Mag 20 PO Mod
 

Removed the Mag 20 off my 2072 today to address what I believe to be an oil leak from the oil seal behind the flywheel. Took off the valve covers to take a peek and found a curious PO mod. It appears that silicone was used to form a "mushroom" around the push rod, and also there is a hole in the middle that was completely plugged. The valves are functioning normally(their movement is not hampered). Any idea why that's there? The other side doesn't have them. Should I remove them?:bigthink:

On a separate note, anything else I should consider replacing while the engine is out of the tractor?

http://s12.postimg.org/rrzq0rzml/IMG_0416.jpg

Looks like JB weld. Not sure what the hole is in the center. Possibly just a breather is what I would guess. Maybe Jon can answer that. But that defiantly looks like JB weld hi temp.

It has a soft rubber like consistency, it's more like RTV silicone than JB Weld.

Yes, you need to remove it. PO's :bash2::bash2:

Make sure the drain there is unplugged, and none of that crap plugs it again. It's silicone.

that's messed up

What do you think that PO was trying to accomplish?
Maybe he was trying to quiet the valve train. :biggrin2:

I'd love to know that as well. It would appear that the silicone serves to limit the amount of oil moving in and out of that "chamber". Why, I don't know , but I have a feeling I may find out once I remove all of it and run the engine :biggrin2:

Behind the top valve spring lower right, is that a piece of metal behind there or jb weld? That's the strangest thing I've ever seen! Hope that's a oil seal leaking behind the flywheel and not a hole/crack in the block!

I just went back to look, it must have been a reflection from the flash, there's nothing there, neither JB Weld nor crack. I too am getting concerned, we will find out Tuesday when my flywheel puller arrives.

I hope it's nothing, sure looks like jb weld or something silver in the back.

Got the flywheel off, good news,no crack in the block. Seal is dripping oil through a crack, that made it easy to identify where the oil was coming from :biggrin2:. Anything else I should do while I have it apart? Should I replace the coil just because it's 30 years old? It works fine. What about the magnets on the flywheel, should I drop some extra JB weld on them?

I wouldn't replace the coil. If its good its good, don't mess with it. Wouldn't hurt to put some JB on the magnets, just make sure that you don't get any on the face of the magnets.:biggrin2::beerchug:

On coil: your choice. I wouldn't.

On flywheel magnets: not unless they are loose. Check them out good. DO: clean it up good.

Thanks Jonathan, I'll give it a good scrub down.

My seal arrived in the mail yesterday and so today I proceeded to pull the leaky one out. Once I did, surprise another seal right behind it. Full of surprises this engine is.

Since I had the valve covers off I decided to check the clearance. As a side note, I've been trying to find some information on valve clearance and how it affects the engine and I haven't been able to find a clear writeup, especially in relation to small engines. I wish someone here with the knowledge would do a technical writeup on valve clearance, theoretical reason behind it, what it does, how increasing and decreasing it affects the engine. But anyway, there's no clearance on the intake valves, 0. The manual says 0.003/0.006, and it looks like the Magnum valves are not adjustable, you have to take it out and grind it. Those things looks like a major PITA to take off and put back on, is it worth the trouble to take them off , the engine runs ok but again, I'm not sure what the impact of that tiny gap of 0.003 is.

Not really much of a tech write up......

Valve clearance is easy. The clearance is so that the valve always shuts all the way. Internal engine parts get hot and expand. If there isn't a gap between the cam and the valves when cold, then when the engine gets hot the expanded parts would hold a valve open. That is why most exhaust valve clearances are wider than the intake. Exhaust valves get hotter. The amount of gap is set so that the tolerance is close at rated engine temps... but not touching. If gap is too wide, then it works just like a hammer hitting a punch. Eventually, it will mushroom the end of the valve. If gap is too close, it will hold the valve open when the engine gets hot.

