NWP piston for 066

[mtngun]

Measuring squish. I followed Mr. Snelling's suggestion and used grease to tack a piece of solder on each side of the piston. No need for rings on the piston at this point. The jug was then bolted down and the starter cord yanked several times. Repeat for measurements front and back.

Squish with no base gasket = 0.027", 0.028", 0.028", 0.029".

The plan is to shave 0.008" off the base of the cylinder, shooting for 0.020" squish with no base gasket.

One more measurement, as long as I had everything apart.

From the top of the exhaust port to the squish band:
BB = 0.981"

OEM = 0.991"

Not a huge difference, but it's not good for the BB exhaust port to be higher, considering the OEM exhaust port is probably too high to begin with.

The 2nd generation BB kits are supposed to have a higher compression ratio and revised porting, which is why I tell everyone who asks to wait for the 2nd generation kits.

That's as far as I got tonight.

 

[Hddnis]

I think those dings are from when your muffler bearing was having a beer with your piston.:jawdrop:



Mr. HE

 

[parrisw]

If your machining the cyl base, might as well take enough off to use a gasket.

 

[Rounder]

Time for a new muffler- amazing the damage saw vibes can do in a hurry. Thanks for the great post- nice to see stuff like this that we can learn from - Sam

 

[mtngun]

Making the mandrel to shave the cylinder base. Normally these are made from aluminum, but that costs money, so I just grabbed a chunk of ponderosa pine from the woodpile ......

Love the smell of freshly cut ponderosa .....

Here's what the mandrel looked like AFTER the job was complete. I left the mandrel in the chuck until the cylinder was satisfactorily shaved because, if I had taken the mandrel out and reinstalled it, it probably would not have returned to zero because the pine crushes a little in the chuck jaws.

I consider this a disposable mandrel, though it could be and probably will be turned down to fit a smaller diameter jug.

Shaving the base. Parrisw talked me into shaving enough to allow for a standard base gasket. Yes, the cutting tool sticks out way too much. It's what was handy and I got away with it since it was only taking a few thou off the aluminum jug.

It took three attempts to sneak up on the correct squish. Cut, measure squish, cut again, measure again ....... final squish was 0.0205", 0.0195", 0.0215", 0.0185".

And that's as far as I got today. Still gotta match the exhaust port to the muffler, weld up the cracked muffler, and do final assembly.

 

[parrisw]

Looks really good. I was thinking of using wood after what the last hunk of alu cost me.

 

[mtngun]

Since the last post, I finished the porting. It looks like a newbie port job, 'cuz that's what it is, but nonetheless, the critical things seem to be correct.

After assembly, compression cold and unfired was 123 psi. Huh ? That's exactly what the old BB blew. I retested and then retested a third time, getting 123 psi each time. Yeah, it'll get better after the rings seat, probably picking up 10 - 20 psi, but I was expecting 145 psi. We'll see.

I spent over an hour welding up the cracks and holes in the muffler. It's hard to weld paper thin rust. Then, as I was bolting the muffler to the saw, one of the short screws stripped out. Oh, well, tomorrow I'll jury rig a bolt and locknut to replace the stripped screw. I bid on an ebay muffler, but it'll be 2 - 3 weeks before it gets here.

I turned the H screw out 1/4 turn and started it up, minus bar and chain, and let it idle for 15 minutes. Then I couldn't resist the temptation to blip the throttle a few times. Despite the +1/4 H setting, it ran up to 13,000 rpm (the BB had been tuned to 12,500). Another +1/4 turn brought it down to a raunchy-rich 12,200.

Darned, this thing wants more fuel than the BB jug. I guess that's a good sign.

I was doing this outside in the dark so no pics. Tomorrow, I'll try to find time to slap a bar on it and do some gentle firewood bucking to help break in the rings. Then recheck the compression.

 

[Meadow Beaver]

Love the 2-stage pop-up you did, think you could do the same for my top end?

 

[mtngun]

Love the 2-stage pop-up you did, think you could do the same for my top end?

Let me practice some more on my saws, and build a proper fixture to hold the piston in the lathe. Then I might feel up to helping a few AS members.

I wish Grande Dog would offer a drop-in, pop-up piston for the 066/660. I bet a lot of people would be interested in an economical pop-up that requires no machining. It would certainly be more popular than the Wiseco deal.

You can only gain so much psi by shaving a pop-up, but the dome could be made plenty tall on a cast pop-up. The dome would add some weight, but I think it would be worth it. The 066 design tends to come up short on compression compared to say, Dolmars.

