When good- goes Bad..... 066 style.

[Bob Hedgecutter]

First reversing the magnetism will not make them run backwards, second unless you change timing and reverse the pullstart youll still be trying to start it in the normal direction of rotation.

But.... what if you take mirror image video of it running?
Does that count?

 

[Bob Hedgecutter]

Refreshed "new" case.

 

[Woodslasher]

First reversing the magnetism will not make them run backwards, second unless you change timing and reverse the pullstart you'll still be trying to start it in the normal direction of rotation.

What I said was, "I too have heard of reversed polarity" and "I've also heard that Dolmar 133's have the ability to run backwards", with the two statements being unrelated to each other. The second phenomenon also happens with my dad's diesel Rammax that is cranked over by hand. What happens is the coil/engine fires prematurely, while still starting the machine, but due to it firing early it pushes the piston down before it reaches TDC, causing the the crankshaft to spin in the opposite direction which makes the engine run backwards. They will run like crap and probably not for long, but they will run backwards.

 

[Bob Hedgecutter]

What I said was, "I too have heard of reversed polarity" and "I've also heard that Dolmar 133's have the ability to run backwards", with the two statements being unrelated to each other. The second phenomenon also happens with my dad's diesel Rammax that is cranked over by hand. What happens is the coil/engine fires prematurely, while still starting the machine, but due to it firing early it pushes the piston down before it reaches TDC, causing the the crankshaft to spin in the opposite direction which makes the engine run backwards. They will run like crap and probably not for long, but they will run backwards.

Okay, okay- how about an old Landz Bulldog tractor that can run forwards or backwards AND at 0RPM?

 

[sean donato]

What I said was, "I too have heard of reversed polarity" and "I've also heard that Dolmar 133's have the ability to run backwards", with the two statements being unrelated to each other. The second phenomenon also happens with my dad's diesel Rammax that is cranked over by hand. What happens is the coil/engine fires prematurely, while still starting the machine, but due to it firing early it pushes the piston down before it reaches TDC, causing the the crankshaft to spin in the opposite direction which makes the engine run backwards. They will run like crap and probably not for long, but they will run backwards.

I took what you wrote as the reverse polarity is what causes the reverse running. Any 2 stroke has the capability to run either direction. I'm very well aware of this, from mercury to club cars they all had 2 strokes that were made to run in either direction, as well as Bob's tractor. Although an interesting design, it like most other oddities went the way of the dodo bird for a reason. Safty being the biggest factor. I would assume you dad's diesel is much like an older lister petter engine? They too can sometimes fire in reverse, normally it's from hitting the compression release before you've gotten the flywheel spinning fast enough. On them you need to get them to stop asap, the oil pump isnt doing its job spinning backwards, and they tend to spin the rod bearing if left for too long without oil.
Anyway, back to our scheduled topic

 

[JayPopple]

I have seen a trained Stihl tech accidentally drop one of the alloy flywheels on the floor after replacing seals- no visible exterior damage- but that flywheel was poked after thumping the concrete!
Something to do with the shock reversing polarity or shattering the internal magnets- I am not totally sure, above my pay grade! But replacing the flywheel fixed the no go after assembly and the tech got a chewing out from the boss- the job didn't make money- it cost money!

I have no idea of the saws past history, so anything is possible. Could have been worse- at least with the poly flywheel 10mm nut 066's, there are pretty limited combinations to try before you run out of ideas as to why it don't run.

 

[JayPopple]

When I worked in a small engine shop many years ago it was common practice to place a piece of ferrous metal on the magnets to maintain their strength when we removed a flywheel for an extended period. Dropping the flywheel could also reduce the strength. I don’t think polarity of the magnets would change the operation of the magneto as it is the building up and collapsing of the magnetic field that developed the spark, not the polarity of the magnetic field.

 

[JayPopple]

Interesting. Did you use a business card to gap it? I have a 461 that had the crank bearings fail and the flywheel nailed the coil pretty hard (read: way nastier looking than yours). No spark with the mashed coil so I put a new coil in, gapped it with a business card, and still no spark. Before I put a new flywheel on, I read the tech book on coil gaps and set it to the .008? it said it required and viola! I had spark! If you used a business card, perhaps the magnets' strength was compromised by the impact and it would require a tighter gap to spark. If you used the fancy tool, my theory goes out the window.

The information I have regarding the magneto air gap is .012” or .3 mm. I am guessing a business card is thicker then that. As the air gap is a fairly critical dimension I recommend using a feeler gauge to set it.

 

[grizz55chev]

What I said was, "I too have heard of reversed polarity" and "I've also heard that Dolmar 133's have the ability to run backwards", with the two statements being unrelated to each other. The second phenomenon also happens with my dad's diesel Rammax that is cranked over by hand. What happens is the coil/engine fires prematurely, while still starting the machine, but due to it firing early it pushes the piston down before it reaches TDC, causing the the crankshaft to spin in the opposite direction which makes the engine run backwards. They will run like crap and probably not for long, but they will run backwards.

Old two stroke outboards actually do reverse that way, hit the kill button till they almost stop, then let it go, you're in reverse!

 

[grizz55chev]

The information I have regarding the magneto air gap is .012” or .3 mm. I am guessing a business card is thicker then that. As the air gap is a fairly critical dimension I recommend using a feeler gauge to set it.

I've built hundreds of saws using the business card trick, never had a problem.

 

[Mad Professor]

I've seen old dirt bikes run backwards. A guy trying to climb a hill failed. It was in gear and it started when he rolled backwards. It was pretty funny at the time.

 

[JayPopple]

I've built hundreds of saws using the business card trick, never had a problem.

Well not to argue but here is a person who is having run issues with his saw. In my opinion setting all adjustments as close to factory setting is one way to eliminate the variables. Don’t you agree?

 

[grizz55chev]

Well not to argue but here is a person who is having run issues with his saw. In my opinion setting all adjustments as close to factory setting is one way to eliminate the variables. Don’t you agree?

Respectfuly no, it's never been an issue.

 

[wcorey]

That a magnet can lose strength or change polarity due to heat and/or impact, it's not surprising that a flywheel or two would suffer this with all the heating and beating they sometimes get with ham fisted attempts to remove a stubborn one.

And as far as I know, just like an alternator, they do need two opposite poles to generate a spark...

 

[a. palmer jr.]

Tim, Bob and I have probably helped more people on this forum than you will ever help. I will only speak for myself when I see you as Mr. clean, Mr. perfect and don't question what I say. You have been here for less that two years but swagger around like you are the owner. Sorry but that is my myopic, long in the tooth, condescending view.

See, they can't help it!

 

[pioneerguy600]

 

[pioneerguy600]

Hey Bob, you learnin anything from this thread?

 

[Bob Hedgecutter]

Hey Bob, you learnin anything from this thread?

I learn lots from many threads- the saw in the original more interesting part of the thread now wears a 36" bar and Stihl .404 semi chisel chain- runs pretty nice.

 

[pioneerguy600]

I learn lots from many threads- the saw in the original more interesting part of the thread now wears a 36" bar and Stihl .404 semi chisel chain- runs pretty nice.

When are you getting into the saw repair vid game?

 

[Bob Hedgecutter]

When are you getting into the saw repair vid game?

Is there room on the site for more video content? I work on more than 6 every couple of years- even rebuild a Kohler 161 a couple of days ago- so there might be some 4 stroke content as well- you might have to upgrade the server to hold more digibites.