Export thread

Ran out of gas with about 4-5 passes of my backyard left to mow yesterday and couldn't get my bricktop to start again after filling up (same gas). It usually starts pretty easily if it's been running, but it just wouldn't go -- the most I got was it firing a couple times amidst many minutes of priming/pulling/etc. It was running strong all the way through running out of gas. To get it to start cold, I almost always have to prime it a ton, then tip it over on the side and open the throttle to let the gas run down into to block, but after that, it would always start right up, level off and run very strong. It feels like it's got pretty strong compression and there's no play in the crankshaft to be detected at the top of the flywheel. Carburetor looks clean inside and the spark plug looks reasonable, plus it was just mowing...

Any ideas?

I'd suspect bad crankcase seals. Often when they go bad, the mower will start cold OK, but not hot, say after shutting off and emptying the grass bag.

Regards

Jeff

jp1961 said:

I'd suspect bad crankcase seals. Often when they go bad, the mower will start cold OK, but not hot, say after shutting off and emptying the grass bag.

Regards

Jeff

Click to expand...

Thanks for the reply, Jeff! How much of a pain are they to replace? This is on one of the older, beige 18" decks and my memory of it is that its assembly at the bottom and mounting to the deck is a little different than the 19" green ones I've had before. I'd like to check exhaust ports, too, but when I tried to unscrew one of the nuts years ago, the stud sheared off, so I left the other alone and never have dropped the muffler. Unlike the square-headed bolts on the 19" ones, the muffler bolts seem to be some sort of studs embedded somewhere in the casting.

I have two other D lawnboys (green 19" bricktops), one that I used for years and got to where it just wouldn't start, but you can grab the flywheel nut and wiggle the whole crank/flyweel assembly back and forth a good 1/16" or so, and another that ran and started flawlessly, but stalled out on me one day and never restarted -- it seems to have very little compression. So I think this old beige one may be the only viable engine of the three.

I've actually never replaced the seals on a D Lawn-Boy. I'd say at a minimum you'd have to remove the flywheel and blade and blade driver to get at both seals. Make sure you can get replacements before starting. NAPA auto parts stores can usually find replacement seals if OEM ones aren't available.

Regards

Jeff

I'd also check the compression with a gauge, don't just go by rope resistance when pulling.

Marginal compression can also be a cause of hot restart problems.

Regards

Jeff

jp1961 said:

I'd also check the compression with a gauge, don't just go by rope resistance when pulling.

Marginal compression can also be a cause of hot restart problems.

Regards

Jeff

Click to expand...

That was my thoughts as well. I'd put a gauge on it first. Sounds like it's time for an overhaul.

As for the crank seals. Those are fairly easy to change on the older D series engines (prior to 1970 and all beige D-400s have the extended snout). Those have the extended snout crankcase which puts the lower seal nearly down to the blade adapter. In the first pic below you can see the short block off to the left has a post 1970 snout while the one the tool is in on the right has the extended crankcase. Usually the lower seal tends to be the first one to leak. Here are a couple of pics that shows the lower seal at the end of the crankcase snout and also the seal removal tool which makes it a very quick job. It's not mandatory that you have the seal removal tool though. A screwdriver will work, just be careful when prying that you don't snap off a section of the aluminum snout in the process. You can simply drive in the new seal with a piece of PVC pipe of the right diameter. Access to the upper seal is a bit more involved, but still an easy task. That's one of the great things about working on these old classics, they are easy to work on. Once again though, I think Jeff is spot-on when it comes to diagnosis of the problem, and that is just low cylinder compression, probably not bad crank seals.

Thanks, guys. I'm semi-familiar with disassembly on these -- pulling carb and reed plates, replacing points/condenser, cleaning carbon deposits, etc. but I've never gone past that, into cylinder disassembly, shaft bearings, seals, etc.

I'm just so hesitant to do anything that requires pulling the muffler on this one, as I'd bet money on the remaining stud shearing off just like the first one did, no matter how long it soaks in penetrant. With that in mind, does anybody have any slick/creative/easy ideas on jury rigging a way to reinstall the muffler if I go that route?

Hmmm,,,broken bolts are always a B*tch to deal with. The numerous ways on Youtube of guys welding things to the broken part, easy outs (never really "easy") and left hand drills to remove broken studs and bolts are in my opinion hit or miss.

It normally just takes patience, a lot of heat, penetrating oil hopefully you have a positive outcome.

I guess in a worst case scenario, I could always drill a broken bolt out and re-tap to the next larger size if there is enough material to do so.

