Covert a pair of cams driven by belt to gear drive- what book would have the maths ?

# Thread: Covert a pair of cams driven by belt to gear drive- what book would have the maths ?

1. Cast Iron
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## Covert a pair of cams driven by belt to gear drive- what book would have the maths ?

I have an engine I'm going to use to power a pto water pump. The engine is completely gear driven except the timing belts for the camshafts(DOHC) are belt driven. Is there a text where I could learn the math to either order or machine a set of gears to replace the timing belt ?

Thanks.

2. The replacing gears have to have at least enough members to turn the cam shafts the same direction as the timing belt did

ALL four stroke cam shafts turn at one half crank shaft speeds - like 20 teeth on the crank nose and 40 teeth on the cam noses

Not much math involved

LUBE issues. The belt needed no lube - the gears will need constant lube

Structural issues - the belt had no intermediate members to support - except maybe a tensioning idler. The gear train will need supports for every gear on the way up to the cams
Last edited by johnoder; 10-13-2019 at 01:19 PM.

3. Titanium
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Originally Posted by geardoc
Is there a text where I could learn the math to either order or machine a set of gears to replace the timing belt ?
If it's a four-stroke, it's 2 to 1. If the engine is a two-stroke it is 1:1 (crank to cam ratio).

Idler gears can be any number of teeth, it doesn't matter. They don't change the ratio, just the direction.

Just measure your center distances and divide 'em up. Them's your pitch diameters. Decide how many teeth you want and that's your diametral pitch for the teeth.

Viola, cello, and double bass, bob's yer uncle.

4. Diamond
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You also have to consider harmonics and max tooth loads, not to mention adding a sh!t ton of complexity to a system that already works.

Why do you want to do this? And, uh, your name is "geardoc", why are you asking us these questions?

5. Diamond
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Originally Posted by geardoc
I have an engine I'm going to use to power a pto water pump. The engine is completely gear driven except the timing belts for the camshafts(DOHC) are belt driven. Is there a text where I could learn the math to either order or machine a set of gears to replace the timing belt ?

Thanks.
The math is simple enough. we call it "historical experience". Ferrari's "Test Rossa" 4-banger wasn't the first. Time was, gears up the front of short-lived competition engines sounded as if they were a bleedin' orchestra, the noise involved. Valiant warriors, but surely weren't no 100,000 miler fuel and forget mills. Plebian pushrods dominate that end of the longevity arena - many of them 200,000 miles, no overhaul, actually.

Spur gears - "DIY" with neither prior history nor ability to simulate I'd guess to have about four times the need of service or 1/4 the life expectancy of OEM designed-in and proven synchronous elastomeric belts. See also roller chain and its need of guides.

Pushrods yet live.

The industry adopted Gilmer (and subsequent) belts for a reason. You happen to have a notoriously BAD example? There will be other faux pas, too. Just go and pick a different engine as already has the track-record for longevity.

Pushrods exist.

Even if your "engineering" skills are up for it and time is cheap, it usually takes more than one go to get it working, cold start. "Crate" price, new engine complete, should be a lot less than the cost of gears plus a new front to mount them, plus R&D lube system, proto-typing & testing.

You ain't exactly the first person ever to want to pump sumthin', but taking-on a project like this?

More likely to be time, money, and aggravation aimed right up yer arse than water that gets "pumped".

6. Don't forget silent chain and if you go with gears, they should be helical.

Tom

7. Diamond
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Originally Posted by TDegenhart
Don't forget silent chain and if you go with gears, they should be helical.

Tom
"Silent" chain is massey. That limits max RPM to much lower figures than lighter elastomer-coated resilient belting with an aramid tension belt. The force tries to make a CIRCLE, putting a good deal of inward pull on the shafts.

Vertical shaft, "crown" or bevel gears, each end have been used to carry rotation to camshafts.

Gears, in general, try to force shafts and studs apart. Helicals also have end-thrust. Herringbones that balance it cost more, may also require more space.

