Cold compression is 103 psi, warm is about 110 psi. No noises when it's running with or without a load and it turns over nice and smooth. Side play in the crank feels fine and isn't excessive

Well I used it today where I can't get with the tractor and I can hear and see the flywheel rubbing on the coil mount

It needs at least a new lower bearing. You're going to have to completely dismantle the engine. I would rebuild it at that point. With the lower bearing basically gone, the crankshaft probably is also damaged. If you don't think you can handle that level of work you have some decisions to make on the mower.

Yeah as I suspected with those compression reading this unit is a little tired . 125# to 130# is minimal for optimium performance. As Sax has advised a complete rebuild is best . You may get a way with only a ring set but inspection will determine if piston ring grooves are also worn requiring piston along with bottom bearing and possible crank resurfacing. If you are mechanically incline you could diy but with possible crank resurfacing , professional assistance is probably warranted ! As Sax has suggested . Let us know how it goes .

The spec sheet I have for the F series engine says 105-110 psi is good. I'm going to pop it apart this afternoon and see what's going on. Total overhaul is no problem for me if needed

Good and Optimium are a long way apart. If memory serves me my old C and D Class Lawnboys had around 115# to 120# Cold after 8 yrs of heavy service. Anyhow let us know what else you find . Ensure to check piston ring end gap tolerances with these 2-strokes. I would suspect you may be surprised . I would kindly suggest your compression is only fair at 103 cold after 5 recoil pulls .

Well it's done. Found a bunch of grass and dirt behind the reed plate/cover, the big end of the connecting rod is scored as well as the piston and cylinder. Guess it's time to get the faithful 1974 Kmart 22" out or get the other Lawn-Boy running. How are the V series engine? It just needs a carb and a couple holes heli-coiled

More or less what I anticipated with those compression readings . I worked on a few V-Series 4.5 HP Silver Lawnboys back in the day . Routine Carb Servicing , Ignition Module Change out , Blade Sharpening Etc. Quite a bit of torque for such small 2-strokes. Liked the offset wheeled units over the newer conventional mowers for maneuverability . I think my brotherinlaws was the newer mower 1993 circa . Most again were recommended at 32:1 Oil Ratios which we never followed . Back then we ran Klotz R Caster Oil @ 50:1 , believe his son still has it out at his camp , running Amsoil Sabre now , since the Klotz R is hard to find locally today lol . Lots of 2-strokes out there Bro , nobody likes the noise and fumes these days but us Old-Timers ! P.S. Actually I kinda liked the aroma of a good running 2-stroke on Premium Grade Caster Based Oil , probably due to my Pro-Mod Snowmobile Racing Days lol . All the Best keep in touch Dude!

I'm a young guy (23) and I love the smell and smoke of a 2-Cycle. My friend has been running castor in a Yamaha Tri-Z 250, good smelling stuff. I'm leary about putting it in my Tri-Moto. Still running the oil injection using Arctic Blue.

Nice Yammi , my Son had both a 125 & 250 moto's back in the early 80,s . He ran Yama-lube Injector Oil in both until the 250 injector unit failed and I introduced him to Klotz R Caster. Actually he still has the 250 out at Moose Camp , since they cannot be insured or plated within Ontario any longer . I would recommend you continue with the injector system but ensure to keep an eye on oil consumption within the tank. I don't recall off hand if your unit has Rotary Valve , Reed Valve or Slide Valve Mikuni or Keihien Carburation , to many yrs ago lol . We use to add an ounce or two of premix as insurance back in the racing days just in case oil metering cable stretched or broke on our snowmobiles .

Anyhow have fun and be safe and warn the kids of the injury potential of having feet off the foot pegs with those large low pressure rear tires (Ankle Breakers) . Chow Bro !

