I just picked up an MS460 Magnum on CL. The previous owner thought the crank or connecting rod was broken, but it turned out that piston (big bore kit from Bailey's) had broken rather spectacularly, the wrist pin jammed down into the crankcase. bits of aluminum everywhere. It appears eminently repairable. What I'm wondering is whether it would be idiotic to attempt the repair without splitting the case. Seems like I could pull the crank seals, and if the bearings are in good shape then I ought to be able to rinse out the debris, install new seals and put it all back together. Does this seem plausible to those more experienced than I? FWIW, the breakage is worst along the exhaust and sprocket sides of the piston. I don't know if that provides any clue as to the cause.
If the crank and bearings are ok, I would do just as you are thinking... I won't split a case unless I absolutely have to...
Yep.., Saw I have now had a bunch of "dirt" and dust in the crank. A little fuel to rinse, then a little compressed air (not very high pressure), then fuel, air, rinse repeat. Wanna sell that one buddy
Why not very high pressure? Worried about driving particles deep into some delicate crevices? I've already blown some air thorough and the crank is rotating freely now, but I haven't pulled the bearing seals yet. Earlier I found a thread on AS where several members had told someone that splitting the case was the way to go in a case like this, but I really don't wanna. Didn't I just read in the Sugihara thread that you already had a 460 on the way?
Jon, I wouldn't split that case unless absolutely necessary, unless of course MM will do it for you cheaply . I'd just go with the repeated rinses, maybe fish a small magnet around in there too, then see what you have. If the bearings and crank feel smooth, and it doesn't leak via the seals, I wouldn't fool with it.
I'd only split the case if it was truly necessary, as already mentioned above. BUT, if you have the know-how and it's already broken down that far, for a couple extra bucks you could throw new bearings and seals in it.....which may be good insurance. make sure to check that rod bearing for any roughness or slop, that could have possibly had a role in the failure. But it kinda sounds to me like the piston may have had a flaw in the casting somewhere....
I always use low pressure with good results. Super high pressures may not damage a seal? But I would rather not risk it.
Or someone like me might have damaged it using a piston stop tool on it at one point ..................
Yeeeeesss....I have a MS170 on my bench right now (all it ORIGINALLY needed was new crank seals), but due to my "cowboy-ing" ways, it now needs a new piston too.......
I actually did that around July......that saw got pitched into the corner of the workbench out of frustration and it's been there since..... Too many tree jobs to do right now!
The rod bearing has a bit of side-to-side play, but not the worst I've seen. I don't detect the sort of radial play that would cause extra impacts on the wrist pin/piston. The crank bearings feel good. I have a seal puller, so it seems like cheap insurance and a happy middle road to pull those seals off, get a good look at the bearings and be sure I rinse out any particles that might've worked in between the balls and races.
wow, that sure looks like a casting failure to me.....can't see what else would cause a break like that.
The aluminum won't be a problem so much as shelling a bearing cage would... I hate splitting cases... Have I mentioned that??
I've only split one case on a saw I intended to put back together. My improvised tools took a while to concoct and didn't end up working very well, but I at least got the general idea of how it's done. I suspect it's a lot easier with better/the right tools. I'll post back here when I pull the seals and get a better look at the bearings, probably in a day or two. Today is fully booked with other activities.
Splitting the case with the proper tools is no biggie at all, (about 15 minutes) but those tools are very pricey, even if you have connections. It's always a risk but in this case, splitting the case will not allow you to access the bearings I would be worried about (con rod, big end) so I would roll with your current plan. How did the cylinder look on that one?
I'd rinse with diesel and rerinse. But I would not split. I talked to a big parts seller on ebay and he said the wrist pins is a common failure point on aftermarket stuff. That the clipsfall out. He told me if i was eve to use aftermarket P/C to use factory stihl clips. Just passing on something. Everyone has an opinion. But he said hehad one fail that way as well as had a customers fail the same way.
