Chainsaw not going - PLEASE help

[Lawn Masters]

Ok, then check the muffler VERY CAREFULLY for a wasps nest or something like that. I cant see the pressure in the crankcase coming back out through the intake, unless theres no other way out for any of the gases.

 

[lostone]

I have seen a couple of threads talk about a sheared key, is this common in some saws? is it just the engine shearing them over time from the torque of the crank against the flywheel that is causing this to happen? or is it from a bearing going bad and letting the flywheel come in contact with something else?

 

[Lawn Masters]

Normally, its either because someone got the really bright idea, to use the flywheel to keep the crank from turning while they pull the clutch off, or its from something else, which I dont know about.

 

[BDA]

Do ALL chainsaws/ 2 stroke engines use reed valves, I have been rung by a mate who says his piston ported chainsaw motor still had reed valves. Its got me stumped

I feel really embaressed by this because I have been a automotive mechanic for 11 years and I don't know how to get my motor going. I have done so close to absolutely no work on 2-strokes before that I am not even sure if I have or have not worked on them.

I did training on 2-strokes back in the day of my pre-apprentiseship but that was when i was 17-18 years old and I was thinking about other things like drugs and loose women.

Please excuse my ignorance.

 

[Gumneck]

Have you confirmed the flywheel is correct for your saw yet? That's an easy one.

 

[JohnL]

Have you tried putting a little fuel mix directly in the cylinder? Will it fire even once?

 

[Al Smith]

I am not familiar with this saw,but it could be several things.Some of these old saws,had pressure oilers,in other words used impulse pressure to pressurize the oil tank to lube the bar.These had a check valve to prevent oil from entering the crankcase and thus the saw.If that valve fails,it will oil up the cylinder,foul the plug,and it won't even fire on starting fluid.Some of these saws used an impulse operated piston pump[McCulloch],on occasion these things would leak oil from bad seals,and cause the same thing.Drain all the bar oil.Rinse the tank with gasoline.Pull the plug,and spray starting fliud into the cylinder,and pull the engine over to force it out,do this several times.Clean the plug,reinstall and try it again.Good luck.

 

[BDA]

Gumneck - I am waiting on a gent in Australia to send me the rest of the canadien 270 manual with parts listing etc. He can only send 2-4 pages at a time cos hes busy and right now hes gone to a funeral out of town and will be gone a few days. So until I get that info I cannot check to see if it is the correct flywheel for this saw. It looks like it is meant to be there and that it has been there for quite some time too.

JohnL - Yup I have tried a mix straight into the cylinder and EZ start (ether) also but not even a pop or a fart from this badboy

Al Smith - (nice last name mate!! hehe) the chain bar oiler is 99.9% empty (just enough in there to stop the magnesium oxidising) and the spark plug is brand new, the old plug that came out was not oily at all just maybe a tad rich looking like it had been started on choke last time but had not got hot enough to flick the choke off.

Thanks heaps for the sugestions guys.

 

[ozflea]

Has the saw been pressure tested as i feel we need to go back to basics and make sure that the seals and gaskets are OK, If you removed the muffler how did the piston look no bad scoring ? or visable scoring of the cylinder walls, has the saw got a head gasket check it hasn't blown. Does the engine have much compression when you pull it over ?
The f/wheel key next to make sure it's not sheared the key.
Check your points gap any old gap is not just good enough try 012-015 thou and see if that helps after giving them a good cleaning.
If all the above is fine then the saw should at least boot or something.

Mc Bob.

 

[BDA]

By pressure testing you mean like a cylinder leakage test, Piston at TDC then put a little pressure into the cylinder and see where all the air is coming out?

It has compression, I think it is heaps of compression but a small engine guy I know, felt it and said that he thinks that its not enough for a 95cc engine.

I've taken it to the saw shop for them to pull the flywheel and that way I can check, clean and adjust the points, at the same time I can check the key way isnt sheared at the same time.

thanks ozflea

 

[Lawn Masters]

The compression test, is just pick it up by the starter handle, if it falls slowly. or dosest fall, its got enough to run, if it falls rapidly, new rings are needed.

 

[ozflea]

When you pressure test a saw you seal off the intake port with a rubber seal under a metal plate, same on the exhaust side then you fit a adaptor to the spark plug hole and using a pressure gauge pressurise the engine to no more than 5 - 7 lb's and watch for leaks you can brush a little kero or diesel fuel over the seals or gaskets to see air bubbles there should be no leaks.
Don't over pressurise the saw as you'll blow the seals out.

Mc Bob.

 

[BDA]

it sure as hell has at least that much compression,

 

[Lawn Masters]

Then it has enough to run, your problem lies elsewhere.

 

[ozflea]

I've seen saws with tons of compression and one seal completely missing, quit messing around and do a thorough test then and only then will you be able to tick that one off the list.

Mc Bob.

Do the repair once and do it properly.

 

[spacemule]

it sure as hell has at least that much compression,

I think you may be missing the point, BD. Compression and sealing of the crankcase are two separate yet related entities. All a good compression tells you is that your rings are sealing well. However, two strokes actually pump the fuel/air mixture through the crankcase, and a leaking seal around the crankshaft will cause poor running and even damage, with no effect on your compression.

 

[BDA]

I have now stripped the motor completely while waiting for a flywheel puller and have found a broken lower ring with over a 1/3rd missing, no scores on the bore.... and light scratch marks on the top of the piston that look like they have been made with a screwdriver, so I'm thinking someone has had this apart before and broken the ring then put it back together broken. I will fix this issue and rebuild the bottom end whilst I'm at it.

So hopefully this has caused the problem and I can fix it.

 

[056kid]

problem solved or so we think. Make sure to check your jug for roundness and give it a good run with the cyclinder hone. other wise you will probably end up with a low compression ring breaking machine.

 

[pallis]

I just had a problem that made me think of your post. I just put a new 7900 jug on my Makita. Got nothing when I tried to start it so I checked fuel and spark. No problem. I checked the compression and got about 80 psi, pulled the jug back off and discovered the ring was broken in two. It was losing just enough compression to make it not start -- a good thing in my case. Hope you get things worked out.

Pat

 

[stihltech]

Ring

While a broken ring is a definite problem and must be repaired, we all know only 1 ring is required for a saw to run. Follow the advice and pressure AND vacuum test the saw before running. It is the only way to be sure it will last.