Is oxidation - pin holes in older magnesium LB decks common? Is it a problem?
#2
robinb66
Actually that was one of the main problems with that kind of deck, and unless you want to put ugly screwed on patches you can't really fix them. Not worth anything scrapping either, nobody will pay scrap for them because you can't recycle magnesium like most metals. To me the lawn boy deck design was the best designed mower deck out there but using magnesium wasn't the smartest thing!! But that's just my opinion!!
I think you can TIG weld magnesium, not 100% sure. Magnesium is 30% lighter than aluminum. You probably could pick up a magnesium decked LawnBoy with one hand,,,lol.
From my experience the pitting issue is common, but worse than that is the cracking. It seems like the mag decks were quite brittle. I think if you can find an older mag deck Lawn Boy with minimal pitting and no cracks or chunks missing, you've made a good find.
Yes the pitting and cracking is more common on a mag deck than an aluminum deck. Magnesium can be welded using an Heliarc welder in A.C. mode with pure magnesium rods. I have had a couple of cracks welded on a 1966 restore back in 2012 and it turned out well. Those mag decks just seem to develop cracks out of no where, in areas that you wouldn't even think were stress points. The big problem these days is the price of pure magnesium welding rods. The welder that did my work says it cost him 90 bucks a pound, so if I want anymore mag welding done I will have to supply the rods myself.
As far as the pitting goes, I think what works really great is a product called Lab Metal (high temp version). If you clean the metal good, media blasting preferred, then you can apply the Lab Metal over the pits, sand it relatively smooth, then take it to the powder coat shop to get it baked and powder coated and it will be almost as good as new. I think some enterprising young person who has the right equipment, knowledge and lives where there are plenty of old mag decks laying around could make good money refurbishing those decks in this manner and selling on ebay. I think someone has already been doing that with the newer aluminum decks.
Remember the famous film about the Lockheed Comet.
The tail used to simply fall off.
It was found to be caused by stress corrosion cracking & metal fatigue.
All metals do this & you use it when you break a piece of wire by bending it backwards & forewards .
Back when the decks were made little was known about magnesium so they just substituted magnesium for aluminium in a mould for aluminium which did not work because the metals are not the same.
Scrap yards do not like having magnesium around because of the fire risk so unless they supply to a foundry that casts magnesium they do not touch it.
magnesium is poision to most aluminium foundries and if they find magnesium in a load of aluminium they will reject the load.
If you run magnesium through a metal shredder it usually explodes.
So yes it can be a problem to recycle.
OTOH it is worth around twice what aluminium is as scrap to some one who wants it.
I have a Lawn Boy 19" with a magnesium deck and I just love it for mowing our front bank, it's much more lightweight than our other push mowers. The deck on mine has been welded by a previous owner and looks like they did a great job! It's probably a TiG welding process, doubt you could weld it with any other welder. Problem with mine right now is it's not running and I can't figure out what the problem is. I'll have to put in a bit more time and try some different parts and maybe it will run again..
You say your little 19 mag deck mower is not running, can you elaborate on that? Maybe we can help if we have a bit more info on the symptoms. Model number would be good. Will it fire at all, or does it run for a short time, then falter?
You say your little 19 mag deck mower is not running, can you elaborate on that? Maybe we can help if we have a bit more info on the symptoms. Model number would be good. Will it fire at all, or does it run for a short time, then falter?
Yes, it will fire after you prime it then it runs for a short while and dies. It starts right back up with a prime, in fact you can keep it running if you prime it while it's running. I've tried different carburetors, at least one of the carbs came off a running mower but wouldn't make mine run. I feel like it might be in the fuel tank because when you take the line off the fuel just dribbles out and that's with the cap off. I cleaned out the line and blew through the outlet with compressed air and it appears to be clear. My next move might be to look at the on/off fuel valve but I'm not holding my breath. I put new crank seals in it earlier in the week so it's not that I guess. I'll try to get the model number tomorrow but it's an F series engine with the plastic carb.
I already found some crud in the little sump on the tank plus found a plastic piece in it also. I'm gonna take the tank off again and see if I can get some fuel flowing. I have a suspicion the valve is the culprit. I sure hope they still sell a rebuild kit for those.
I tried to get mine running again today with no luck. I cleaned the tank, put a new fuel line on it and got it so fuel flowed good out of the tank with the valve open. I then took the carb off again and cleaned it and checked the float level which was fine. I blew through the carb inlet to make sure the float valve was working right and it seemed to be. I put it all back together and it did the same thing, running for about five seconds and quitting. I tried it without the air filter with the same results but I did notice some fuel settling where the filter was, don't know if that means anything or not..I work on two stroke engines all the time but have to admit this one has me stumped..
Well at this point I think I would check compression, not much else it could be. Sounds like maybe you have enough vacuum to draw the fuel from the carb throat, but not enough to make the venturi pull it through the nozzle. Seals or rings could be the culprit. A leak in the crankcase, or an air leak at the carb flange could reduce the vacuum as well.
