Timing Advance s- When \ When Not To Do - Questions

[merc_man]

Has any one done a timing advance on a ms 290. Gonna do a muff mod and just wondered if a 20 thow off the key would help it too.

 

[bennne]

The key is integrated into the flywheel so it's not as easy as other models that are a separate key

 

[MustangMike]

My 362 has an integrated key, I was able to get in there with a triangular file. Not perfect, but it worked.

 

[Greenthorn]

Ok, so I know what it is like when timing is advanced too far, I guess my question is, what exactly is going on the combustion to cause the pop corn popping sound? To little fuel, to much fuel or is it something with the coil, sorry for the dumb question, but I am still trying to figure somethings out.

 

[Mastermind]

Good question.......I think the pop is caused by a misfire from the spark occurring too far ahead of TDC.

 

[RIDE-RED 350r]

To much ignition advance and the engine is trying to run against itself in a manner of speaking. Basically, it's pre-ignition. It robs power, and in extreme cases can cause knocking because your peak cylinder pressure as the fuel mix burns is occurring too early in the piston cycle.

 

[Moparmyway]

Ok, so I know what it is like when timing is advanced too far, I guess my question is, what exactly is going on the combustion to cause the pop corn popping sound? To little fuel, to much fuel or is it something with the coil, sorry for the dumb question, but I am still trying to figure somethings out.

When the advance is too much, the spark ignites the mixture too early, trying to push down on the piston while the piston is still trying to get close to TDC, too far away from TDC, effectively trying to slow down the piston speed.

When the advance is just right, the spark ignites the mixture and pushes down on the piston just as its in the sweet spot, helping it get past TDC and forcing it down

 

[Terry Syd]

There's a lag in burning of the mixture after the plug fires. I forget, it is something like 10-12 degrees, then the burn really starts to propagate. According to Blair, the optimum in burn is 50% of the mixture at something like 7.5-10 degrees ATDC.

Reading Blair's work on ignition surprised me as I always thought the mixture was reaching 100% closer to TDC.

 

[RIDE-RED 350r]

There's a lag in burning of the mixture after the plug fires. I forget, it is something like 10-12 degrees, then the burn really starts to propagate. According to Blair, the optimum in burn is 50% of the mixture at something like 7.5-10 degrees ATDC.

Reading Blair's work on ignition surprised me as I always thought the mixture was reaching 100% closer to TDC.

And all of that is dependent on the type of fuel being burned, and whether or not the optimum fuel/air mixture exists. Running rich or lean in relation to optimum mixture effects that burn "timing". It's actually fairly interesting and intricate science.

 

[mdavlee]

I advanced the 044 today to .043 left. It was almost half the key.

 

[MustangMike]

That should be half the key, most of the ones I have checked are right about 80/1000s.

 

[mdavlee]

076" I believe is what that key was

 

[MustangMike]

I've measured .078 and .080, (and maybe other widths), don't remember which was 046/460 and which 044/440, or if that mattered. The integral one in the 362 was much wider.

I just usually take 20/1000 off cause I think that is a safe amount. I like more performance, but want it to be a work saw. From what I have heard, the timing is not consistent on all saws of the same model, so I shy away from being aggressive. Randy (in the 461 build thread) said that is about 6 degrees, and that is what my crude calculating also came out with.

 

[mdavlee]

I usually go 1/3 for all of them any way. This one was a tiny bit further. I just happened to think to measure it before I put it in.

 

[Magic_Man]

I check total timing on my saws when I advance them. It's pretty easy to do with a timing light and drill with a socket on the flywheel nut.

 

[bulletpruf]

Bump for some pretty good tech.

 

[Chainsaw Jim]

After this whole jms problem I'm starting to think over-advancing the timing can cause piston failure.

 

[wyksta]

Half a keyway - poppopppa poppa pop pop

 

[Wonkydonkey]

Just catching up on a good thread,
I would prolly not have found this buried amongst everything else

i do find this stuff very useful info. And it brings other info that I've read before into the right place of my head. IE where peeps say about 20thou and when I watched treemonkey playing with a timing light in a YouTube vid

Cheers

 

[Fruecrue]

After this whole jms problem I'm starting to think over-advancing the timing can cause piston failure.

I would imagine that it creates tremendous stress and flexes the piston. when you’re reaching TDC, the piston is moving less per degree of rotation, creating more torque to overcome the resistance of chamber pressure . Couple that with chamber pressure peaking at the same time, and it sounds like a lot for a cast piston to take.

I’m sure uneven bases and widened ports at to it as well.