.404 chain on Dolmar 7900 BB? Also, bar questions

[Tempestv]

So I just got my new (to me) 7900, which the previous owner had modified with a ported big bore kit, bringing the displacement up to 85cc, and did a muffler mod. The saw came with an 8pin 3/8 sprocket, and I added an old 24" Oregon bar and chain I had kicking around for the time being, but I'd like to get a better quality bar of the same length.
I've never used .404 chain before, but it seems like this saw might have the power to benefit from it. What does everyone think? Is it worth trying, or should I stick with 3/8"?

Also what brands of bars would be worth looking at? I've used a couple Cannon bars that I liked, and I've been impressed so far with GB. I've also been hearing a lot of good things about the Sugihara bars, and the lightweight aspect is appealing. Any others I should be looking at?

 

[Adirondackstihl]

I wont comment on which bar to use but I will comment towards the chain........
Run the 3/8 !

 

[Ambull]

At a GTG we were racing Dolmar 166's in fairly big wood, and the saws that were running 3/8" chain were significantly faster than the saws running 404.

There really is no benefit to 404 that I know of.

 

[adam32]

If 3/8" is fast enough for racing, then it's fast enough for working...

 

[Swamp Yankee]

3/8 works for me.

When I run my PS7900 with a 28 inch bar, I use Stihl RSF chain 3/8 X .050 on a GB Titanium bar.

Take Care

 

[nmurph]

Why did a ported saw not already have a MM?

 

[Tempestv]

Why did a ported saw not already have a MM?

I'm not following your question- when I got the saw in the mail, it already had a MM, and a ported big bore kit. I don't know in which order this work was done, but I would assume the MM was done first.

 

[nstueve]

I'd get a 24in Total Super bar from a Tilton Dealer! They are super sexy on these saws and can be argued to be the best wearing bar out there for the money!

I haven't tried 404 but I do know it has more life/sharpenings in it compaired to 3/8, doesn't strech as much, and cuts almost as fast! Try a 404 and report back!

You might have to swap back to a 7pin if you run 404 though...

 

[mdavlee]

If you're in dirty stuff all the time .404" will last longer than the 3/8". I would go to a 7 pin for it since the 8 is around the same size as a 9 pin in 3/8".

 

[Tempestv]

I guess I'll stick with 3/8 chain
How much weight would I save by using one of the Sugihara bars?

 

[nmurph]

I'm not following your question- when I got the saw in the mail, it already had a MM, and a ported big bore kit. I don't know in which order this work was done, but I would assume the MM was done first.

I was reading it from my ph right bf I went into church!! Sorry, I can see it was already MM when you got it.

 

[kodiakyardboy]

I guess I'll stick with 3/8 chain
How much weight would I save by using one of the Sugihara bars?

You don't save much weight unless you're running a 20" or shorter Sugi but they are rumored to wear a long time and are really stiff. Some sort of Japanese super alloy or really good hardening process.

 

[SawTroll]

If you're in dirty stuff all the time .404" will last longer than the 3/8". .....

My brother tells me the same, but I'm not sure if he uses it on saws as small as 84cc, and most of his saws are very far from stock!

A stock BB kit (84cc) on a 7900 (or a 6400) will likely make less rather than more power than an OEM 7900 top end.

 

[Tempestv]

A stock BB kit (84cc) on a 7900 (or a 6400) will likely make less rather than more power than an OEM 7900 top end.

what's the reasoning behind that?

 

[deye223]

what's the reasoning behind that?

fact

 

[SawTroll]

what's the reasoning behind that?

fact

Mostly narrower transfers, as I remember it - so it takes a lot more work to make them perform really well.

Then there are the mods that is needed on intake and outlet + the carbs and mufflers, but that's more or less needed on any saw model that has reasonably decent transfers, if you want top notch performance.

Personally, most of my saws are stock, or very close to - but I have a very good source for modification info!

 

[MCW]

As somebody who has done a lot of comparos on 3/8" vs. .404" stick with 3/8".

.404" does have it's advantages as mentioned above and on a powerful saw .404" can cut just as quick in the cut (or quicker) while lasting a LOT longer between sharpening (especially in semi chisel).
I run a ported and pop upped 7900 that will have substantially more grunt than your saw and I would only ever run a 20" bar with .404" on it despite trying it up to a 32" bar (I have a Husky 3120 so have a few .404" bars to compare.
As also mentioned above a 7 tooth .404" rim has the same overall diameter as an 8 pin 3/8" rim so that works the saw even harder.
By all means have a crack at it but I'm 99% sure you'll end up running 3/8" chain.

Here is one of my 7900's with a 20" .404" Tsumura. I intended to keep using .404" on the 20" bar but the logistics of running a heap of saws, a heap of bar lengths, plus different pitch chains meant I whacked a 3/8" nose back on it to avoid any more confusion.

 

[nstueve]

what's the reasoning behind that?

the reasoning is that the 84cc BBK is a 79cc kit that is bored 2mm over stock. When you bore out a stock jug you MAY loose some of the port width but you definatly loose 1mm transfer depth on each side. IE: your transfers are slightly smaller and will take a smaller fuel charge than the 79cc kit... which in turn means less fuel to the top end.

I ran my stock bbk back to back with a 79cc OEM saw this last weekend and when all is stock you don't notice much at all difference in cutting speed or times. I actually suspect that if you were to do a little port work on the transfers to move some more fuel/air mix... You'd see more power than a stock 79cc kit. However most guys don't like using AM kits to do port work on due to sometimes inferior casting quality over a mahle OEM jug. I just got a mini mill so I am going to make a cant so Andy (ancy) and I can compair apples to apples and see which if either saw runs harder or faster.

In short: If you leave all else alone and are just swapping a bigger P&C on a 6400/6401... You are looking at spending $80-$90 more for the OEM kit which has a little better casting and negligible if any more power. If you start doing port work... it's a whole different story...

 

[Tempestv]

If you start doing port work... it's a whole different story...

what is the story with port work? The previous owner claimed he did some mild port work.
I haven't run it that much since I got it Tuesday night, but it's definitely powerful. On the other hand, the biggest saw I've run with anywhere close to the same bar length would be a 460, so that isn't much to go on.

 

[nstueve]

what is the story with port work? The previous owner claimed he did some mild port work.
I haven't run it that much since I got it Tuesday night, but it's definitely powerful. On the other hand, the biggest saw I've run with anywhere close to the same bar length would be a 460, so that isn't much to go on.

you'd have to pop the cylinder off to see what's been done. "mild port work" says to me than the PO cleaned up the intake and exhaust with no work on the transfers...

most guys that do professional port work won't grind a AM cylinder like the 84cc BBK. reason for that is the inferior casting. I don't know if i've seen someone do port work on a 6400 with bbk on it yet...???

I have the tools but not the knowledge to do port work on the BBK. i just installed mine without a base gasket to Decrease squish some for more compression. I could probably pop it off and do some intake and exhaust and clean the transfers up so they flow better and have more or same volume as the 79cc kit. I don't know how to measure the duration and blow down etc etc etc... You need to know how to use a degree wheel and where to add size on transfers, exhaust and intake to make the saw more powerful...

Maybe someone has done a pro port job on a AM bbk and writen about it but I haven't seent he thread if someone has...