I checked compression some time ago and it was kinda low but still in the usable range but I can try checking it again. I installed the lower crank seal last week because I've heard that one goes out first but it appeared to be okay, may get around to the upper one soon. I sealed the carb flange to the engine so I don't think that's it. I kinda ruled the ignition out but not even sure about that. It is like the fuel isn't going from the carb bowl into the engine. Doesn't it just suck it up the tube that's in the bowl into the venturi? I've checked it and the passage is clear. The reeds look good from what I can see. I've also checked the exhaust ports and the muffler and didn't see anything blocked..
Yes the fuel is drawn up through the nozzle in the carb, but not directly. When the air being drawn through the carb is at a sufficient velocity it creates a venturi effect and draws a sufficient amount of fuel/oil mix up to the throat of the carb via the main jet/nozzle. Air leaks anywhere in the system will take from the required velocity to draw fuel up into the throat. These 2 strokes are very simple by design, but not as forgiving when it comes to leaks. 9 out of 10 times when one of these 2 strokes will run on primer only it is due to a clogged carb nozzle, but since you say it's been cleared 100% then I would lean toward crankcase compression being the culprit. Recheck the seals, upper and lower, it's not uncommon for those to just completely pop out on you.
Yep, I've worked on hundreds of chainsaws but not too experienced with Lawn Boys. Chainsaws that will run with a prime will generally keep running if the fuel system is okay but I'm not seeing that here. I'll go out and check the compression in a few minutes but the Lawn Boy doesn't look like it will lend itself to a pressure/vacuum test like a saw will because of the muffler but I might be able to make a plate to go over the intake and exhaust and do a pressure test on it..
I just went out and checked the compression on the mower, it measured just above 110 psi cold, after about 5 or 6 pulls. Not that great but I've had them run on less, especially the reed valve engines but I guess it could still have a crankcase leak.
I've made a kit to check crankcase pressure in chainsaws, all I need to do is make a couple of block offs for the LB and I'll be able to test it. Should be cool enough to work out in my little shop in a couple of days. I'll let you know how the test came out. I haven't done any work around the crankcase but I guess a seal could be leaking. I have plenty of soapy water to find out where the leak is!
Also I have a decent running Lawn Boy with a steel deck which doesn't get used much. The engine looks a little different or is it just the aluminum plate under the engine that is different? If it's possible to put that engine on my 19 I might do that until I can get this one sorted out.
Just the aluminum plate is different, the engine should be interchangeable.
Edit: since the carbs might different between the two engines you may need to leave the original carb on the donor engine if you go that route. The reason being is that the throttle cable-to-carb setup may not be the same.
No, none of these have a throttle cable, they all use the same type plastic carb. I have a little work to do to the donor engine though, noticed the old fuel was left in the tank so that'll have to be cleaned out. I hate to swap engines before I'm sure the one going in will run. They do have a different shroud around the top of the engine so I'll probably just swap the whole thing rather than just the block.
I swapped engines today. While I had everything apart on the bottom of the engine I went ahead and put a main seal in the engine. Just the plate and muffler were different, I had to use the ones that came on the alloy deck. I put some Dirko on the seal to kinda insure it won't come out so I didn't try to start the engine until that dries. I probably won't be around much tomorrow so I'll probably try to fire it up Wednesday, grass is kinda needing cut anyway..
I'm wondering now if I shouldn't go ahead and change the upper crank seal in the engine. Since my first post I've acquired a couple more Lawn Boy mowers, all mine have aluminum decks except the one with the mag deck, all run now but two of them run too fast and apparently run too lean, I won't use them until I get them fixed..
Yep, I'll try to get them all sealed up before next Spring. I have a couple that are running okay. I plan on making a couple of plates for the intake and exhaust so I can do a pressure/vacuum test on them like I do on chainsaws.
Sure, I make an aluminum plate to fit over the intake and exhaust flange, the plate is covered with rubber on one side to prevent leakage. I have a nozzle that's threaded to fit in the sparkplug hole which I inject air into like I'm blowing up a balloon only I just use about 7 psi. of air. I have an inline gauge to check for leaks hooked to a blood pressure bulb to blow air into the engine. If the seals and seams of the engine are good it will hold seven pounds of air for a long time, otherwise I look for the leak using soapy water. Some people also use a vacuum test on the engine also by just sucking on the hose attached to the spark plug hole until you get between 5-7 hg. vacuum, I have an inline switch to hold the vacuum. If the engine won't hold pressure and vacuum it won't run right. On a Lawn Boy it requires removal of the bottom plate that holds the muffler.
It really doesn't matter, you're checking the crankcase but sometimes when you turn the crankshaft a bit the pressure or vacuum will drop which means you need new main seals. Any leakage at all means you have to get the soapy water out and check where the leak is. I'll be using the intake and exhaust gaskets as a template for the plates. Kinda cold around here today but I'll get to it before next Spring.
