Forum

[Phil Ashbrook]

Is the Fury head a twin plugger ? I converted my ported STD head to twin plugs and the tick over became so much better as did the fuel burn , still in planning stages for my Fury conversion , no info on the true specs of the Fury head , are the ports polished or not ? My true dream is to get 50 BHP from my 612 .

[Mark M]

I don't know how well prepared the head is from our Hosts but it is definitely capable of twin plugging. Twin plugging on it's own won't make a bike faster but it will allow you to run less ignition advance with some of the advantages you mentioned. Good luck and let us see the results, the Bighead is one of the best looking single cylinder engines ever in my opinion!


REgards, Mark

[apparently lucky eddie]

During the classic tt coverage on itv4 one of the commentators mentioned that one of the Norton singles was producing 70bhp. How useable that power was and whether it was all compressed and only available in a very narrow powerband like an old japper I don't know. Old jap bikes always had supposedly high bhp figures but did n't have the torque to open a matchbox. By comparison brit singles had very low horsepower but torque enough to pull a loaded double-adult chair.It all seems a compromise.

[Adrian]

As Mark M points out, the Big Heads are twin-plug capable, as they normally use the same decomp valve as the ordinary Bullet cylinder head, so apart from checking plug position it's a case of blocking off the vent into the exhaust port.



For my NotaFury project I've had the head welded and machined by Bullet Whisperer to put a more modern-style squish band into the combustion chamber (the piston crown is also modified to suit), something like this should help with better combustion and remove the need for twin plugging, though you could still have both. As you're several thousand miles apart, If I remember correctly, you'd have to check with him exactly what's involved if you want to reproduce this locally.







Photo courtesy B.W.



I think it would still be possible to have a (relocated) decomp valve and twin plugs, I'm sure Tim in NZ has done it.



A.

[Phil Ashbrook]

It looks totally right for my Accralite forged piston ...and my God look at the size of the exhaust valve !I'm using the competition valve kit on my 612 and that has bigger valves but this looks even better . Not sure about 70 BHP from a single as I think the new Jawa speedway engines have hit the limit at 60 BHP and they are not push rod plus if you read their manuals you have to junk many parts like the slipper piston and cam chain after only a few meetings or they blow up . The Royal Enfield 612 can pump 45 BHP on race cams so it's not impossible to scrape an extra 5 BHP with a Fury head and crank based ignition system so as to remove the timing gears , the Enfield was bit of a slug compaired to the Gold Star or Velocette Thruxton but it's a healthy 3rd place for a road engine . I love making things go faster and started at 16 with my Yamaha RD50 which I got to 60 mph in the end but it was guttless under 12,000 rpm .

[Bullet Whisperer]

There is a squish banded 'Big Head' fitted to this engine, which can reach over 9000 rpm ...
https://www.youtube.com/watch?v=Foo8ayftQrY
Regards, Paul.

[Phil Ashbrook]

This photo is very cool and it shows the angle of the inlet port , would love to see inside of the ports to see how big the valve guide humps are as they can be reduced with the guides out as I did with my head but only if there is meat to keep the guides solid , the humps cause turbulance on top of the guide it's self , the comp valves are waisted to help as well , I took a fair amount of time porting my head to get the shape right...well in fact I tried to copy the Honda /Cosworth CB77R 350 I once had so the Fury head is a dream come true for my bike . It would be great if our hosts re-issued the headstock with tacho plates and the timing case and drive , the real bikes are in museums in the USA but I cant find a photo with one with a tacho fitted and with the 191 made prices are sky high . I've seen photos of the cast alloy rocker feed on some but there is no info on this .

[Adrian]

Phil,



I managed to find another of Bullet Whisperer's photos of my cylinder head, this shows the inlet port opened out for 1.5"/38mm for the PHM Dellorto that's going on there. You can see where the original 2" centre stud holes have been filled with threaded alloy rod. By the time I got around to ordering the head for my NotaFury our hosts were nearly out of stock. The one Fury head they had left in stock had one or two problems, so I used the better of their two remaining "ordinary" Big Heads, which B.W. ported to Fury spec.











Hope this helps.



A.

[Phil Ashbrook]

Wow just flipping wow !!!!!

[Phil Ashbrook]

I had a flat slider Dellorto on my works replica MZ TS 250 and I found it trouble free , but this was a extra ported 2 stroke with a 3rd port and windowed piston , lots of power and great in the woods , the East Germans were great at making things that could start covered in snow !