Dolmar 6400 upgrade questions

[NJAdam]

I want to upgrade my 6400 and cant figure out if I should go OEM or big bore. I was dead set on OEM after reading every thread I could find. Than I realized the OEM cylinder I was looking at was the new 7910 and not the 7900 that are in the old threads. I know the 7910 is advertised as less hp than the old 7900. My 6400 is the old style with the red top and decompression on the left (starter side). Now I'm just as unsure as when I decided to do this. Thanks in advanced.

 

[wde_1978]

What You want is a "PS-7910 P&C Conversion kit"!
It will be a bolt on to Your PS-6400 and should include a fitting cylinder cover!

Take a look here:
http://performanceoutdoorequipment.com/products/cylinder-and-piston-kit-ps-7900-038130910

If power and longevity are Your goal for this upgrade then go OEM!

As You can see in my sig I own both, a PS-6400 and a PS-7900 - the difference in power is amazing!

Disregard the specs for the PS-7910, they are only relevant to that saw as a whole and will not reflect (negatively) on Your intended upgrade.
Specifically, the PS-7910 is choked down by a lower limited coil (12.800rpm instead of 13.500rpm) and the dreaded SLR/CAT muffler (the PS-6400's muffler is "empty" aside from the deflector/bird cage).
As these "features" are not present on Your PS-6400, upgrading her with a PS-7910 P&C conversion kit will technically speaking make her more of a PS-7900 then a PS-7910.

Unfortunately "Red Tops" are NLA in the US, so You'll either accept the black top, paint it red, or get a "Red Top" from Europe.
Alternatively You can try to adapt Your "Red Top" to the new cylinder (the DeCo valve hole position is most likely changed).

Good luck with Your upgrade and tell us how it went!

 

[NJAdam]

Thanks for the reply and clearing up the 7910 top end questions. Seems like a no brainer to go OEM now. The new black top cover is a good excuse to get the HD air filter now lol.

 

[computeruser]

Wilhelm pretty much covered it. A different air duct shroud is used in the starter side with the new decomp location, too.

If your red top covers are in good shape, I'd be interested.

 

[Bearcub]

What You want is a "PS-7910 P&C Conversion kit"!
It will be a bolt on to Your PS-6400 and should include a fitting cylinder cover!

Take a look here:
http://performanceoutdoorequipment.com/products/cylinder-and-piston-kit-ps-7900-038130910

If power and longevity are Your goal for this upgrade then go OEM!

As You can see in my sig I own both, a PS-6400 and a PS-7900 - the difference in power is amazing!

Disregard the specs for the PS-7910, they are only relevant to that saw as a whole and will not reflect (negatively) on Your intended upgrade.
Specifically, the PS-7910 is choked down by a lower limited coil (12.800rpm instead of 13.500rpm) and the dreaded SLR/CAT muffler (the PS-6400's muffler is "empty" aside from the deflector/bird cage).
As these "features" are not present on Your PS-6400, upgrading her with a PS-7910 P&C conversion kit will technically speaking make her more of a PS-7900 then a PS-7910.

Unfortunately "Red Tops" are NLA in the US, so You'll either accept the black top, paint it red, or get a "Red Top" from Europe.
Alternatively You can try to adapt Your "Red Top" to the new cylinder (the DeCo valve hole position is most likely changed).

Good luck with Your upgrade and tell us how it went!

PLUS 1 on the go OEM plan

This is the route I took as well as a full on woods port job by Mastermind

The faster coil from the 6400 is a definite plus as stated above

It results in one hell of a strong running saw

Don't replace the 6400 side sticker and it's a total sleeper

 

[wde_1978]

PLUS 1 on the go OEM plan

This is the route I took as well as a full on woods port job by Mastermind

The faster coil from the 6400 is a definite plus as stated above

It results in one hell of a strong running saw

Don't replace the 6400 side sticker and it's a total sleeper

View attachment 501843

Nice stump vice!
Makes that poor excuse of a saw look good...

On a serious note, LIKE for the saw picture.

EDIT:
You might wanna consider small European spikes to make Your PS-6400 even more of a sleeper.

