Makita® 6421 With UPGRADES vs. Stihl® 500i

Filmed over the 2020 summer while I was “Staying home”…
This was a work in progress. Initially, the thinking was the dcs6421 was in excellent condition based upon the outward physical appearance. I ran it through my “33-point safety inspection” and found that the crank was bent one the drive side ~ 2.5/3 thousandths. Doesn’t sound like much. But, considering the end result will have a saw working a few thousand rpms higher than the stock version it enough to knock out the bearing. Upon further inspection, I found that the rod/journal/bearing had end play. That will disqualify a saw build alone. After a few exchanges with the owner, he decided a complete overhaul was in order.
I installed a new crank, bearings, seals 7910 cylinder assembly (could not readily find an oem 7901 topend for a timeline accurate build) muffler, gaskets, etc., etc. Total, ground up rebuild. It was a costly endeavor. In the end, I can only hope and pray that the owner is well pleased and thinks it was money well spent. With any luck, he will chime in on this video.
At this point, my buddy Dave has had the opportunity to use his 500i for a decent stretch of time. Mr. Reed has also had some use on his completely rebuilt and upgraded 6421. I’m hopeful that they will post their thoughts.
Bore, stroke, and displacement numbers;
Makita® 7900 52mm x 37mm for 78.58cc.
Stihl® 500i 54mm x 34.6mm for 79.24cc.
Both saws were taken the the Psy-Ko level ZippKit wise so it is a relative and fair comparison in that regard.
32” Oregon lw bar and full complement Windsor chain in the solo run. 32” Stihl lw bar with full skip chain in the session with the Zipped 7900 Makita & 500i.
I re-measured the large cut and assessed the smaller log. In the 6421 solo run it was 18” in diameter. With the Zipped saws it was actually 23” x 24”. Sometimes the assistant is off a little…
Looking at the timed runs:
Stock 6421, 18” log at 12,320 rpm high Idle 11.96 down, partial/stall up 10.87, and 10.76
Psy-ko 500i, 23” log at 11,100* high idle 10.43 down at 10,510 and 9.60 up at 9400.
Psy-Ko 7900, 23” log at 13,260 high idle 10.03 down at 10,320 and 10.13** up at 10,080.
Qualifiers –
EDT-9 does a poor job reading the signal in the 500i saws. They “usually” cut in around 13,350 to 13,670.
** I had a ton of pressure on the Makita handle bars & pistol grip while cutting up. It would have dropped a ½ second or so had the pressure been a little less. As mentioned, I tuned it for torque and wanted to test it out fully. We could see the log being lifted the whole time.
I’m well pleased with the performance of the lower displacement Makita with it’s 15/20 year old technology. We watched it, while nowhere near turning the corner, holding it’s own against the 500i and giving up 0.66 of a cc in displacement to boot. In later test sessions, I fitted the Makita with the alternate air filter. We will see some improvement so “stay tuned”…
I’m currently available for custom saw modifications. Please shoot me an email if you are interested.
[email protected]
Thanks for watching.