Okay, who has done this? I need info as I might want to take a crank or two apart and put them back together again.
Any info appreciated.
Any info appreciated.
Pressing Apart The Crank
- Thread starter Nitroman
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Dan_IN_MN
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Nitro
I was thinking about the same thing..... Are you thinking about replacing the bearing(s)?
I have access to a press.....
Dan
Kunes
The Kid
i have a 20 ton shop press just make sure you have something like a bearing puller. and the 2 standard steel blocks with v notches in them
Saw Dr.
Junk Collector
When I worked in the motorcycle shop, we would do it all of the time. The rod and bearing kits were available for bike cranks, though. Presssing the cranks apart is not a very big deal. Getting them together straight is. We had a special crank press that fit in the standard 60-ton shop press to keep the wheels aligned. I'm sure you could do it freehand, but with ALOT of fooling around. It was not uncommon for us to make one good crank from two with bad ends.
If you have found a source for saw rod kits, please let us know. I'm sure that there are alot of dead cranks (rod or bearing failure) lying under people's benches.
If you have found a source for saw rod kits, please let us know. I'm sure that there are alot of dead cranks (rod or bearing failure) lying under people's benches.
Tzed250
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You will need the press, but the V-blocks will be no help at all. To true a crank after rebuild you will need to place it between centers. A bench center, an engine lathe, or a crank truing fixture is required. You will aso need two indicators that will reslove at least .0005. The main bearing journals should have a TIR of less than .0005 when it is done.
A bench center looks like this,
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Before you guys attempt this.
The crank halfs must be perfectly
aligned when pressed back together.
Lee
The crank halfs must be perfectly
aligned when pressed back together.
Lee
Saw Dr.
Junk Collector
:agree2:
That is what I was saying earlier about the crank press tool. I believe it was about $1000 back in 1991. I'll see if I can find one online. If you just press it back together and then try to true it, you may spend your whole life beating on the thing. Also, the crankpin can only be moved in the wheel so many times before it starts to become loose.
Tzed250
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No matter how good the assembly fixture is the crank will still need to be run between centers and the TIR checked...
Saw Dr.
Junk Collector
True. I'm just saying that it is alot easier to get it straight when you're starting at a few ten-thousandths out, than 1/16". I have never tried one free-hand. I know most of the ones assembled on the jig were within spec and did not need further adjustment. We checked them all, just in case.
Gentlemen,
Thanks for all the replies! Nope, haven't found a kit yet, but you can find any bearing you want by going to www.Timken.com and downloading their catalog. It will take some time though, because it is a comprehensive catalog.
Time for more research.
Thanks again!
Thanks for all the replies! Nope, haven't found a kit yet, but you can find any bearing you want by going to www.Timken.com and downloading their catalog. It will take some time though, because it is a comprehensive catalog.
Time for more research.
Thanks again!
Ax-man
Addicted to ArboristSite
I was wondering about how this is done and trying it on a few cranks.
If someone has done this and can do a show how it is done type thread with pics it sure would be interesting to read. I don't think we have ever had a thread on how to take a crankshaft apart and put it back together with a a new bearing for the con rod.
Since I have gotten some tools to split crankcases apart easily and a press for the bearings working on the bottom end of a saw has made a difference in how they turn out on a rebuild. Be interesting to carry it one step further on a rebuild.
Larry
If someone has done this and can do a show how it is done type thread with pics it sure would be interesting to read. I don't think we have ever had a thread on how to take a crankshaft apart and put it back together with a a new bearing for the con rod.
Since I have gotten some tools to split crankcases apart easily and a press for the bearings working on the bottom end of a saw has made a difference in how they turn out on a rebuild. Be interesting to carry it one step further on a rebuild.
