Stihl 660

[brshephard]

Until the piston or band get some carbon on them

Exactly. Not a very practical number.

 

[brshephard]

FWIW I tested a high compression 660 jug similar to the OP yesterday.
AM at 102/122/77. Blew 245 dry.

Torque was awesome. RPMs were kind low.
The problem, though, was all the heat it made. It would lean out like a half turn in a 10 second cut.
Also dieseled hard when shutoff.

Basically, way too hard to keep the carb dialed and hard starting. Not good for a work saw.

 

[drf256]

FWIW I tested a high compression 660 jug similar to the OP yesterday.
AM at 102/122/77. Blew 245 dry.

Torque was awesome. RPMs were kind low.
The problem, though, was all the heat it made. It would lean out like a half turn in a 10 second cut.
Also dieseled hard when shutoff.

Basically, way too hard to keep the carb dialed and hard starting. Not good for a work saw.

Thanks. Exactly what we were trying to say.

Most guys have gotten 200 psi gasketless with a Cross 660 jug. Did you do other mods to see 245?

 

[brshephard]

Thanks. Exactly what we were trying to say.

Most guys have gotten 200 psi gasketless with a Cross 660 jug. Did you do other mods to see 245?

This was a different brand jug.
I started at 97/127/82 and took a mile out of the band.
I didn't want the compression, but don't have a way to cut the chamber.

 

[drf256]

You can manually relieve the edge with a large carbide ball. Make it more bell shaped than Hemispherical.

 

[Allen Miller]

I'm looking forward to seeing how this turns out.

When you get ready to check your port timing, Mastermind has a good video on setting a wheel up.

Numbers are read as: Exhaust/Transfers/Intake
Exhaust is read when the exhaust opens in degrees after top dead center (TDC)
Transfers are read when the upper transfers open in degrees after TDC
Intake is read when the intake port closes in degrees after TDC

You want to end up somewhere around 100/120/80

Here are a couple good threads:
http://opeforum.com/threads/mastermind-meets-the-ms660.244/
https://www.arboristsite.com/community/threads/066-ms-660-port-s-please-share-your-stock-s.263751/

Exhaust110 Intake 85 transfer port 115 that wear cylinder was at the time of post. Just started working on again .

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[brshephard]

Cool man, where do you want your final numbers?

Double check your transfer number. Since you decked .075 and took .063 you should have lowered your transfers a couple degrees. That should take you above 120.

 

[MustangMike]

I think if you leave the exhaust at 110: 1) not enough blow down, and 2) you may need an electric start!

Also, with the intake there, it will drink fuel.

 

[huskihl]

Sumpin ain't quite right with the port timing numbers. I expected more like 108 135 88 after removing .075"

 

[brshephard]

With .075 off the base and .063 off the piston (.012 of deck for exhaust trans).
Figure around 102/122/82 start.
I get 103/123-124/87-88

Special thanks to Shaun for that measurement. Here is a chart specific to this saw that shows the bore distance across various timing changes.
It works as follows:
1. Find your current port timing number.
2. Follow the row across until you find the timing number you want.
3. The corresponding value is the distance between the two in ten thousands of an inch.
4. A positive value means you would need to grind material. Negative would require decking or epoxy.

Example: Suppose I dropped the exhaust to 105 and I want to go to 90 to do sick piss revs. Go to the 105 row, then look at the 90 column. I would have to grind up .1961" (highlighted yellow).

You can also use the tables to predict where timing will end up when decking. Suppose my transfers are at 115 and I knock .050 off the base. Go to 115 and scan across the row for .050. 120 is at .0528 so I'll end up around 119.5.

Let me know if it works for you guys

Exhaust
View attachment 122894

Transfers
View attachment 122892

Intake
View attachment 122893

 

[huskihl]

My bad. I missed the pop up part

 

[MustangMike]

I think his intake # may be right.

 

[brshephard]

My bad. I missed the pop up part

I hope I didn't come across as trying to give you a hard time. You're a heck of a lot more knowledgeable than me.

What do you think of that popup? I measured .133 crown to land on a Cross piston, that leaves around .070 after milling.

I heard the rule was .100 minimum.
What happens if you break the rule?

I think his intake # may be right.

I think so too.

 

[Bigmac]

If you don’t want the compression why not take some material off of your pop up, then you can easily dial in your compression

 

[huskihl]

I hope I didn't come across as trying to give you a hard time. You're a heck of a lot more knowledgeable than me.

What do you think of that popup? I measured .133 crown to land on a Cross piston, that leaves around .070 after milling.

I heard the rule was .100 minimum.
What happens if you break the rule?



I think so too.

Nope not at all. By reading your post i realized I'd forgotten about the pop up.
I think every piston/saw model is probably different. I took .070" off a 346 race saw piston to lighten it up. The added heat to the crown (I'm guessing) allowed the ring pin to wallow out and become loose. I caught it before any damage occurred. Not sure if it was due to the cheap AM piston or what.

 

[Allen Miller]

If you don’t want the compression why not take some material off of your pop up, then you can easily dial in your compression

I'm going to machine some the Dome off the piston but first I was going to work on getting then intake the exhaust and the port timing right just got a new meteor piston so as soon as I get it where I want it I'm going to make a new piston for it. I only want 190 to 200 max. Had to start somewhere. I don't use this saw more less give me something to play with.

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[Bigmac]

I'm going to machine some the Dome off the piston but first I was going to work on getting then intake the exhaust and the port timing right just got a new meteor piston so as soon as I get it where I want it I'm going to make a new piston for it. I only want 190 to 200 max. Had to start somewhere. I don't use this saw more less give me something to play with.

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Just as a reference, I had an oem jug that I had 40 thousands taken out of the band, netted 100ex duration and 200psi and had to epoxy the intake to get it back up to 80

 

[Bigmac]

Even if you don’t do a pop up and stack base gaskets to reset squish, your transfer and exhaust numbers will be the same and it will lower your intake number, and probably net you over 200psi

 

[Allen Miller]

Just as a reference, I had an oem jug that I had 40 thousands taken out of the band, netted 100ex duration and 200psi and had to epoxy the intake to get it back up to 80

How did epoxy work out. .030 change everything. Raising jug up .030 makes E100 Int82 but transfer I'm going to grind them . Has anybody ever tried a double step piston

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[smokey7]

Are you talking about a piston with 2 height changes?