Royal Enfield Interceptor Owners
There is a fundamental problem in the S II 's Lubrication System ! And you don't know you have the problem unless you mount a pressure guage. I did this just for fun back in the seventies - when I was young and without the technical insight I have now. When on long trips in the summer - oil pressure would suddenly ( instantaneously, not gradually !!) drop from around 12 -15 psi to Zero !
The first time I immediately stopped and readied myself for some awfull sight. There was nothing to be seen, of course, so the next times it happened I would stop, take a breather and continue. Sometimes the oil pressure would come on - and sometimes it didn't !? Eventually I was persuaded by the buddies (to whom I was a pain in the neck - with all those extra stops to allow for cooling ?!), that nothing was wrong - that it was actually probably the damned guage that was the problem - and so I just dismantled it and forgot about the problem. - Like the ostrich tucking its head under the wing !
No need to tell you that I tried curing the symptom by trying out all the oils on the market at the time (except R-oil) and I also mounted the Enfield Oil-Cooler. The guage monitored the pressure to the Heads which should be up to 15 psi (1 bar) - its max being controlled by the secondary Relief Valve.I can think of two explanations to what I saw ( and the "truth" could of course be a mixture ?) -
a) The Pump experiences cavitation which reduces its output to some unknown extent ? ( This is a theory I've heard from other S II owners. Personally I've allways thought it was the second, following explanation :
b) Oil pressure at the Pump Exit quietly drops - because of larger consumption from the Big Ends ( thinner oil - more flow ) - until finally it is not able to keep the primary, 60 psi Relief Valve open. From this point oil no longer passes to the Heads !
The fact that my bike - and probably most other S II's ? - "gladly" runs under these conditions mostly supports the second theory (?). The Big Ends are still getting fed - allthough with less than 60 psi ( we all know that the "centrigugal-pump"-effect of the large Oil-volume in the Crank Journals at high revs is substantial and therfore a positive contribution to maintain the necesary Big End pressure!)The bad part is that the Heads are not getting any oil ! And this is for sure - no matter which theory is right ! From a lubrication point of view occasional lack of oil-feed to the Heads is not such a big deal ! We all remember the real old engines with open valve gear and consumption-lubrication ! The Camshafts - and Lifters are also ok for some time because they have their own "puddle" of oil. ( luckily the side-stand is on the left side so these puddles don't get emptied when you stop to check what's wrong !)
From a thermal point of view, however, the loss of Head-oil is Bad Medicine !! - It causes excessive wear a lot of places - not only in the Heads but also in the lower Cylinder area. Fritz Egli of Switzerland ( "Egli-Vincent" + succesful tuning of lots of other more modern engines ) has played a lot with Bullets and with an Interceptor I. Their lube-system is completely different from the S II's, but the guys at Enfield seem to have had the same idea about Top lubrication on all models. Fritz's lubrication-modifications on the other RE's have been aimed at substantially increasing the flow of oil to the Head for Cooling purposes !
( only then can they survive the power he pulls out of them !)
He's been kind enough to have a close look at the S II's Lube sytem and his recommedations are as follows:
1) Increase pump capacity (33 %) by augmenting Pump Piston diameter from 9,525 to 11 mm.
2) Tune Pump-porting to match larger flow.( "Cheese"-formed holes insead of circular !)
3) Decrease primary Relief Valve ( Big End ) relief-pressure from 60 to 45 psi.
4) Increase secondary Relief Valve ( Heads ) relief-pressure from 15 to 20 - 25 psi ??
5) Grind " Relief Paths" in the Rocker gear to allow generous oil through-flow at this point.
The idea is to "cascade" the top of the engine with oil to transfer heat away from the Head-, Cylinder- and Camshaft-area. Adding oil-coolers doesnt really help if the oil doesn't come near the hot parts of the engine !! ( Many years ago I drilled small holes in the Con-Rods - a'la Commando - to get some oil up from below - but I still saw all the usual wear.) Spouting good "cool" oil out of the secondary 15 psi Relief Valve is definately a waste !
If the problem is a) cavitation, then incraesing Pump Piston diameter won't exactly help. Tuning the Pump-ports should help though !? Another possibility could be to dump the "Rocking Body"-Valving system and replace it with modern Check Valves inserted in the right places and directions. ( Using ceramic balls instead of the traditional steel balls gives a real responsive function thanks to the much lower weight of ceramic balls !)
If b) is the correct explanation then the "average" S II owner could apply
"Egli"solutions 2) - 5) without too much trouble and get much more lifetime !
Michael, I'd love to hear yours - and other S II owners opinions and thoughts on this issue (and many other issues later on !)
Cheers Ole
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