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Author Topic: Adjustable cam spindles?  (Read 930 times)

AgentX

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Adjustable cam spindles?
« on: June 17, 2013, 09:01:04 AM »
Can someone explain to me what the Samrat adjustable cam spindles actually do?

I've heard they can move to take up gear lash in the timing train, but I don't understand how you could take up lash in one direction without making it worse in another, nor how you could adjust to take up lash without making the cam run in an eccentric path.

Or do I have it wrong, and they adjust to take up end play, and not gear lash?  Or something else entirely?

Thanks for the guidance...

-Mike

ERC

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Re: Adjustable cam spindles?
« Reply #1 on: June 17, 2013, 10:10:00 PM »
They're designed to take up the backlash to make them less noisey.   ERC
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ace.cafe

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Re: Adjustable cam spindles?
« Reply #2 on: June 17, 2013, 11:30:29 PM »
They were originally introduced with the AVL engine, and people started putting them into the Iron Barrel models to reduce gear lash noise.

Personally, I think they are a waste of time, and something to just go wrong from unnecessary complexity.
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Arizoni

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Re: Adjustable cam spindles?
« Reply #3 on: June 18, 2013, 12:32:19 AM »
The diameter the cam bearing is riding on is slightly eccentric to the spindles locator diameter that fits into the pilot diameter on the engine housing.

Rotating it in the engine housing will change the cam gear mounting distance from the gear center that is driving it.

As the crankshaft position is fixed, the exhaust cam gear spindle needs to be adjusted first to obtain the optimal mounting distance and gear backlash.

Yes, doing this will alter the gear center distance to the other cam gear.

The other cam gear is also mounted on a eccentric spindle that must then be adjusted to correct for the exhaust cam gears movement so that the proper mounting distance and backlash between the cam gears is maintained.

As Ace said, the benefits of doing this adjusting is debatable.  IMO, the cushion of the oil film on the gear teeth will usually dampen out the thrust reversals caused by the forces generated by the cam lobes.

Had Royal Enfield used helical gears instead of spur gears on their cams then none of this would  even be discussed but helical gears cost more to manufacture and they come with their own set of end thrust problems due to their angular teeth.
« Last Edit: June 19, 2013, 11:58:20 PM by Arizoni »
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AgentX

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Re: Adjustable cam spindles?
« Reply #4 on: June 19, 2013, 06:33:48 AM »
The diameter the cam bearing is riding on is slightly eccentric to the spindles locator diameter that fits into the pilot diameter on the engine housing.


Arizoni, ok, my head nearly exploded.  But now I get it.  The eccentric moves the shaft which is driving the cam gear, but the cam gear and shaft always remain in line.

Thanks!!!

Ace, appreciate the advice and I made the tentative assuption that the complexity was not worth any corresponding benefit.  Had just been talking w Chumma over the weekend about gear lash while we were setting TDC on my bike, and this topic came up.  Just wanted some insight on how it might work.

singhg5

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Re: Adjustable cam spindles?
« Reply #5 on: June 20, 2013, 12:19:44 AM »
CJ had once mentioned about this article written by RE Guru Nandan on cam-gear backlash and adjustable (eccentric) spindles found at this link -

http://cybersteering.com/cruise/feature/bullet/camgear.html
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AgentX

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Re: Adjustable cam spindles?
« Reply #6 on: June 20, 2013, 01:35:46 AM »
CJ had once mentioned about this article written by RE Guru Nandan on cam-gear backlash and adjustable (eccentric) spindles found at this link -

http://cybersteering.com/cruise/feature/bullet/camgear.html

Far be it for me to doubt Nandan, but isn't the existence of some lash necessary for meshed spur gears to actually turn?  (ie, it's not just an artifact of bad manufacturing?)

Arizoni

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Re: Adjustable cam spindles?
« Reply #7 on: June 20, 2013, 04:38:48 AM »
IMO, the answer to the need for some backlash is, yes.  A small amount of backlash is needed to allow for the oil film that needs to exist between the gears.

The article mentions the increase in the distance between the gear centers because of thermal expansion.
A close estimate of the thermal expansion between the gear centers depends on the size of the gears and the temperature rise from room temperature where the gears were adjusted.

I don't know what the size of the gear teeth are on the RE cams but they look like 20 pitch.
If this is true, the 20 tooth drive pinion on the crankshaft would have a pitch diameter of 1.000 inches.  The 40 tooth cam gears would have a pitch diameter of 2.000 inches.
That makes the theoretical mounting distance between the gears (1.000/2) + (2.000/2) = .500 + 1.000 = 1.500 inches.