Resisting any of these forces raises mass and costs - especially where a device was designed for a DIFFERENT set of them than the new goal brings in.

Water, OTOH, has been successfully pumped with hot-bulb monsters, Fairbanks-Morse hit and miss, Lister(oids), Wisconsin air-cooled Vee-Twins and piston-valved 2-strokes... pretty much ANYTHING that can supply power since human or livestock muscle wanted to see itself replaced with wind .. or even just other water.

See "hydram", as G'Dad used immersed in a creek to keep a stock watering tank up the hill full.

Hydraulic ram - Wikipedia

Moving water ain't exactly rocket insemination. 'Specially not HERE, as the PUMP already in-hand has RPM limits, too.

8. Hot Rolled
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The maths is simple: driver/driven x input speed = output speed.
For pulleys you use the diameters, for gears its the number of teeth.
One of the first engineering formulas I ever learned, over 4 decades ago.

9. Diamond
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yeah...the big question is 'why'....? In any case, just go to the Ford dealership and ask to speak to one of their ASME trained certified technicians. Tell him you'd like to pick his brain on this topic, what with his experience in keeping the SOHC engines running.

10. Originally Posted by thermite
The math is simple enough. we call it "historical experience". Ferrari's "Test Rossa" 4-banger wasn't the first. Time was, gears up the front of short-lived competition engines sounded as if they were a bleedin' orchestra, the noise involved. Valiant warriors, but surely weren't no 100,000 miler fuel and forget mills. Plebian pushrods dominate that end of the longevity arena - many of them 200,000 miles, no overhaul, actually.

Spur gears - "DIY" with neither prior history nor ability to simulate I'd guess to have about four times the need of service or 1/4 the life expectancy of OEM designed-in and proven synchronous elastomeric belts. See also roller chain and its need of guides.

Pushrods yet live.

The industry adopted Gilmer (and subsequent) belts for a reason. You happen to have a notoriously BAD example? There will be other faux pas, too. Just go and pick a different engine as already has the track-record for longevity.

Pushrods exist.

Even if your "engineering" skills are up for it and time is cheap, it usually takes more than one go to get it working, cold start. "Crate" price, new engine complete, should be a lot less than the cost of gears plus a new front to mount them, plus R&D lube system, proto-typing & testing.

You ain't exactly the first person ever to want to pump sumthin', but taking-on a project like this?

More likely to be time, money, and aggravation aimed right up yer arse than water that gets "pumped".

<Ducking and running for cover ...>

11. Diamond
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Why does every OHC, pushrod-less engine I've ever driven have such a soft bottom end power delivery? Drive any 'modular' Ford V8, for example, and it's like mush until the revs come on.

12. Diamond
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Originally Posted by GregSY
Why does every OHC, pushrod-less engine I've ever driven have such a soft bottom end power delivery? Drive any 'modular' Ford V8, for example, and it's like mush until the revs come on.
Cam timing. Doesn't have to be, but because OHC engine can run to higher RPM, the cam timing is designed to get the higher top-end power, at the cost of less low-end grunt. Intake and exhaust paths will be similarly tuned.

Since pushrod engines are typically designed with a lower max RPM, cams are made for lower-end torque (ditto I/E paths), so that's what you get.

Most modern OHC engines with variable valve timing will mitigate some of the loss of low-end torque, but to do it right you really need variable geometry in the intake and exhaust paths to get best flow at all the RPM/load parameters.

Or just throw on a turbo or supercharger, or NOS.

13. Diamond
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Switch to gear or chain drive and you need to spray oil onto the gears and gear bearings. Better if the bearings are directly pressure lubed This oil dripping back down has to be sealed off and drained into the crankcase. The cover over a timing belt is not sealed it is just to keep off dirt and splashed water from the belt.
Bil lD

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As many have already stated, the concept is simple but the execution is fraught with peril. I used to work at the US branch of Cosworth Racing, and there was more engineering in the cam drives of the DOHC Indy engines than in the entire rest of the engine. They were designed with torsionally compliant gears and damping, as well as using prime numbers of teeth in the intermediate gears to spread the wear evenly amongst the teeth. I'm not sure why you would need the high RPM benefits of a DOHC to drive a water pump, but ironically, the first Cosworth F1 engine, the DFV, was developed as a substitute for the Coventry Climax, which was originally developed as a fire pump prime mover.

