playing with a pop-up, 066 BB

[mtngun]

You're saying the exhaust opens at 86.5° ATDC? The last one I measured was at 96°.

Martinm210's BB opened at 92 degrees.

Anyway, that's what the computer is predicting based on the pencil & paper port map. A port map is probably not as accurate as a degree wheel.

Also there is the question of how to figure the generous factory port chamfers. A pencil & paper port map is probably "seeing" the far edge of the chamfer.

Plus this last chart was for 2nd gen exhaust spec, not 1st gen. 2nd gen exhaust is 2mm higher.

Brad, have you received an actual 2nd gen jug yet ? If you are going to be reviewing it, I look forward to your report.

 

[mtngun]

I don't feel comfortable with this program deciding my No's.
Your measurements have to be so dead accurate, I just kept coming up with different No's to the point it just frustrated me.

I agree the pencil & paper mapping method is not super-precise. However, it is fast and it can be done with the jug off the saw (I've got another jug on my saw right now, and I don't have a 2nd gen jug to measure).

A degree wheel would be much more accurate, but then you'd still have to deal with the sloppy factory chamfers.

 

[blsnelling]

86.5° is well into piped-saw only territory. Why not throw a degree wheel on it? I would think that's quicker and easier than measuring everything.

 

[AUSSIE1]

I agree the pencil & paper mapping method is not super-precise. However, it is fast and it can be done with the jug off the saw (I've got another jug on my saw right now, and I don't have a 2nd gen jug to measure).

A degree wheel would be much more accurate, but then you'd still have to deal with the sloppy factory chamfers.

Yep, but don't forget that those sloppy chamfers are part of your timing no's.
If your No's are reasonably conservative, a degree here or there won't be the end of the earth.

 

[Meadow Beaver]

I agree with brad 10 degrees of advance is alot, with such advanced timing the saw will have good top end but lack bottom end compared to OEM. I could be wrong...

 

[mtngun]

86.5° is well into piped-saw only territory. Why not throw a degree wheel on it? I would think that's quicker and easier than measuring everything.

Brad, I do plan to degree the jug once it is installed, but that's a few weeks down the road. Plus, the last chart was not from my jug, it was a hypothetical case based on Grande Dog's verbal description of the 2nd gen BB.

I understand you are skeptical of my newbie port data, but remember what Mr. Timberwolf said.

The porting numbers on these new stihls is high, it did not seem right to me, triple checked and it is indeed that high.

If your No's are reasonably conservative, a degree here or there won't be the end of the earth.

Ya, IF THE NUMBERS ARE CONSERVATIVE. What Timberwolf was trying to say, and what my data shows, and what Martinm210's data shows, is that many of the 660 and BB jugs are anything but conservative.

And ......the soon-to-be-released 2nd gen BB will have the exhaust advanced 2mm. That's coming straight from Grande Dog. Talk to him if you don't believe it. I didn't believe it either so I asked him again to be sure.

10 degrees of advance is alot, with such advanced timing the saw will have good top end but lack bottom end compared to OEM

That is why I canceled my plans to buy a 2nd gen BB.

 

[Meadow Beaver]

Did you get that muffler?

 

[blsnelling]

And ......the soon-to-be-released 2nd gen BB will have the exhaust advanced 2mm. That's coming straight from Grande Dog. Talk to him if you don't believe it. I didn't believe it either so I asked him again to be sure.

Are you sure he didn't say that it was the floor of the exhaust that was raised 2mm? Also, I'm pretty sure we're on the 3rd gen of the 066BB. 4th gens are in house already.

 

[timberwolf]

I agree with brad 10 degrees of advance is alot, with such advanced timing the saw will have good top end but lack bottom end compared to OEM. I could be wrong...

Also exhaust that high will negate the compression gains from the pop-up.

On the pop up, why not cut a bevel 45 deg or less? The gains from improved flow over the piston crown and elimination of a heat/stress riser would more than make up for the fraction of a PSI gained by having a 90 deg transition on the crown.

 

[mtngun]

Are you sure he didn't say that it was the floor of the exhaust that was raised 2mm? Also, I'm pretty sure we're on the 3rd gen of the 066BB. 4th gens are in house already.

Brad, that was pretty much my response to Grande Dog. See the conversation here.

I was trying to be polite about it, so I didn't argue with the man. If you want to argue with Grande Dog, be my guest.

OK, 3rd gen, 4th gen, whatever. Regardless, I'm not buying another one unless they hire Timberwolf to design it.

The pop up does have a bevel, I didn't bother to calculate the angle at the time. Here's the relevant g-code. Moves across 0.010", moves away from the piston 0.020", off the top of my head that sounds like 60 degrees. In the future, I'll take your advice and aim for 45 degrees.

G00           Z-0.025        ; point A
M00       ;    install tool now

G01 X-0.954    F1            ; point B
G01 X-0.930   Z-0.020  F1

G01 X-0.750   Z-0.017  F1    ; point C

G01 X-0.740   Z0.003  F1    ; bevel the pop-up

G00 Z2
M02

Also exhaust that high will negate the compression gains from the pop-up.