The difference in the rate of thermal expansion between aluminum and steel is approximately 6 X 10^-6 inch per inch per degree F.

At a crankcase operating temperature of 250 degrees F that would be equal to a temperature rise of 250-70 = 180 degrees.

180 X (6.0 X 10^-6) X 1.500 = .0016 inches so the distance between the crankshaft and the exhaust cam center will increase by that value.  This conceivably could create enough backlash in the gear mesh to allow for a lubricating film but what happens at 40 degrees F?  Or (for those brave riders who go forth in the wintertime) 28 degrees F?  (Been there, done that).
At these sub room temperatures, if the gear system was adjusted to zero backlash at room temperature, it would be running with a interference between the gear teeth at the temperatures below 70 degrees.

A interference between running gear teeth makes heat and wears the surface.  Heat expands the gear leading to a increase in interference.  Definitely bad.

As I mentioned earlier, IMO it is better to have a slight amount of backlash between the gears at room temperature.  That backlash allows for a constant oil film to lubricate and cool the gear mesh and to allow for cold conditions during the winter.

My apologies to those who don't like math.  Just ignore the number stuff and read the rest.  ;D
« Last Edit: June 20, 2013, 04:42:31 AM by Arizoni »
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singhg5

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Re: Adjustable cam spindles?
« Reply #8 on: June 22, 2013, 12:26:54 AM »
@Arizoni:

I love your math ;D ! Agree with what you said that small amount of backlash is needed.

According to one of the guys with these gears, initally they were set very tight but got better after running a couple of hundred miles. Essentially some space gets created, perhaps due to the type of metal used to make them. Very much like breaking in a new engine of RE that does not run as well when fresh of the boat and transmission is not smooth - after 3K miles it is a different bike.
« Last Edit: June 22, 2013, 04:38:40 AM by singhg5 »
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ace.cafe

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Re: Adjustable cam spindles?
« Reply #9 on: June 22, 2013, 11:54:07 PM »
From what I have seen, these things are often associated with the desire to have as silent mechanical noise as possible, and sometimes with total disregard for the health of the engine in the process.

I have read some valve adjusting techniques written by a "guru" that mentioned adjusting the lash zero when warm, so the lash is tighter than zero when cold. This is a recipe for a burnt valve. There is no need to have "quiet valves". They are meant to make noise.

Somebody else posted that link about adjusting cam spindles a while back, and Kevin Mahoney came on here and stated emphatically that NOBODY should ever adjust their cam spindles like that. And I definitely agree.

So my recommendation is to not worry about trying to eliminate normal running noises.

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AgentX

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Re: Adjustable cam spindles?
« Reply #10 on: June 23, 2013, 02:55:17 AM »
So my recommendation is to not worry about trying to eliminate normal running noises.

If my bike didn't sound like a sewing machine sitting on top of a .50 caliber machinegun, I'd be concerned...

GreenMachine

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Re: Adjustable cam spindles?
« Reply #11 on: June 23, 2013, 02:55:11 PM »
Agent X:   If my bike didn't sound like a sewing machine sitting on top of a .50 caliber machinegun, I'd be concerned..

Haaa Good one..That pretty much explains the sound even thought the .50 cal is a bit louder.. ;D
Oh Magoo you done it again

AgentX

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Re: Adjustable cam spindles?
« Reply #12 on: June 23, 2013, 03:27:32 PM »
even thought the .50 cal is a bit louder.. ;D

Marginally...

Kevin Mahoney

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Re: Adjustable cam spindles?
« Reply #13 on: June 24, 2013, 08:42:55 PM »
Samrat has been selling these since the beginning of time. When I started this business in 1998 they were making them and they were old then.
The Indian customer is FAR more concerned about engine noise than we are in the US. The only reason for the existence of this part is to quiet down the engine. A mechanic in India was(is) graded on his ability to quiet down an engine and get the best thump (two different things).
The gears on the UCE can be run with what amounts to zero backlash, but they are a special cut type of tooth. The cams on the iron barrel need a bit of clearance. You can use Samrat spindles and run them to zero but you will pay the piper sooner or later with reduced life.
An Indian mechanic is more likely to have a wall of cams and selectively fit them for the best fit. Most often the quietest fit is not the best fit.  Unless they are horrible I think it is best to leave things be (and I sell the spindles)