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Old 04-28-2020, 02:11 AM   #1
hardtimes
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Default Timing gears use.

When building a warmed up A/B , is it best to use straight cut timing gears over, say...helical cut gears ?
I’m mindful of the FORWARD motion being forced on the cam (against cam button/spring). Can most of this forward motion/wear be eliminated with use of straight cut timing gears ?


ANSWER:
Well, according to Dan's answer/contribution to this thread...the answer to my question is...YES !
Thanks Dan. That's kind of what I remember from a convo with you from a loong time ago.

Last edited by hardtimes; 05-03-2020 at 12:46 PM. Reason: ..........
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Old 04-28-2020, 11:54 AM   #2
Bob Bidonde
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Default Re: Timing gears use.

In general, as the gear tooth angle increases, so to does the thrust loading they produce. Straight cut teeth on the Model A's camshaft drive gears have the least thrust loading, and the thrust loading they do produce is due to mostly to tooth wear and manufacturing tolerances.

So then, why is the thrust plunger in Model "A" necessary? The oil pump-distributor drive gear on the camshaft is a worm screw type which produces considerable thrust loading.
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Old 04-28-2020, 12:22 PM   #3
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Default Re: Timing gears use.

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Originally Posted by Bob Bidonde View Post
In general, as the gear tooth angle increases, so to does the thrust loading they produce. Straight cut teeth on the Model A's camshaft drive gears have the least thrust loading, and the thrust loading they do produce is due to mostly to tooth wear and manufacturing tolerances.

So then, why is the thrust plunger in Model "A" necessary? The oil pump-distributor drive gear on the camshaft is a worm screw type which produces considerable thrust loading.
Hey Bob,
Same thoughts here.
I'm thinking that the considerable forward thrust, created via camshaft drive gear, can be 'eliminated' by use of a different type ignition type (vs conventionally location distributor).

I've got couple sets of straight and bevel types new made by Dan. Matched jewelry grade sets. Building/planning new project and want least wear and least HP robing equipment possible.

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Old 04-28-2020, 01:24 PM   #4
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Default Re: Timing gears use.

Does the oil pump drive gear add any thrust?
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Old 04-28-2020, 01:43 PM   #5
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Default Re: Timing gears use.

The most common way to adjust cam end thrust is to modify the cover. Get rid of the spring stuff and tap a hole for a 3/4-16 socket head cap screw with a thin jam nut. Some apply a thin layer of brass on the end of the screw. Set the clearance around .005 to .007.
This should be done in a machine so the hole is straight.
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Old 04-28-2020, 02:01 PM   #6
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Default Re: Timing gears use.

Pete IMHO, has the correct solution.

The helical gears work fine for stock and mildly modified motors.
The real question is the amount of valve spring loading is applied to the cam which accentuates the thrust loading.

John
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Old 04-29-2020, 01:59 AM   #7
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Default Re: Timing gears use.

Quote:
Originally Posted by Pete View Post
The most common way to adjust cam end thrust is to modify the cover. Get rid of the spring stuff and tap a hole for a 3/4-16 socket head cap screw with a thin jam nut. Some apply a thin layer of brass on the end of the screw. Set the clearance around .005 to .007.
This should be done in a machine so the hole is straight.
Hey Pete,
I have front covers set up as you suggest, thanks.
Seems to me, that use of straight cut timing gears have less wear on cam driven gears and less forward thrust to deal with. Canít think of any negatives from such use ?
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Old 04-29-2020, 02:45 AM   #8
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Default Re: Timing gears use.

Strait cut gears are NOISY!
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Old 04-29-2020, 11:30 AM   #9
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Default Re: Timing gears use.

VERY NOISY! If it ain't broke, don't fix it! The OP/dist drive gear tend to pull the cam to the rear.
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Old 04-29-2020, 12:29 PM   #10
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Default Re: Timing gears use.

Jim, Hardtimes,

One issue with the straight cut gears has been the backlash, some are better than others.

IMHO, Dan McEachern still makes the best gears around.

J

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Old 04-29-2020, 03:08 PM   #11
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Default Re: Timing gears use.

I have used Dan's gears in most of my engines. If the backlash is set properly, the noise is minimal. Spur gears are for racing engines anyway with open exhaust.

Some people like gear whine. For certain engines cam drive gear sets can be had that are purposely machined so they will be noisy.
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Old 04-30-2020, 01:35 AM   #12
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Default Re: Timing gears use.

Quote:
Originally Posted by Jim Brierley View Post
VERY NOISY! If it ain't broke, don't fix it! The OP/dist drive gear tend to pull the cam to the rear.
Hey Jim B,
‘dist drive tend to pull cam to the rear’....hmm, never have heard or knew of that info !! Thanks. Then how important is cam button/spring ?
Is this rearward pull much increased with high RPM ? ?

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Old 04-30-2020, 01:52 AM   #13
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Default Re: Timing gears use.

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Originally Posted by johnneilson View Post
Jim, Hardtimes,

One issue with the straight cut gears has been the backlash, some are better than others.

IMHO, Dan McEachern still makes the best gears around.

J

John
Hey John,
Danís gear sets are only timing gears Iíve used.
Backlash is very important issue.
Iíve used his straight cut gear sets before (bronze/steel), without problems.
I like the noise, but am somewhat surprised at how quiet they were!
Full disclosure....I do have hearing machines in both ears.

