Chainsaw Repair

Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Dolmar Makita => Topic started by: KilliansRedLeo on June 18, 2014, 12:07:02 pm

Title: 7900 Muffler
Post by: KilliansRedLeo on June 18, 2014, 12:07:02 pm
Anyone know if later black top 7900s have a cat muffler?
Title: Re: 7900 Muffler
Post by: 660magnum on June 18, 2014, 12:35:32 pm
I bought a 6421 that was a 2010 model and it had a cat muffler. It came from the factory set rather rich as did my 2010 5105 that also had a cat muffler which I changed to a 5100 muffler.

I have a 2006 7900 and it had a regular muffler.

I immediately converted the 6421 to a OEM 7900 and put a regular muffler on it. Both my 7900's have the HD filter that I installed.

I stihl have these saws.
Title: Re: 7900 Muffler
Post by: Nathaniel Vansickle on June 18, 2014, 01:06:58 pm
7900-7910 don't have cat muffler. 7910 has SLR. 6400 has the cat
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 19, 2014, 07:35:06 am
Thanks 660 and Nate. I was wondering since the mufflers seem quite heavy compared to a Husqvarna or Stihl.
Title: Re: 7900 Muffler
Post by: Nathaniel Vansickle on June 19, 2014, 10:27:12 am
If it is a 7900 muffler don't spend to much time on a mm. It doesn't seem to help much. Enlarge the opening and that's it. I keep the spark screen in place. 7910 with the SLR crap and 6400 with cat muffler respond to gutting the mufflers or just swapping to the 7900 muffler. 
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 19, 2014, 11:06:54 am
Thanks Nate, did you get the package I sent?
Title: Re: 7900 Muffler
Post by: 660magnum on June 19, 2014, 11:21:18 am
Keep in mind that there is a difference in the mounting of the catalytic and regular muffler.

The difference that effect us is that the top bolt is a different length and so is the spacer that goes along with the bolt.

So if you order a muffler you need to get the correct bolt and spacer also.
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 19, 2014, 11:31:02 am
Thanks, Jim!
Title: Re: 7900 Muffler
Post by: Nathaniel Vansickle on June 19, 2014, 11:44:11 am
Thanks Nate, did you get the package I sent?

yes I did. thank you!!!!
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 19, 2014, 11:48:57 am
Found out that Hyway makes a replacement for the old 'windowed' 7900 piston. Ordered one and it came in today. Looks pretty nice, I will get pictures of it up a little later in the day.
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 19, 2014, 03:57:18 pm
Piston worked out great 165PSI with the metalized base gasket. Popped on the second pull ran on the third, blip the throttle idles at 25-2600, has a full tank that it has to idle on for a half hour. All in all the piston measured the same as the OEM one, I'm happy, now I can send this orange boy home!
Title: Re: 7900 Muffler
Post by: Nathaniel Vansickle on June 19, 2014, 07:43:53 pm
Where did you get the hyway piston? ebay? I just looked through my emails with VEC and they list a 7900 piston as well. so far for me they have been decent pistons.
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 19, 2014, 09:30:11 pm
I got it from a guy in Florida. They are also avilable from the guy on e-Bay from Greece!
Title: Re: 7900 Muffler
Post by: aclarke on June 20, 2014, 02:35:46 pm
FWIW, just received the piston/cylinder from Greece. Piston Is nicely cast and machined. Wrist pin bore is light press fit and circlip grooves are machined properly. Looks like the ring is 1.2mm

Cylinder is nice, no extraneous chrome plating in ports or squish. Minor chrome flaw in narrow bridge between the two transfers(both sides) looks like a pinhole.   A few of the oem Stihl ms460 cylinders (Brazil) I've had had similar flaws and were not an issue.
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 20, 2014, 03:19:17 pm
Adam, that's great! Did it come in a plain box or was it marked e.g. maker?
Title: Re: 7900 Muffler
Post by: aclarke on June 20, 2014, 05:02:24 pm
Tim, generic cardboard box,  very nicely packaged, box in box.  Not gonna port it, curious to see how it works stock. The Bailey's BB was a joke stock! Heavy piston and +.004 thousandth variation in squish from sloppy chrome job. Real pain to machine that irregular buildup from the squish band. Certainly not cost effective unless you have machine tools and then your still out set-up time. Real question in my eyes is if the AM is worth a chit as a bolt on... 
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 20, 2014, 05:18:24 pm
Looking forward to your report! Thanks Adam!
Title: Re: 7900 Muffler
Post by: aclarke on June 25, 2014, 11:24:48 pm
Ran the stock AM jug and piston for a 3-4 tanks last week at the yard bucking up wood in our dump pile. Ran great and after the 2nd/third tank it was noticeably more powerful. I'm not too keen on the Asian AM jugs and I feel this kit is superior. 

Couldn't resist and conservatively ported the cylinder. Widened out the transfers a small amount, widened intake(no lowering) and widened and raised the exhaust a small amount.  Ended up using an 046 piston and a 1MM spacer under the jug with thin paper on both sides. This combinations yielded .014 squish which is too tight. Milled the top of the piston to get 23-24 thou and ran it with a single ring.  Really peppy and still a ton of torque. Gonna run it in a stock appearing 5 cube gas race this coming weekend, let you know how it places. Adam
 
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 26, 2014, 08:15:18 am
Cool, I will order one up. You put this on a stock 7900 or a stroked saw? What attracted you to an 046 piston over stock? Good luck at the races! ;D
Title: Re: 7900 Muffler
Post by: adam32 on June 26, 2014, 09:16:59 am
Ran the stock AM jug and piston for a 3-4 tanks last week at the yard bucking up wood in our dump pile. Ran great and after the 2nd/third tank it was noticeably more powerful. I'm not too keen on the Asian AM jugs and I feel this kit is superior. 

