Makita 6401 Upgrades

[Jutt77]

So I got a wild hair and decided to upgrade my pawn shop special 6401 to a 7900...not that it really needed it but thought it would be a fun project.

I decided to spend a bit more and go with the OEM Mahle 7900 P&C vs the Bailey 84cc Taiwan made BB kit. The 84cc BB kit is supposed to be a pretty good option but I went with OEM. Here's a pic of the 6400 and 7900 Cylinders side by side. 7900 is on the right:

Pistons. 6400 on left, new 7900 piston on right. The size difference is evident:

Carb, muffler, and original cylinder removed. Original piston shown here. Also, I used a T27 torx T-handle wrench for almost all bolts. I got the cheap Grip-on torx set from Toolking (the T27 is in the pic here). Complete garbage. The torx bit portion twisted when removing the rusted muffler bolts. Pay the extra money and get the Wiha or other high quality set. I usually dont buy cheap tools and I paid for it here.

New cylinder mounted. I used the metal gasket that came with it but was lazy and didn't measure squish. Oh well, if I get another wild hair maybe I'll tear it back down and measure squish. I used the piston ring compression tool set from Baileys for this job. Well worth the 8 bucks.

Here's the HD air kit mounted. The difference between the stock filter and HD filter is huge. I also trimmed down the H adjustment screw on the carb to allow it to adjust a bit richer if need be.

Old sprocket on left, new sprocket on right. Old one was pretty worn out and it looks like the design was changed a bit (same brand and model):

Old and new fuel filters. I also changed the sparkplug:

Some old parts:

Done! Got the black sparkplug cover too. Also new 22" bar and chain from Baileys

Original saw from pawn shop:

I started the swap last night and finished it up around midnight so I havent got a chance to cut stuff up yet but it started on the 4th pull. I used this post from Arboristsite for instructions on how to do this as I just started working on chainsaws last month (changed the carb in my 026): (broken link removed).. Props to that guy! All parts were ordered from Cassadaga Edge and Engine. They had the best prices and shipping was pretty quick. All in all, it was a pretty easy project, the hardest part was popping the &*$# wrist pin clip back in...one went flying and is MIA, so I used one of the old ones.

 

[Freeheat]

That didn't look that hard. A little time consuming. How old is the saw ? Let me know how the power increase is

 

[smokinj]

Nice work....Do you feel the new jug is up to par with the stock?

 

[Beetle-Kill]

Great photos J, can't wait to hear about the difference in performance.

 

[Jutt77]

That didn't look that hard. A little time consuming. How old is the saw ? Let me know how the power increase is

yeah, took me about 2.5 hrs and I took my time but that is a really easy saw to work on. The first 4 numbers of the serial number are 0301 so it's either a 03' or 01'.
A Dolmar 7900 which is what this saw is now is listed at 6.3hp not including the HD air kit. The 6401 is listed at 4.5hp. So probably around a 1.8 to 2hp gain.

 

[Jutt77]

Nice work....Do you feel the new jug is up to par with the stock?

thanks Jay. The 6400 cylinder seemed to be a bit better finished as far as some of the machined parts compare but both are pretty similar and are good quality.

BK - I'll be running it Saturday through some giant cottonwood logs so I'll let y'all know how she runs.

 

[lukem]

I'm surprised the stock carb and muffler work witht the larger displacement cylinder. Are they the same on both models? Seems like you would need better flow thru each to realize the power gain.

 

[HittinSteel]

Very nice Jutt! You're going to have one heckuva a powerful saw. Great job of jumping right in to it. I'm jealous you were able to finish in one night. When I rebuild a saw, it seems like it's a half hour here and an hour there.

Jay asked about the fit/finish of the new cylinder. Isn't it a Mahle?, which should be what the OEM was?

Lukem, that carb is large enough to fuel the larger displacement....of course it needs richened up some to flow more fuel.

 

[Jutt77]

I'm surprised the stock carb and muffler work witht the larger displacement cylinder. Are they the same on both models? Seems like you would need better flow thru each to realize the power gain.

Yepper, I know the carb is the same on both models and I think the muffler is as well. I probably wouldn't see any real gains with a muffler mod unless I ported it as the stock muffler is supposedly pretty good as is.

 

[Jutt77]

Very nice Jutt! You're going to have one heckuva a powerful saw. Great job of jumping right in to it. I'm jealous you were able to finish in one night. When I rebuild a saw, it seems like it's a half hour here and an hour there.

Jay asked about the fit/finish of the new cylinder. Isn't it a Mahle?, which should be what the OEM was?

Lukem, that carb is large enough to fuel the larger displacement....of course it needs richened up some to flow more fuel.

Thanks man...I cant wait to saw some $%*# up with this thing! Both jugs are Mahle but the 6400 cylinder seemed to be just a little better finished and polished. Your spot on about the carb, I trimmed the H screw tab so that I could adjust for a richer setting.

 

[wendell]

Welcome to the Black Hat Club! You will love that saw.

I noticed the same in the fit and finish. The 6400 jug was an absolute work of art. I'm thinking of having mine mounted so I can put it on the wall!

 

[smokinj]

Welcome to the Black Hat Club! You will love that saw.

I noticed the same in the fit and finish. The 6400 jug was an absolute work of art. I'm thinking of having mine mounted so I can put it on the wall!

Thats the way I see it. Hard to take something off like that and replace it. Time will tell how good the bb kits are, and darn sure would not let the oem parts out of my hands.

 

[Jutt77]

Welcome to the Black Hat Club! You will love that saw.

I noticed the same in the fit and finish. The 6400 jug was an absolute work of art. I'm thinking of having mine mounted so I can put it on the wall!

Thats the way I see it. Hard to take something off like that and replace it. Time will tell how good the bb kits are, and darn sure would not let the oem parts out of my hands.

Jay - I agree so I didn't get the BB kit, I got the OEM Mahle 7900 P&C...cost twice as much but I wanted the OEM piece of mind. Same one you get if you went and got a Dolmar 7900. The 6400 is also made by Mahle it just happens to have been finished a bit better is what we're talking about.

Ran the saw through some 28" wet cottonwood and its definitely a big difference but I have it running pretty rich for break-in. How long do I need to break it in for?

 

[Jutt77]

Welcome to the Black Hat Club! You will love that saw.

I noticed the same in the fit and finish. The 6400 jug was an absolute work of art. I'm thinking of having mine mounted so I can put it on the wall!

Thanks man, the saw is just ridiculous now. Only had to go with about 80% throttle to get through some pretty big wet cottonwood logs that I was using 100% throttle before. Lots of fun!

 

[Beetle-Kill]

Damn it. J, check your PM