Makita - Dolmar 6400 - big bore photos

[heyduke]

This NWP 84cc top end from Baileys was installed some time ago. I wasn't happy with it, 120 psi compression at first, squish clearance .036". I did it again without the base gasket and that got it up to 130 psi, squish at .021". The kit came with an odd ring, grooved, almost looks laminated. This is the latest attempt, rings from Husqvarna, a 385, I think, brought the compression up to 145 psi, warm, not broken in. I can live with that. I photographed the operation because I've recently seen posts with questions about this subject.

First, before sticking the torx driver into the machine screws that hold the cylinder, pull the impulse tube off its barb. If you don't, you'll need a new impulse tube.

OEM and Big Bore comparison, note the open transfer ports on the OEM (Mahle) cylinder and the thin cylinder walls on the big bore cylinder

 

[heyduke]

Makita - Dolmar 6400 - big bore photos - more

One reason I did this was to show how easy the Makita/Dolmar is to work on. It's a well designed machine.

Install the cylinder

now the carb

the muffler

 

[heyduke]

Makita - Dolmar 6400 - big bore photos - yet more

Measure squish, .021", mount starter, handlebar, spark plug, airfilter, plastic stuff. Did I forget anything?

Cut some cookies

fresh makita BB - YouTube

 

[w8ye]

I've worked on saws that were easier in the Anti-Vibration area but up around the cylinder and air cleaner/heavy duty air cleaner are good to work on. The oil pump area is a lot like a Husqvarna 372 except the Dolmar doesn't have a sleeve for the pump worm gear to ride on.

The Husqvarna 372 clutch tool works on the 6400/7900.

 

[heyduke]

I've worked on saws that were easier in the Anti-Vibration area but up around the cylinder and air cleaner/heavy duty air cleaner are good to work on. The oil pump area is a lot like a Husqvarna 372 except the Dolmar doesn't have a sleeve for the pump worm gear to ride on.

The Husqvarna 372 clutch tool works on the 6400/7900.

yes, i was looking at the husky clutch tool and thought it might work on the dolmar/makita. i haven't had to work on engine mounts yet. the oil pump is generous compared with my 272, can be a little messy but i like it. i'm wondering how to get the fly wheel off. probably won't ever have to do it.

 

[DexterDay]

You say 145 warm? Have you tested cold? Highest readings will be when cold? Not warm.

Other than that? Great write up and pics.mvery descriptive thread and lots of good stuff.

 

[procarbine2k1]

Keep that old cylinder handy. I sold mine, for a whopping 10 bucks. There are so many on the market, they just don't bring much. Worth tucking away for a backup/ rainy day.

 

[w8ye]

Speaking of which, I have a new take out 6400 P & C that was only run at the factory. Keeping it for a rainy day for my 7900's.

 

[heyduke]

You say 145 warm? Have you tested cold? Highest readings will be when cold? Not warm.

Other than that? Great write up and pics.mvery descriptive thread and lots of good stuff.

I tested the compression after running the saw intentionally. I think it's more realistic to test after warm-up, and after the oil I used for assembly is burned off. I'm hoping that compression will rise after the new ring is broken in. Also, I have no way of knowing how accurate my AutoZone compression gauge is. I think it reads a little low.

 

[heyduke]

Keep that old cylinder handy. I sold mine, for a whopping 10 bucks. There are so many on the market, they just don't bring much. Worth tucking away for a backup/ rainy day.

Speaking of which, I have a new take out 6400 P & C that was only run at the factory. Keeping it for a rainy day for my 7900's.

Yeah, I have two old 6400 top ends in my collection of old stuff. I used to save them up until I had a decent haul, then leave them for the homeless scavengers where I used to work. Now I guess I'll take them down to ACME metals myself.

 

[Kegonsa]

Sorry to bring it back from the dead, any way to get the pictures restored. Thank you

 

[heyduke]

Sorry to bring it back from the dead, any way to get the pictures restored. Thank you

no problem, i'll have to look around but i can find the jpegs. also, io'll bring the project up to date. this saw is a beast.

 

[heyduke]

Sorry to bring it back from the dead, any way to get the pictures restored. Thank you

as requested, i dug up the jpegs from this post, i suppose they were lost in the hack exploit a few months ago. i'll also try to remember my chain of thought, showing what i think is the "easy" way to do a top end on the makita 6401.

first thing, always disconnect the impulse hose from the cylinder before wrenching on the bolts that hold it down. if you don't, you'll be buying a new impulse hose which will be cut by the torx driver and head of the bolt under it.



then you can remove the cyllinder. it will look like this:



note that the boot, partition and hose are removed attached to the cylinder. it's much easier to deal with the hose clamp with the cylinder off.

here are two pictures showing the 64cc and 84cc cylinders. you will not the the stock 64cc is an open port type design while the big bore kit features closed ports.





