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McCulloch Chain Saws
- Thread starter Bruce Hopf
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Aaron Rybicki
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I can use a little help with Kevin's (2broke2ride) 7-10. I did go through the carburetor and gave it another good cleaning, all of the parts are in good condition and it holds pressure very nicely. I tried switching carburetors between his 7-10 and my better one, mine runs fine with either carburetor but his won't idle and the tuning keeps changing. I took it all the way down to allow a good pressure test and it hold pressure with a very gradual drop off, but you can hear it burping through the oiler and the crankcase seals and seams are not leaking at all.
I did try holding the saw on its side while idling and it definitely changes, clutch side down speeds up and flywheel side down dies out. I did not check the crankcase to see if it would hold vacuum, is it time to take it all apart again and check the seals under vacuum?
Mark
I did try holding the saw on its side while idling and it definitely changes, clutch side down speeds up and flywheel side down dies out. I did not check the crankcase to see if it would hold vacuum, is it time to take it all apart again and check the seals under vacuum?
Mark
I would tear it down to the shortblock (or at least far enough) for a vacuum test of the seals. Think of them as a one-way valve (in this case) that may close under pressure but open under a vacuum. Seems to be exhibiting the classic symptoms of leaky seals.
That's that I was thinking. I was hoping it was all associated with this intake gasket.
Mark
Mark
Kevin hayes
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chicks dig scars[emoji23]..how did you pull that off anyway
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Kevin hayes
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2broke2ride
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Those intake gaskets where new at my last go with this. I coated them with Indian head, hence they where glued on there pretty good.
I am.also questioning the crank seals at this point. They same to be the only stone left unturned this last go-round by me anyway.
Kevin hayes
ArboristSite Operative
Kevin hayes
ArboristSite Operative
had that problem with my super 80 changed the bearing runs awesome now..also had that issue with my 805 turned out to be a wobbly low adjustment screw but since you changed the carbs out almost has to be the seal if everything else checks out you but you know what your doing better than most
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Changing out the seals just means a bit of time, something I don't seem to have much of these days...you will never know how busy you can be until you retire.
Mark
Mark
...and start building a museum!
Like I preach every chance I get, pressure only tests a seal in one direction and often leads to a false conclusion that the seal is good when it will actually leak under vacuum. When there's any doubt whatsoever, do a vacuum test and check the seals with a little grease or oil to see if the leak stops or the grease/oil is drawn in around the crank or seal bore. 'Bout the only way to be certain in dealing with elusive leaks when everything else but seals has been ruled out.
It's just too bad the MityVac 8500 has doubled in price over the last few years. Think I paid $54 for mine a few years ago. Paid for itself the first time I didn't have to tear a saw down twice chasing an air leak I should have found in 15~20 minutes. Wouldn't be without it now.
Like I preach every chance I get, pressure only tests a seal in one direction and often leads to a false conclusion that the seal is good when it will actually leak under vacuum. When there's any doubt whatsoever, do a vacuum test and check the seals with a little grease or oil to see if the leak stops or the grease/oil is drawn in around the crank or seal bore. 'Bout the only way to be certain in dealing with elusive leaks when everything else but seals has been ruled out.
It's just too bad the MityVac 8500 has doubled in price over the last few years. Think I paid $54 for mine a few years ago. Paid for itself the first time I didn't have to tear a saw down twice chasing an air leak I should have found in 15~20 minutes. Wouldn't be without it now.
I have the tools, just get anxious or complacent at times...
The drawer has a lot more in it today, not nearly as neat and orderly...
Mark
The drawer has a lot more in it today, not nearly as neat and orderly...
Mark
2broke2ride
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Agreed, but of course in my mind, the fact that the seals are new and pass a pressure test should pretty much rule them out but apparently there are no absolutes lol.
Mark, have you checked the runout on the main bearings? A worn bearing will check good because the seal will hold it straight while not running and leak while running. Also I have seen condenser cause this kind of problem where it is not firing every time. Just a couple things to check. I had a PM6 once that would not rev up. It turned out to be the points shorting out when it revved up where I left out a insulator on the points. Had a condenser that would short out when revved up once on a 10-10.
Brian
Brian
I will investigate everything more thoroughly the next time through.
Mark
Mark
Points and condensor could be checked off the list by throwing an ignition module in there and check it again. Easy to temporarily put in and check.
I've got a 7-10 that's driving me batty as well.It's got sdpark & has 135 psi compression.I put a rebuild kit in the carb.If I give it a prime,it'll fire,but anything more than that is out of the question.I'll be following 2 broke's saw results with baited breath.
Ed
Ed
I've got a 7-10 that's driving me batty as well.It's got sdpark & has 135 psi compression.I put a rebuild kit in the carb.If I give it a prime,it'll fire,but anything more than that is out of the question.I'll be following 2 broke's saw results with baited breath.
Ed
Ed
Not to beat a dead horse, but I always do a vac/pressure test on new seals before any further reassembly. Takes 10 minutes and eliminates seals as a potential leak source if there are problems later. Rebuilt a Stihl clamshell saw last week with brand new OEM seals at $17 each. They both leaked around the crankshaft. Stiff old stock evidently. Glad I checked them before throwing everything back together. Was actually able to get a refund on em, too.
And speaking of sealing, my 10-10A tank is now nice and tight thanks to either a slightly thinner gasket or the MotoSeal..., or both. Teflon tape on the fuel line is holding well also.
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