Gear Drive Cam Kits?
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Cruiser
Joined: Nov 2010
Posts: 244
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From: NE
Gear Drive Cam Kits?
Anyone have any feedback on these? I was told it adds 8-10hp, stock valve springs acceptable, increases valve timing by eliminating timing CHAIN lash and loosely fit stock chain drive. The kit i was looking at includes: cams, inner gears, outer gears, inner and outer bearings and gaskets, and recommends adjustable pushrods be used. Thanks in advance!
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Joined: Sep 2010
Posts: 14,744
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From: Phoenix '53, '88, '09 Big Twins
power gains ( or losses) would be due to the cams, not the drive system.
gear drives are considered to be more precise in cam ( and therefore valve) timing and wear longer.
A chain may stretch, there are tensioners & all the things you mention. ( but I gotta bunch of old Chevs and Caddy's in the yard, all with chain drive cams, so... maybe this isn't an issue)
the cons are cost & noise.
the adjustable pushrods are for ease of install.
On a H-D motor the solid pushrods are installed with the heads off.
It is common when doing just cam or lifter service to lift the pushrod covers and cut the pushrods with a bolt cutter ( rags used to catch any shards)- the adjustables are 2 piece, so the 2 pieces can be slide up and down into place, joined in the middle where the adjustment hardware is, and set to spec.
solid pushrods are often considered more precise, and sometimes swapped in later in the same motor has the heads off for any reason.
the adjustables save the cost of top end gaskets and the removal of the tank, intake heads and etc. etc. ( but they may go out of adjustment if the jam nut backs off - occasionally happens)
That's probably why the kit suggests them.
2.) If I were looking at replacing the cam drive on my bike ( talking about the drive system, separate from the cams) --- I would probably go with a gear set if from a well known source ( S&S for instance) and the cost was no more than 40% more for the parts ( 'cause the labour would be the same pretty much for either gear drive system)
again performance claims would be for what the cams do, not how they are driven.
mike
gear drives are considered to be more precise in cam ( and therefore valve) timing and wear longer.
A chain may stretch, there are tensioners & all the things you mention. ( but I gotta bunch of old Chevs and Caddy's in the yard, all with chain drive cams, so... maybe this isn't an issue)
the cons are cost & noise.
the adjustable pushrods are for ease of install.
On a H-D motor the solid pushrods are installed with the heads off.
It is common when doing just cam or lifter service to lift the pushrod covers and cut the pushrods with a bolt cutter ( rags used to catch any shards)- the adjustables are 2 piece, so the 2 pieces can be slide up and down into place, joined in the middle where the adjustment hardware is, and set to spec.
solid pushrods are often considered more precise, and sometimes swapped in later in the same motor has the heads off for any reason.
the adjustables save the cost of top end gaskets and the removal of the tank, intake heads and etc. etc. ( but they may go out of adjustment if the jam nut backs off - occasionally happens)
That's probably why the kit suggests them.
2.) If I were looking at replacing the cam drive on my bike ( talking about the drive system, separate from the cams) --- I would probably go with a gear set if from a well known source ( S&S for instance) and the cost was no more than 40% more for the parts ( 'cause the labour would be the same pretty much for either gear drive system)
again performance claims would be for what the cams do, not how they are driven.
mike
Last edited by mkguitar; Sep 30, 2011 at 02:29 AM.
Road Captain
Joined: Dec 2009
Posts: 540
Likes: 3
From: Nooga, TN
If I am not mistaken, your crank runout is much more critical when using gear drive. I think the HD spec is around 10 thousands and for gear drive cams it is in the 3 to 4 thousands range. So you may not even have the option unless you want to do some crank and flywheel work.
Thread Starter
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Cruiser
Joined: Nov 2010
Posts: 244
Likes: 0
From: NE
Actually they had a booth in Sturgis and It took 10 times the strength to turn the chain drive with the lil plastic guide than it did the gear drive.
power gains ( or losses) would be due to the cams, not the drive system.
gear drives are considered to be more precise in cam ( and therefore valve) timing and wear longer.
A chain may stretch, there are tensioners & all the things you mention. ( but I gotta bunch of old Chevs and Caddy's in the yard, all with chain drive cams, so... maybe this isn't an issue)
the cons are cost & noise.
the adjustable pushrods are for ease of install.
On a H-D motor the solid pushrods are installed with the heads off.
It is common when doing just cam or lifter service to lift the pushrod covers and cut the pushrods with a bolt cutter ( rags used to catch any shards)- the adjustables are 2 piece, so the 2 pieces can be slide up and down into place, joined in the middle where the adjustment hardware is, and set to spec.
solid pushrods are often considered more precise, and sometimes swapped in later in the same motor has the heads off for any reason.
the adjustables save the cost of top end gaskets and the removal of the tank, intake heads and etc. etc. ( but they may go out of adjustment if the jam nut backs off - occasionally happens)
That's probably why the kit suggests them.
