Question for the Dolmar folks

[wde_1978]

I have sold probably 100 cylinder kits in the last year or 2 and none of them have come with a base gasket so not sure which gasket you ended up with. 957531160 is the base gasket for the 7910 and it is a steel gasket with rubber coating??? and it is .013"/.33mm thick.

My Dolmar PS-6400 had a "soft" factory base gasket, the OEM replacement gasket is steel coated in graphite or something like that.
It is definitely steel though, it kept getting attracted by the flywheel magnet upon assembly!

...you cant go gasketless with the OEM kits. with the base gasket you still only end up around .025" squish

I checked squish with and without the OEM replacement gasket on my Dolmar PS-6400 - I didn't feel comfortable deleting the gasket.
I am not sure where squish ended up, but I still have the solder pieces and could re-measure them if desired.

I re-used my factory cylinder with a AM piston that measures the same from piston pin to piston crown as does the factory piston.

 

[HandLogger]

the cat muffler needs gutted if installing it on a 7900/7910. Personally, all i do is uncrimp it, remove the cat plate and the spacer plate, remove the bird cage baffle and put it back together. stock size outlet is plenty big for my taste and i leave the screen in every muffler i do. This minimal approach IMHO gives them plenty of room to breathe and they are quiet enough to use even in city settings plus it retains the factory spark arrester screen.

muffler modding a 7900 or 7910 muffler is a different story. i enlarge the outlet on those muffler because for some reason they are smaller than the 6400 cat muffler.

its personal preference but i like to use the 6400 cat muffler over a 7900 muffler. It seems to be a better made/thicker/heavier muffler and it has the reinforcement bracket on the front of it which eliminates some of the cracked muffler problems that the 7900's had.

When one our MS200Ts became impossible to adjust, we replaced the carb with a ZAMA unit -- works great. When we need plugs, filters, bars and chains, we change them in the field. When it gets much heavier than that, we have a mechanic in town who services our equipment. We are not saw mechanics, so please excuse some of the questions that may seem basic to a saw doctor.

Nate: Given the fact that the saw that inspired this thread is an ex-rental Makita DCS 6421, the plan is to purchase anything needed to increase the displacement to Dolmar 7910 spec's. I've seen the OEM PS-7900 038130910 Cylinder and Piston Kit on the POE website, so I'm assuming that this -- and the proper gasket -- will do the trick when it comes to the top end work. I'm also assuming that the DCS 6421 being modified has the "cat muffler" you wrote about (above), so the first paragraph (above) seems to apply to our situation. Is that correct? In other words, are you saying that the muffler on the DCS 6421 needs to be gutted in order to get the most out of the new OEM PS-7900 top end? I'd also really appreciate it if you would clarify which gasket we will need for this particular situation. By the way, it is our intention to order from you.

Thanks for input, learning a lot, so please keep 'em coming...

 

[fordf150]

When one our MS200Ts became impossible to adjust, we replaced the carb with a ZAMA unit -- works great. When we need plugs, filters, bars and chains, we change them in the field. When it gets much heavier than that, we have a mechanic in town who services our equipment. We are not saw mechanics, so please excuse some of the questions that may seem basic to a saw doctor.

Nate: Given the fact that the saw that inspired this thread is an ex-rental Makita DCS 6421, the plan is to purchase anything needed to increase the displacement to Dolmar 7910 spec's. I've seen the OEM PS-7900 038130910 Cylinder and Piston Kit on the POE website, so I'm assuming that this -- and the proper gasket -- will do the trick when it comes to the top end work. I'm also assuming that the DCS 6421 being modified has the "cat muffler" you wrote about (above), so the first paragraph (above) seems to apply to our situation. Is that correct? In other words, are you saying that the muffler on the DCS 6421 needs to be gutted in order to get the most out of the new OEM PS-7900 top end? I'd also really appreciate it if you would clarify which gasket we will need for this particular situation. By the way, it is our intention to order from you.

Thanks for input, learning a lot, so please keep 'em coming...

Yes the 6421 muffler is a cat and i wouldnt put a 7900 cylinder on without gutting it. To much heat and restriction for my liking. They are pretty easy to uncrimp but almost require 2 people to do them in a timely manner.

038130910 cylinder kit and 957531160 base gasket is all you will need. check over the A/V springs, specifically the upper one from wrap handle to cylinder to make sure they arent bent. Carb is the same from the 6400 to the 7910 and will just need tuned to match the larger displacement.

 

[fordf150]

How do you get them uncrimped? Maybe a pic of the tools that you use and the general process?

I use a propane torch and a screwdriver. Two people make it super easy.

cutting torch with a screwdriver for me. and 2 people is the difference between it taking 15 minutes, start to finish, or 1 person spending an hour to do it.

 

[heyduke]

Yes the 6421 muffler is a cat and i wouldnt put a 7900 cylinder on without gutting it. To much heat and restriction for my liking. They are pretty easy to uncrimp but almost require 2 people to do them in a timely manner.

038130910 cylinder kit and 957531160 base gasket is all you will need. check over the A/V springs, specifically the upper one from wrap handle to cylinder to make sure they arent bent. Carb is the same from the 6400 to the 7910 and will just need tuned to match the larger displacement.

nate-

i'm a little confused. what is the current 79cc model. is it the 7910? does the current model use a cat like the 6421? the domar web site isn't very useful.

thanks

 

[7sleeper]

NO the 7910 has the SLR system, where exhaust ist returned into the cylinder to be reburnt.