 

[heyduke]

i have installed both the nwp 84cc and the oem 7910 79cc. i prefer the oem though it costs a little more, especially if you need the plastic. the decomp valve has moved from the left side to the upper right side. with a little careful preparation and thought it should be possible to reuse the old plastic by either drilling or melting a hole thru it. if you decide to drill, you might want to find a specialized plastics bit. regular high speed bits tend to catch and crack plastics. i found that the new plastic, which was an oem part from my dealer, didn't fit very well. hope that's just a fluke.

the work to retrofit the new top end is pretty easy. to save time, leave the carburetor attached to the cylinder. i like to remove the muffler and handlebar. be sure to disconnect the impulse line from the barb on the cylinder before you try to loosen the cylinder bolt beneath it or you will need a new impulse line. there are some howtos here, easy to find. here's one that i started. it was my first, as i recall, and i did remove the carb before the cylinder but now i leave it on and bolt it up again before i reassemble the new top end. you have to scroll down a ways to get to the fotos because the originals were lost in a destructive hack a while back and i had to restore them.

http://www.arboristsite.com/community/threads/makita-dolmar-6400-big-bore-photos.244247/

 

[NJAdam]

Wilhelm pretty much covered it. A different air duct shroud is used in the starter side with the new decomp location, too.

If your red top covers are in good shape, I'd be interested.

There in pretty good shape. I want to hold on to them until after I get the new top end. I will let you know in a week or so.

i have installed both the nwp 84cc and the oem 7910 79cc. i prefer the oem though it costs a little more, especially if you need the plastic. the decomp valve has moved from the left side to the upper right side. with a little careful preparation and thought it should be possible to reuse the old plastic by either drilling or melting a hole thru it. if you decide to drill, you might want to find a specialized plastics bit. regular high speed bits tend to catch and crack plastics. i found that the new plastic, which was an oem part from my dealer, didn't fit very well. hope that's just a fluke.

the work to retrofit the new top end is pretty easy. to save time, leave the carburetor attached to the cylinder. i like to remove the muffler and handlebar. be sure to disconnect the impulse line from the barb on the cylinder before you try to loosen the cylinder bolt beneath it or you will need a new impulse line. there are some howtos here, easy to find. here's one that i started. it was my first, as i recall, and i did remove the carb before the cylinder but now i leave it on and bolt it up again before i reassemble the new top end. you have to scroll down a ways to get to the fotos because the originals were lost in a destructive hack a while back and i had to restore them.

http://www.arboristsite.com/community/threads/makita-dolmar-6400-big-bore-photos.244247/

Thanks for the info I'm sure it you saved me from replacing the impulse line at the minimum. Ill put a few pics up as I go.

 

[Bearcub]

Nice stump vice!
Makes that poor excuse of a saw look good...

On a serious note, LIKE for the saw picture.

EDIT:
You might wanna consider small European spikes to make Your PS-6400 even more of a sleeper.

Yeah, the stump vise was a present from my chainsaw addicted son

He is a fan of those orange and white saws.... I forget the brand

The funny thing is I have never run into another saw "nut" up here

Lots of wood cutters but none that are "saw hobbyists"

Just guys running saws as tools; so, they don't have a clue about high zoot ported saws, and stuff...

Poor deluded bastards....

The spikes stay

They work too damn well

 

[wde_1978]

i have installed both the nwp 84cc and the oem 7910 79cc. i prefer the oem though it costs a little more, especially if you need the plastic. the decomp valve has moved from the left side to the upper right side. with a little careful preparation and thought it should be possible to reuse the old plastic by either drilling or melting a hole thru it. if you decide to drill, you might want to find a specialized plastics bit. regular high speed bits tend to catch and crack plastics. i found that the new plastic, which was an oem part from my dealer, didn't fit very well. hope that's just a fluke.