15. Diamond
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Hey Sidebite,
We have a number of people here involved with the racing industry, if you ever feel inclined to start a thread about your experiences in it I'm sure a lot of folks would be interested.

16. Titanium
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Vintage Bentleys had a system of cam drive that used three pushrods,on eccentrics to drive the OHC.......musta been a good idea ,cause people pay millions for the cars now...Salmsons had DOHC driven entirely by skew gears.....which negated expansion problems.....one of the Morriss had a SOHC driven by skew gears too,in the fifties.

17. Diamond
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Originally Posted by GregSY
Why does every OHC, pushrod-less engine I've ever driven have such a soft bottom end power delivery? Drive any 'modular' Ford V8, for example, and it's like mush until the revs come on.
"Mush" is actually righteous, it reduces tired commuters and soccer-mums stalling outright and blocking traffic. Sounds as it you grew up on Pierce powered fire trucks, big Packard OHV's, or early MOPAR Hemi's as could shift a 2-speed slush box into high range at 15 MPH, stay in the same gear to around 120-plus MPH?

4.2 Fomoco Jaguars, the "NA" 295 HP flat-out EATS the poopercharged, not fartercharged "R" models off the line. Settling for 172 MPH top-end vs 206 or wotever is not really any great loss, jailbird life as it could be, even off the back of 'tronic governing to a max 150-152 MPH. Sanity check, it is just a by-product of tall gearing for decent MPG delivery, "real world" highways.

Meanwhile, MOPAR and GMC have built motors with power curves so damned end-to-end flat they'd trip an EKG monitor in an Intensive care ward into "flatline" of Cardiac arrest.

All about what the application needs, ain't it?

"Cavitating" a water pump never made a lot of sense to me, either, BTW.

Serious pumping work to be done, no mains 'lectricity? A Diesel set right-on optimal RPM is your probable winner, one-lung air or water-hopper cooled on-up to "many", bit of mounting frame welding and shaft coupling the only "machine shop" work needed, if-even that much. Rice-farmers do this all over Asia, after all.

Belgian-American Leo Goosens, Harry Miller's good right hand, knew about as much about geared OHC drives as anyone who ever set India ink to vellum.

Even so? Far, far more 351 Ford "Cleveland" based or Dagenham 116E 4-banger based mills actually FINISHED and WON races than his Novi V8 ever even finished.

Horses for courses... or now and then? Even a few of Cosworth's clever MULES?

18. Aluminum
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I own a couple of Honda v4 motorcycles that have gear driven cams; a 1985 vf1000r and a 5th gen vfr800. Honda went to a lot of trouble to spring load the gears in the valvetrain to reduce backlash. The bikes sound great with the gear whine singing out over the v4 exhaust choir.

19. Hot Rolled
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Originally Posted by GregSY
yeah...the big question is 'why'....? In
Yeah, why? Sounds like an bad idea, and if you have to ask about the math for the gears, you are not the right one to do it.
CarlBoyd

20. Diamond
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Originally Posted by Metalurgent
I own a couple of Honda v4 motorcycles that have gear driven cams; a 1985 vf1000r and a 5th gen vfr800. Honda went to a lot of trouble to spring load the gears in the valvetrain to reduce backlash. The bikes sound great with the gear whine singing out over the v4 exhaust choir.
Yah, sure. Two-wheelers are a lot of FUN, priced accordingly, coin of the realm, body damage, yours and theirs, either or both.

But WTF? OP wants to operate a WATER PUMP, and figures he has to re-invent an existing IC engine? That sounds either wrong for the job to BEGIN with, ELSE suffered mostly from nothing more complicated than half-assed maintenance? Or none at all?