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Cam timing

Dean'0

Dean'0

Getting there...
Location
Australia
Hi All.
I have a question regards cam timing. I have heard you can retard the inlet cam by one tooth to get better performance, has anyone done this and does make a noticeable difference.
 
On a Conti GT535 no, on pre unit 500 yes.
It works and which give more overlap to the valves which gives better cylinder fill.
The quickest pre unit stock bore Bullet 500 in Washington State got a little quicker when that trick was applied. There's always hidden horsepower in an Enfield just waiting to be freed.

Steve Linsdell: Isle of Man record setter with his Bullet. It's the fastest in the world.

Paul Henshaw: His two valve four speed Bullets cause the Manx Norton four valve head six speed gearbox racers to go into convulsions.

The UCE engine is better in every way than the pre units.
If you really want really wake up your engine, take a deep breath and empty your wallet onto Hitchcock's parts counter. Carbs, cams, four valve heads... these bikes can be built for power and speed.
 
I've got the standard Hitchcocks +Amal +rewiring+ expertly done squish unshouded inlet valve Hitchcocks pipe. Based on my experience the only place that that a radical valve timing works is on the race track, 500 or 535. My local expert opined that it was about as twice as much as is normally done, but given the unadjustability of the cams it's either or. Years ago Yamaha brought out a race kit for their SRX600 single. When tested it it was slower on the road as it had lost the midrange grunt. I had similar experiences with my KLX 250 singles. One had the Kawasaki optional race cam, fine for racing but it lost some [much needed] low end grunt, so worse on the trail. The simplest cheapest mod for the 535 is the Big Gulp air filter arrangement; makes a huge difference and takes half an hour to fit. The standard arrangement blocks the air intake. The Hitchcocks airbox mods simply tinker round the edges of a poor flowing design.
Once fitted the bike revs more freely and loses nothing any where else. It also makes the cam timing mod utterly pointless. I had to go up one on the main jet. After a rebuild and head and exhaust work my bike is running leaner on the cutaway, takes longer to run cleanly, running in so no idea yet about the main jet. The engine might produce more power with a 34 but the only easily fitted one is an Amal Mk2 Concentric, and the bodies are no longer made, and anyway after blowing the big end I'll try and keep nearer the engine's proscribed rev limits where a bigger carb makes less sense..
I'm aiming for Venom type performance, not Thruxton.
 
PS A contributary factor to the big end's very early demise may have been the barrel base not being laterally square. The top still had honing marks whilst the bottom was well worn on one side.....
 
cloggy said:
I've got the standard Hitchcocks +Amal +rewiring+ expertly done squish unshouded inlet valve Hitchcocks pipe. Based on my experience the only place that that a radical valve timing works is on the race track, 500 or 535. My local expert opined that it was about as twice as much as is normally done, but given the unadjustability of the cams it's either or. Years ago Yamaha brought out a race kit for their SRX600 single. When tested it it was slower on the road as it had lost the midrange grunt. I had similar experiences with my KLX 250 singles. One had the Kawasaki optional race cam, fine for racing but it lost some [much needed] low end grunt, so worse on the trail. The simplest cheapest mod for the 535 is the Big Gulp air filter arrangement; makes a huge difference and takes half an hour to fit. The standard arrangement blocks the air intake. The Hitchcocks airbox mods simply tinker round the edges of a poor flowing design.
Once fitted the bike revs more freely and loses nothing any where else. It also makes the cam timing mod utterly pointless. I had to go up one on the main jet. After a rebuild and head and exhaust work my bike is running leaner on the cutaway, takes longer to run cleanly, running in so no idea yet about the main jet. The engine might produce more power with a 34 but the only easily fitted one is an Amal Mk2 Concentric, and the bodies are no longer made, and anyway after blowing the big end I'll try and keep nearer the engine's proscribed rev limits where a bigger carb makes less sense..
I'm aiming for Venom type performance, not Thruxton.
Click to expand...

Excellent points !

For street use and spirited riding a camset ground equivalent to the Redditch S cams of the Bullet Big Head and Fury would be the bees knees.
In pre Unit Bullets they retain the easy starting and smooth lazy idle of the stock cams that the Bullet is famous for while delivering more of everything on up. They also extend the rev range.
S cams are not race cams and should not be though of as such.

I see no reason why the timing/lift/duration of the S cams wouldn't work equally as well if not better in the UCE lump. Especially since both engines have the same bore and stroke.

There is a UCE Bullet variant becoming available soon near me. If we can agree on a mutually satisfactory price, my wallet will hate it. Hitchcocks and Henshaw might like it though.
 
Hitchcocks list two 32mm carbs for the 535/612. The flow on those carbs when tested back in the day by Cycle magazine was shown to be almost identical. The Mikuni has been stated to give more of a performance bonus than the Amal. Their Amal utilises the standard Enfield 535 airbox filtration. Their Mikuni uses a pod filter inside the airbox, dispensing with the standard gubbins. This adds weight to the Big Gulp claims, [which I can verify]. Another owner had the airbox modifed at the rear, said his standard 535 went from 75 to 85 with no other mods. I have seen a Hitchcocks built 612/4 valver. It was fitted with a larger bodied 34mm up Mikuni VM. The 4 valve head makes more engineering sense on the Long Stroke, if one had the money.......
 
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