How to measure Piston Ring Gap, ect?

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CraigKennedy
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How to measure Piston Ring Gap, ect?

Postby CraigKennedy » Thu Mar 19, 2015 7:10 pm

Hey yall, in my previous post I am set out to find the source of metal shavings in my oil pan, I have the engine on a engine stand and have the crank, pistons, and head removed. While I am in there I want to check my piston ring gap. I know that I need to remove the compression rings from the piston and lay it straight in the bore and measure the end gap.
Where do I measure the lower compression ring and the oil control ring??
How to know if my engine needs to be rebored?
How do I tell if my valves need to be replaced?
any tips or tricks I should know??
My compression test a year ago ranged from 115-95lbs
Thanks, Craig

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Re: How to measure Piston Ring Gap, ect?

Postby Eugene » Thu Mar 19, 2015 7:23 pm

Determine the cause of the metal particles first.

Obtain a copy of the service manual, then read it.

Visit your local library and borrow a small engine text book. Some will have descriptions/pictorials on how to do a task as well as an explanation.
I have an excuse. CRS.

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Re: How to measure Piston Ring Gap, ect?

Postby ricky racer » Thu Mar 19, 2015 8:38 pm

Eugene wrote:Determine the cause of the metal particles first.

Obtain a copy of the service manual, then read it.


I couldn't agree more. Located at the top of this page are manuals that will answer most of your questions but nothing beats having a service manual in your hands. If you have someone near you that has actual rebuild experience, now might be a good time to enlist some help to guide you through what to do and want not to on this project. Most guys would enjoy being part of this rebuild. It would be a fun learning experience and when you're done, the old Cub should run like new for another 50 years. :-:-):
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Re: How to measure Piston Ring Gap, ect?

Postby CraigKennedy » Thu Mar 19, 2015 11:02 pm

yall, I pulled the gear off the cam a while ago, and the inside of the thrust plate is loose against the end of the cam. Is this normal? maybe less than 1/8" movement all the way around. I didn't see any shavings coming from it?
Also with every other gear removed, my idler gear has about a 1/16" play side to side, I had it off this past weekend when I was about to re install my governor, didn't see any scratches. ect. Is this normal?
thanks

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Re: How to measure Piston Ring Gap, ect?

Postby Eugene » Fri Mar 20, 2015 1:03 pm

Tolerances and measurements are in thousands of an inch. Tolerances are usually single digits when recorded in thousands of an inch.
I have an excuse. CRS.

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Re: How to measure Piston Ring Gap, ect?

Postby bob in CT » Fri Mar 20, 2015 6:55 pm

Craig,

Here is a direct link to a scan of my Blue Ribbon service manual in pdf format located in the pdf manuals section above. All the chapters are bookmarked for easy navigation and are keyword searchable (not perfect, but not bad)

This will have all the specs you need and it is a good place to start.

http://www.farmallcub.com/[ Sorry, direct links to manual section is not allowed. ]/files/Service%20Manuals/Blue%20Ribbon%20Service%20Manuals/GSS-1411%20W-Rev%201%20Cub%20and%20Lo-Boy%202-76%20OCR.pdf

That is a lot of slop on the cam thrust washer.

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Re: How to measure Piston Ring Gap, ect?

Postby CraigKennedy » Fri Mar 20, 2015 7:40 pm

Bob, Do you think my thrust plate is worn? 1/8" is a generous figure put it nowhere a press fit? didn't see any shavings around it and didn't look like its been grinding

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Re: How to measure Piston Ring Gap, ect?

Postby bob in CT » Fri Mar 20, 2015 7:56 pm

CraigKennedy wrote:Bob, Do you think my thrust plate is worn? 1/8" is a generous figure put it nowhere a press fit? didn't see any shavings around it and didn't look like its been grinding


Read the linked manual on the topic. Search for "thrust" and you will come to the installation instructions and specs. Measure and report. At this point, I don't think. I measure. :lol:

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Re: How to measure Piston Ring Gap, ect?

