Has anyone here (maybe Swiffer or VFROEM or BLS) had their cam sprockets lightened? Seems to me there's a lot of scope for drilling the sprocket centre to take some reciprocating weight out of it. What do you guys reckon?
Here's a pic of one of my cams prior to removal of the scissor gear (you need to cut three rivets off to remove it, I'll post an 'after' pic soon).
You can tell in the pic how much metal there is between the gear itself and the camshaft:
[image: IPB Image]
Removing the scissor gears helps reduce friction losses - the amount of tension the springs place on the scissor gear is surprising. It makes the engine noisier of course, but no less reliable. It also reduces the reciprocating weight, which is the aim of this particular exercise. As a reference point, RC30/RC45 doesn't have scissor gears, and the VFR400 racebike I crewed on a few years ago also had them removed to help it make 73hp.
Here's another pic showing the cam in situ, notice how much metal there is on the sprocket. The four holes revealed when the scissor gear is ditched are all around 10-12mm, another 5-7 10mm holes could be drilled to reduce weight.
[image: IPB Image]
The actual geardrive sprockets themselves may also be open to some weight paring, but I'll leave that till I get into the bottom end (one day, am in no rush to touch it just yet).
Just in passing, I noticed last night that my cam holders don't have the aftermarket mod to eliminate the cam knock issue that the early 4th Gens had, but mine (December 1994) never knocked. Reading the technical bulletin, it says "When camshaft journal diameter is close to upper limit, camshaft inclines during valve movement and the cam sprockets generate a thrust force which causes the knocking noise". I guess my cam journals aren't close to the upper limit? Not sure where I'd find the spec, the service manual doesn't seem to have it - no matter, it all worked fine before so I'll just reassemble it. BTW I did my valve clearance check last night - last checked at 68k and all in spec, now at 95k and all in spec! Awesome stuff, and this engine has definitely not been babied.
I wouldn't be drilling out the cam gears mainly because it's a cast item. Yes every bit of weight helps when engine internal mass is involved but to start doing that sort of thing you really need to strip engine & get blue printed (internals balanced). Cast steel is allot weaker that something made from a solid billet so due to known strength of cam gears & you have already removed shock removal scissor gear, I would pass on drilling out gears for little gain in hp safety would be a stronger issue.
Wait till EC track day & see how mods you have already done do against the red beast with no internal mods :-)
The gears are not reciprocating parts so balancing is not an issue. They do have mass so they have inertia which affects engine acceleration.
The first and last gears in the cam drive train pass the torque through the gear web from (first) or to (last) shaft. The other two gears are just idlers which pass the torque from tooth to tooth so the web of those gears has little load. Only the second of the two idler gears is lightened (quite a lot), all the others have solid or very nearly solid webs.
I am not familiar with how the springs are attached to the scissor gear pairs but would increasing the holes affect that? (I appreciate that you have removed the scissors gears).
I am not familiar with how the springs are attached to the scissor gear pairs but would increasing the holes affect that? (I appreciate that you have removed the scissors gears).
I'm having problems getting the camera to connect to the home pc - caused by leaving the USB cable at work : ) - so the pics will have to wait till Monday AUS time.
The two springs simply sit between a fixed (by means of three pressed rivets) pressed steel plate, and the movable scissor gear - sort of like a clutch spring arrangement.
The side of the cam sprocket that the springs and scissor gear sit on has barrel-shaped reliefs for the springs, and some webbing.
Although the cams themselves are cast, the cam sprockets are definitely pressed on and now I'm wondering whether they are cast or forged, but since I proposed lightening them I've realised that the webbing and reliefs would make it a bit tricky.
I think you're wondering whether it would be possible to refit the scissor gears if you went down the path of lightening the cam sprockets - the answer would most likely be no, if you had drilled out the sprockets enough to make it worth the effort. Pics will make it clear.