Well the model 10201 is up and running good. The V series engine sure has a different sound to it but I don't mind. The old Yamaha is the most reliable machine I own, it's a reed valve engine with a Mikuni carb. It's a blast to cruise around on once you get the hang of it, I use it for putting around town with and I've ridden it on an 80+ mile trail ride multiple times and it's never missed a beat. I'm always keeping an eye on the oil, I always got smoke and it uses about 1 quart to 3.5 tanks of gas...so about 7 gallons

yt125 Sounds like you have a handle on the Oil Injection Precautionary Measures Bro ! Yeah the Yamaha 250's are pretty well Bullet Proof with normal Mtce . My 13 yr old Grandson has same 250 as yours in a 1989 4x4 Moto Quad , scary fast . As for the 10201 alls left is for you to find some Klotz R Racing caster oil and your Buddy will be envious , OMC Lawnboys really loved the Caster Based Oil .Yeah the V Series did sound different , actually a little higher compression and run a little hotter , but have better Cooling Design Heads (Surface Area) . Even though ensure to keep the heads clear of debris on these 2 cyclesl . Well Youngin , This 65 Old-Timer is out to Fire up the Husky and Buck up some Canadian Maple before the Temps get to Hot . Have fun with that Salvaged Lawnboy !

Keep your eye on the 10201/V engine. They used 'Tround' self-tapping bolts/screws on them and they tend to come out. Make sure the muffler plate to engine is snug and the muffler cover has a good seal. They're actually not aggressively loud if the muffler cover is sealed and the inner baffle is good. The sheet-metal muffler covers go bad quickly but they are still available. Just be sure the cover bolts are not backing out and hitting the blade. The lower bearings also wear out so check your vertical play. If you maintain your air filter element properly, no foreign material will ever get into the engine. Also watch the steel air shroud mounting screws as they tend to loosen from starting torque. It's been a long time since I had one, but I think you also have to make sure the exhaust gasket is good to reduce exhaust noise.

1Saxman /yt125 : Well , done with the hardwood Bucking for the Sauna Heater . Ambient temps climbed to 30 Deg. C approx. 90 Deg. F way to hot then I anticipated for this Elder. Nothing like a Cold Bottle of Labatt's Blue to Quench your thirst , ok maybe two ! Great points Sax , just a few of the ongoing mtce measures required on Older Vintage 2-Strokes that vibrate your fillings out. Actually we fabricated (reverse engineered) new systems c/w stainless body and fasterners. We also double walled and used Roxal insulation semi rigid style and graphoil gaskets on the new stainless exhaust flange surfaces to permanently resolve Noise Harmonics and Blow by issues . Sure made for a much quieter and efficient system long term . Did require rejetting with a Suzuki main jet , along with mild intake and exhaust porting and polishing. Did this with a few older C&D Class Lawnboys also . Just continutation of Snowmobile and Chainsaw Hotsaw Expansion Chamber Tuned Design Systems we did in the early 70's . Anyhow off to the Garage to Pm the Husky and Echo Saws for use this weekend , suppose to start cooling of mid week ...All the Best Dudes !

It's 87 with 70% humidity here in western WI. I read that the muffler and plate from an F series will fit and quiet it down, I think I'll try that tonight if it cools down. Thanks saxman for the warning about the bolts. Blue loctite and lock washers should help I'd imagine.

You don't have to overtighten, just remember to check them once a month during the season.

Several things here:

1. The muffler off a "F" engine will not fit.

2. I don't know of any "F" or "V" engine lawnboys that had thrust bearings.

3. The lower roller bearing on "F" and "V" engines have nothing to do with the vertical play of the crankshaft. (Up and down movement.) The crankshaft counterweight has a machined surface that sits on a ledge inside the crankcase casting that limits its downward movement. This, of course gets lubricated with the gas/oil mix. I wouldn't be too worried about vertical play. If you have 110# compression the bearings and seals are pretty good, as well as the rings.

4. For any repair on a lawnboy above, or below deck, you should use Locktite on all the screws, no exceptions.

Thrust bearings came standard on all the later F series engines (approx 1995 and later). Like I had already stated, the thrust bearings in the pic are from an F series engine, model 10401. they were most certainly designed to address end play, or vertical play. It would for sure add life to these old engines and furthermore reduce friction and probably provides a small increase in power.

It doesn't look too bad other than the one area of the piston. Looks like it was being maintained well, fuel mix wise, but might of got a short straight gas event by a previous owner. I can't really tell from the pic but it looks like the liner was spinning in the rod? I hope you can at least salvage the cylinder assembly. Those Lawnboy F cylinder sleeves are really tough. I've had to toss one in my lifetime and that was because the connecting rod let go and a few needles got loose and wedged themselves between the piston skirt and cylinder wall.