Postby Eugene » Fri Mar 20, 2015 8:05 pm

CraigKennedy wrote:Bob, Do you think my thrust plate is worn? 1/8" is a generous figure.
Probably .123" of an inch more than necessary for a proper fit.

I think it was previously suggested, obtain come competent or professional help.

I use to teach auto mechanics and small engines at high school and tech school level. One reason you are not getting sufficient answers is that, from the questions currently posted, it would take a semester in the class room to explain.
I have an excuse. CRS.

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Re: How to measure Piston Ring Gap, ect?

Postby CraigKennedy » Fri Mar 20, 2015 8:38 pm

Eugene, Can you tell me the inside diameter that the thrust plate needs to be?
Thanks Craig

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Re: How to measure Piston Ring Gap, ect?

Postby Eugene » Fri Mar 20, 2015 9:05 pm

CraigKennedy wrote:Eugene, Can you tell me the inside diameter that the thrust plate needs to be?
Thanks Craig
No I can't, off the top of my head, I don't know. I'm having medical problems and just don't feel like doing research.
I have an excuse. CRS.

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Re: How to measure Piston Ring Gap, ect?

Postby brewzalot » Fri Mar 20, 2015 9:26 pm

Craig,
I have been following this thread with interest but I don't work on engines much and have not felt competent enough to chime in. I do however work in maintenance on large industrial hones with gearboxes. If you are seeing as many flakes as you say, my money is on that you will be able to SEE what is wrong or worn. I have to ask, I didn't see anything in your posts, was your oil pan completely cleaned at some point before this? Were the flakes suspended in the oil or caked to the bottom of the pan? I ask these questions just to rule out some previous problem and these are left over flakes you are seeing.

I see you have another thread going, that must be a different tractor?

Take this purely constructively- slow down and listen to the veteran members and try to answer their questions. They will diagnose your problem quicker than going alone. JMHO

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Re: How to measure Piston Ring Gap, ect?

Postby Smokeycub » Fri Mar 20, 2015 10:59 pm

I'm gonna stick my neck out here and speculate that a couple things are going on. What you are seeing in the bottom of your pan may coming from the timing gears themselves and the thrust plate. There should barely be any perceptible movement except for backlash in the timing gears. The backlash should be between .003 and .006". I think your tolerances will be off the chart, so to speak. The idler would be where I suspect the troubles started and began a process of galling the teeth which may not be readily noticeable, the idler runs on a bushing which also oils the rest of the gears. The trust plate will gall as well and apparently has worn considerably. These things can make a pile of shavings. I agree with Ricky and the others, it would be helpful to have an extra set of eyeballs on your project. Good luck and let us know what turns up. :coffee:
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Re: How to measure Piston Ring Gap, ect?

Postby CraigKennedy » Sat Mar 21, 2015 10:22 am

Tim, Smokeycub, I removed the oil pan last year and cleaned it out completely when i did my Rear Main seal job. All of my posts are on the same tractor, I couldn't get a reply at the time.
The thing is that I don't see anything worn out. The i.d. of the thrust plate fits loosely on the end camshaft, it doesn't feel like its been ground down, I'm not sure if its suppose to be a loose or tight fit?
Thickness wise, again the plate doesn't appear to be ground down.
The Idler gear has a small amount of play in it from side to side, this is without the crank, cam, governor gear in. I removed the Idler about two weeks ago and did not see where the bushing was wore, as a matter of fact it was a tight fit when i was re installing it.
The metal flakes were mostly in the bottom of the oil pan, I did however see flakes on the inside top lip of my oil pan gasket, and also directly under the hydraulic pump gear. I have find the source yet...
I have searched and read one more post on here about metal flakes in the oil pan and it kind of dead-ended..
Will look more today, Thanks Craig

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Re: How to measure Piston Ring Gap, ect?

Postby ricky racer » Sat Mar 21, 2015 11:55 am

Craig, the manual specifies .003" - .012" end clearance on the cam shaft. It sounds, from your description, like you have a lot more than that. Spend some time looking there to see what is causing your excessive end play.
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