2.) If I were looking at replacing the cam drive on my bike ( talking about the drive system, separate from the cams) --- I would probably go with a gear set if from a well known source ( S&S for instance) and the cost was no more than 40% more for the parts ( 'cause the labour would be the same pretty much for either gear drive system)
again performance claims would be for what the cams do, not how they are driven.
mike
gear drives are considered to be more precise in cam ( and therefore valve) timing and wear longer.
A chain may stretch, there are tensioners & all the things you mention. ( but I gotta bunch of old Chevs and Caddy's in the yard, all with chain drive cams, so... maybe this isn't an issue)
the cons are cost & noise.
the adjustable pushrods are for ease of install.
On a H-D motor the solid pushrods are installed with the heads off.
It is common when doing just cam or lifter service to lift the pushrod covers and cut the pushrods with a bolt cutter ( rags used to catch any shards)- the adjustables are 2 piece, so the 2 pieces can be slide up and down into place, joined in the middle where the adjustment hardware is, and set to spec.
solid pushrods are often considered more precise, and sometimes swapped in later in the same motor has the heads off for any reason.
the adjustables save the cost of top end gaskets and the removal of the tank, intake heads and etc. etc. ( but they may go out of adjustment if the jam nut backs off - occasionally happens)
That's probably why the kit suggests them.
2.) If I were looking at replacing the cam drive on my bike ( talking about the drive system, separate from the cams) --- I would probably go with a gear set if from a well known source ( S&S for instance) and the cost was no more than 40% more for the parts ( 'cause the labour would be the same pretty much for either gear drive system)
again performance claims would be for what the cams do, not how they are driven.
mike
Road Captain
Joined: Oct 2009
Posts: 666
Likes: 5
From: Bay Area, CA
If I am not mistaken, your crank runout is much more critical when using gear drive. I think the HD spec is around 10 thousands and for gear drive cams it is in the 3 to 4 thousands range. So you may not even have the option unless you want to do some crank and flywheel work.
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HDF Community Team
Joined: Jun 2006
Posts: 12,774
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From: san antonio
Lot of information but some of it is mileading.
Heads and intake do not have to be removed to install OEM pushrods; remove or just raise the tank. Just remove rocker boxes and loosen the rocker arm supports; the pushrods can be pulled from the top. Another 30 minutes of work but no hassle with adjusting pushrods and no worries about an adjustor nut coming loose. Rocker box gaskets can be re-used without issue.
Andrews makes all the gear drives, including the S&S gears.
The MoCo runout spec for warranty purposes was .003" until the '07 model year when it was increased to .012". .003" is the generally accepted rule of thumb as the max runout acceptable for gear drive cams. Some have been run at .0035"-.-004" but OS or US gears are required and the results may be a bit noisy. A set of gears intalled with proper lash on the inner and outer gears will be as quiet as the OEM chain drive setup.
Smoke and mirrors. The parasitic drag on power from a set of gears is at least the same as a chain drive system; could be more. It is true that cam timing is more accurate but that doesn't translate into better dyno numbers. Maintaining accurate cam timing would be an issue if we could spin the TC motor to 12000rpms.
the limiting factor on cam size is the case clearance on the inner lobe of the rear cam; doesn't matter which way the cams rotate in the cam chest.
Back in the day, before the upgraded hydraulic tensioner/roller chain setup, gears were the only alternative to the early spring loaded tensioner setup. However, the upgraded OEM cam drive system is soooooooo much easier to work with. Unless one is building a drag motor or a high compression, long cammed street motor, there really isn't any reason to install a gear drive system, unless you just want to. JMHO
On a H-D motor the solid pushrods are installed with the heads off. The adjustables save the cost of top end gaskets and the removal of the tank, intake heads and etc. etc. (but they may go out of adjustment if the jam nut backs off - occasionally happens)
I would probably go with a gear set if from a well known source ( S&S for instance)
I think the HD spec is around 10 thousands and for gear drive cams it is in the 3 to 4 thousands range.
Actually they had a booth in Sturgis and It took 10 times the strength to turn the chain drive with the lil plastic guide than it did the gear drive.
ive been told that you can run larger cams with the gear drives because the cams rotate different than the chain drives(the lobes dont run together)
Back in the day, before the upgraded hydraulic tensioner/roller chain setup, gears were the only alternative to the early spring loaded tensioner setup. However, the upgraded OEM cam drive system is soooooooo much easier to work with. Unless one is building a drag motor or a high compression, long cammed street motor, there really isn't any reason to install a gear drive system, unless you just want to. JMHO
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Road Master
Joined: Jun 2008
Posts: 868
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From: Trenton,N.J.
Anyone have any feedback on these? I was told it adds 8-10hp, stock valve springs acceptable, increases valve timing by eliminating timing CHAIN lash and loosely fit stock chain drive. The kit i was looking at includes: cams, inner gears, outer gears, inner and outer bearings and gaskets, and recommends adjustable pushrods be used. Thanks in advance!