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Brettw

Broken M20 camshaft

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Brettw
Picked up a Sunstar with a broken camshft in the M20. The PO's brother (a supposed mechanic)took it all apart to discover this. So I have a few boxes of M20 parts. My question is, what would cause the camshaft to break? Haven't had the time to look it in detail, connecting rods, crank and cylinders seem intact and fine. Seems a strange failure to me?

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427435
I've had 2 cams shuck gear teeth on M20 engines (the vertical shaft ones). I think there was a design flaw as the gear teeth seem to wear at one point (probably where valves are lifting) until they break off. I've just bought new cam shafts and put the engines back together again.

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Brettw
No blown rods, cylinders look great, inside of the engine is clean. However, one of the lifters/push rods, was broken (missing the "top" or the part that runs on the camshaft) and was not free. I had to tap it out of the block. Oil pump gear has a damaged tooth. I noticed parts of what must be the governor setup (brownish plastic) in the bottom of the block, and the camshaft itself has two damaged teeth on the driven gear besides being broken in half. All of the valves move freely and appear to be undamaged. Crank looks perfect including all bearing surfaces. Pistons and rods look good (minor dings on one rod). The camshaft's break does not appear to be clean almost as if it ran and the two broken surfaces were rubbing, in other words, the faces of the broken surface are "worn" a bit. There are other misc parts that appear to me to be from the governor assembly. Perhaps that is what let go and took out the cam. No idea. Anyway, here is a pic to add to your technical journal, another exploded view of an M20 (as I received this engine)


Broken parts, slight block damage at the lifter/push rod guide.








Salvageable? Would need governor setup, oil pump gear, camshaft and at least one lifter, and whatever else was lost when the PO's brother disassembled it and tossed it into boxes.

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ardisam
Brett, I would a governor setup out of one of my KT series crankcase if you want it? I haven't had time to check part numbers for the camshaft like we talked about. I'm pretty sure it would work, since it is the same crankcase. Not sure if I would have a oil pump gear, but I lifter I would have. Let me know.

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Brettw
Thanks guys, I will be letting all of you know what I really need once I get thsi thing sorted out and cleaned up. Sad part is I sold the good parts left from a KT17 II and a 19, just last year. I may try to resurect the 20. It's worth quite a bit as parts from what I have seen, but I would love to have a spare 20 though. A new carb rebuild kit came with this tractor/engine too. From my CSI (Camshaft Seems Imploded) forensics investigation, most of it all seems to be there. There is nothing but parts from the governor setup though, and not much of them at that. Chicken and the egg. What went first, the governor or the cam?

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powerking_one
Brett, I believe the KT series engines and the later M-series twins were/are notorious for grenading the plastic governor gears, so my guess is the governor gear let loose first and then the pieces jammed into the cam/lifter areas an hence broke the cam. Al Eden knows all about this Kohler "feature". I think what usually happens is the engine runs into a wide open throttle state and within seconds (if you don't shut it down)throws a rod and ventilates the block; end of engine. Also, if you are going to rebuild and use this engine, there is no way I'd put in a used governor gear (JMHO). Tom (PK)

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Brettw
Thanks, Tom. I did look, and a new gear is only about 35bux, so I had already sort of come to that conclusion. So then it's just cam, tappet and oil gear. Gasket set, prolly rings while I'm at it too. Have to tally up the costs........sigh.

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Brettw
I found a cam from an M18 that was quite reasonable, shipped, and I am waiting for it to get here before ordering any new parts. I figure with the cam, new governor setup, new oil pump gear, a tappet, a gasket set and rings, I think I'll have about $200 in it. I haven't had time to really dive into it in detail just yet, so there may be other parts or issues I am not aware of. I also picked up a KT19 series II recently. Supposedly a running engine. Has compression on both cylinders so we will have to see. It came out of a 7119, so it came with the muffler and heat shield, and as an added bonus, a front PTO, mechanically activated, with the lever and rod. Quite a sweet deal. So if all goes well, I will have two Kohler twins running and ready.

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maxtorman1234
Hey Brett, I read this topic earlier when you posted it, and I though, wow, I've never seen a broken cam in one of these engines.... Well I sold a running M18 and the guy trade his old M18 on it also. Hole in the side of the block.... So I start tearing it apart, find a sheared flywheel key. Finally split the block, find the cam in 2 pieces! Everything else is Ok, except I beleive the broken cam caused a lack of oil/pressure to the connecting rod causing it to seize. More interestingly, I have 2 M18's and 1 M20 apart and 1 KT17. When assembling the M20, I noticed it's Cam has larger lobes for the valves. The M18 and KT17 cams have the same size lobes. Now, I compared the cam from the M18 I just received. It's the same cam as the M20! The engine had never been apart. The 2 M18's I have, have different cams? The broken one has the same casting # as the M20 cam. So I'm pretty confused as to what kohler did with these cams, The M18 has significantly smaller lobes. I'm thinking this is partially due to the longer stroke of the engine, and the M20's cylinders are longer to accommodate the longer stroke. So I guess this makes the 'deck height' different.... So, I'm wondering how an M18 cam will work in a M20....

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Brettw
quote:
Everything else is Ok, except I beleive the broken cam caused a lack of oil/pressure to the connecting rod causing it to seize.
I would think that likely it was just the opposite. The engine would not run long enough with a broken cam for the rod to seize because of it. More likely, the rod seized, broke, and the grenaded parts, still being driven by the good cylinder, got tangled up with the cam. As far as cam lobes, I am of the understanding the cams on the M18 and M20 are the same. Your lobe sizes being different may be a sign of wear? If the casting numbers are the same I cannot imagine two different sizes. I was not aware that M20 cylinders were longer. I thought they were the same, and stroke was handled by the crank and connecting rod. I know the compression is higher on the 20. Someone with more knowledge will have to chime in on these questions.

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maxtorman1234
Hey, I Wouldn't think it would run long with the broken cam, but the break is discoloured, and it was sitting exactly in place when I opened up the engine, there is absolutely no damage to anything on the cam, And It sure wouldn't take too long for the rod to seize when mowing, but the sheared flywheel key is still a mystery. I'll take some pictures of the cams from the 18's, it is definitely not wear, the lobes are overall smaller, and appear to have less duration. At one point at least, kohler had 2 different cams for these engines. I'll look up some parts numbers based on my engine specs for more info. The smaller cam from the 18 has no casting number at all, the 18 with the larger lobes is identical to the 20 cam in all ways. (casting#) I'll take some pictures of the cylinders for comparison, but after closer inspection, I believe the stroke couldn't be handled by the crank alone, as the deck height of the 18 wouldn't allow for the longer stroke without the piston hitting the crank, therefore the engine must have been widened, the 20HP cylinder has an extra cooling fin also, and this appears to be the reason for the different cylinder cowling. The 20 and 18HP cylinders are not interchangeable.

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maxtorman1234
I just looked at the spec numbers for my engines, and there are indeed 2 different cams used. However, the M18 with the 20hp cam, is a M18QS quiet model, and is older than the M18 with the smaller cam, identical to the KT17. Maybe noise reduction is their reasoning? Also, there is a kit that comes with tappets for certain engines. Looks like tappets are different also. Basically, it looks like the parts in these engines can vary a fair bit.

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