Do Navigators and Electras share the same cylinder casting? That is to say is an Electra barrel just an over bored Navigator casting?
I believe Electras did not have the spigots to locate the heads, this modification migrated to Navigators and Jubilees eventually.
Are there any differences between crank cases because of the larger bore?
I understand that the Electra flywheel part of the crank case is narrower, presumably to clear the larger pistons and/or the cylinders.
The reason I ask is that I wonder if anyone has fitted Electra pistons to a Navigator and, if its possible, what work is needed to do the job.
Are they the same casting?
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Navigator/Electra cylinders
Thanks for the reply Peter. I was prompted to think along these lines after reading a recent thread about re-sleeving Navigator cylinders. Why not make sleeve them to take Electra pistons? What concerns me is the engines flywheel getting in the way.
Seems to me that if I were to re-sleeve my cylinders I could offset the cylinders, that is to say a larger centre distance between. Along with some suitable clearance in the liners and pistons, should get everything to fit without any alteration to the flywheel.
I think it would be necessary to fit the liners on the original centre lines of the cylinders and then bore offset. This would preserve the spigot for the head. Easier with non-spigoted heads.
This is just speculation and a few measurements with a rule, this suggests it may be possible.
As for the performance, I'm not interested in any extra, just what it does a little easier. And, of course, the technical challenge!
I think it unlikely I will do this at the moment, the cylinders I am going to use are presently standard bore with very little wear but somewhat corroded, a +0.010" rebore may sort them out.
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Navi/Electra Barrels
Not sure I understand the 'offset' mentioned above.
The centre line of the cylinders - be they Jubilee, Navigator or Electra is fixed. If you introduce an offset, the conrod will run at an angle.
Electra Barrels are 2mm taller than (spigotted) Navigator barrels, as Peter explains above. There are some (late 1964-on) Navigator barrels the same same height without spigots well.
These taller barrels use cylinder heads that have had 2mm taken off them. Easily identified as they have no cut-out for the spigot, and the face is more or less smooth right across from the push rod tunnels. The earlier heads have a recess for the spigot, and clearly identifiable 'islands' for the push rod tunnels.
I have succesfully grafted an Electra engine (crank, rods, barrels, heads & cams) onto late Jubilee crankcases (post engine 109838). I had to ensure the crankcase base was level (Jubilee uses separate barrels, so may not be level), and I had to open the Crankcase mouths to accept the barrels. Taller engine studs were also needed. Everything else fitted.
HTH
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Offset
The "offset" would be very small, maybe 1mm or less. This will not cause the rods to run at an angle, the engine won't notice it.
I originally started this discussion as at the time I was speculating as to what I needed to do to the engine of my Navigator to get it in to good condition. The idea of fitting Electra pistons appeals to me if I can squeeze them in without altering the flywheel. I'm surprised Norton took the approach they did by adjusting the flywheel size to accommodate the bigger bores, why not just cut away the cylinders and, if necessary, the pistons to clear the flywheel? Neither of these need metal in this area.
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Late Navi barrels
I was looking at boring out a late Navigator as the barrels are already +30 and very worn.With not much chance of finding original oversize pistons, I purchased the smallest bore iron liners ( 67mm) I could find and ZXR600 crank rods and pistons off ebay (67mm pistons would make it 395cc) It will need some flats machining on the sleeves and the flywheel slimming down, crank cases boring out and new longer rods to match the pistons. which will probably be too expensive. So at the moment my project hasn't progressed much beyond that.
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Hi John,
You need to understand that Navigator barrels are not the same as Navigator barrels. Early barrels with a spigot at the top are the same height, when measured from the base of liner to top of spigot as the later barrels when measured from base of liner to top of spigot/barrel.
So the casting, once machined for a later spigot-less design, is taller by 2mm than an early machined casting.
I believe, and I may be wrong, that the same casting has been used throughout the Navigator/Electra series. The casting is bored to a larger diameter to take the larger Electra liner.
The casting has less machined off it, height-wise, for the spigotless Electra and later Navigator.
Crankcases are different Navigator to Electra.
Crankshaft flywheel on Electra is narrower because the larger cylinder liners, on same centre distance as Navigator, get too close to allow regular Navigator crankshaft flywheel to fit between. To compensate for less width, flywheel is slightly larger diameter. In addition you will see that the liners are machined to allow extra clearance to the flywheel.
I know of one Navigator crank-cased engine, with larger holes for Electra cylinder liners. Running Electra barrel and pistons and an Electra crankshaft. No starter mechanism.
I don't think you will notice any more performance with the lower compression Electra set-up.
Best wishes
Peter