Prove it to me....Camshaft Gear Drive is a HP Killer

[Jeff Lee]

I always thought the big HP advantage of gear drive over chain was the chain stretch and cam retard at high rpm's. Not apples to apples because of the rpms run, but scores of diesel engines have gear drives, they do it for the accuracy of cam and injection pump events. I don't know how to scientifically prove it, but it seems a roller chain would just also have to have less friction loss compared to a straight cut gear. As mentioned only true way would be to switch on a dyno and see. But could it be more than say 5HP loss with the gear drive?

Some engines because of design gears are the only option, some tests have shown loose belts will only retard the cam at higher rpm increasing top end power.

The biggest loss in power I have seen reported was 7 hp but I don't remember what system or engine combo.

Here are several articles talking about them, my personal experience with a Pete Jackson type was big fluctuations in timing and breaking the front main web out of my block on a 7000 rpm SBC.
https://www.bing.com/search?form=MOZSBR ... power+loss

So you have used a junk gear drive and now condemn them all? Bad policy. Mostly belt drives are used for convenience. They are easier to degree (the gear drive isn’t hard, just different and you can’t line it up “dot to dot” to start” and it is easier to move cam timing on the dyno or even at the track.

Cup cars, Pro Stock, probably Comp Eliminator and maybe some Super Stock guys (I’d have to look to see if belt drives are legal is SS because I don’t remember) are about the only ones I can think of who would do that.

Belt drives are legal for NHRA SS. However, oil pump must be driven per OEM method. On an AMC V-8, that would be by the distributor.

[Dave Koehler]

In the early 80’s the multi position crank sprockets for AMC we’re in the wrong place… not enough advance.
I used Dumont broach and made my own.
I put the cam where I wanted it without crank key marked it and scribed the position broached it and presto exactly where I wanted it.
Any competent machinist / mechanic can do it.
All that is needed is an arbor press.

Rambler guys get all the fun.

[Dave Koehler]

my personal experience with a Pete Jackson type was big fluctuations in timing and breaking the front main web out of my block on a 7000 rpm SBC.

Front main web? Dang, that took some effort. Did the H balancer have a card in that game?

[Jeff Lee]

Again, the focus of the conversation is 3-gear, not 4-gear gear drive. The problems w/ 4-gear seem pretty well known.

[Dave Koehler]

Again, the focus of the conversation is 3-gear, not 4-gear gear drive. The problems w/ 4-gear seem pretty well known.

So, what have you learned so far?

[Jeff Lee]

Block is at machine shop for new hone using profilometer, (last hone was way to smooth, not enough depth and I had steel top ring and top and second rings were .125” radial width), new Molly rings and pistons with more radial depth, going from .9mm to .043”.
And since I found no real support on the Milidon 3-gear being a HP hazard, I’ve got the machinist setting the Milidon up while he’s at it. Guess I’ll be the only SS racer with one. Or at least will publicly admit it…

[ClassAct]

Block is at machine shop for new hone using profilometer, (last hone was way to smooth, not enough depth and I had steel top ring and top and second rings were .125” radial width), new Molly rings and pistons with more radial depth, going from .9mm to .043”.
And since I found no real support on the Milidon 3-gear being a HP hazard, I’ve got the machinist setting the Milidon up while he’s at it. Guess I’ll be the only SS racer with one. Or at least will publicly admit it…

Been using a Milodon GD since 1986. Buy once, cry once. Never once have I seen an issue with vibration, harmonics or any other such things that could be traced to the GD.

[Dave Koehler]

Block is at machine shop for new hone using profilometer, (last hone was way to smooth, not enough depth and I had steel top ring and top and second rings were .125” radial width), new Molly rings and pistons with more radial depth, going from .9mm to .043”.
And since I found no real support on the Milidon 3-gear being a HP hazard, I’ve got the machinist setting the Milidon up while he’s at it. Guess I’ll be the only SS racer with one. Or at least will publicly admit it…

You will be fine. When the noses get turned up and ask why. You respond " There is a reason for it" and walk away. Heads will explode.

[289nate]

Have you looked at coatings and surfaces with the level you compete at Lee? You hear it and it’s not perfectly ideal. But everything is the best compromise at your level.