Larry
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Definately the shaft must be true and in alignment!!! The reason that no one does this on a chainsaw crank is that you MAY get it back together straight and in alignment and you MAY find the correct bearings BUT the inside of the conrods big end is also the outer bearing race and if the bearing was worn out or scored so is the race. So for all your effort you still have a POS crank when you were done. You would also have to scource new con rods. So after you buy a new rod (NEVER seen one for sale!!) new bearings,a trueing stand and indicators and do all the work how much have you invested?? Enough to go and buy a new crank from Sthil or Husky!! (And then some!!) The powers that be (engine designers) have already set the parameters of what repairs can and cannot be made!! If you need a new crank throw the old one away!!! Go get a good used or brand new one and save yourself some grief!! Unless you have a most remarkable machine shop and can just make everything you need!!! I have spent many years assembling and trueing Harley cranks they are made to come apart and go back together not like little twostroke saw cranks. When they are done they are done and that's that!! IMHO
Sorry to rage but it's my 100th post!!
tdi-rick
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FWIW, and bear in mind this was what was considered 'best' twenty years ago, my kart engine builder would only use FAG bearings on the bottom end, and Thompson little ends, regardless of which brand of engine (usually Italian though) he was building up.
They were good for 20,000RPM then.
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Yes those older large mac and homelite motors had conventional one piece cranks. The con rod had removable bearing caps. These were rebuildable by design. Modern saw motors are not intended by the designers to be remanufactured thus there is no core charge if you were to go to saw dealer and purchase a new crank. Nor is there any replacement con rods for sale even to dealers let alone us humble civilians. Also as B200driver stated you canot move the crankpin in the counterweight many times before it will become loose. These are an interference press fit only. Nothing to hold things in place except that fit. No nuts and keys as in other larger built up cranks. I have great respect folks who are willing to try to repair all things. Usually success can be obtained with thoughtful work and much research but if rebuilding modern chainsaw cranks were worthwhile or profitable you would see them for sale everywhere. Replacement parts as well. This is not the case.
I have broken my fair share of internal combustion engines. Every time a crank/rod fails is an eyopener!! I've had saws explode in my hands and I had a Harley flathead explode right between my legs at 80mph!! I am sure I had the same look on my face both times!! Needless to say I have some consern and respect for all spining things large and small.
I don't mean to rain on your parade Nitroman but you can't move past where the design stops. The designers, in their never ending quest for lighter more powerful saws have designed the lightest AND safest crank that they could come up with. As I said earlier with the tools (which you have located at around $600)(and a press and trueing stand with indicators $???.??) you can probably get them apart and back together. As you said you can probably get bearings but you are still limited by the bigend rod being the outer race for that bearing. Unless you can find a new con rod your rebuild will be incomplete.
tdi-rick
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Nope, no Macs, either Parilla, PCR, BM, Komet, Rotax, DAP, etc. reed and rotary engines with one piece rods.
Macs were long gone here by the time I started racing ('87) and I think I only ever saw one running ?
Lack of spares by then and they weren't competitive against the Italian screamers.
Pressed together cranks and the rebuilding of them is nothing new. Many (if not most), Jap bikes, Harleys, all PWC's, and snowmachines use this sort of construction. It is relatively easy with the right tools. Yes, rod and bearing kits aren't there, but I can make pretty much anything I want, and if I cannot, then I can have it made. I started the thread out of curiosity, not to create a stink.
Is it feasible to sleeve the bearing races in the connecting rod?
I'd say that it is totally possible to rebuild a chainsaw crank, even if the connecting rod and crank bearing surfaces are shot.
It might not be worth the time and effort, but then hobbies rarely are.
Trying to say that they were not designed that way so it shouldn't be done is foolish. We've all done many things that were not designed into chainsaws.
Mr. HE
It might not be worth the time and effort, but then hobbies rarely are.
Trying to say that they were not designed that way so it shouldn't be done is foolish. We've all done many things that were not designed into chainsaws.
Mr. HE
Saw Dr.
Junk Collector
Welllllll, there is a way around just about anything. If / when the crankpin gets loose, or if you are turbocharging a machine to 3x its normal output, the fix is welding the crank. Not sure if I've seen this on 2 strokers, but I don't see why you couldn't do it. Just get the thing true, and then weld the pin to the crankwheel. Of course, that makes the crank VERRRYYY hard to rebuild again..... Falicon welds them every day.
Nitro making his own rods. Sounds interesting. I'd love to see pics.
