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A few months back, I acquired a pristine 10518. Engine ran good once warmed up. Took some effort from the primer to keep it running. After about 30 seconds, it would purr. I did notice when mowing , it seemed to lack power. With it at near
full throttle, it would bog to the point of dying when you hit 3'' tall grass. My duraforce could be pushed through 6'' of wet grass and keep on rocking. Between the low power and hard to keep running, I chocked it up as needing crank seals and put it away for the moment. Only got the chance to mow twice with it before mothballing it.
aw
I drug it out today and got started tearing it down. Didn't notice any oil leakage around the seals, but I did notice something broken on the carb ( see the pic with the bailing wire) and upon removal of the exhaust, I could see scoring on the piston. I decided to further tear it down. The connecting rod seemed kind of sloppy at the crankshaft and the needle bearings fell out upon taking the cap off. Not sure if there was some sort of a holder that came apart or if they get installed with a dab of grease to hold them in place. Is it normal for them to have play? The crank looks to be in really good shape. The reeds look like new.

The cylinder is scored up a bit, but nothing deep. I think it would clean up with some honing.

So as best as I can tell, need a piston with rings, possibly new needle bearings, a cylinder gasket, and a carb. I realize I wont find the carb or piston on any of the usual parts sites. Does anyone have part numbers that I can use to check ebay?

The wife got a kick out of me hoisting the mower to my work platform. I have major back issues and try to lift as little as I can. Hung a chain fall from my porch and was able to do all my work without lifting anything other than the engine.

Also, has anyone replaced the plastic carb with a metal one from one of the older models?

Hello,

The bearings (upper and lower crankshaft, wrist pin and needle bearing for the connecting rod to crank) are still available from L.B. The piston is not, but the part number is 92-4925.

The piston is flash scored, caused by metal breaking away from the ports. I'd but a chamfer on the ports.

I'd tally up the cost of the 4 bearings, piston, piston rings, seals, gaskets, etc needed for the rebuild and see if you can find a decent F engine somewhere.

Jeff

You should be able to fix the carb very easily. You need a governor spring part number 924944. (where the bailing wire is) and a new needle and seat part number 92-9697. Very cheap fix, as parts are available. As said, before you purchase anything, find out the total cost of parts. I think you will be surprised.

Cost for the 4 bearings and 2 new oil seals would be 83.42, but then he would have to find a piston and rings.

Jeff

Try running a search for stens replacement piston and rings, use the part number for the ome rings and pistons and look up for the stens replacement option this lawnboy should be new enough to have a stens copy out there

I have located a piston with rings for $21 with free shipping & both the wrist pin and crank needle bearings for $35. I already have the seals on hand. Just need to inspect the thrust bearings and if need be , find a better deal on them. Do I need to replace the retainers for the needle bearings , or can I reuse the old ones ? Anyone know a torque spec on the connecting rod ? The carb parts are under $10. Going to give honing a shot this weekend. If the bore cleans up, I will order it all .

Does anyone have the fsm in pdf form for this machine ?

Cleaned the cylinder up tonight. Got most of the scoring gone with minimal honing. Whats left I don't think will cause any issues as I can't feel it with my fingernail. Now I need to figure out how I'm going to chanfer the ports without causing any cylinder wall damage.

Any of these tools would put a chamfer on the ports. A round needle file may work also.

The Lawn-Boy Mechanics Handbook doesn't say to replace the connecting rod bearing liner, but I'd inspect them for signs of damage.

It does say to install the Lawn-Boy piston stop (part# 677389), as it's possible to insert the piston too far into the cylinder causing the top ring to become lodged.

Jeff

You won't need a piston stop. When assembling an F series just install the piston and rod to the crank prior to pushing the piston into the cylinder. This will prevent the piston from traveling too far down in the jug and possibly locking itself into the cylinder.

In regards to converting the plastic carb to a metal Walbro. Yes you can do this fairly easily. Just use the parts catalogues for your 10518 and a 1993 model 10515 to determine what parts will be required. Should just be a carb, air box and throttle cable from a 10515. I converted a 1997 F series model 10401 to a 1993 model 10400 and those parts listed above were pretty much all I needed except maybe some hardware and an optional throttle/choke decal.

jp1961 said:

Any of these tools would put a chamfer on the ports. A round needle file may work also.

The Lawn-Boy Mechanics Handbook doesn't say to replace the connecting rod bearing liner, but I'd inspect them for signs of damage.

It does say to install the Lawn-Boy piston stop (part# 677389), as it's possible to insert the piston too far into the cylinder causing the top ring to become lodged.

Jeff

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I would do like Jeff suggested and try to chamfer the ports with the back end of the Sharpie. It might take a little while longer, but you don't run the risk of going too far too fast...

Well, I was all set to order and realized I was looking at a 92-4923 piston with rings. Cheapest I can find a piston is $100 with rod and pistons. I may watch ebay for a while.

Check out NOS parts haul thread, you may be able to get a F short block cheaper than the individual parts needed for the over haul.

Jeff

jp1961 said:

Check out NOS parts haul thread, you may be able to get a F short block cheaper than the individual parts needed for the over haul.

Jeff

Click to expand...

I Replied to his post. That may be the better way to
Go. I looked at a potential donor yesterday on
Craigslist . I had the idea that I could put the extra parts in the shed for down the road. Turned out to not really be much good on the machine and it wouldn't start for me.

jp1961 said:

Check out NOS parts haul thread, you may be able to get a F short block cheaper than the individual parts needed for the over haul.

Jeff

Click to expand...

In talks with him about the short block on the lower right. My machine is self propelled , is there anything special about the shaft ? I checked mine and do not see a key way.

Well its almost finished. Received the short block in the mail today after usps made a mess of things. Swapped my reeds in, installed crank seals and fully assembled the machine tonight. I still need to order the carb gov. parts and now a primer. I was all excited to run it, filled it with fuel and put my finger through the primer bulb when pressed. Got the parts on order.

I'd like to give a shout out to Unclelee. Top notch guy. I would do business with him any day! Thanks again Lee!

Glad to help!! Hope to hear about a running mower soon.
Lee

Finally got all of the carb parts for the throttle control installed. Mower runs great and has tons more power. Unfortunately, it looks to never have the power my duraforce has.

kmaysob said:

Finally got all of the carb parts for the throttle control installed. Mower runs great and has tons more power. Unfortunately, it looks to never have the power my duraforce has.

Click to expand...

Duraforce is a beast!!
You should post a video

Tulsa Engine Warehouse (google it), an online vendor, has the "F" series engine piston and ring set for $15.95. All "F" series pistons are the same. This piston is also supposed to fit the slightly newer Silver series 4.5 hp engine, but not the DuraForce.