So.... when you ask if it's worth it to get the gap correct..... YES. Now, on your mag motor, it's not adjustable. Yes, you have to grind the valve stem to set clearance if it is too tight. However, those motors spec range is very wide. I suppose you could do it on your own, but it is better to use a valve grinder to "trim" the stem. It needs to be perfectly flat because if not, as the pushrod hits the valve, it needs to hit squarely or it will "beat" it flat and the gap will be too wide. If you have a bench grinder, you could set up the steady rest so that you can hold the valve on the side of the wheel. Also, you would need to get a very fine grit, soft stone. You would need to check it with a square to be sure that the rest and wheel are at a 90 deg angle.

Make sense? :biggrin2:

Was the piston in the right position when you measured?

Getting the valves out isn't bad if you have compression tool. getting the little keepers on during reassembly can be tricky but the mags are easier than the k series to me.

The spec is .003" - .006" on intake. Exhaust depends on SN of the motor.

Thanks Jonathan. Seems like a valve grinder is a fairly expensive piece of equipment, especially for a one time job. It also seems like you can't just take the valves to someone, they'd have to have the whole engine to get the gap right. So how is this typically accomplished, you take the whole engine to a shop?

Timbo2, I measured at TDC on the compression stroke, couldn't get even the thinnest feeler in. The exhaust is at 0.008, out of spec as well.

Yes, you would take the whole motor. Going that far, I would go ahead and do a valve job. Unless the parts are shot, it really shouldn't take much money or time. No 3 angle stuff... just give it a new sealing surface and lap them.

Well, after going to all the trouble with this engine, it decided it had enough and broke a rod. Exactly why, I do not know, first thought was oil, but it was to the full mark with no gas in it. Oil pump works, maybe it was the 2200 hours it had on it. Just wish it had done it before I went through all the trouble to take it out clean it up put a new oil seal and put it back in. No damage done to the block, camshaft or bore. The rods are NLA, only thing available is used ones on eBay. After taking the cylinder jugs off, I saw a lot of deep pitting on the top and scratches I was not able to see before. Seemed like a really bad idea to dump more money into it, was getting ready to pony up for a B&S Vanguard when I spotted an ad on Cragslist for a 1535 with a broken clutch. Sure enough ,the owner was more than happy to sell me the Mag "15" for $250.

It had been sitting for 2 years under a tarp, some surface rust, but it turned freely and had compression. Brought it home, started tearing it apart. Starter is bad, two magnets fell off the flywheel and stuck to the stator, presumably from sitting outside because no damage was done to the stator. Took the heads off, nice crosshatch on the cylinder walls, no scratches, no pitting, looks like it hasn't seen that much run time. Some deposits on the back of the valves which I took care of , valve clearances are within spec, feel like I won the lottery, this thing looks to be in really good shape. The good old Mag 20 kindly donated its flywheel,stator,ignition coil and carburetor. I am unsure of the condition of the ones that came off the M15,They may be fine, but I know the ones off the M20 worked and I don't feel like taking it apart again. Tomorrow it goes into the tractor, fingers crossed it should fire up and give me many years of service. Guess it's a 1872 now :biggrin2:

I guess it's true every kick in the ass is a step forward :beerchug:

If the "new" motor has no crosshatch still present, I'd say it's got quite a bit of run time. Maybe you worded that wrong?

You can still get KT and Mag rods here:
http://www.psep.biz/store/kohler_aft...cting_rods.htm


My mistake. I thought I saw the right number, but I double checked and I read wrong. I'll keep looking, pretty sure I've found them before, unless now they are NLA even in aftermarket.

Nope, I said nice crosshatch :beerchug:

That is the first place I went to, no rods for the M20 listed. Rods for the M18 are still available, both aftermarket and OEM. Why the M18 parts are plentiful and the M20 are not, I do not know.

I edited my post, I misread the part number I was looking for.... and apparently your post.

I'll keep looking...... now it's a game. :biggrin2:

The part number off the rod for the M20 is 52-059-10.There's a couple used on eBay. Others listed as M20 rods but under a different part number, don't know what the difference is, I'd hate to spend $80 to find out it won't work. But, the crankshaft journal is scratched/damaged, and with the cylinders in bad shape, I don't think it's worth dumping money into, it's done its job for 2200 hours, RIP :beerchug:

I'm thinking of buying a couple of M18 rods,they're only $35, maybe a good crankshaft if a cheap one pops up on eBay, put them in a box and be ready for when this one throws a rod in 8-10 years.

