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Discussion Starter #1
I have a 2012 JD LA140 started using a lot of oil. This is one of the ones with the compromised air filter. A few years back I switched out the parts to use the newer style canister filters. I still was seeing dirt inside the housing with a oily coating that had to be coming from the breather from excessive blowby. I did a leakdown test and one cylinder had 10% leakage the other 50%. I took apart the engine and found the 50% leakage cylinder head had a bit of exhaust leak from deposits under the valve. When I removed the pistons the top ring end gap was 3/4 of an inch so that is a classic sigh of dirt ingestion. Here in central texas I mow in a cloud of dirt dust so it is about as extreme a condition as you can get. Anyway the manual says max taper is .003 and that is what I am seeing exceot and the very top where it goes to about .0035 then the very top looks to have a relief on it. Anyway I have a precision hone and I can hone it straight but I would think to get a good cross hatch the top will need to be at a minimum .004. I wanted to go .010 over but all I see is .020 piston/ring sets. I'm thinking I will just hone the bore straight and round and replace the rings. Has anyone done this and did it work out OK? I will need to hone straight then check bore size. Wondering what the max piston skirt to bore clearance is as it is not in the manual just the max bore of 3.120. Thanks for any help on this. I am also going to need to see why dirt appears to get around the cartridge filter.
 

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I think you are asking for trouble

Why not just go with the .020 over piston and rings?

I think if you bore .005 over you will have piston slap and excess oil consumption then will wonder why you didn't go all the way.
 

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Run a fine hone in the bad cylinder and look for vertical scratches. If you find any no amount of honing will get rid of them. You will need to bore it out first. Them scratches will cause oil consumption every time.
 

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Discussion Starter #4
Run a fine hone in the bad cylinder and look for vertical scratches. If you find any no amount of honing will get rid of them. You will need to bore it out first. Them scratches will cause oil consumption every time.
Thanks guys for your feedback, so I just took some more measurements and the taper up to a half an inch of the top is .0022. The big issue is and something I have never see before is what looks liked a machined recess on both cylinders that is .005 larger I can't for the life of me figure out how that happened but I am sure it was not factory and now I will have to go .020 over even though .010 would work. Looks like there are no .010 piston ring sets to be found. Here are some pics of the measurement and the recess. The bore was smooth as glass and if not for this strange top wear I would have been able to hone straight and re-ring. DSC01165.jpg DSC01167.jpg DSC01168.jpg
 

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I wouldn't worry about boring it out, but would just hone it and then measure it and see what it is.
 

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Discussion Starter #6
rebuild progress

I went ahead and ordered two pistons .020 over. I also ordered some other parts including the valve seals and two intake valves. I reground the valves but one intake has .002 stem wear so I just ordered both. Exhausts have chromed stems and had little wear. I have so far been unsucessfull in getting off the old valve seals. Looks like they press onto the valve guide and are on pretty tight. DSC01170.jpg
 

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Discussion Starter #7 (Edited)
I started honing and after removing .006 the worn top area is still there, looks like at least .010 till it is gone. Finished cleaning up the heads and am waiting on two new intakes and a 6mm pilot so I can cut the seats. Thinking of milling the heads to give them a better finish to hold the gasket and to insure flatness. Crank looks great and pistons should be here tomorrow. Picture on Amazon shows them with a moly looking coating on the skirts, old ones had no coating. Still wondering why Briggs only sells .020 over pistons and rings. They used to supply .010,.020, .030 years ago. DSC01171.jpg DSC01172.jpg
 

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did you try simply lapping the valves?
 

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Discussion Starter #9
no lapping on this one, the valve seating area on the valve was recessed and required grinding, one valve to clean up the seating area wound up with insufficient margin but I did not want to replace just one valve so I ordered both intakes. The exhaust seats actually look OK but the intake seats were not flat. Lapping is fine if seats and valve surfaces still are OK in this case they were not. I also like to cut the seats to make sure they are concentric with the guides.
 

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Hmmm, Maybe I'm old school here, but I've never heard of honing a bore round. With time & patience, you can hone a bore straight, but a hone "follows" the out of round bore...and you'll end up with a straight top to bottom egg shaped bore. I'd bore .001 under spec'd size and then hone for size & finish/cross hatch. Bob
 

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Discussion Starter #11
you must be referring to a spring hone, this is a precision hone with a micrometer adjustment designed to make it round which it does rather quickly. The hard part is making it straight, that requires practice. The lower right if the picture is the hone but I can take a better picture of it if you are interested. All engine cylinders are honed, also rod journals are honed round.

DSC01167.jpg .
 

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Discussion Starter #12
Here is a better picture, it has grits from 80 to 500, I use the 80 for fast metal removal, the final .002 I do with either 320 or 500, then I run the ball hone in reverse for about 15 revolutions to get a plateau finish then wash it in a tub of tide using the gray fine scotchbrite and bore brush to get any residue out of the bore.

DSC01175.jpg
DSC01176.jpg
 

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Discussion Starter #13
Well made some more progress, heads have to wait as a 6mm neway pilot was too loose in the guides so I am waiting for a expandable pilot. I finished the honing process and am at the tighter side of the spec at 3.139 and had a top ring end gap of .006 which seems too tight. I filed them so they were at .010. Manual just gives a reject dimension of .030 but no tight limit. I coated the skirts with Dow Molycoat then assembled the crank pistons and rods. Tomorrow I will finish cleaning the sump and assemble the bottom end. There is a screen in the sump over the oil pump and it fell out when I turned over the motor during disassembly. I will need to positively locate it so it does not fall out before assembling the bottom end.
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Discussion Starter #14
Finished up the engine rebuild and deck rebuild. Engine starts much faster and runs great. Not much different from the wore out one other than no smoke or smell of burning oil!
DSC01187.jpg DSC01188.jpg jd3.jpg jd4.jpg
 

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I am curious as to what you did to clean the block and heads...

They look like brand new castings. I recently rebuilt my FD611v and the castings look 15 years old as they are.

Thanks
 

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Discussion Starter #16
I bead blasted the heads as they were nasty. first used a ultrasonic cleaner which got off a lot of the carbon and burnt oil then dry and beadblast.
 
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