Need someone to cut squish on 681

[Hillwilliam]

I'll be needing someone to cut the squish, etc. on my recently-acquired Solo 681. I don't build enough saws to justify having a lathe.

Help from somebody with experience would be much appreciated, and I'll pay.

Thanks

 

[Moparmyway]

52mm bore

Do you know exactly how much you want cut ?

Do you also want the base cut ?

 

[Hillwilliam]

I'm still figuring that out. Likely just enough out of the the squish band to get 'er nice and flat and pretty. The base will need to be cut as well, but I'd like to minimize that, because I'm wary of advancing the intake too much - at first, anyway.

I'll want to have a tight squish, but I don't know how tight. (I'd be interested in your advice.) Turns out I had been running it at .018" all summer. The plan is to build the 681 exclusively for competition. I've only ever built strong work saws, but that's not enough anymore. With nothing to go by, I'm going to have to port in stages. Gotta figure out what carb I'm going to use too.

I just got the jug gasket I'll be using and, once I get the bottom end back together in a couple of days, I'll be able to figure out more.

Thanks for getting back to me.

 

[Hillwilliam]

I finally had the chance to get the bottom end together and check the squish using a Dolmar gasket. The gasket is right at .020", and I plan to use it since I'll have to take the jug back off a number of times while porting. The gasket is aluminum - or metal anyway - and I don't expect it to compress much. The squish is currently at .038" with the gasket.

With the gasket, my desire to not get the intake too low should be less of an issue. What has to be taken off the base depends, of course, on how much comes out of the squish band at the top. Running the saw all summer with a squish of .018" didn't seem like a big deal at all, and I'm thinking of setting the squish at something like .016" for a competition saw.

Interested in helping me out?

 

[Moparmyway]

Sure, pm me and let me know how much you want out of the chamber

 

[Dolkitafreak]

Tighter squish is not better, achieve compression through a larger cut, not tighter squish. A head is ideal for a true competition saw. Also, don’t worry about intake as these saws like the duration, and many saws built for racing can handle a large intake duration.
For reference, recent 7900 is .050”/.050” cut with .025” squish and a 180psi with exhaust at 96. Runs very well.

 

[Dolkitafreak]

Especially being the band shape these saws have, .016” squish is not a good idea at all. For competitive use a head is by far the best option, what exhaust height are you wanting to run?

 

[Hillwilliam]

Thanks, Dolkita, for all that advice. I'm thinking that too much compression (and too tight a squish) could inhibit the kind of RPMs I want.

The Solo is a nice simple saw, but an odd one to me. Also, a full-on competition saw is a new thing to me.

For exhaust height, all I know so far is I'll be higher than 100 and have a long blowdown.

I'm gonna need to do some ponderin' and cipherin'.

 

[Hillwilliam]

Sounds like you're suggesting I take .050" out of the squish band. Now you have me thinking I'll want to go for .021" to .025" for squish clearance.

Your Dolmar must be a a real rip-snorter!

I don't plan on using a head - yet anyway. I'll see what i can do without going that far.

Thanks again for your insights and experience.

 

[cus_deluxe]

a head is nice cuz you can get a smaller chamber without cutting the heck out of the base. not sure how thick the base is on a 681…i havent messed with dolmar/solos much, but for a 5 cube racer youre gonna end up wanting to go well beyond ex opening at 100 atdc.

 

[huskihl]

Some folks are plenty happy with a proper woods ported saw, as opposed to a race saw

 

[Hillwilliam]

Thanks. 35 years ago, I would compete and usually win with my work saws and racing chains, but I can't even be in the game anymore. Now that my son is getting interested, we need something much more competitive.

I don't cut timber anymore, but I just love my old ported Pioneers for firewood.

 

[Dolkitafreak]

Thanks. 35 years ago, I would compete and usually win with my work saws and racing chains, but I can't even be in the game anymore. Now that my son is getting interested, we need something much more competitive.

I don't cut timber anymore, but I just love my old ported Pioneers for firewood.

Really we need to know what kind of racing you’re doing also, but it sounds like a head is out of the question. Yes I would cut at least .050” from the band.

