dolmar 6400/7900 big bore kits. how are they holding up?

[Mac 6-10]

so I picked up a Makita 6421 while AS was down and the cylinder is alittle scored so replacement is in the near future. I have searched for an answer but everything is 3 years old and i'm not finding my answer.

how are these aftermarket kits holding up after the years on the 6400/7900 chassis? yes, I prefer the OE dolmar cylinder but at half the price for use on a firewood saw it is worth it to me to check.

thanks in advanced

 

[Mac 6-10]

No bad news then?

 

[gmax]

No problems with mine, talk to site sponsor "watsonr", he sells decent kits.

 

[shootingarts]

No bad news then?

I just scored a Makita 6401 so I'm very interested in this too. I read old complaints of poor quality castings and people unwilling to try to port the aftermarket cylinders, think I read that one porter was doing it without problems most of the time too. All stale information, I'm hoping somebody comes to your thread with current info from recent experience.

I think it is mostly the garbage factory chain, despite being the same saw, the 6400 is a pro saw and the 6401 is a homeowner saw. It doesn't feed into the wood well at all. Waiting to hear if the local Stihl dealer has a chain loop or two to let me see what I have stock. Then unless it really wakes up I'm thinking at least the 7900 P&C, some gentle porting and polishing, a little timing advance, and once I have the cubes up a muffler mod and the less restrictive air filter.

Probably little progress on mine other than chain until after the first of the year, a lot of funds dedicated to other things right now.

Hu

 

[nmurph]

...despite being the same saw, the 6400 is a pro saw and the 6401 is a homeowner saw...Hu

Huh, HU, how can the color of the dye in the plastic make that much difference?????

 

[jimdad07]

The 6400 and the 6401 are the same saw, just different colors. They are part for part the same machine. If you get the safety chain and you're used to non-safety then you won't be happy. Your Stihl dealer should be able to get you good chain. As far as the AM kits they are pretty decent, the casting issues are fixable for the most part. Just make sure that any edges that'll catch piston rings are smoothed out and they'll run just fine stock. The 7900 oem performs better than the am bb kit but the bb kit is pretty dam good. I haven't heard any complaints on their lifespan. If you run em right you should be fine.

 

[w8ye]

Not feeding into the wood is a chain problem.

I bought a new 6400 with a 24" bar, 3 or 4 years ago and the Windsor chain cutters were not finished on one side. I evened the chain up with the 511A grinder and it works OK.

I did a lot of reading on the Big Bore kits at the time and and went with OEM. At installation, the new 7900 started up like it had just been run the day before. I have not had any problems with the saw other than the bad chain from the factory.



Since making up the new 7900, I've purchased a 2006 era 7900 that I use more often but there is really no difference in the way they run. The 2006 one has been up dated with the AV limiter stop, the new style clutch, new style ignition gound, and rebuilt the oil pump and replaced all the rubber tubes of the oil pump, so both saws are alike.

 

[Mac 6-10]

I figured the OE 7900 would preform better but I bet at 113.99 and free shipping I won't be unhappy with my purchase.

 

[watsonr]

I've ran several on 6400-6421s and have recently put one on a saw for mill duty. The older versions were lower quality and compression, but the newer stuff is really good.

 

[remduck1]

I have built 4 of the BB saws on this platform and have been pleased with all of them performance wise. The last one was earlier this summer with a BB kit from Watsonr and it was by far the best quality of all the kits. That saw is being used weekly by a small firewood company and they have no complaints.

 

[watsonr]

I figured the OE 7900 would preform better but I bet at 113.99 and free shipping I won't be unhappy with my purchase.

Which kit was it?

 

[tjbier]

I put the 84cc BB kit on my 6401 and have not had one problem with it, I put my BB on 3+yrs ago and still going strong.
Starts every time and obviously a large performance gain for $110 and a few hrs time. Not an oem kit but I have no reason to bash it or go oem instead of the bb kit

 

[shootingarts]

Huh, HU, how can the color of the dye in the plastic make that much difference?????

Shhh, don't be saying nothing! I don't think I would have bought the "pro" saw with the original factory bar and chain still in good shape for $80. If my other mod's don't make it run to suit me plan "B" is a can of orange spray bomb, maybe even some Dolmar decals to fool the chainsaw!

Hu

 

[Mac 6-10]

Watsonr, I was looking at your WEM7900-H30640-B kit. You have the best price and I know you have the best service! Just have to get the OK from the wife.

 

[remduck1]

Watsonr, I think it was a class A kit.

 

[shootingarts]

The 6400 and the 6401 are the same saw, just different colors. They are part for part the same machine. If you get the safety chain and you're used to non-safety then you won't be happy. Your Stihl dealer should be able to get you good chain. As far as the AM kits they are pretty decent, the casting issues are fixable for the most part. Just make sure that any edges that'll catch piston rings are smoothed out and they'll run just fine stock. The 7900 oem performs better than the am bb kit but the bb kit is pretty dam good. I haven't heard any complaints on their lifespan. If you run em right you should be fine.

The local Stihl dealer about fifteen miles up the road was open till one today and I needed to go to the hardware nearby. A 72DL loop of RSC was $27.00, a couple dollars higher than I expected. Then they mentioned the second loop half price sale. Left with two loops for $44.00 including tax. That was more like I had in mind.

Went and tested on the same large pecan log right next to the factory chain cut from a day or two ago. This time the log seemed to melt from under the saw, rexactly what I had in mind! The saw ain't a monster cookie cutter by any means but it is definitely a working saw now.

Should keep me happy until I get in the mood to mod just for chuckles. I do have an itch to put the big P&C on it. The RS chain has a side benefit. One reason I went with it, can't loan out the saw with the RS on it to friends and family, too dangerous. I did save the safety chain for nasty work but I won't be mentioning that. I believe never loan out a tractor, chainsaw, or coon dog!

Hu

 

[WKEND LUMBERJAK]

I have had no problems with the BB kit I purchased from Watson R /Weedeaterman. I feel it runs as well as my 7900 seems to have a little more grunt. Casting was good to excellent.

 

[shootingarts]

I have had no problems with the BB kit I purchased from Watson R /Weedeaterman. I feel it runs as well as my 7900 seems to have a little more grunt. Casting was good to excellent.

Looks like he sells the black coated kit and the uncoated one too, unless there is another Weedeaterman out there. Did you buy the bare metal one or the black one?

Hu

 

[MCW]

There are a few versions of these kits on the market and quality does vary. Randy sells some good kits but I have seen some shockers over the years. It pays to buy from somebody who checks their kits prior to sale as I have seen some pretty average casting flaws in the combustion chambers on some of these kits (I still have a few in my shed that aren't saleable). They run well and are reliable but there is always a risk of getting a bad kit if you buy from somebody who doesn't inspect them prior to sale.
I had an intial batch of kits come in years ago that were absolutely perfect (like the one gmax has on his saw plus Andyshine, parrisw etc) and they have not missed a beat.
If money isn't a problem then go OEM but 99% of people will be happy with the BB kits.

 

[Trzebs13]

So I Installed a AM BB kit on my 6400 and and a little confused about 1 thing. It came with a thin metal gasket and a thick almost what I would call a spacer. Probably like .08" thick (guessing I did not measure) when I first put the cylinder on and rotated the flywheel, the top of the piston was coming about .08" from the bottom of the exaust port. So I put the spacer plate in and just some Gasket maker material on both sides. Now the top of the piston comes real close to the bottom of the exaust port. checked compression and it shows about 150psi I guess I'm ok with that but when I checked squish. It was a ton, in fact it didn't even dent the solder I was using.

Any help/advice would be appreciated