the work to retrofit the new top end is pretty easy. to save time, leave the carburetor attached to the cylinder. i like to remove the muffler and handlebar. be sure to disconnect the impulse line from the barb on the cylinder before you try to loosen the cylinder bolt beneath it or you will need a new impulse line. there are some howtos here, easy to find. here's one that i started. it was my first, as i recall, and i did remove the carb before the cylinder but now i leave it on and bolt it up again before i reassemble the new top end. you have to scroll down a ways to get to the fotos because the originals were lost in a destructive hack a while back and i had to restore them.

http://www.arboristsite.com/community/threads/makita-dolmar-6400-big-bore-photos.244247/

Agreed:
- get yourself a piston ring compressor set (doesn't cost that much), it will make piston and cylinder joining much easier
- dump all the fuel
- remove starter assembly
- remove muffler and handle bar, I also removed the chain brake lever which gives a pretty nice access to the cylinder and joining surface
- remove fuel line from carb
- remove impulse line before cylinder disassembly
- remove and reassemble the cylinder WITH the carb attached to it, it will look more complicated but actually saves time and reduces frustrations
- before You reassemble the cylinder smear 2-stroke oil all over the piston and piston ring, considering You'll be taking off the current piston thoroughly oil the piston pin needle bearing with 2-stroke oil

Some piston and piston ring replacement pictures, piston ring compressor set with piston pin pusher and piston holder:


PS-6400 during disassembly/reassembly:

 

[heyduke]

Agreed:
- get yourself a piston ring compressor set (doesn't cost that much), it will make piston and cylinder joining much easier
- dump all the fuel
- remover starter assembly
- remove muffler and handle bar, I also removed the chain brake lever which gives a pretty nice access to the cylinder and joining surface
- remove fuel line from carb
- remove impulse line before cylinder disassembly
- remove and reassemble the cylinder WITH the carb attached to it, it will look more complicated but actually saves time and reduces frustrations
- before You reassemble the cylinder smear 2-stroke oil all over the piston and piston ring, considering You'll be taking off the current piston thoroughly oil the piston pin needle bearing with 2-stroke oil

Some piston and piston ring replacement pictures, piston ring compressor set with piston pin pusher and piston holder:
View attachment 501940 View attachment 501941

PS-6400 during disassembly/reassembly:
View attachment 501942 View attachment 501943 View attachment 501944

nice post wde,

dang, that thing is clean!

just two other things i can think of. there's a little piece of black "inner tube" rubber behind the carb. i pull that out with a needle-nose. after than, lift the back of the carb about a half an inch. that will pop a little white plastic ball gizmo out of it's socket and free the carb for removal. also, you don't have to remove the impulse line. just disconnect it from the barb on the cylinder and move the end of it out of the way of the torx wrench before you unscrew the bolt beneath it. during reassembly, just reach down with a needle-nose and reconnect it after the cylinder has been torqued down.

 

[wde_1978]

nice post wde,

dang, that thing is clean!

just two other things i can think of. there's a little piece of black "inner tube" rubber behind the carb. i pull that out with a needle-nose. after than, lift the back of the carb about a half an inch. that will pop a little white plastic ball gizmo out of it's socket and free the carb for removal. also, you don't have to remove the impulse line. just disconnect it from the barb on the cylinder and move the end of it out of the way of the torx wrench before you unscrew the bolt beneath it. during reassembly, just reach down with a needle-nose and reconnect it after the cylinder has been torqued down.

Thanks @heyduke , and I again agree with Your post.
When I disassembled my PS-6400 I wondered why I couldn't get the carb out, well it was still seated in that rubber mushroom thingy - it took a firm pull to get it out of there.
Also, You are correct, one doesn't need to entirely remove the impulse line, but rather just unplug it from the cylinder to allow access to the bolt underneath it!

Cheers

P.S.:
If by clean You mean my saw, well it wasn't until after I blew her off with high volume 6 bar compressed air at work.
By high volume I mean to point out that there is nothing I can do to make the pressure drop/spend the available air.
I don't own a compressor at home, nor do I disassemble my saws to clean them thoroughly, thus my PS-6400 was quite dirty with oily sawdust all over.
Also, the pictures of the PH & cylinder are from the assembly, meaning the cylinder got washed thoroughly with a brush and brake cleaner.

