Porting a JRed 670 (little help please)

[Huskyslinger]

Hello to all, new to this site, so I acquired a Jonsered 630 that came with a 670 top end. someone had started the work and give up, quit or was just a little in over their head. This is what I have so far;

Squish is .024"/.025"

Ex 102

Trans 123

In 74



The exhaust and transfer numbers were double checked by installing a ring in bore and pushing it up with piston to insure I was right on the money. So I have searched and searched, closest saw I came up with was a 268XP but the thread fizzles out before good hard numbers are given. I did find numbers for a 272 that are close but really would like someone that has a lot better working knowledge of this possibly give me a hand?



From what I can tell is that the transfers are going to have to go up to around 120 and intake needs to land somewhere around ??????????



Will post pictures of the build as it goes once I get the numbers.

 

[Dub11]

Welcome and side question do you have all the correct intake bits since the 630 used a block and the 670 used a boot?

And I'm no expert but 102 seems really off for intake. Most any saw wants to be around 75-80 iirc. Mayhaps @Stump Shot could chime in please.

 

[Stump Shot]

Welcome and side question do you have all the correct intake bits since the 630 used a block and the 670 used a boot?

And I'm no expert but 102 seems really off for intake. Most any saw wants to be around 75-80 iirc. Mayhaps @Stump Shot could chime in please.

You are correct about the intake numbers, something is off there.

 

[Pincher]

Even if 106 was duration, it would only be 53 intake.

 

[huskihl]

I think he read it in degrees after TDC. So 74* btdc.

 

[huskihl]

102 120 78 is pretty decent if you can raise the uppers

 

[Huskyslinger]

so yes on intake number it is 74 wasn't positive on which way it should be read. Yes I have all the parts to perform said swap. I am capable of cutting the uppers just wasn't sure how far.

 

[Stump Shot]

so yes on intake number it is 74 wasn't positive on which way it should be read. Yes I have all the parts to perform said swap. I am capable of cutting the uppers just wasn't sure how far.

78 is good and if you end up at 79 that will be fine too, grind as little as you can to achieve it and no more, the 670 has a large intake to begin with compared to all the other saw's on that chassis. So you do not need more area, it will be okay to match to your boot. Also try and find a 670 top cover and fit a 272xp muffler to get all the benefit from your efforts. I'd go with a winter filter on the intake even if a Husqvarna one from a 266/288. You can also upgrade to the new style 272xp clutch with modern C-springs in it for smoother performance.

 

[Huskyslinger]

So what bout shaving bottom of piston skirt on lathe? To get numbers. Than if it was no good i could throw in another piston.

 

[Huskyslinger]

So this has the westcoast filter set up on it. Also i bought a brand new 670 muffler and modded it. Will post pics later today

 

[Huskyslinger]

 

[Stump Shot]

So what bout shaving bottom of piston skirt on lathe? To get numbers. Than if it was no good i could throw in another piston.

Would need to make sure you don't end up free porting on the exhaust side.

 

[huskihl]

I like longer pistons. More stable in the bore. Pretty easy to draw a flat line at the intake floor using a piston upside down in the bore and grind to that

 

[Huskyslinger]

My spacer for cutting transfers

 

[Huskyslinger]

Got a bunch more pictures but taking too long to load. Have to do it tomorrow at work

 

[Huskyslinger]

 

[Huskyslinger]

 

[Huskyslinger]

 

[Huskyslinger]

 

[Huskyslinger]

so here is a few more pics. bored carb out to .750" as per another member.