stihl 441 carnage twice what am i doing wrong?

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huntdiamondjim

ArboristSite Lurker
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hi everyone long time lurker and reader of this site. i have a 441 that i've been working on its blown up twice in short order, second time about 15 seconds. Now i've been using the very cheap cylinders and pistons from fleabay,but still think they should last longer than 15 seconds. It looks like the rings are breaking and get wedged in exhaust port. Yesterday it broke the top of the piston off. i checked the intake boot and it is good shape. nothing in my no so good eyes jumps out at me. Can a connecting rod get bent on these? it was a very sudden stop yesterday. i would send pictures but dont think i can with no posts. Also now you know why I am only lurking on here by my typing skills and abuse of the english language. This little paragragh took 15 minutes.
 

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15 seconds? Most likely just bad, real bad luck. I fix a lot of stuff, and when it is new to me, a first time, I go slow. Lots and lots of things need to be just right. When I was a kid, I use to ruin as much as I fixed. Everything destroy was a lesson learned. I expect it is the same for everybody, as it is still for me.

Just yesterday I fixed a plumbing problem under the sink. Coupler between the compression nut and the valve broke at the threads. I had to cut the pipe coming out of the wall. All new to me, and called a neighbor to come watch me and give advise. Turned out it was a piece of cake, but getting help can be a real boon in getting it right the first time.
 
Looks like you will be splitting the case now , check real well for any damage , rod could have a bad needle bearing. Also not trying to be a pain but you did put the needle bearing in the connecting rod correct? Only time I saw something that bad that quick is when a buddy of mine forgot the needle bearing when he did a top end rebuild
 
Can you post a picture of the inside of the cylinder?
If the ports are rough around the edges, the rings catch and this happens.

I port every aftermarket cylinder I install, they all need some grinding.
Some get degreed and widened some just get a quick clean up and smoothing of the port edges so I dont catch a ring.
 
thank you guys for the replies.i was thinking of going a step up on a meteor jug and piston. are they any good? also by all four bearings you mean crank and rod bearings correct? the crank and rod are one assembly correct ? if rod is bent which looking at it is doesn't seem to be,it seems this saw may have gone to chainsaw heaven as that would be rather costly, i hate giving up on something but sometimes you have to cut your losts. also sam i did have bearings in rod.i had the rings in the locators but it does seem that the one locator is very close to a port.chinese junk is the real problem.would i use a dremel to finish edges of ports in cylinder.The piston had the arrow on it. put it towards the exhaust, thanks again for all your time. jim
 
Cylinder quality aside, the piston on the right looks to have had the ring pins on the exhaust side :eek:... that would definitely do it! (Good grounds to get a refund)
The other piston looks to have a pin at the side where it may catch a transfer port. That piston has obviously had loose material catching in the exhaust port so make sure you thoroughly check & clean the crankcase & exhaust or you may have debris in there that will cause you more grief. If you flush any debris out try & identify what it is as it may be that a bearing cage is coming apart.
Have you identified what caused the saws original failure?
Do you still have the OEM cylinder/piston?
Have you been vac/pressure testing the saw after assembly?
Meteor cylinders/pistons are generally regarded as the next best thing to OEM.
 
Cylinder quality aside, the piston on the right looks to have had the ring pins on the exhaust side :eek:... that would definitely do it! (Good grounds to get a refund)
The other piston looks to have a pin at the side where it may catch a transfer port. That piston has obviously had loose material catching in the exhaust port so make sure you thoroughly check & clean the crankcase & exhaust or you may have debris in there that will cause you more grief. If you flush any debris out try & identify what it is as it may be that a bearing cage is coming apart.
Have you identified what caused the saws original failure?
Do you still have the OEM cylinder/piston?
Have you been vac/pressure testing the saw after assembly?
Meteor cylinders/pistons are generally regarded as the next best thing to OEM.


Yes , it is on the exhaust side. ??? But, it is the one on the left as well if you blow the photo up compared to the arrow.
It likely did not bend the rod. I have had it, but only on smaller blowers where the rod was pretty flimsy.
Make sure all the debris is out of the crankcase. Shouldn't have hurt the main bearings, or the big end bearing.

I had a MS660 that I put one of those best thing since sliced bread Mastermind copied top ends on it. Lasted about a week. Hung a ring. I put an OEM top end on it and a guy who has a firewood business has put umpteen hours on it for maybe four years. No problems from the grenaded piston.
 
Are the cages for crankend bearings breaking up? Two major failure like that-either something is wrong with crank/rod/bearings or an assembly issue.
but buying a more expensive cylinder may only cost you more when it blows up too until reason know.
cheap cyl usually rattle and loose compression-but maybe these are cheaper than cheap??
 
by all four bearings you mean crank and rod bearings correct? the crank and rod are one assembly correct ?
1. Correct.
2. Well, just say, very very few people separate the crank halves to get at the lower rod bearing on chainsaws.

Maybe a bit off topic...can you post a pic of the original cylinder and piston?

Roy
 
looks that way. Clearly installed the piston backwards. Arrow facing intake port = top end go bye bye.
I can't see an arrow on what should be the exhaust side of that piston so if there was one it's gone with chip off the top & that would mean it was on what should've bèn the intake side to start with
 
hi guys couple more pictures. i had the arrow both times facing exhaust. no mistaking that part. but after close examination the locating pins are in different places on each cylinder and seem to line up with a port. i dont know if it shows on pic but the longer part of skirt on piston is on intake side. i never did do a pressure test on saw. don't really know much about that. . maybe i should read up on that. seems like that might be a problem. but i dont know if a piston would last longer than 15 seconds with this happpening.]
 

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