 

[Hillwilliam]

They don't use cants around here anymore. It's peeled logs, maybe 14" diameter, and it's down to 20" bars. Usually only two cuts, rather than three. Screamin' RPMs appears to be an asset.

The weapon of choice for medium class (maybe stock-appearing, if they used that term) is the 681, built at great expense by an obscure saw builder in CA, I think. And they are indeed hot.

Most of them run what looks like a Tilly HL. Never thinking I'd be trying to build one, I never took note of just what carbs they use. I may just go with a RWJ4 or maybe a WJ118 until I get something else figured out. I've read that a bigger carb doesn't make a lot of difference on ported work saw 681s.

Any insights you could share? You'd be welcome to shoot me a PM, if you'd like.

I keep no secrets about any of my saw builds, but I fully understand anyone being tight-lipped about a competition saw. Therefore, I have very little to go by, but I've been learning some things from you. Thanks.

 

[Hillwilliam]

I just thought of another consideration: Here at 8,000' elev., there isn't a lot of air in the air. I believe we end up with only 80% of the compression one would have at sea level. Still, I don't think I want to get too carried away with compression if it will impede RPMs.

 

[Dolkitafreak]

They don't use cants around here anymore. It's peeled logs, maybe 14" diameter, and it's down to 20" bars. Usually only two cuts, rather than three. Screamin' RPMs appears to be an asset.

The weapon of choice for medium class (maybe stock-appearing, if they used that term) is the 681, built at great expense by an obscure saw builder in CA, I think. And they are indeed hot.

Most of them run what looks like a Tilly HL. Never thinking I'd be trying to build one, I never took note of just what carbs they use. I may just go with a RWJ4 or maybe a WJ118 until I get something else figured out. I've read that a bigger carb doesn't make a lot of difference on ported work saw 681s.

Any insights you could share? You'd be welcome to shoot me a PM, if you'd like.

I keep no secrets about any of my saw builds, but I fully understand anyone being tight-lipped about a competition saw. Therefore, I have very little to go by, but I've been learning some things from you. Thanks.

On a work saw I like and have good success with the stock carbs. This is a 7900 plain work saw build, stock carb, zero modifications on carb. Beat a 681 running stock carb and a 681 running an RWJ, all 3 saws are very close to each other. For what it’s worth I know one of the saws it beat has far more compression. Some of the fastest saws I’ve run don’t pump up to high. 170 is good imo

https://youtube.com/shorts/BaqThYxwc_w?feature=share

 

[Nutball]

On a work saw I like and have good success with the stock carbs. This is a 7900 plain work saw build, stock carb, zero modifications on carb. Beat a 681 running stock carb and a 681 running an RWJ, all 3 saws are very close to each other. For what it’s worth I know one of the saws it beat has far more compression. Some of the fastest saws I’ve run don’t pump up to high. 170 is good imo

https://youtube.com/shorts/BaqThYxwc_w?feature=share

What length of bars were those running? The XS7900 I had wasn't far behind in a video I compared. I was cutting a 20" Ash log with aggressive round filed full skip firewood chain with 8t 3/8 rim in less than 8 seconds for one cut.

 

[Dolkitafreak]

What length of bars were those running? The XS7900 I had wasn't far behind in a video I compared. I was cutting a 20" Ash log with aggressive full skip work chain with 8t 3/8 rim in less than 8 seconds for one cut.

20 on 7900, 20 on one 681, 24 on the other. You’d probably be faster with full comp, just my opinion though. That competition also doesn’t allow square chain, could’ve shaved another 15% off but they want strictly firewood saws and round chains.

 

[Hillwilliam]

Those are fast saws indeed! You aren't losing much RPM in the cut. It's sounding more and more like I want to run 'fast and loose', rather than going hog wild about compression. I'm learning little by little.

I'd be out of my element if I wasn't allowed to use a chisel-filed chain - like not being allowed to wear pants. That's all I've used for work chains, including for firewood, for over 40 years. One Pioneer I've had for 40 years has never suffered the indignity of a round-filed chain.

 

[Nutball]

Starting at 0:27 is when I cut the 20" ash log

https://img.masterblasterhome.com/data/video/107/107904-5591cb90facc2882539798c328d34f44.mp4