Holzfforma G660 / Ported Cylinder for Milling

[farminkarman]

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I was very impressed with the quality of the Duke's Reserve cylinder. I cut 0.040" from the band which got the exhaust to 99, the intake landed at 84, and I raised the transfers to 120. Once I got the saw tuned right it was a beast with a long bar. The intake duration was a bit long for a racier build, but seemed to work very well for what I built it for.

Edit: I forgot to mention that the upper transfers on the Duke's jug blow harder back toward the intake than a FT cylinder, which I think is a plus for a long bar saw.

 

[Agent Smith]

I was very impressed with the quality of the Duke's Reserve cylinder. I cut 0.040" from the band which got the exhaust to 99, the intake landed at 84, and I raised the transfers to 120. Once I got the saw tuned right it was a beast with a long bar. The intake duration was a bit long for a racier build, but seemed to work very well for what I built it for.

Edit: I forgot to mention that the upper transfers on the Duke's jug blow harder back toward the intake than a FT cylinder, which I think is a plus for a long bar saw.

I too thought the uppers were nice. Nice entry angles. How was it to grind on? Plating seem as good as oem or close?

 

[farminkarman]

I too thought the uppers were nice. Nice entry angles. How was it to grind on? Plating seem as good as oem or close?

I had no issues with plating lifting.

 

[Paul Fithian]

After deciding not to use the Cross cylinder, I ported the cylinder that the saw was built with. First real port job I've done:




Stihl piston pin bearing, 0.010" gasket , and Motoseal


Exhaust mod


Assembled with a Caber top ring and Holzfforma bottom ring. Ready to run, may fire it up later today.

 

[Paul Fithian]

Additional pictures




Timing check after assembly:
- Exhaust: 97
- Transfer: 117
- Intake: 82

 

[MustangMike]

Nice work and nice #s, hope it runs real well.

I know everyone likes a lot of arch on the top of the exhaust port to prevent from hanging a ring, but if it does not run to your liking you may want to do what I did to the Asian one (w/Cross jug) that made 8.6 Hp and reduce the arch, just make sure you bevel your ports well.

It really made a big difference on that saw.

Also, did you advance the timing to go along with your porting and exhaust mods? A low restriction air filter also helps.

For milling, probably the Max Flo is best, but for regular cutting I often run the steel screen winter filters. They fit right under the stock cover.

Did the saw come with the metal bottom protector, or did you add it?

It looks nice!

 

[Paul Fithian]

Thanks Mike!

Plate came with the powerhead, but I removed it. Left the timing advance stock per Doc’s prescription for a milling head.

Ran it for over an hour today with a 20” bar, all good. May try out the long bar tomorrow with a Granberg milling chain

 

[Funky sawman]

I was a bit paranoid about using that Cross jug on my 660, which was pretty much a new saw when I did the swap. That flat exhaust roof really had me sceptical, but all I did was a nice small bevel, on the upper edge of the port only. Now that the saw has over 100 gallons of gas run through it, I no longer loose sleep about blowing up this 1500 dollar saw. Had a 064 built years ago, the builder was on the safe side, he made a arched exhaust port roof. I never like how that saw ran, i took it to my buddy that builds 2 stroke bikes and right off the bat he pointed out that exhaust roof. He believed the shape of the port had more to do with power than the actual size of the port. Interesting indeed.

 

[huskihl]

 

[drf256]

Paul, that Cross exhaust roof doesn’t look good to me either. I am surprised, because one I had here looked nothing like that.

Your porting looks good, so do your numbers with a gasket.

At least for me, the 066 seem to do well with a higher physical exhaust. At the NY GTG a few years ago, one with a 92 exhaust roof beat us all through a big log with a 36” 404 bar. All the saws were ported by reputable guys too.

I think the narrow piston skirt and the subsequent narrow exhaust port hold the saw back. A higher ex roof creates more time x area.

 

[Paul Fithian]

Thanks Doc!

Nice exhaust picture, Huskihl, but what is it from?

Glad you fellas taught me what to look for on these cylinders. Some minor changes can have a huge impact on performance and longevity. No way I was gonna install that Cross cylinder, fearing it might fail and destroy the bottom end of a new saw.

I’ll run this G660 hard as a milling head and see if it performs or fails, then share results. Either way we learn.

 

[huskihl]

Thanks Doc!

Nice exhaust picture, Huskihl, but what is it from?

Stihl something. Not certain

 

[Paul Fithian]

Ran the big bar with a new Granberg milling chain to split a fat red oak stump

View of piston/rings from the exhaust side looks great after one tank of fuel


This G660 runs perfect. It's the most powerful saw I've ever used.

 

[MustangMike]

Glad it runs so nice!

Looking at your picture of the piston in the exhaust port I notice more arch on the top of the exhaust port then on the bottom.

A ring can hang in either direction, so I don't see the reason for that. IMO, the faster a port fully opens, the better it works. The maximum pressure is before it opens, if pressure drops before it fully opens not as much exhaust escapes. Just my thinking, but it seems to have worked on a few saws I modified, and they didn't fail.

I don't get why folks are more afraid to reduce the arch on the top of the port than on the bottom???

 

[Funky sawman]

Exactly MustangMike. Ive seen dirt bike motors with nearly flat port roofs, and they never snag rings, and those engines have extremely wide ports.

 

[Funky sawman]

I've actually seen some high performance snowmobile engines that ran in the 9000 to 11,000 rpm range that had trapezoid exhaust port shape, yep, completely flat across the top. However, i do recall the rings had to be changed often due to wear.

 

[Paul Fithian]

Good observations and comments fellas. I shaped the exhaust to mimic the arch the cylinder was built with. Perhaps I could have gone flatter when I was grinding on it.

I want this saw to deliver reliable, powerful performance. Not looking for minor power gains with greater failure potential. And to see if my first porting job works!!

 

[Duce]

Is this my phone, or are those rings already wearing?

 

[farminkarman]

Is this my phone, or are those rings already wearing?

hard to tell...could be a funny lighting thing, but I see what you are talking about.

 

[Duce]

hard to tell...could be a funny lighting thing, but I see what you are talking about.

If I blow the picture up, looks like it’s about to score right up middle of piston. Build up under ring.