I have a Bridgeport in my basement, so I can do repairs the averagely person can't.

Regards

Jeff

jp1961 said:

Hmmm,,,broken bolts are always a B*tch to deal with. The numerous ways on Youtube of guys welding things to the broken part, easy outs (never really "easy") and left hand drills to remove broken studs and bolts are in my opinion hit or miss.

It normally just takes patience, a lot of heat, penetrating oil hopefully you have a positive outcome.

I guess in a worst case scenario, I could always drill a broken bolt out and re-tap to the next larger size if there is enough material to do so.

I have a Bridgeport in my basement, so I can do repairs the averagely person can't.

Regards

Jeff

Click to expand...

Yeah, I really kind of wish I knew exactly what they were anchored in, casting-wise, as it'd be nice to be able to just drill them all the way out and run bolts through the deck like my other D engines have (with the little square-headed bolts). Something tells me there's a high likelihood galvanic corrosion has them locked permanently in place, even if they're just studs and that drilling them out of the softer aluminum would be tricky.

You think there's any rebuild hope of my two dead ones? One ran great and started easily, but always felt really easy to turn over and then just died and never started again, mid-mow. I have to assume it's a compression issue. The other got to be like this one is now: increasingly hard to start, then eventually impossible. It's got a lot of side-to-side play in the shaft, though I'm not sure it feels quite as soft as the other dead one, compression-wise. (I don't have a compression meter)

I don't think OEM pistons or cylinders are available for D engines. You can check eBay as there might be somebody selling OEM parts for the D. New rings would in my opinion do little to boost compression.

Finding out the compression reading is paramount to further diagnosis,,,kinda like when you're and old fart like me and you go to the doctor, they want "blood work"first before they do anything else.

The D and F series Lawn-Boys were durable engines (in fact somebody is more than likely mowing grass with one now), but they don't last forever.

Maybe try to find a Duraforce Lawn-Boy, they were the last 2 cycles made and parts are available but won't be for long.

Regards

Jeff

Couple things. Check sparkplug, if wet clean it up good or replace. Give it a shot of starting fluid in the spark plug hole. I sometimes use a drill and a socket on the top flywheel nut to rotate the engine to start it up when it gets stubborn. Spins it over pretty good and saves the shoulder from pulling the rope.

Spent some more time with it after work, yesterday. I pulled the spark plug, to make sure it's getting spark (it is). I pulled and disassembled the carburetor and it was totally clean inside, jets clear/open. It gets gas to the carb, I can feel it suck air when you pull the cord (it'll suck my palm against the air filter if I put my hand up against it) and you can also hear what I always assumed were the reed valves quack at the end of the spin. It did start one time out of many, many pulls, but just ran a couple seconds and I couldn't get it to stay alive with the primer. By the way, that's how it usually was; it would start and then try to die and you could get it to surge back up by pressing the primer once. Typically, you'd have to do that 1-5 times before it'd level off and run on its own, but now it won't really even start.

So what's next? Should I buy a compression gauge and see if I'm wasting my time? Am I being dumb in overlooking something?

With no compression gage available then I would just remove the spark plug and put a tablespoon of oil into the cylinder and try to start it. The oil will temporarily boost the cylinder compression. If it cranks much quicker and runs good for a bit then that would confirm the marginal cylinder compression as at least one of your issues to deal with. Just remember that with 2 strokes you have cylinder compression and crankcase compression to deal with. Both need to be in specs to provide the power stroke and vacuum to draw the fuel in and to also expel exhaust gasses. Make sure it's breathing good to, no exhaust restrictions, check the ports for blockage. A restriction will definitely effect crankcase compression.

jp1961 said:

The D and F series Lawn-Boys were durable engines (in fact somebody is more than likely mowing grass with one now)

Regards

Jeff

Click to expand...

Yes sir! I've been mowing this little D-400 with the upgraded dual bronze bushing, extended crankcase snout for a few years now, and if my knee will let me, I'll be using it again later today. If only these folks around here in West Texas ever used one they would be in love with them to. Maybe we should continue to keep them a secret so that demand doesn't go through the roof, along with the prices for parts? LOL

Lawnboy77 said:

Yes sir! I've been mowing this little D-400 with the upgraded dual bronze bushing, extended crankcase snout for a few years now, and if my knee will let me, I'll be using it again later today. If only these folks around here in West Texas ever used one they would be in love with them to. Maybe we should continue to keep them a secret so that demand doesn't go through the roof, along with the prices for parts? LOL

Click to expand...

I would kill to have either a lawn or lawnmower anywhere near that clean-looking!