 

[Hddnis]

Maybe there would be a market, albeit a small one, for a guy to tig a dome onto pistons. It takes a good steady hand and a good understanding of the metal and heat distortion.



Mr. HE

 

[volks-man]

perhaps your compression did not increase due to the second teir in your pop-up?
you tightened the squish around the band but you may have a compression killing gap in the corner at the base of the second step.

 

[mtngun]

The 2 -tier pop-up increases the pop-up volume more than a single dome. Not much, but every little bit helps.

My pop-up does increase the compression ratio as shown by cc-ing the chamber volume in a previous post:

zero squish volume with OEM piston = 9.5 cc

zero squish volume with pop-up = 8.75 cc

However, the 0.75cc reduction is not a huge difference, compared to what I'd like to see. I'd like a 2cc reduction in chamber volume. AT LEAST.

As for how my 0.75cc pop-up compares to the work done by other modders, I don't know, since they rarely post any detailed data. I was tempted to shave a little more off, but this saw is used for milling, so I wanted to keep it safe and sane.

That said, in hindsight, I could have made the dome diameter a wee bit larger, and I could have made the outer tier a wee bit higher. That might have gained a couple of psi or so. I didn't have a way to measure the chamber profile so I just eyeballed it as best I could and cut the pop-up based on my eyeballed numbers.

If I do this type of project again, I'll make several solder impressions of the stock chamber before dissembling the saw (this jug was already off the saw when the project began) so I can map the chamber contour and cut the dome to match. I have a CNC lathe so I can cut any profile, it's just a question of having accurate measurements to go by.

BTW, the 2nd generation BB kit is supposed to have a 1cc smaller chamber. IHMO, that is not enough. It should be 1.5 - 2.0 cc smaller. Maybe we'll be able to get that extra cc by setting minimal squish ??? It would be nice if the manufacturers would just design the darn things for decent compression -- as Dolmar does -- so we don't have to jump through these hoops.

Another issue with the 066/660 is the exhaust port is way too high, which limits the compression stroke. I honestly don't understand what the Stihl engineers were thinking (or smoking ) when they spec'd this jug. Lakeside told me it probably had something to do with HC emission issues..

The 1st generation BB kit apparently copied the OEM exhaust port timing, so it's F'd up, too. I'm curious to see if the exhaust timing has been corrected on the 2nd generation kits. Grande Dog said they fixed the freeport problem, but I don't know what other changes have been made to the ports.

 

[Meadow Beaver]

Let me practice some more on my saws, and build a proper fixture to hold the piston in the lathe. Then I might feel up to helping a few AS members.

I wish Grande Dog would offer a drop-in, pop-up piston for the 066/660. I bet a lot of people would be interested in an economical pop-up that requires no machining. It would certainly be more popular than the Wiseco deal.

You can only gain so much psi by shaving a pop-up, but the dome could be made plenty tall on a cast pop-up. The dome would add some weight, but I think it would be worth it. The 066 design tends to come up short on compression compared to say, Dolmars.

I think the reason they don't is because the majority of people don't want 180-200psi out of a saw, unlike us.

 

[volks-man]

The 2 -tier pop-up increases the pop-up volume more than a single dome. Not much, but every little bit helps.

My pop-up does increase the compression ratio as shown by cc-ing the chamber volume in a previous post:

However, the 0.75cc reduction is not a huge difference, compared to what I'd like to see. I'd like a 2cc reduction in chamber volume. AT LEAST.

As for how my 0.75cc pop-up compares to the work done by other modders, I don't know, since they rarely post any detailed data. I was tempted to shave a little more off, but this saw is used for milling, so I wanted to keep it safe and sane.

That said, in hindsight, I could have made the dome diameter a wee bit larger, and I could have made the outer tier a wee bit higher. That might have gained a couple of psi or so. I didn't have a way to measure the chamber profile so I just eyeballed it as best I could and cut the pop-up based on my eyeballed numbers.

If I do this type of project again, I'll make several solder impressions of the stock chamber before dissembling the saw (this jug was already off the saw when the project began) so I can map the chamber contour and cut the dome to match. I have a CNC lathe so I can cut any profile, it's just a question of having accurate measurements to go by.

BTW, the 2nd generation BB kit is supposed to have a 1cc smaller chamber. IHMO, that is not enough. It should be 1.5 - 2.0 cc smaller. Maybe we'll be able to get that extra cc by setting minimal squish ??? It would be nice if the manufacturers would just design the darn things for decent compression -- as Dolmar does -- so we don't have to jump through these hoops.

