these heads were Champion N5  

Attachments
Heads-pair.png

Good morning Peter,

Apologies for the delay in my reply but Easter week was very full on and I have only now got some time off to spend on the Electra!   Thanks for the attached picture and for confirming that my heads aren't fundamentally different from yours.   Andy's photos on his reply are very similar to mine too so clearly Plumstead machined them almost back to the first cooling fin.  I will have a careful look today and see if  I can file 0.020" off my heads the way you have to help the clamping force - it can only help! 

I have checked with a steel rule and both heads seem to be flat, the combustion chambers are the same dimensions and it was running fine before I stripped the top end so I will be putting them back on with a new set of guides and valves and composite Jubilee head gaskets with a smear of Hylomar round the push rod tunnels to help seal them.   I have replaced all 12 head studs because the threads were obviously stretched and will be using new head nuts and washers too torqued to 15 ft lbs to the patern shown in the workshop manual.   I will also be following the head re - torquing routine you, Andy and others have recommended - it has always worked in the past with my Jubilee and Navigator so fingers crossed with the Electra! 

Off to hunt for the +0.040" Hepolite pistons the Electra really needs - it is right on the wear limit..........sadly the club and Norvil don't have them but I am an eternal optimist!!!    

Onwards and upwards!   

Nick

   

Submitted by nicholas_clarke on Tue, 09/04/2024

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Hi John,

Wise words but given the design of the head I don't think filing 0.020" from the area involved will be a problem.  

Nick

Hi John,

Yes I have and they are the same - it was running fine before I stripped it down so I think the heads are fine to reuse.

Nick

Hi Paul,

Thanks for your advice, see my answers elsewhere!   From years of Jubilee, Navigator and now Electra ownership curing their oil leaks and fettling them to take account of some of their design flaws is all part of the obsession and fun of ownership!   Once you have made good all the maintenance failings of past owners they really are a joy to own and ride......it just takes time, patience and drawing on the advice of those who have been there before!   

Nick

 

Hi again Andy,

Thanks for the attached pictures, along with Peter's comments they are very reasuring, I was worried that a previous owner had them skimmed in an attempt to cure the leaking head gasket and had gone too far!   I have checked them for flatness and combustion chamber dimensions and have replaced all the head studs and nuts because they had obviously been over tightened badly in the past.   

Rest assured I will be sticking to 15 ft/lbs and the tighteneing routine you and Peter suggest - it has served me well in the past.   I really don't want to have to do the job again - stripping the strengthening plates off is a real pain! 

As for plugs - the Norton maintenance manual recommends KLG FE 80 which I have read across to NGK B7ES or Champion N4C.   Do you find Champion N5 a better choice with modern fuels?

Back to the workshop for a day of fettling - wish me luck!

Nick

 


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