Chainsaw Problem

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  #1  
Old 09-02-02, 08:52 AM
trendar
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McCulloch MacCat 18" chainsaw automatic oiler problem

This may be a bit esoteric, because I don't know how much commonality there is among chainsaws, but I'm having a problem with the automatic oiler on my chainsaw.
There's a diaphragm actuated needle/rod that goes into the pump assembly which meters out oil as the engine runs, by pushing the needle in and out from engine pressure/vacuum, and also a manual pump actuating rod that normally dispenses additional oil when pushed.
On my chainsaw, it seems that the needle is not able to retract fully, blocking the opening to the output, which results in no oil output, and manual actuation doesn't work either, due to hydraulic lock.

I've taken the pump off (attached by a wire bail clip), and there are no visible obstructions or debris in there. The needle and diaphragm assembly is spring loaded to push out towards the body of the chainsaw, and if I don't put on the clip, the manual actuator works, indicating the opening is not blocked. If I secure the pump with the clip, however, it apparently just pushes it in enough to close off the opening. Are these things set up that closely that the tiny amount of change in position will make the difference?

I was going to try getting a new o-ring gasket for the pump mount, to see if the compression of the old gasket is allowing the needle to get pushed in just a bit too far and sealing the opening, but I just find it hard to believe these things would be sensitive to that type of circumstance.

Any ideas on this mechanism, and likely solutions?
 
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  #2  
Old 09-02-02, 02:54 PM
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Does the diaphragm feel stiff instead of flexible and supple, like a new one? If so, It may not have the flexibility to operate like it should. Make sure the port that supplies the pump with the needed pressure/vacuum to operate is unobstructed.

When you checked operation of the pump with the spring clip off, where did the oil come out? Did it come out at the bar, where it is supposed to come out?
 
  #3  
Old 09-02-02, 04:09 PM
trendar
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Fixed it!

The manual oiler was locked up whenever the pump was installed in the engine, and if I pushed hard enough, it would pop out the nipple fitting on the inlet for the pump, due to the back pressure.

After trying some compressed air on the passages, it stopped pumping even out of the engine, apparently due to the check valve ball being blown out of position.

Looking into the body of the pump, I realized the metal insert that accepts the diaphragm piston was a press fit, and I was able to grab it with needlenose pliers and work it out of the housing. I think what happened was that the thing must have worked itself out of the seated position, and resulted in the openings no longer lining up with the housing cavities.

Anyway, I put the tiny check ball into the metal valve body and inserted the spring, then slid the valve body back into the pump housing, and it looks like it's okay now; the manual pump works, and when cycling the diaphragm in and out, a small amout of oil is sent out the output.

It looks like a pretty simple concept, now that I know how it works, but I'm wondering if the press fit is going to work itself out again in short order- there isn't any positive retention of the thing in there, so it may have been designed to be non removable. I suppose I could apply some epoxy to help retain it, but it's already back in, and getting the bail clip on and off is a genuine pain, so I think I'll leave it for now.

My next problem is finding a replacement throttle cable, because it broke, apparently weakened by corrosion creeping in at the carb end, and all my fussing with it pushed it over the breaking point. Do they sell just the wire, and you bend the ends to suit, or are they tailored for each chainsaw? If I can just find the wire, I could easily match it back up, and reuse the housing.
 
  #4  
Old 09-02-02, 11:19 PM
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You will most likely have to purchase the entire cable, housing and all. They aren't expensive normally. Glad you got it working again. Maybe, if the pressed insert works out again, you can peen the edges of it to hold it fast.
 
  #5  
Old 09-03-02, 07:18 AM
trendar
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I called the authorized McCulloch dealer, and they told me they don't have replacement cables, and don't even know where to get it- (?). I don't know if they just don't want to deal with parts or something, but I don't know how they would do repairs without having throttle cables available-



The valve body doesn't sit flush with the housing, so it may be hard to peen it (that's also what make it less than obvious that it backed out, actually). Possibly could clean it well and put a small ring of epoxy to it to help retain it. It did seem to be fairly tight pushing it back in, so maybe it'll be okay, but with the all the vibration from the engine, I can't really count on it-



Maybe I'll have to hit the local hobby shop to get some wire from remote controlled airplanes, the McCulloch at 800-521-8559, from the website www.mccullochpower.com. purchased the name only, and is not the same as the original manufacturer of the chainsaw, which went bankrupt. Looks like there's no more support for this at all, but they suggested trying Original Equipment at 800-645-2031, out of Arkansas.. They have it for $26.65 shipped- I'll probably look for something generic first; it's not something that really requires anything too specific...
 

Last edited by trendar; 09-03-02 at 07:47 AM.
  #6  
Old 09-03-02, 08:30 PM
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Check around with your local lawn mower/small engine repair shops. There's a pretty good chance one of them will have a junked saw like yours that you can get the cable off of for a few bucks. If not, they might even have a new cable (old stock). Good luck! McCulloch parts are getting scarce, so I keep all the junked equipment I get...just in case. It has payed off several times already.
 
  #7  
Old 09-03-02, 09:29 PM
trendar
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That'll be my game plan for tomorrow; there's a local power equipment shop that I can try. I really don't think I have to use the specific cable spelled out for my discontinued model; I think I'd be inclined to buy a new saw before I go and pay $27 for a 12" piece of springy wire that would be otherwise worth about 27 cents .
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Found my solution, after hitting dead ends from the mower shops and Home Depot-

New models of chainsaws apparently don't use cables, but instead use linkages, so there was no substitutes readily available.

I realized I had it in my garage all this time; a spool of 0.023 stainless steel MIG welding wire- it's a bit thinner than the 0.030 wire used in the cable, but it'll serve nicely. A bonus is that it won't corrode, which was what helped take out the old one.
 

Last edited by trendar; 09-05-02 at 07:25 AM.
  #8  
Old 09-04-02, 08:56 PM
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Good Job! No substitute for ingenuity.
 
  #9  
Old 09-05-02, 07:40 AM
trendar
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I like it when you find no-cost solutions to otherwise expensive problems-

The wire is also available from www.mcmaster.com , by searching for music wire (or piano wire), and picking either steel or stainless steel- they sell it in all diameters, and they have the 0.031 diameter that came stock with the saw- (along with pretty much any diameter you might want)
It seems like an excellent site for all the sundry hard to find items, very nice setup for drilling down to the specific item you want.

Spring-Temper Carbon Steel: Has a hard temper, making it difficult to bend. Also known as music wire. Wire coils meet ASTM A228; wire cut lengths meet ASTM A229.

A 1/4 lb spool, or about 100' only runs about $3- I figure the spool should be able to make about $2500 worth of throttle cables, at the price they wanted for the original.. What a deal!

There was someone in another forum that was in the same boat, and he ordered up the spool, and was nice enough to send me some of it to work with-
 
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