I intend to use Danís equipment in a (off topic, for this crowd) 4 Cyl project.
Thanks for sharing your experience/help !
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Old 04-30-2020, 02:08 AM   #14
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Default Re: Timing gears use.

Quote:
Originally Posted by Pete View Post
I have used Dan's gears in most of my engines. If the backlash is set properly, the noise is minimal. Spur gears are for racing engines anyway with open exhaust.

Some people like gear whine. For certain engines cam drive gear sets can be had that are purposely machined so they will be noisy.
Hey Pete,
Ha, I do like a bit of noise /whine with my smelly four bangers !
Your skills/knowledge had me thinking of calling you for this build ! But you are so far away. Yeah, racing comes to mind when you come to mind, so spur gears will be appropriate!
May not race, but with 5, 4 bolt mains , etc.... I think you would make something special of it !
Rick
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Old 04-30-2020, 08:48 AM   #15
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Default Re: Timing gears use.

Rick,

Dan's gears will work just fine, modify the front cover for the set screw to set end play.
IMHO, this is more of a function to try and keep control of the ignition timing when you start running close to detonation.

The amount of cam walk is typically a function of valve spring pressure and the flexing of the cam. You mention 5 mains, I assume 5 bearings on the cam too.
If you are running something like a 4 port Riley with 8 intake valves, you just have to watch the spring seat pressures are not too high. You have two springs per lobe and then the rocker arm ratio multiplication. The good news is, those can be adjusted without disassembling the entire motor.

Stay safe these days, J
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Old 04-30-2020, 12:35 PM   #16
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Default Re: Timing gears use.

The motion of pulling the cam by the OP drive gear is minimal. With crank, cam and dive gear installed, turn the crank by hand and you'll see what I'm talking about. The button is still needed for complete control.
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Old 04-30-2020, 01:40 PM   #17
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Default Re: Timing gears use.

Quote:
Originally Posted by johnneilson View Post
Rick,

Dan's gears will work just fine, modify the front cover for the set screw to set end play.
IMHO, this is more of a function to try and keep control of the ignition timing when you start running close to detonation.

The amount of cam walk is typically a function of valve spring pressure and the flexing of the cam. You mention 5 mains, I assume 5 bearings on the cam too.
If you are running something like a 4 port Riley with 8 intake valves, you just have to watch the spring seat pressures are not too high. You have two springs per lobe and then the rocker arm ratio multiplication. The good news is, those can be adjusted without disassembling the entire motor.

Stay safe these days, J
Hey John, yes 5 brng cam (Jim B).
Great info and lots to think on , thanks !
Iíve always been advised that...cast iron & alum...not best used together! Iím a believer. So itís a matter of locating alum head that will Ďlight it upí. Iíd bet that you know whose head Iíve been waiting on ! Have been Ďholed upí for tooo long, trying to stay healthy. NEVER bored, as plenty to do !
Be safe !
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Old 04-30-2020, 07:53 PM   #18
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Default Re: Timing gears use.

Rick,

I find more old wives tales taken as gospel on Model "A"s than ever, including my wife.
Using a cast iron head on the alum block. Or the other way around, alum head on iron block. If it was, I would have a couple problem motors with alum girdles and iron blocks with alum heads.
Have had some pretty good results with 4 port cragar heads lately, modified and really modified (read lots of welding)
Whatever you build, do the work to tune it properly. That is when the hard work starts.

Enjoy, J
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Old 05-01-2020, 11:27 AM   #19
hardtimes
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Default Re: Timing gears use.

Quote:
Originally Posted by johnneilson View Post
Rick,

I find more old wives tales taken as gospel on Model "A"s than ever, including my wife.
Using a cast iron head on the alum block. Or the other way around, alum head on iron block. If it was, I would have a couple problem motors with alum girdles and iron blocks with alum heads.
Have had some pretty good results with 4 port cragar heads lately, modified and really modified (read lots of welding)
Whatever you build, do the work to tune it properly. That is when the hard work starts.

Enjoy, J
Hey John,
Well, with the amount of work that you do and type of engines you work, you sure have enough experience and finished product to qualify , IMO, as an expert on this subject.

I am aware of expansion / contraction rates , when different metals heat/cool.
I'm not an engineer , but a shade tree type mechanic. Still I wonder what the longer term negative aspects (oxides) can be/are when using copper/alum/iron (head install) in an engine ?

My 'instinct' is to torque properly and often, use sacrificial anode and good coolant and let nature sort out the rest !

Be safe and listen to wife, as they know more than you suspect...me thinks..lol

Oh, BTW....I could be wrong but don't think that the iron OHV 4 port Riley has what's needed to do this job~ i.e. - to make 200 or more HP?

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Old 05-02-2020, 06:19 AM   #20
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Default Re: Timing gears use.

Quote:
Originally Posted by johnneilson View Post
Rick,

I find more old wives tales taken as gospel on Model "A"s than ever, including my wife.
Using a cast iron head on the alum block. Or the other way around, alum head on iron block. If it was, I would have a couple problem motors with alum girdles and iron blocks with alum heads.
Have had some pretty good results with 4 port cragar heads lately, modified and really modified (read lots of welding)
Whatever you build, do the work to tune it properly. That is when the hard work starts.

Enjoy, J
John Neilson, can you discuss your work on 4-port Cragars. I have a Dan Price version and would be most interested in what you are doing with the intake ports.,
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