 

[NJAdam]

Ok I was ready to order the newest style oem P&C kit with that comes with the new top cover and before I did my friend told me baileys has old style dolmar 79cc piston kit made by mahle with the old style cylinder with the left side mounted decompression release. Does anyone know the differences if any? Or if one is better than the other for the old 6400. I'm just trying to measure twice and cut once if you know what I mean. From what I can figure one is a 7900 and the other is a 7910.

 

[heyduke]

Ok I was ready to order the newest style oem P&C kit with that comes with the new top cover and before I did my friend told me baileys has old style dolmar 79cc piston kit made by mahle with the old style cylinder with the left side mounted decompression release. Does anyone know the differences if any? Or if one is better than the other for the old 6400. I'm just trying to measure twice and cut once if you know what I mean. From what I can figure one is a 7900 and the other is a 7910.

i'd go with the older one. That's what i would have got last time if i had known about it. the 7910cylinder, if it has any differences, would likely be made to function better with the new scavenging tecnology. which your older saw doesn't have. i bought the new oem kit and wasn't really pleased with the fit of the new, right hand compression release plastics. both are mahle so that isn't an issue.

 

[NJAdam]

That's how I went. I appreciate the info. Btw 7910s are on amazon for $750 right now. Search Dolmar 79cc. I'm close to 700 into this 6400 lol. But I will have a 7900 when its done which makes me feel a little better.

 

[wde_1978]

Ok I was ready to order the newest style oem P&C kit with that comes with the new top cover and before I did my friend told me baileys has old style dolmar 79cc piston kit made by mahle with the old style cylinder with the left side mounted decompression release. Does anyone know the differences if any? Or if one is better than the other for the old 6400. I'm just trying to measure twice and cut once if you know what I mean. From what I can figure one is a 7900 and the other is a 7910.

If You have a choice go OEM PS-7900!
The PS-7910 conversion kits are being sold by Dolmar/Makita because they stopped making (and selling) the original PS-7900 kits.

I have a PS-7900 kit sitting in a box, waiting for its turn - hopefully not for a long long time!

The PS-7900 kit will bolt on better to Your PS-6400 than the PS-7910 one, or more precisely Your PS-6400's muffler will fit more seamlessly onto the PS-7900 kit as the PS-7910 kit features the SLR muffler port.

The listed PS-7900 I occasionally peak at is holding a firm 870 Euro.
For whatever reason the PS-7300 is listed at 50 Euro more.
Tough decision which one to buy if I where in the market for a new saw.

I never considered converting my PS-6400 into a PS-7900, I just bought a complete PS-7900 and now happily use both saws in turn or according to the work at hand.

 

[NJAdam]

Where did you find a 7900 for sale. I tried to find dealer websites outside the us and didn't have any luck. I did find a new Makita 7901 in Australia but its around 1500 American dollars.

 

[Babaganoosh]

I've got the 6421 makita. It's gonna get a 79cc conversion soon.

Any suggestions as to which kit I should get.

 

[cgraham1]

I've got the 6421 makita. It's gonna get a 79cc conversion soon.

Any suggestions as to which kit I should get.

OEM 7910.

 

[wde_1978]

Where did you find a 7900 for sale. I tried to find dealer websites outside the us and didn't have any luck. I did find a new Makita 7901 in Australia but its around 1500 American dollars.

Are You asking me?

At least two places still list Dolmar PS-7900 saws as available, they must be unsold leftovers - but I wouldn't see any issue purchasing one if I had the desire or need!
One place is a former main Dolmar distributor for Croatia, the other place is a small engines repair shop that also sells Dolmar and Makita.
I haven't called and asked whether it is outdated information on their websites as I don't intend to buy one of them at this point.
If desired I can PM You the links.

1500USD for a PS-7901???
Maybe I should buy all leftover PS-7900's and re-sell them!?

I've got the 6421 makita. It's gonna get a 79cc conversion soon.

Any suggestions as to which kit I should get.

OEM 7910.

Even though it has all been said in the posts above:
@fordf150 , http://performanceoutdoorequipment.com/products/cylinder-and-piston-kit-ps-7900-038130910