Author Topic: Idler gear backlash  (Read 769 times)

32 coupe

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Idler gear backlash
« on: April 16, 2021, 11:47:03 PM »

Anyone have specs or a link for setting backlash ?

Asking for a friend........

Metro 6/1 turning a ST 7.5 KW gen head
Changfa 1115 turning a ST 15 KW gen head
Ashwamegh 2/25
John Deere 110 TBL
New Holland TC 30

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BruceM

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Re: Idler gear backlash
« Reply #1 on: April 18, 2021, 01:47:24 AM »
https://listerengine.com/smf/index.php?topic=8063.msg91441#msg91441

I haven't found XYZer's (Daves) definitive piece.  By braille there should be some movement, but not gross. Music wire to idler tooth from dial gauge improves braille training.  I expect even 15 mils would be tolerable.




gadget

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Re: Idler gear backlash
« Reply #2 on: April 18, 2021, 03:17:46 PM »
First check I would do is to make sure its consistent all the way around. Mine is not. Its tight in one spot and loose in another. I think my Cam is bent.

32 coupe

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Re: Idler gear backlash
« Reply #3 on: April 18, 2021, 04:41:20 PM »
Bruce,
Yes,  I seem to remember trying for about 10 to 15 thou. Just couldn't recall.

Gadget,
I had one like that and I thought the hole was not centered. Got a new bronze/brass gear and it
was centered correctly.

Gary

« Last Edit: April 18, 2021, 11:18:30 PM by 32 coupe »
Metro 6/1 turning a ST 7.5 KW gen head
Changfa 1115 turning a ST 15 KW gen head
Ashwamegh 2/25
John Deere 110 TBL
New Holland TC 30

"I was sitting here reading this thinking what an idiot you are until I realized it was one of my earlier posts !"

BruceM

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Re: Idler gear backlash
« Reply #4 on: April 18, 2021, 09:40:57 PM »
Hey Gadget. It might be a good idea to mark your tight spot on the idler, then as a test, temporarily reposition the idler 90 degrees and see if the tight spot moves with the idler and the mark is still the tight spot. 

If so, Gary's situation (mis-bored idler) has a twin.   If it moves relative to your mark, a bent cam is a possibility though I wouldn't think that a bent cam would be so far out as to affect idler lash to the point of tightness, as it is typically huge on a Rajkot product.  Let us know what you find out, please, Gadget.  It might be a novel situation.


38ac

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Re: Idler gear backlash
« Reply #5 on: April 19, 2021, 11:06:16 AM »
First check I would do is to make sure its consistent all the way around. Mine is not. Its tight in one spot and loose in another. I think my Cam is bent.

The way gears are hobbed makes it virtually impossible to make one out of round,,,,,,,well OK it's India,,,,,,,

It is much more likely that the cam shaft is bent or that they somehow managed to barf up the cam gear when they sledgehammered the pin. If your engine isn't new you will have more slop at the places where back lash reverses due to wear. Correct backlash would be anywhere from none to .003 would be called acceptable at my shop.
Remember  that tooth contact occurs at two places. Thus the correct amount of offset and the position of the off set is  not a simple matter of X lash equates to X offset needed.  The idler position could be incorrect to the cam, or the crank  individually, or incorrect to both in and even distance, or incorrect to both in varying distances.
« Last Edit: April 19, 2021, 11:09:24 AM by 38ac »
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38ac

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Re: Idler gear backlash
« Reply #6 on: April 19, 2021, 11:11:39 AM »

First check I would do is to make sure its consistent all the way around. Mine is not. Its tight in one spot and loose in another. I think my Cam is bent.

The way gears are hobbed makes it virtually impossible to make one out of round,,,,,,,well OK it's India,,,,,,,

It is much more likely that the cam shaft is bent or that they somehow managed to barf up the cam gear when they sledgehammered the pin. If your engine isn't new you will have more slop at the places where back lash reverses due to wear. Correct backlash would be anywhere from none to .003 would be called acceptable at my shop.
Remember  that tooth contact occurs at two places. Thus the correct amount of offset and the position of the off set is  not a simple matter of X lash equates to X offset needed.  The idler position could be incorrect only to the cam, or only to the crank, or incorrect to both.  In and even distance, or incorrect to both in varying distances.
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32 coupe

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Re: Idler gear backlash
« Reply #7 on: April 19, 2021, 04:32:19 PM »

Now I'm not sure if my 10 to 15 is where I was......it's been several years.....sounds like a far cry from 3.

I did go out to the shop and dig out the " out of round " gear and take some measurements.

The center hole appears to be round. But when I measure from the edge of the hole to the outside of
the gear it looks like it is out of round by about .006

I do understand how gears are made/cut so how this could have happened is beyond me.

I do remember checking the camshaft for straightness but can't remember the sequence.
I also remember when I changed the old gear to the new brass/bronze gear the problem went away.

I must have had the cam/gear/idler bolt (with offset) together many times before I was happy with the results.
The engine has low hours (if I had to guess I'd say 50 or so hours) and I don't see any wear on the brass
gear so I have to assume it must be close.

These discussions always frustrate me because my memory is not what it used to be and I always feel
like I put my foot in my mouth no matter what I say.

I brought up the lash question because someone asked me about it and I didn't want to give bad advise.

The engine I had the problem with is the Ashwamegh.....my Metro gearset is still original and after at least
100 hours of run time I don't see any abnormal wear.

I haven't run the Ashwamegh for a couple of years. I'm considering settling it up with a medium load and letting
it run for several days non stop only to satisfy my concerns about wear.

Gary

Metro 6/1 turning a ST 7.5 KW gen head
Changfa 1115 turning a ST 15 KW gen head
Ashwamegh 2/25
John Deere 110 TBL
New Holland TC 30

"I was sitting here reading this thinking what an idiot you are until I realized it was one of my earlier posts !"

BruceM

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Re: Idler gear backlash
« Reply #8 on: April 26, 2021, 08:19:28 PM »
I have similar memory issues, Gary.  It's frustrating. 
Re: your out of round idler, Rojkot can do some astounding things.

It's very helpful to know 0-3 mils is the goal, 38ac.  I never got that close, even with a .055 inch offset idler bolt, the biggest one Dave (XYZer) made. 

cujet

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Re: Idler gear backlash
« Reply #9 on: May 05, 2021, 01:23:32 PM »
First check I would do is to make sure its consistent all the way around. Mine is not. Its tight in one spot and loose in another. I think my Cam is bent.

That's the variable valve timing feature. Much like modern cars!
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