Author Topic: offset idler bushing  (Read 5847 times)

32 coupe

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offset idler bushing
« on: April 29, 2012, 11:23:00 PM »
After considering the options and my tools and skills I decided to use the offset bushing idea. A couple of hours at the old Atlas lathe and I have about a .045 offset which is pretty close for my needs. Thought you guys might like to take a look.

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« Last Edit: April 30, 2012, 01:02:39 AM by 32 coupe »
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mike90045

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Re: offset idler bushing
« Reply #1 on: April 30, 2012, 06:22:43 AM »
What locks it onto the shaft so it does not spin ?

ronmar

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Re: offset idler bushing
« Reply #2 on: April 30, 2012, 03:13:16 PM »
I would say probably the same thing that holds Dave's offset idler bolts in place, the nut being tightened down and the clamping force of the bolt in the case wall...  The bushing might be a little more difficult to set in place than the offset bolt, but once set and the bolt tightened in place, it shoud work OK...
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Re: offset idler bushing
« Reply #3 on: April 30, 2012, 03:41:30 PM »
Yes guys,
The bolt will hold it in place when tightened. It is a pretty snug fit and I will assemble with "locktite" when I get to that point.

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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
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xyzer

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Re: offset idler bushing
« Reply #4 on: April 30, 2012, 06:50:06 PM »
I made a bushing like that in the beginning to figure out the offset It needed, and it was a bear to adjust. Once it is in the right location you are gold but getting it there was a chore. I would shrink the bushing on the bolt and make it turn with it. The offset needs to oriented to keep the oil groove on top. Anyway you can offset will fix it for the better! 
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Re: offset idler bushing
« Reply #5 on: May 01, 2012, 01:07:49 AM »
Looking at the the Metro 6/1 I have I can see where setting the lash and the bushing I made would be a real pain.

The twins are a different animal...the crank will support itself on the center bearing and one end so removeing the bearing housing from the govenor/injector/gear end gives a perfect view of the crank to idler setup as well as a view of the adjustable bushing position.

In my case the injector/govenor cover must be in place because the cam has so much "float" on the center bearing that the cam will not line up without the cover in place, but here again, in my case the top end is off the engine so getting a view of the cam to idler lash is pretty clear through the top of the block and I can still view the bushing, crank gear/idler at the same time.

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Metro 6/1 turning a ST 7.5 KW gen head
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Quinnf

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Re: offset idler bushing
« Reply #6 on: May 01, 2012, 11:08:23 PM »
There's actually a couple different ways you can do that.  

1.  Machine a bushing that the gear rides on to offset the idler gear on the big end of the idler pin, or

2.  Offset the entire idler pin.  

If you choose #1, you need to either press fit the bushing onto the pin, or Locktite it.  There's a special flavor of Locktite that's made for locking gears onto shafts.  Can't recall what it's called offhand.
If you choose #2, no need to Locktite the bushing in place.  The shoulder on the pin will bear against the crankcase wall when you tighten the nut.

I turned down the idler pin where it passes through the crankcase wall to accommodate the ID of the eccentric bushings.  Then I machined a series of brass bushings 0.010" to 0.050" offset.  Held them in a 4-jaw chuck clamped to teh table of the mill.  If you don't have a mill you can also make it entirely on a lathe if you don't mind messing up your headstock/tailstock alignment. 

Tried each bushing in turn until the backlash just about disappeared.  Once it was in place and I had the eccentric pointed in the right direction.  

http://www.microcogen.info/index.php?topic=936.msg26850#msg26850

The difference the offset idler bushing makes in engine sound is amazing.  No more "clack-clack" as you crank it over.  Very little backlash.  Engine runs with much less mechanical noise.

I suspect the problem with broken gears on these engines is 90% attributable to excessive backlash caused by improperly located idler gears.

Quinn

« Last Edit: May 01, 2012, 11:17:02 PM by Quinnf »
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Re: offset idler bushing
« Reply #7 on: May 01, 2012, 11:23:09 PM »
Quinnf,
I am sure that pic is where I got the idea. The forum is a wealth of knowledge, no doubt.

My bushing @ .045 is still short of being as close as I would like to see. I'll turn a larger one in a few days and see where I end up.

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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 !"

cujet

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Re: offset idler bushing
« Reply #8 on: May 02, 2012, 01:32:45 AM »
Wow, that looks like one of my bushings, you know, the ones that I was trying to machine perfectly concentric!

On a serious note, once you know where it fits, you could TIG weld it in place.
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