[Jeff Lee]

I use MicroBlue on crank pins, rings, ring lands, bearings. DLC on wrist pins. Also REM & MicroBlue on rear gears. MB on spindle and spool bearings, ceramic on axle bearings. Piston skirts get…I forgot!
When I can afford a clutch-less trans, I’m sure I’ll go through it also. But first I need to go fast with what I have.

[GARY C]

my personal experience with a Pete Jackson type was big fluctuations in timing and breaking the front main web out of my block on a 7000 rpm SBC.

Front main web? Dang, that took some effort. Did the H balancer have a card in that game?

Not sure but I didn't have that problem with the replacement block using the same balancer, the timing issues started after shortly after switching to the gear drive, several people told me it was the gear drive so I went back to a chain.

On the stock 400 block there is a casting seam in a triangle from the cam bearing to the out side of the main, by the time I found the issue all that was holding it together was the timing chain and cover.

[Tom68]

International thought gear drive was OK on their 8s and 4s.

lngblkpic.jpg

[Jeff Lee]

Update on my Milodon Gear Drive:

I have seen a lot of confusion on the internet about this so I thought I would ad this for posterity.

Just degreed the cam today. This is the easiest deal in the world to degree.

I used a 9” diameter Crane degree wheel instead of my monster sized Moroso so that I could keep the degree wheel on as I made adjustments to the cam gear. I did this on my short-block with piston assembly in #1 only.

Gear drive assembly is assembled LESS the cam gear.

Set up TDC of the #1 piston. Use positive stop and determine true TDC as there is dwell time at TDC. True TDC is the 1/2 way point of the dwell time. Alternatively, if you have a feel for it, you can hit TDC of the piston and ad 1 degree extra clockwise rotation of the crank. You’ll see the dwell time in action.

Set up degree wheel and a pointer at TDC.

Set up your system to measure intake lobe lift. Start with both the intake and exhaust lobes on the base of each lobe and set your dial indicator at 0”.

I have solid roller cam and found that a pair of 3/8” pipe plugs fit inside the body (flat side up) of the .904” lifters so your dial indicators probe has a large, flat surface to ride on. This goes under the “geez, can’t believe I didn’t think of that 20+ years ago!

Now rotate your crank CCW from TDC to the amount shown on the cam card for “Intake Valve Opening” BTDC. In my case it was 30° BTDC. Leave crank position alone.

Now rotate your camshaft CW from zero lift to .050” lift. (This is assuming you are setting up the cam per the cam card at .050” install method).

Your crank and cam are now installed per the cam card.

Now install the cam gear to the cam hub. There are (7) threaded bolt holes in the hub and you will have to align the (7) counter-sunk bolt holes of the cam gear to the cam hub. There is only (1) combination that will align all (7). Once you align all (7), install the (7) bolts. They will go in smooth as silk if you are aligned correctly. So if you find yourself forcing the threads in, stop! Get it right.

The camshaft is now installed in the “straight up” position per the manufactures cam card. Mark any one of the bolt holes as #1 (I used silver sharpie) and remaining bolt holes CW 2-7. Doesn’t matter what bolt hole you start with, number all (7) in a CW direction.

If you want to advance or retard the camshaft, Milodon includes a chart (also available online). The chart will tell you which # bolt hole will be used for alignment purposes. In my case, I am considering retarding the cam timing 4°. If I do, I will take out the (7) bolts and per the chart, will align cam gear bolt hole #5 with the cam hub after rotating the cam CCW (for retard). (You would rotate the cam CW to advance). This is just a move it and try it operation; once a threaded bolt hole on the cam hub aligns with the prescribed bolt hole on the cam gear, in the appropriate rotation, then you are set to put the (7) bolts back in.

I also checked the exhaust lobe to the cam card (Asymmetrical cam). Both the Intake and Exhaust lobes came in exact per the cam card.

Don’t forget to LockTite all the bolts used in the full assembly.

Hope this helps somebody. All Milodon instructions are online.

[prairiehotrodder]

good work, thanks for posting this. I would run a milodon gear drive in a heart beat. Especially if i was using a cam driven fuel pump for alcohol.
Brian

[PackardV8]

We Studebaker guys had years of fun sneering at the cheapo GMs shredding their plastic cam chain gears while Studes just motored on with standard fiber cam gears or performance/truck applications with an aluminum cam driven gear.

The Packard V8 uses a big, wide Morse link chain. I've never in sixty years seen one of these do more than get slightly loose.



But no, I wouldn't take most aftermarket gear drives as a gift.