Mastermind
Work Saw Specialist
I got a pile of saws a few days back, two Homelite 360s, a Partner P55, a Partner P70 were in the mess. Jon, my son-in-law, built a nice 360 Pro out of the two Homies.
I checked out the Partners and found the P70 to be in good shape although it had a broken rear handle. Luckily, the P55 had a good handle and is interchangeable.
I didn't take a pic of the P70 before I tore it down, but it looked about like the P55. Here it is.
Nasty huh?
The P70 really surprised me. Under all the crud it was in nice condition, no scoring at all, smooth bottom end, Tilly carb, 70cc top end. Plus it has a Mahle closed port jug and a Mahle piston.
One thing that caused me to scratch my head quite a bit was the exhaust port. It has a slot in the top center of the port that is used for compression release.
This made it hard for me to determine the port opening point. I wondered if I should allow for it in my timing numbers.
Without a base gasket the squish is .030
The timing numbers, no base gasket:
Intake Duration: 130°
Exhaust Duration: 155° (measured at 5° above the port to allow for slot)
Blowdown: 25°
These numbers seem very conservative, especially the intake. I think it would make gobs of torque but not a lot of rpm. What do you guys think?
I made a pattern of the case to match the transfers, it was off pretty bad from the factory.
In this pic you can see the scribe lines I will cut to, this will match the transfer openings to the case. Check out the Tee shaped exhaust port.
The lower transfers roughed in.
And the uppers. I widened them toward the intake two mm.
I lowered the intake port to bring the duration up to 145°. This port is bridged and the ring end centers one of the openings. I widened the port to 35mm which is 70% of the bore.
Here's a shot of the exhaust port after roughing it in. I raised the port 2-3°. The compression on the saw was at 170 before I tore it down. The increase in duration should overcome to slight loss in compression. That brings the exhaust duration to 160°. This port is also at 35mm wide.
I checked out the Partners and found the P70 to be in good shape although it had a broken rear handle. Luckily, the P55 had a good handle and is interchangeable.
I didn't take a pic of the P70 before I tore it down, but it looked about like the P55. Here it is.
Nasty huh?
The P70 really surprised me. Under all the crud it was in nice condition, no scoring at all, smooth bottom end, Tilly carb, 70cc top end. Plus it has a Mahle closed port jug and a Mahle piston.
One thing that caused me to scratch my head quite a bit was the exhaust port. It has a slot in the top center of the port that is used for compression release.
This made it hard for me to determine the port opening point. I wondered if I should allow for it in my timing numbers.
Without a base gasket the squish is .030
The timing numbers, no base gasket:
Intake Duration: 130°
Exhaust Duration: 155° (measured at 5° above the port to allow for slot)
Blowdown: 25°
These numbers seem very conservative, especially the intake. I think it would make gobs of torque but not a lot of rpm. What do you guys think?
I made a pattern of the case to match the transfers, it was off pretty bad from the factory.
In this pic you can see the scribe lines I will cut to, this will match the transfer openings to the case. Check out the Tee shaped exhaust port.
The lower transfers roughed in.
And the uppers. I widened them toward the intake two mm.
I lowered the intake port to bring the duration up to 145°. This port is bridged and the ring end centers one of the openings. I widened the port to 35mm which is 70% of the bore.
Here's a shot of the exhaust port after roughing it in. I raised the port 2-3°. The compression on the saw was at 170 before I tore it down. The increase in duration should overcome to slight loss in compression. That brings the exhaust duration to 160°. This port is also at 35mm wide.
opcorn:
