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Measuring The Bore?


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#1 coldone OFFLINE  

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Posted January 31, 2013 - 09:42 PM

I have a K341 that has been giving me problems for about two years now. It came on a snapper 1650. It would start and idle fine but when reved up it would make the front of the tractor jump around. I pulled it apart and removed the balance gears and reassembled it. It did fine for a few test runs and then started the jumping again. I took it apart again determined to find the problem.

 

The first thing I found was that the flywheel key had sheared. I guess I installed it wrong.

Next I decided to get the tools and start measuring everything. The piston is on the edge of being at the max wear limit. The cylinder has no ridge around the top and looks good but I didnt have a way to measure it. 

 

I finally broke down and got some bore gauges. I had some trouble getting repeatble readings with them. I decided to drop the piston in the bore, that way I could have atleast one solid plane that I didnt have to feel for. I started to get consitant results that way. The preliminary measurements werre all in the 3.748 to 3.750 range. Now I have not seriously sat down and measured, I only had  few minutes today and it wont be until saturday before I get any time.

 

I am looking for tips and tricks to get good measurements on the bore. I am trying figure out if it needs to be bored over or not.

 

I have the HF dial and digital calipers and the telescoping bore gauges.I also have a set of cheap mics but they dont go big enough for the bore.


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#2 Texas Deere and Horse OFFLINE  

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Posted January 31, 2013 - 10:57 PM

I use internal telescoping snap gauges and them measure them with O.D. mics.


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#3 boyscout862 OFFLINE  

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Posted January 31, 2013 - 11:00 PM

To measure the bore you want to measure at the top middle and bottom of the ring wear areas. Check section 11 of the Kohler service manual which is available in the Manuals section. They recomend to measurements at 90 degrees to each other at each level. The trick to bore gauges is a light touch to get the cylinder and then with the caliper. There should be a very slight snugness to each measurement. Practice it by doing the set of measuments several times.

 

I doubt that the piston or cylinder is your problem. I would suspect the flywheel or what the PTO is attached to as being out of balance.

 

If you take the piston out pay very close attention to the notes for torquing the rods. Some need to be over torqued. It is critical to do it right. 


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#4 Texas Deere and Horse OFFLINE  

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Posted January 31, 2013 - 11:01 PM

I get my snap gauges into the bore at ah angle and tighten then up slightly. When you pull them up to level in the bore, they will get a good reading.


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#5 marlboro180 OFFLINE  

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Posted January 31, 2013 - 11:14 PM

Ditto on the 90 degree's that Boyscout said. On another note:

 

Take one of the compression rings and push it into the bore with the piston, keeping it as true as possible to the bore. This should give you same parallel wall references to work off of with a bore gauge, no matter the orientation to the wrist pin.


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#6 chris m OFFLINE  

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Posted February 01, 2013 - 12:31 AM

Well I would say everyone has you set on measuring the bore. Question though, How are the bearings on the Crank shaft? Even though it is uncommon for them to wear out. I had the flywheel end bearing bad on a K301 and that had caused one heck of a shake above idle.


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#7 JDBrian OFFLINE  

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Posted February 01, 2013 - 09:23 AM

I'm surprised it would run with a sheared flywheel key. The wheel must have stayed in place. If your tractor has rubber motor mounts they could be a source of the movement. If they are weak or broken the engine will move whenever there is any change in the load or in the engines operating conditions. If the ignition is intermittent or you have a fuel problem then the engine will buck every time these issues occur. A good once over/tune up would be a good idea to rule out these issues.


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#8 crittersf1 OFFLINE  

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Posted February 01, 2013 - 10:26 AM

You have something else going on. I seriously doubt it has anything to do with the piston/bore.


Edited by crittersf1, February 01, 2013 - 10:26 AM.

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#9 Alc ONLINE  

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Posted February 01, 2013 - 09:20 PM

Guess everyone has their own way of using telescoping bore gauges and inside mic's I  hold one end in the location I'm trying to measure with one hand ( fingers ) and the other work the other end to get just the right up/down side to side feel . Boy i wish I could explain things better , lol Al


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#10 crittersf1 OFFLINE  

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Posted February 01, 2013 - 09:30 PM

I just use my Mity-toyo dial bore gauge, no guessing.


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#11 coldone OFFLINE  

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Posted February 01, 2013 - 09:33 PM

Thanks for all the replys.

 In 2 years I may have had the engine running for a total of an hour. It and the tractor have been a work in progress. I am not sure if the cylinder or piston have anything to do with my problems, but since I had it torn down I figured i might as well check it too. I plan on a new piston, rod and rings. New valves too. I want to try my hand at an actual rebuild.

 

As for the key shearing, I think it was my fault. I think I installed it wrong. It sheared and there is evidence that the flywheel made at least one round on the crankshaft. I will see if I can get some pics of the damage.


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#12 marlboro180 OFFLINE  

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Posted February 01, 2013 - 10:35 PM

Hope you get it figured out. :thumbs:  Nothing like trying yer hand at something new, we're here for ya !


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#13 JDBrian OFFLINE  

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Posted February 02, 2013 - 07:13 AM

I find those telescopic bore gauges to be awkward to use as well. I'm getting some tips here that should make it easier. I know a former mechanic who has a direct reading gauge of some kind that he will lend me. I might get that the next time I need a bore measurement and see if I can get the same results with the telescopic gauges. 



#14 Tennblue59 OFFLINE  

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Posted February 02, 2013 - 09:41 AM

With the cheap (no disrepect intended - they are what I use as well, as opposed to a different design that costs big $$$ but is easier to use...) bore guages it is a finess thing - comes with practice. Lightly cinch the set screw and rock the guage. it will only rub when parallel. If set too wide, rocking it will close it up some to the right dimensions - needs to be cinched enough to keep from snapping open, but not too much to keep if from adjusting.

 

For measuring the TOP dimension, you can use a square across the top of the bore to keep the guage shaft parallel. Same adea about using the piston as a guide if it is a flat top piston.

 

Setup is more a pain than it's worth, but if you have a drill press and can get the bore fastened true on the table, tie the guage to the quill and use it to maintain true. (I do this with a tap to thread holes as well). I have an adapter on my vertical mill to hold indicators/tools and such that makes this easy...

 

As noted, you take measurements in three heights on the cylinder and on two planes with respect to the crank. Most cylinders fail tolerance because they become egg shaped (big at the bottom) from the lateral pressure of the piston caused by the crankshaft.

 

Probably doesnt apply to a 1 or 2 cylinder mower type engine, but bad ignition timing can make an engine shake and shudder as well. It could be an unbalanced piston/spinning assembly - that could cause the shake... ?


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