Finally Going To Do One, Just To See

dubbed = square chain that the square corners have hit something messed up not sharp. No real corner anymore.

 

Those saws stock won't cut but about 1/2-1/3 as fast if it has the higher limited coil.

The old dollars had a longer stroke than most also. The 166 family has a long stroke also.

 

48mm stroke with 56mm bore. I had a race and work 166. Also the 48mm stroke was why racing guys were putting 60mm-66mm tops on them. Only thing was the cranks were weak for the rpm racing produced. Many of broken cranks.

Rebuild video I did on my 166 after snagging a ring. 1st cuts really really fat. Mine was stock bore with piston in backwards.






Letting Al Smith try a cold start with it later on after a few runs on it. He has the same problem I had with the 3120. Not pushing hard enough through cuts.

 

Spoke to Solo in VA this AM, they actually HAVE the crank in stock and are shipping today! Can't believe it, also asked if the 681 top end kit was available, plant in Germany shut down for holiday not to reopen until late July so won't know if they can get the top end until late July then have to wait a month for it to arrive if they can still get it.

 

Also, if I can get the C/P from Solo, I will use that. Rumor has it that there are porting differences between the Solo 681 and Dolmar 7900 cylinders.

 

Well Randy cleared up the confusion, and saved me the cost and frustration of trying to get the C/P kit out of Germany, according to Mastermind the only difference in the Solo and Dolmar jugs is the location of the decomp. Solo on top, Dolmar on the side. The port timing is exactly the same!

Since the target of this is a NOS Dolmar 7300, I will be using a Dolmar jug because the decomp matches the top cover!

 

By putting the spacer under the 7900 jug, you'll be doing more than just adding to the stroke...
There will also be added crank case capacity and .5mm additional "charge" time...
Thus the increase in net HP.. "This is just a theory"

To pose another question...
McCulloch SP125
Low torque revving machine?
Or powerful torque monster?
Bore = 58mm
Stroke = 46.6mm

 

Well crap...
Seems I killed the thread again..
Anyone care to join in the bore-stroke-case volume brain storming session?
Kevin??
I know you got some thoughts on this matter...
All I got is theory and a smidge of practical application...

 

The Mac 125 isn't that low of rpm really. I think they still turn over 11k or so. They do have good torque and you can push on them a good bit. A healthy 3120 is still faster cutting though. I never got to try them both in real big wood with say a 60".

 

Hedgerow, you killed nothing, was busy yesterday. On the SP125, I could only venture an opinion since I have no practical experience with that saw. However, given the B/S measurements it would be under square. That its' max rpm is around 11K it reminds me of a 125cc MX engine, my personal opinion is that it would probably be considered a torque machine. A very interesting aspect would be to compare its' max torque and max HP revs. On some of the old race bikes those two rev ranges were so far apart it made the bike uncompetitive.

Interesting thought about the spacer in the Dolmar and its' overall impact on the engine performance. Everything you said certinly makes sense. When the crank gets here I'll put a wheel on my stock 7900 and the modified one and make some measurements. Had a guy measure the spacer that comes in the BBKs, and it is thicker than originally thought. It measures 1.5mm or 0.590, so your thought about CC capicity and charge time now becomes very interesting.

 

I guess I've been living under a rock but I've never heard of chainsaw racing before!

 

Kevin, Randy, Shep, Adam and I were discussing on Chainsaw Repair the differences between the jugs used on the Dolmar and Solo saws. Shep brought up the tid bit that the Solo jug and the Dolmar jugs used on the 6400 and the Solo 665 are in fact quite different. The Solo jug is quad closed port and Dolmar 6400 is open port. Would be very interesting to find a Solo 665 to compare against a 6400, or better yet put the stroked Solo crank and jug off the solo in a 6400.

So if anyone knows of a running Solo 665 for sale, I'm interested.

 

Second YT video is my 125C,100% stock.36"+ diameter White Oak it just laughed at last winter....

 

Well, I guess by the vids that Thistle just answered the question, 36 inch bar, big oak, laughed at it, definately a torque saw!

 

No kidding.Even here in the great rolling fields of flyover land its got its devotees,though few in number.

 

They have good torque, and in the right hands, produce a lot of horsepower.
That being said, the race guys use 3120's, and stroke them on top of it!!!
So equating speed in the cut with shorter strokes and long stroke machines being lower rpm machines is sorta out the window..
Looks like we got some other factors at play here...
I too would be interested in seeing the closed port solo 4 cube jug..

 

Racin' saws is just fun...
We'll race anything around here..
Even vintage saws!!

 

We have to be careful not to confuse chain speed, speed in the cut, horse power and torque.

Here is how I think of it right or wrong.
It takes torque to get the chain moving and pull it through the wood.
The more torque the engine can produce near or at its' max HP the better. Engine needs to continue to pull the chain through the wood even at high RPMs.
After the engine is past its' max torque/HP RPM ranges both these figures begin to fall off e.g. we are turning more RPMs but not getting anything for them, just wear and tear on the engine.
So the best situation would be to have the two ranges overlap at some place in the rev range of the engine. Resulting in the most overall torque/HP available in an in-use situation.