Couldn't resist and conservatively ported the cylinder. Widened out the transfers a small amount, widened intake(no lowering) and widened and raised the exhaust a small amount.  Ended up using an 046 piston and a 1MM spacer under the jug with thin paper on both sides. This combinations yielded .014 squish which is too tight. Milled the top of the piston to get 23-24 thou and ran it with a single ring.  Really peppy and still a ton of torque. Gonna run it in a stock appearing 5 cube gas race this coming weekend, let you know how it places. Adam
 

Don't worry Adam...I'll post a video of my 372 spanking your 7900 for all to see...hahahahhahaha
Title: Re: 7900 Muffler
Post by: aclarke on June 26, 2014, 09:43:19 am
Thks!

046 piston has a wider skirt and compression height is lower than the 272 piston that is commonly used.  Looks to be about. 040 or so taller thank the stock piston
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 26, 2014, 09:50:35 am
OK, so it appears that the stock piston was too narrow in skirt width to allow for the widening of the ports? Is it the 272 or the 046 slug that is 0.040 taller?
Title: Re: 7900 Muffler
Post by: aclarke on June 26, 2014, 01:24:26 pm
Tim,
the 272 piston I placed next to the stock AM piston and the 046 piston was much taller and I didn't want to have to butcher the the base of the intake port to gain back intake timing from raising the jug too high to accommodate the 272 piston. I think this was a better compromise. I used a 1mm steel base gasket/spacer commonly found in the BB 7900 kits to accommodate the 1mm taller (longer stroke) 681 Solo. The AM piston that came in the kit is nice quality and would allow a little more port widening but I needed a little more width. The 046 piston can be used without mmodification if the 1mm spacer and a couple of base gaskets were used (one each side of steel spacer.

This 7900 is stock stroke.  The other Saw used a 3 mm stroker crank , 272 rod and 54mm AM piston/cylinder, made tons of torque and ran good until the crank twisted out of phase.  May have it trued and welded and re-visit that project later

I'll measure overall and compression heights later and get back to ya
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 26, 2014, 02:34:14 pm
Thanks Adam, do you happen to know which BBKs for the 7900 will contain the spacer?
Title: Re: 7900 Muffler
Post by: aclarke on June 26, 2014, 03:48:41 pm
NWP, perhaps they will sell it A la carte!     

Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 26, 2014, 04:35:24 pm
Already tried that, the mental midget on the phone couldn't spell NWP, I had to give them the stock number for the kit. Jerk said yes they come in the kit! I asked, do you not understand the English language twice once in English and once in Spanish. Still could not figure out what I wanted, I asked to speak to his/her supervisor....they hung up on me! Some guys have good luck with Bailey's I wouldn't go across the street to pizz on them if they were on fire!
Title: Re: 7900 Muffler
Post by: aclarke on June 26, 2014, 05:32:12 pm
Hahahahahaha, clowns like that certainly don't help their struggling business. Saw Shop here in town has about 3-4 counter people and 3 mechanics, only one who knows her stuff is Suzy, rest of the dudes are worthless as far as any ordering any parts.
Title: Re: 7900 Muffler
Post by: Nathaniel Vansickle on June 26, 2014, 06:00:04 pm
Good help is hard to find!
Title: Re: 7900 Muffler
Post by: adam32 on June 26, 2014, 09:25:28 pm
Hey Tim, give Madsens a call, they know their stuff.
Title: Re: 7900 Muffler
Post by: 660magnum on June 26, 2014, 10:18:57 pm
AFAIK all the 7900 BBK P&C kits from Baily's have the spacer. Or at least they used to.

The people are all different at Bailey's from what they used to be. They moved from Labonville or where ever in Northern California it was they used to be. The showroom and operatives are adjacent to the shipping warehouse near Sacramento now.
Title: Re: 7900 Muffler
Post by: aclarke on June 27, 2014, 03:11:15 pm
Had a few folks pm -about the Greek cyl kits.   As far as I know the DLA Store and Dandrikop (sp.?) sell the same Episan mfg pistons.  Not Not sure where they source the cylinders, but from past experience they are very nicely made and appeared to be from the same mfg.  Chrome is applied well and didn't flake off when I ported the cylinder


 Adam
Title: Re: 7900 Muffler
Post by: Cut4fun . on June 27, 2014, 03:15:15 pm
Adam post any links you know of to the greek stuff if you like.  Some folks just dont ebay search very well.   ;)
Title: Re: 7900 Muffler
Post by: aclarke on June 27, 2014, 03:29:58 pm
Kev,  Out in the field right now, I'll post some links this evening.

Thk

Adam
Title: Re: 7900 Muffler
Post by: KilliansRedLeo on June 27, 2014, 10:07:59 pm
Just ordered a P/C kit from Greece. The last 7900 piston I got from them came in a Hyway box.
Title: Re: 7900 Muffler
Post by: pete on June 29, 2014, 08:40:59 am
Thanks for the link I have had small bits and pieces from dandrikrop and think I read of a guarantee on p&c kits could be mistaken
Title: Re: 7900 Muffler
Post by: aclarke on June 30, 2014, 01:14:53 am
Ran the 7900 basic port/046 piston today in the 70-80cc gas stock appearing class and place 4th with a nice chain. Got smoked by two Really fast 7900's but had a great time and met a lot of really good people!!   

Adam Artzer placed 3 in gas hotsaw and 2nd open hotsaw 3120.   97 In the shade today!! Just got home, time for a cold beer and a good nights sleep!  Adam
Title: Re: 7900 Muffler
Post by: mdavlee . on June 30, 2014, 02:24:50 am
Sounds like a good weekend Adam.