Porting a JRed 670 (little help please)

[huskyslinger]

Hello to all, 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.

 

[Yotaismygame]

Those numbers look good. The intake is definitely not 106. Did you measure from top dead center? Intake is one from BDC but all you would do is take 180 total degrees minus your 106 = 74. I'd just cut a .020" pop up and widen. Add bridges, advance the timing. I'll have to look at my notes when I get home to see what the last 266 I did was. It's been awhile.

 

[huskyslinger]

I figured someone would correct my intake number! I wasn't sure but either way it came out the same on my end. how can I cut a .020" pop up if my squish is already at .024"? the cylinder has already been turned down.

 

[Yotaismygame]

Cut the piston and cylinder. I do machine work for a small fee. There is also AM pistons with small pop ups on them already. Maybe try the 74 intake before you grind it down. 76 sounds better too me though. If compression is pretty stout already then just widening, bridges, timing advance and maybe grind the intake down is all that's needed. I know those saws without a base gasket make pretty good compression as is. Just depends on what you want. 180psi or 200 plus? Are you planning to work the muffler? You'll want to match the muffler to the exhaust port after you grind it.

 

[Yotaismygame]

Could do a squish band cut but then you'll want to bring the exhaust back up a little which then will lengthen your blow down. I'd just do a pop up which will leave your numbers but gain some intake duration and compression.

 

[Yotaismygame]

Here’s the stock numbers I pulled.
107 123 70.5

Finished at 99 117 79. Decent saw, made 185 psi but didn’t wow me. I’d leave the intake higher. I say stick with the numbers you got, grind the intake down to 76 and widen the rest. If you want more compression cut a pop up or get another piston. I’ve only ported that one 266 and it was early in my “career”.

 

[huskyslinger]

So what bout shaving bottom of piston skirt on lathe? To get my numbers. Than if it didnt work i can throw in another piston.

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

 

[Yotaismygame]

Sure you could do that. I wouldn't even both with a lathe for that. Just hit it with some sand paper. Leave the exhaust skirt alone though. I'd be very surprised if 74 was better than 76

 

[huskyslinger]

 

[Yotaismygame]

No bridges? They definitely help with getting more transfer into the combustion chamber and with direction.

 

[huskyslinger]

where abouts did you put yours? how wide did you make them?

 

[Yotaismygame]

I use a sphere burr and make it roughly 1/4". I’ve seen deeper and bigger bridges by others but this saw came out real strong.

 

[huskyslinger]

what bits are you using for your transfers?

 

[Yotaismygame]

cone or football shaped. But i use a 90 degree hand piece.

 

[Yotaismygame]

 

[Yotaismygame]

Check out my Youtube channel that's in my signature. I try to give a lot of information on porting and tools being used. Wouldn't say I'm the greatest porter ever but I do a good job and because I'm newer to the game it helps with being relatable to others who are looking to learn.

 

[Ronie]

I put a 670 cylinder and carb on a white top 61. The numbers I used are close to what you have, 102-122-78, with a muffler mod and base gasket delete. WOT RPM ended up at 13,940. It's not going to win any races but it does pretty good. He's a couple of videos of it so you can see how mine ran with those numbers.

 

[Yotaismygame]

That runs pretty good! In that first video you can really hear the timing advance. How far did you go? Huskyslinger those videos make me think 76-78 on the intake will be best. Ronnies case compression looked pretty good at 78. If you have enough patients maybe try 76-77 first.

 

[Ronie]

That runs pretty good! In that first video you can really hear the timing advance. How far did you go? Huskyslinger those videos make me think 76-78 on the intake will be best. Ronnies case compression looked pretty good at 78. If you have enough patients maybe try 76-77 first.

Thanks, I didn't advance the timing. That breaking up sound was because it was a little rich in the first video. I leaned it out a little and it cleared up in the second one.

 

[North by Northwest]

Nice running saws guys . I was involved with Snowmobile engine porting back in the day . Quality tools go a long way with final product . Nice bridge work and furnishing . I have a 8 yr old 357 xp that the owners Son straight gassed . Buddy is woodporting it for me this summer when this pandemic settles down . Nice pics & video, s , keep up the great work !