Testing different timing advances on tree monkeyed 661

[jmssaws]

This is a detonating monster at 040 or 035 off the key.
050 or 025 off the key and it doesn't do it

 

[tree monkey]

do you have a pic of the damage to the piston? was there any damage to the squish band of the cylinder?

 

[Moparmyway]

This is a detonating monster at 040 or 035 off the key.
050 or 025 off the key and it doesn't do it

You can hear mine detonating away in the video I posted.
Initially it sounds like the limiter, but you can hear it speeding up as the miss hits

 

[Moparmyway]

A few observations I made -

a while ago @Redfin sent me his ported 661. I ran several tanks through it, testing it etc. etc. It had a key milled down to .018. To me it had like a lean idle or something I couldn't get rid of. But even at .018 (.057 off!!!) it wasn't missing or popping.

I tried a few things to make the idle issue go away. Nothing worked until I went to the a thicker key. .035. Then to me it idled normal. It seemed to run best and run the fastest with the .045 key. I've tried .0425 and .0475 keys and times dropped off. So IMO, somewhere around .045 seems to be ideal.

I've seen .045 be perfect with one coil, yet detonate away with another coil
The key thats installed in my 661 in my detonating video is .055 (.020 off)

 

[Magic_Man]

What would be more interesting to me is actual ignition timing numbers. Are the saws running best at 25, 30, or 35 degrees BTDC or somewhere in between ? A certain amount off the key of one saw is going to be different on another. Combine all the tolerances of coils, flywheels, etc and I would guess a 10 degree or better spread across several saws. I applaud your time and work on this Redbull, you do a lot of cool testing.

 

[tree monkey]

engines don't detonate without damage. lets see the pics

 

[Moparmyway]

engines don't detonate without damage. lets see the pics

Maybe its pre-ignition ........... but listen to the video
You'll hear it miss as she still gains speed

 

[tree monkey]

I hear a pop, like a backfire

 

[tree monkey]

what do you have for comp?
how much blowdown?
what kind of fuel?
any Freeport?

 

[jmssaws]

do you have a pic of the damage to the piston? was there any damage to the squish band of the cylinder?

I didn't take a pic but it was little tiny holes on the edge of the crown and on the band.
Spot about the size of a quarter

Compression is not high either

 

[Moparmyway]

what do you have for comp?
how much blowdown?
what kind of fuel?
any Freeport?

180 psi (new piston and rings)
21-23 degrees, staggered openings
VP SEf 94
No freeporting

 

[jmssaws]

170lb compression and I think the pop is a limiter.

Trooney's saw will pop at 13,140 rpm Everytime.
Still mtronic

 

[jmssaws]

Detonating happens under a load.

It's not detonating now but still pops.
I can get it till do it piss revving

 

[jmssaws]

You won't hear it detonating.
It does it when it doesn't have enough load on it.
Listen to it when I lift,acts like a limiter or a weird 4 stroke

 

[Moparmyway]

It does it when it doesn't have enough load on it.
Listen to it when I lift,acts like a limiter or a weird 4 stroke

Yup, when there aint enough load, mine does it too, except that its still gaining RPM when it does it
To me, that aint m-tronic limiter

 

[awol]

This is just a theory, but I think to much ignition advance may let a few un-ignited charges in a row into the muffler, and the popping popcorn sound we hear is that fuel-air mixture igniting in the muffler. It could also just be the dynamics of scavenging......

I've experienced the effects of detonation several times, and it has always been catastrophic. The saw would run fine with no popping, but when put into a long cut, slow down slightly and then die as fast as if it had locked up. After a brief cool down, it would start back up and run fine, but upon disassembly the band and piston had been hot enough to melt and remove chunks of aluminum. This was on a 288 with about 250psi. and a timing bump. I'll see if I still have that piston and jug after work tonight.

 

[jmssaws]

I've had a few that were detonating and I never knew they were until I pulled the cylinder and seen it.

The other 661 is setup the same as this one and didn't do it,it does pop but I think it's a rich condition making it do it.

This saw doesn't detonate now and it was detonating from to much ignition
It's 165-170lb with a 023 squish and 040 was to much but it didn't run bad.

I've had it at 010 from the key and it still done it.
I got it at 020 now,I'll see if it still does it.

I could have used a higher octane gas and it would have been fine.

 

[Moparmyway]

I could allways run a tank of 110 to see if it goes away, but VP94 SEF should be just fine at 180#

 

[jmssaws]

This is just a theory, but I think to much ignition advance may let a few un-ignited charges in a row into the muffler, and the popping popcorn sound we hear is that fuel-air mixture igniting in the muffler. It could also just be the dynamics of scavenging......

I've experienced the effects of detonation several times, and it has always been catastrophic. The saw would run fine with no popping, but when put into a long cut, slow down slightly and then die as fast as if it had locked up. After a brief cool down, it would start back up and run fine, but upon disassembly the band and piston had been hot enough to melt and remove chunks of aluminum. This was on a 288 with about 250psi. and a timing bump. I'll see if I still have that piston and jug after work tonight.

I think it's the nature of the beast.

I can close up the muffler and make it stop but I think it's does because it's not as strong and not turning as much in the wood.

 

[jmssaws]

I could allways run a tank of 110 to see if it goes away, but VP94 SEF should be just fine at 180#

I'm running vp 87 efree