Looking for guidance 670 (272) mild porting ideas

[weimedog]

I've been building mufflers for my work saws for a bit...now want to build a warmed over 630 J-Red/ Husqvarna 268 hybrid out of my pile of parts.(Husqvarna bottom end, top end, muffler & intake parts, J-red plastic, handle/tank) SO..here's the question:

IF you (you experts on the subject) were to suggest a path on a mild modification to the cylinder & piston what would it be?

What I have planned to this point is as follows:

Build a muffler with no baffles, two 5/8 tubes in the corners extending outside approx 1/2 inch and inside approx 1 inch. No internal baffles, and cut to match whatever the final exhaust port shape is.

Use a 272 top end, carb, intake horn, air filter etc.

Open a semi circular hole in rear of top cover just in front of the handle..approx 1" dia

Widen the exhaust to approx. .200 from the transfer ports inside & transition in the port so the top & bottom moved approx. .050 closer to their respective edges. Can't widen the exit side to side as there isn't anymore meat. So have to add x-sectional area up & down instead.

No base gasket & raise exhaust port approx the thickness of a base gasket. Same with the intake port, Also lower the bottom of the intake approx .025 & match the intake manifold while cleaning the intake tract out. Leave transfers alone & leave piston alone. (Chamfer all edges)

That's it....so? What should I really do to the cylinder? I'm basically clueless about saw porting


(PS I have a pile of larger diameter carbs from Homelites and stuff...ie from 1050's and the old 100plus cc gear drives that could be "blended")

 

[Danger Dan]

Read about the 272 jug swap, but never tried it. Sounds like a nice project though.
Ebayed a basket case 670 with modding intentions, but after putting it together it looked to good to mod...so I sold it.
Bet there's all kinds of info in here...do a search

 

[NWCS]

272 cylinder? the 670 is a 266 is i remember properly. if that fits it will be news to me, would love to see pics.

 

[weimedog]

My project ended up all 272. you are right....now trying to blend a closed port cylinder of some sort to a 61 next. And then a 630 blend of what ever I can conjure after that. The 630 case looks to be similar enough to the Husqvarna's to where parts should swap.

 

[weimedog]

 

[Farley9n]

272's Respond Nicely To

Some Mild Porting!
http://www.arboristsite.com/attachment.php?attachmentid=166687&d=1293901012 [/IMG]
.......( I'm just trying to get the hang of this new configuration )
This set is on a 61 and it's twin is on a 66. Both run very nicely!......Bob



looks like I need to pratice some more for the pictures to appear.....Sorry!

 

[Farley9n]

Here's The 66 (If I Can Learn To Post Pictures)

[/IMG]View attachment 166700View attachment 166701





Well I'm still in the corner with the pointy cap!......Bob

 

[trappermike]

Want some port specs for a 670 Jons. or similar saw? Here's some general specs,definitely not full race,but will add very good reliable power;
Build a good muffler-dual exit. For the cylinder raise the exhaust port 2mm,widen it 1mm each side.BE SURE to chamfer the top edge of the ex. port you just ground(a round file through the spark plug hole works if you don't have a special tool. Lower the intake port 2mm,and chamfer the bottom edge well,grind away any odd bumps in the port,finish it with fine emery roll,leave a fine "brushed" finish is best. You can polish the ex.port.You can also polish the piston crown,it will run cooler and not form carbon as quickly. Make a very thin cyl. gasket,5-6 thou thick,use sealer on both sides.Use a Bosch WS5F spark plug or equivalent.
The best thing you can do is bore the carb out. First it must be stripped completely,shafts and butterflies removed too. Clamp the carb in a drill press vise and carefully run a 3/4" drill bit through it,(Use "Rapid-Tap"for cutting oil,or otherwise some good lube.This mod is for Tillotson HS carbs common on most of those saws.Carb will run very well and produce substantially more power.The stock carb on most chainsaws is ridiculously small,so anything you do to increase it's size and you will be rewarded.I've bored 100's of them.
The end result is that compression is slightly lower than stock,but this means little,exhaust duration has a far more profound effect on power when you raise the port 2mm.
Do it carefully and correctly and you will have a powerful and reliable saw! Good luck.