BTW I realised that 'reciprocating' was the wrong term after I posted, but figured you guys would understand : )
The Phantom, Aug 4 2006, 06:25 AM Has anyone here (maybe Swiffer or VFROEM or BLS) had their cam sprockets lightened? Seems to me there's a lot of scope for drilling the sprocket centre to take some reciprocating weight out of it. What do you guys reckon?
As a reference point, RC30/RC45 doesn't have scissor gears, and the VFR400 racebike I crewed on a few years ago also had them removed to help it make 73hp.
No I did (not yet rolleyes.gif ) drill the sprockets centre. I did remove all the scissor gears / tensioning gears and also used a race alternator for less rotating mass.
The RC30 and RC45 do have tensioning/scissor gears. In the HRC (racing) manual they recommend to remove the tensioning gears. When you hear the sound of a V4 without tensioning gears you will notice it forever... (sound musik20.gif small stones inside you engine)
Probably Thorsten Durbahn can tell you more about lightening the sprockets inside the engine. (www.durbahn.de)
vfroem, Aug 9 2006, 04:47 AM The RC30 and RC45 do have tensioning/scissor gears. In the HRC (racing) manual they recommend to remove the tensioning gears. When you hear the sound of a V4 without tensioning gears you will notice it forever... (sound musik20.gif small stones inside you engine)
Aha, and I did find some pics of RC30 cams yesterday which appeared to haev them
A mate raced a VFR400 and he'd removed the gears, you're right, the noise immediately makes you understand why Honda fits them. I like it, it makes the engine sound very purposeful (and that noise is only really on idle or low rpm overrun). Under load it sounds normal. And with my Indigo header to Wolf underseat 4-2-2 system, reducing engine noise is a bit of a waste of effort : )
This got me to thinking about having new cams made. So I called Megacycle Cams (next to Factory Pro in San Rafael, Ca)and asked about their services. Making new cams (from Billet or something) is not reasonably priced. They can grind down the existing cam lobes and weld on new high performance nickel alloy lobes. The owner said that the VFR cams are really complex and it's pretty expensive. They require copper heat shielding and a lot of extra care involved. So they can rework the existing cams, if there is enough interest to do it. Hotted up cams would be cool.
Interesting stuff, Jimolaya. Others here have mentioned Megacycle cams, which leads me to believe that perhaps they already have data on VFRs? Which in turn would make it a bit easier to select cam profiles based on other mods you might have.
I have the pics of the cam sprocket minus the scissor gear, will post them shortly.
vfroem, Aug 9 2006, 06:34 PM The cams are not very difficult to reprofile.
[image: IPB Image] vfrproject.nokkenas.01.JPG
[image: IPB Image] vfrproject.tandwielen.01.JPG
I posted an inquire thread a couple months back and asked if anyone new the diam. of the valve stems.
I live close to a majician of sorts with headwork.--He has taken 65 hp jawa engines and grinds another 10 hp with lightening the valves from 6mm to 4 mm and special RD valve springs. Lightened internals equals horsepower.
In my defence, on the 13th of August my first son (second child) arrived, so I have been kind of busy with non-bike stuff : )
[image: IPB Image]
OK Mr M, here's the weight according to my needle-style kitchen scales (calibrated by verifying the weight of an unopened jar of Vegemite and a 40g Mars Bar : ) Actually I don't really trust their accuracy but we'll see an indicative figure anyway.
Weight of scissor gear, retaining plate and two springs = 100g
Weight of bare cam = 850g
So, 100/950 = a 10.5% weight saving when the scissor gears are ditched.
Removing 400g of rotating mass has got to help with engine responsiveness...
The Phantom, Aug 9 2006, 07:32 PM [image: IPB Image]
Now I see: scissor gear = anti-backlash gear. I have fit those for rotational transducers, and I imagine that they do add some possibly significant friction and rotational inertia.
Do not reduce the mass of the camshafts. Gear driven cams are subjected to violent acceleration and deceleration compared to camchain and tensioner drives. These forces are transferred to the valve springs during opening.
Lighter cams, turning faster, can cause valve surge during compression and valve float on the closing ramp.
End of thread · 20 posts recoveredWayback Machine snapshot 17 Oct 2006