Ya, it would be crazy to advance the exhaust more than it already is. I hope Grande Dog will come along and explain that this is all a big misunderstanding. But, go look at the conversation, and ask him yourself. He might actually listen to you.

 

[parrisw]

Also exhaust that high will negate the compression gains from the pop-up.

On the pop up, why not cut a bevel 45 deg or less? The gains from improved flow over the piston crown and elimination of a heat/stress riser would more than make up for the fraction of a PSI gained by having a 90 deg transition on the crown.

I've been planning on 30° bevel on the popup, I think that's what you did for me on the 2101 piston? Cant remember.

 

[mtngun]

Did you get that muffler?

Yep, brand new muffler and cover.

If I have time, I want to do timed cuts comparing a muffler with the internal cage vs. without.

BTW, while I was cleaning up the BB, I dug one tiny piece of steel out of the top of the piston, and a similar piece of steel out of the chamber. They were random shaped, thin sheet metal, and had sharp edges. I'm pretty sure they were pieces from the shattered muffler. Wonder if they got sucked in while the piston was free porting ?

 

[Meadow Beaver]

Yeah doesn't take much to mess up a cylinder. So it's possible that a piece came in through the muffler.

 

[mtngun]

I finally got back to this dubious project.

Tonight's job was shaving the base of the jug. I had to modify a cutting tool for the lathe, but otherwise, the modular mandrel worked fine.

I was cautious and snuck up on the correct squish a little at a time, rather than trying to cut it all at once. Measure squish, cut, measure squish, cut again, and so on.

Final squish with standard base gasket was 0.0195", 0.020", 0.020", 0.021".

BTW, I'll probably have to enlarge the ID of the base gasket a little, to clear the 56mm piston skirts.

This is why this project will probably fail. Massive freeport.........EEEUUUUWWW

It was freeporting before the pop-up, now it freeports twice as much.

I haven't decided whether to port this jug.

On the one hand, I'm 99% sure this project will fail due to the freeport, so why bother ?

Furthermore, it remains to be seen if porting is helpful to any milling 066, because porting tends to shift the peak powerband to higher RPMs. Milling saws need mid-range power, not high RPM power.

On the other hand, I need more practice porting, and this would be a good guinea pig.

 

[Meadow Beaver]

After seeing the whole deal with raising the entire exhaust 2mm will keep me from buying an 066 bb. Not does it free port, but the short exhaust duration will give you less than mediocre compression. It also makes it impossible to fix the floor of the exhaust and then raise it again. I would think your best bet for a milling saw would be to put a ms650 top end on it.

 

[mtngun]

After seeing the whole deal with raising the entire exhaust 2mm will keep me from buying an 066 bb. Not does it free port, but the short exhaust duration will give you less than mediocre compression. It also makes it impossible to fix the floor of the exhaust and then raise it again. I would think your best bet for a milling saw would be to put a ms650 top end on it.

Ya, raising the entire port 2mm on the new kits was a dumb idea.

They could have merely raised the floor and left the roof alone. The floor should have very little impact on flow, since the majority of the flow occurs when the port is first cracked open.

650 ? I'm hoping to stumble upon a pre-emissions 066 jug. Supposedly they had more compression and saner porting.

 

[Evan]

this has been good reading over a few cups of coffee, also way over my head.

we still have not heard from Grand about the new kits. i still plan to buy a kit for my 066

 

[mtngun]

Grande Dog has discussed the new kits on the Bailey's forum.

As I understand it, the combustion chamber was downsized 1cc , the port shapes are oval instead of rectangular --- but then he went and raised the entire exhaust port 2mm .

I believe the new kits start shipping sometime next week.

People who use the kits for cutting cookies may be delighted with the new specs. It should scream at high RPMs.

However, a milling saw operates at 8500 - 10,500 rpm. The 2mm higher exhaust port seems likely to hurt power at that speed.

A lot of this is over my head, too, Evan. I'm going through the motions and hoping it gradually starts to make sense.

 

[Evan]

any thing in math book or has numbers and equations attached to it is over my head.
i wonder if you ran the new bb kit gasketless if it would kinda counter the 2mm raise in the exhaust port and bumpcompression alittle. kinda a win win if you can maintain .20 without a gsket

 

[stihlboy]

Grande Dog has discussed the new kits on the Bailey's forum.

As I understand it, the combustion chamber was downsized 1cc , the port shapes are oval instead of rectangular --- but then he went and raised the entire exhaust port 2mm .

I believe the new kits start shipping sometime next week.

People who use the kits for cutting cookies may be delighted with the new specs. It should scream at high RPMs.

However, a milling saw operates at 8500 - 10,500 rpm. The 2mm higher exhaust port seems likely to hurt power at that speed.

A lot of this is over my head, too, Evan. I'm going through the motions and hoping it gradually starts to make sense.

i have had that kit for a while..........

it is a nice kit you can do a pop-up piston on it with little to no free porting

i have a 4th gen bb on my 064