Another issue with the 066/660 is the exhaust port is way too high, which limits the compression stroke. I honestly don't understand what the Stihl engineers were thinking (or smoking ) when they spec'd this jug. Lakeside told me it probably had something to do with HC emission issues..

The 1st generation BB kit apparently copied the OEM exhaust port timing, so it's F'd up, too. I'm curious to see if the exhaust timing has been corrected on the 2nd generation kits. Grande Dog said they fixed the freeport problem, but I don't know what other changes have been made to the ports.

i do think that the inside corner at that step is hurting you. mind you i am only thinking outloud and learning as i read your posts. i could only hope to accomplish what you have already in my limited experience. perhaps a single large dome next time with no gap producing 'steps'?

a simple lubing of the combustion chamber with oil and pressing clay in to the chamber with the piston would give you a nice impression to fool with.

for a more permanent impression solution you could use 'durams rock hard water putty'.
it sets up like plaster and can be mixed and poured very thin (perhaps poured through the plug hole). oiling the piston and cylinder should facilitate it's easy release. with the water putty version you would be able to saw the impression for cross section inspection/measuring.

 

[rxe]

Could you explain how you've attached the pine "bar" to the jug? What is stopping the pine from just spinning in the cylinder bore? (I'm a complete noob at this sort of thing....)

 

[mtngun]

I think the reason they don't is because the majority of people don't want 180-200psi out of a saw, unlike us.

Perhaps, but that doesn't explain why other Stihl models have reasonable compression and reasonable port timing.

Some of Timberwolf's comments from his excellent 460/660 thread:

460 surprised me with 172 psi compression.
Squish 0.032
RPM 13,800 16 inch bar and chain
Head Volume 8.2 cc

660 I could not get over 150 psi compression.
Squish 0.029
RPM 13,100 same bar and chain
Head Volume 10.0 cc

Port Durrations:

460

Exhaust 160.0 deg
Inatake 144.0 deg
Transfers exhaust side 112.6 deg
Transfers intake side 121.6 deg

660

Exhaust 180.8 deg
Intake 153.4 deg
Transfers exhaust side 116.6 deg
Transfers intake side 123.0 deg

These two saws stock are ported very differently.

The porting numbers on these new stihls is high, it did not seem right to me, tripple checked and it is indead that high. 660 is higher than the 460 yet at 180 deg. Thats higher than I would port a work saw, more where a stock appearing racer would be.

Also on the 660 jug the porting on exhaust is about 10 deg longer than I would like to see and the plating and machieling in the top 1/8 of an inch is very poor. I'd like to be able to mill the squish and lower the jug, but plating just want allow for that. If you have any original 066 jugs hang on to them the 660's are junk in comparison.

Volks-man, I'll have to create a CAD drawing to explain what is going on with the 2-tier pop-up. Maybe tonight.

Update: I checked compression this morning, hoping last night's brief idling session had helped seat the rings. Nope, in fact, compression was down, 110 - 120 psi. I peeked through the plug hole and through the muffler and didn't like what I saw -- fine vertical lines on the cylinder. Nothing serious, but it shouldn't be doing that at all.

I'll go ahead and put a few tanks of gas through it and pray for a miracle, but right now it looks like the rings aren't going to seat and I'll have to write this project off as a learning experience. Either the rings don't like the cylinder, which is possible, because the cylinder took a beating in a previous sawdust poisoning incident, or else the rings don't like my newbie port job, also possible, even though I lightly chamfered the tops and bottoms of the ports.

 

[parrisw]

Could you explain how you've attached the pine "bar" to the jug? What is stopping the pine from just spinning in the cylinder bore? (I'm a complete noob at this sort of thing....)

You just use the tail stock, apply a little pressure to the top of the cylinder and its just a friction fit.

 

[mtngun]

You just use the tail stock, apply a little pressure to the top of the cylinder and its just a friction fit.

Yep, it works fine because you are only taking light cuts.

BTW, it was parrisw and his machining threads that inspired me to do this pop-up. It looked like fun, and it was. Eventually it will all come together.

 

[parrisw]

Yep, it works fine because you are only taking light cuts.

BTW, it was parrisw and his machining threads that inspired me to do this pop-up. It looked like fun, and it was. Eventually it will all come together.

Yup, works good. Good luck with it. Hope you get the comp you want. How did you clean the cylinder? You could try to hone it, hopefully the rings will seat a little better.

 

[Jacob J.]

Will inspired me to take a five-day hiatus in a padded cell.