7

 

[fordf150]

7900 with NO support bracket is a standard bird cage baffle muffler
6400 with front support bracket is a CAT muffler
7910 muffler with front support bracket is SLR

 

[Poleman]

Yep...no matter what the process the in sides (cat-SLR) need to be removed to from the mufflers. The Cat for flow and heat and the SLR because of the severe restrictions it has. Like Nate said...if you have a good torch and a friend to help its a lot faster...if not its a lot slower. I only have a propane torch and that is marginal for heat required to heat the three layers of SS on the Cat muffler.
A definite retune will be required as the saws will breath a lot better and be happier.

The saws don't need the carb modded but it sure helps with the bottom end power. I've found the 6400 series have a slightly smaller jet configuration and the 7910 to have larger that 7900. The hot carb is the ZAMA 18 off the 7910's, it's main is bigger than the 7900. All are GOOD usable carbs so don't think you need to change anything.

 

[wde_1978]

For reference, non CAT/SLR muffler off the Dolmar's PS-6400/7300/7900!

Stock, regular steel, un- and re-crimped "cold":


After a humble "flow" treatment:


I wanted to keep the cage in order to prevent excessive heat buildup of the mufflers front half.
I also aimed to retain the stock spark screen which turned out quite nice.

This modded muffler is on my Dolmar PS-7900 and it sounds great at WOT under load!

 

[HandLogger]

Two more questions for the Dolmar Folks:

What type of 20-inch bar and chain would you recommend for a modded Makita DCS 6421?

Does anyone have any idea where one might be able to get the plastic/cosmetic pieces for a Makita DCS 6421?

 

[wde_1978]

Two more questions for the Dolmar Folks:

What type of 20-inch bar and chain would you recommend for a modded Makita DCS 6421?

Does anyone have any idea where one might be able to get the plastic/cosmetic pieces for a Makita DCS 6421?

I use OEM Dolmar (Oregon) 20" bars, though I do have one AM bar as well.
The OEM Dolmar (Oregon) bars are very good quality if looked after, as for the AM bar I have yet to see how it will hold up!
Both OEM and AM that I use/have are laminate, non lightweight and non replaceable nose sprocket bars.
I wouldn't worry about the nose sprocket, my Dolmar PS-6400 is still on her factory bar and going strong at 10 years age.
I think my Dolmar PS-6400 & PS-7900 handle nicely with a 20" B&C setup!

For Makita colored covers and parts try Nate @fordf150 , just keep in mind he said he needs to order Makita parts as he doesn't stock them yet!

 

[SteveSS]

Two more questions for the Dolmar Folks:

What type of 20-inch bar and chain would you recommend for a modded Makita DCS 6421?

Does anyone have any idea where one might be able to get the plastic/cosmetic pieces for a Makita DCS 6421?

Have you bought the saw yet? Around here, once they get put on the shelf for sale to the public, they don't last very long.

You can get replacement top covers in black from Nate to replace the ugly grey covers that come stock on them. Normally that's all you'll need to spiff them back up along with a good cleaning. I posted pics of mine in this thread with the matte black top covers.

I wouldn't be surprised if that saw is long gone by now though.

 

[heyduke]

Two more questions for the Dolmar Folks:

What type of 20-inch bar and chain would you recommend for a modded Makita DCS 6421?

Does anyone have any idea where one might be able to get the plastic/cosmetic pieces for a Makita DCS 6421?

you can find a selection of bars and chains at http://www.baileysonline.com/, though i recommend you use a "burner" debit card. 20" bars seem to be the universal norm, long enuff so you're not doing stoop labor and short enuff that you can keep the nose out of the dirt. a professional, not low kickback, chisel or semi-chisel chainis are what you want.

so are you going to keep this in a display case, on the mantel or hang it on the wall in the living room. or just maybe you're going to take it out in your truck and cut some wood. if you do very much of that you're both, you and the saw, going to get beat up and dinged. if that's a problem, aspirin and cosmetic surgery for you and parts from nate or makita direct 866 597 3850 they have a web site too.

 

[HandLogger]

If you go back to the original post, you'll read that the saw isn't mine...but, yes, it was purchased the day after this thread was started. As it's not my saw, I really can't say exactly what it will be used for, but one thing is clear: the folks at the box store etched store data into the plastics -- which I mentioned in another previous post -- and it looks like [quoting previous post] "...something our dog leaves on the lawn."

I've read tons of discussion on open forums about bar and chain combinations for different saws. Once again, as per the original post, we own and manage forest land using Stihl equipment. The point being that we have our favorite saw/bar/chain combinations and there's only a 3 or 4 of us using the saws...I've never owned a Makita/Dolmar saw...Was there something unusual about the questions?

This is an open forum, right? Aren't questions part of the process? Please try to relax and have a good one.

Any and all productive posts are appreciated and will be well received. Thank you.

 

[heyduke]

If you go back to the original post, you'll read that the saw isn't mine...but, yes, it was purchased the day after this thread was started. As it's not my saw, I really can't say exactly what it will be used for, but one thing is clear: the folks at the box store etched store data into the plastics -- which I mentioned in another previous post -- and it looks like [quoting previous post] "...something our dog leaves on the lawn."

I've read tons of discussion on open forums about bar and chain combinations for different saws. Once again, as per the original post, we own and manage forest land using Stihl equipment. The point being that we have our favorite saw/bar/chain combinations and there's only a 3 or 4 of us using the saws...I've never owned a Makita/Dolmar saw...Was there something unusual about the questions?

This is an open forum, right? Aren't questions part of the process? Please try to relax and have a good one.

Any and all productive posts are appreciated and will be well received. Thank you.

Just trying to be helpful. Actually the bar that comes with the rentals is really good. You shouldn't need another. But if you do Baileys is where I usually go. Likewise makita direct. I'll stand by the rest. A few days of honest labor and that home depot grafitti will be "buffed" out. Wear your scars proudly.

peace

 

[7sleeper]

Tsumura or Sugi hara are the choices for replacement bars. About the best money can buy!

7