here's the case with the new rings and cylinder installed:



again, mount the cylinder with the intake boot and impulse hose attached. then mount the carb.





and all the other stuff. this job was done to replace the aftermarket ring with a husqvarna ring of the same dimensions. i think it was a 385 ring. if you're doing this job, i'd recommend tossing the ring that comes with the big bore kit. also, i mentioned in the original post that i was dissatisfied with the compression of the big bore kit and that i could only get 130 psi out of it. what i didn't know is that at my altitude, 6000 feet, 130psi is excellent. after putting quite a few hours on the saw, the compression has improved to the point that i don't forget to use the compression release and it now measures over 140 psi at 6000 feet, takes a real hombre to drop start the thing. it makes good power and throws fat chips a long way. i hope these photos help. this is a nice saw to work on, takes less than half an hour to go from removing the bar and chain to removing the cylinder. let me know if you have any questions.

 

[cgraham1]

I prefer to put the carb on before I put it all together, and I remove the jug with the carb still attached too... I did a big bore on my old Makita and it was a very strong runner! It's the very same saw that Rich (Poleman) has been testing his modded Zama carbs on. They are similar in power to a stock 7900... and the split rings are not recommended, I believe you can get the BB kit from Weedeaterman with Caber rings.

 

[heyduke]

I prefer to put the carb on before I put it all together, and I remove the jug with the carb still attached too... I did a big bore on my old Makita and it was a very strong runner! It's the very same saw that Rich (Poleman) has been testing his modded Zama carbs on. They are similar in power to a stock 7900... and the split rings are not recommended, I believe you can get the BB kit from Weedeaterman with Caber rings.

what ever works best for you, different strokes... i remove the carb because i find it's easier to disconnect and reconnect the throttle cable and hoses, but i did think about doing it your way. as i said, i live at 6000ft and 140psi is probably close to 170psi at sea level. i really had a hard time doing the last compression check. i'm no gorilla but i'm not a pantywaste either. i usually drop start this saw, without the compression release. i've installed two of these big bore kits and have to say the makita/dolmar saws are well designed and a pleasure to wrench on.

 

[Kegonsa]

Thanks for the fast update. I bought a Dolmar 7900 and love it. I dont know a lot about the history of the saw, but the previous owner put a HD intake, muffler mod, and 85mm big bore. I think the oil pump drive gear is worn and stumbled upon this post looking for a compatible clutch tool that was not $30. Now I might have to look into the squish and compression with the possible ring upgrade. Thanks again

 

[heyduke]

Thanks for the fast update. I bought a Dolmar 7900 and love it. I dont know a lot about the history of the saw, but the previous owner put a HD intake, muffler mod, and 85mm big bore. I think the oil pump drive gear is worn and stumbled upon this post looking for a compatible clutch tool that was not $30. Now I might have to look into the squish and compression with the possible ring upgrade. Thanks again

sorry for asking but have you adjusted the oiler for max flow?

did you see this thread? http://www.arboristsite.com/community/threads/dolmar-makita-6400-6401-clutch-removal-tool.86916/

if you have a compression tester, it would be great to see what the saw is putting out. could you post it here?

 

[Kegonsa]

Thanks for the link, I did see that and liked the comment someone said about using a spark plug socket so you can get a wrench on it. unfortunately I do not have a good way to cut it, sawzall would drive me crazzy, so I ended up ordering the Husqvarna 372 clutch tool. I have also verified the oiler is up all the way. I will post the squish and compression on here, I am out of town next week so hopefully I can make time this weekend. As far as the compression test on a chainsaw do you test the saw dry or wet for compression? guess I could always use the search button.

 

[cgraham1]

I test the compression on a cold saw. Leave the switch in the "off" position, pull the choke lever and push it back in (opens the butterfly in the carb), then pull the rope repeatedly until the gauge stops moving.

I believe my 7900 was around 165 last time I checked it (1850 elevation), but I haven't checked since I got it back from Mastermind today.

Here's some interesting reading for you...

http://www.arboristsite.com/community/threads/dolmar-7900-carb-upgrade.229528/page-3

 

[heyduke]

Thanks for the link, I did see that and liked the comment someone said about using a spark plug socket so you can get a wrench on it. unfortunately I do not have a good way to cut it, sawzall would drive me crazzy, so I ended up ordering the Husqvarna 372 clutch tool. I have also verified the oiler is up all the way. I will post the squish and compression on here, I am out of town next week so hopefully I can make time this weekend. As far as the compression test on a chainsaw do you test the saw dry or wet for compression? guess I could always use the search button.

when cutting a socket to make a clutch tool, i usually use a bench grinder. a small grinder works best. that's what i use for a husky 272. haven't removed a clutch on a 372. i agree with cgraham1's comments re. compression testing, though i don't bother to open the throttle.