KH-52-067-71 is the number I found for the rod in an M20.

I hear you about it being shot. I wouldn't fix it either. I don't mess with the Mags/KT's. They are just not worth the trouble. I may try to play with one every now and again, but they are just not a "rebuildable" motor.

I hope it lasts you a long time!! I'm getting scared of mine. It's really racking up the hours.....

According to Kohler...........No such number

The New & Correct number 52-067-71S which is NLA

I think the "S" is for the .010" undersize rod..... :bigthink:

NOPE.........52-067-72 is the undersized Rod.

"S" is standard. That even makes sense. I think I've had enough tonight.... :beer2:

See you guys later.

That rod has been a bit of a mystery, the part number you mentioned is indeed listed as the correct rod for a M20 engine. No mention anywhere of the rod I have. Yet here it is :

http://s11.postimg.org/707atcnz7/Scr...9_31_48_AM.png

Of course, the crankshaft part number in the machine is different as well from the crankshaft listed on the Cub Cadet site for the M20. I'm guessing the specifications would have to be the same even though they have different part numbers, and therefor the "new" rods would work with the existing crankshaft. But they're nowhere to be found , so it doesn't matter. Still baffled by the abundance of replacement parts for the M18 and the lack of parts for the M20.

:Poof::Poof::Poof: 500 :Poof::Poof::Poof:
:biggrin2:

That number is probably an Engineering or production number that only mean something to the Kohler Engineering Dept. As for the replacement parts end....it is nill.

So I got everything back together, only thing I'm missing is the armature for the PTO. The PTO that came with the "new" engine is trashed, bearing is bad,pulley is rusted. I was able to use the coil off the M20 PTO, the rotor off the M18 PTO, but the shaft on the M20 is 1/8" bigger than the M18, so the M20 armature is too big for the shaft. I placed an ad in the wanted section, but I'm also considering using a 1 1/4" OD x 1 1/8 ID bushing on the M20 armature to make it work on the smaller shaft size. If I can find one. Any reason that wouldn't work?

Nope. :beerchug:

So the M20 had a mechanical fuel pump where a lobe on the camshaft pushes on a metal "tongue" moving the diaphragm up and down. The M15 came with a fuel pump which appears to be vacuum operated. I believe they both work fine. Which one is the better one to use?

I'd use the vacuum operated pump only because if it fails it won't fill your crank case with gas.

:IH Trusted Hand:

Did some more work on the 2072 this evening, got the PTO working. Only one item remaining, the engine is gasping for gas really bad as soon as it goes past a quarter throttle. I bypassed the fuel pump to take that out of the equation, no change. But it stabilizes nicely with about a quarter choke. Guess I should have done that first. So I know the drill, clean the carb, look for vacuum leaks, but in this situation it begs the question: is this carburetor that came off the M20 even acceptable for use on the M18? The number on the flange is 52 053 18. If there's a vacuum leak, is high temp RTV ok to use between the manifold and the block?

Last but not least, I notice a little bit of wobble in the driveshaft, I aligned the engine best I could to it and it's very little, but it bugs me. What's the best way to fine tune the alignment? I was considering loosening the bolts just slightly on the engine and running for a few minutes it to see if it would line itself up , but I'm not sure if it's a wise thing to do.

---Don't like rtv in that heat situation, best to use correct gskt.
----not a wise thing to do as far as loosing things than running it.
Better to chalk/grease pencil shaft while running, stop and then loosen, push in correct direction re tighten might get it closer that way.
Carb sounds lean, if main jet is not adjustable, pull and clean it thoroughly.:beerchug:

My k341 was gasping hard at wot also. I went through a few things like timing and carb cleanings but nothing helped. Eventually I swapped the carb off a k321 and it worked fine, so I knew it was the carb.
My float tab needed adjusting to allow more flow, all better now.