First Woods Port Attempt - Husky 372

[JohnnyBoy1986]

timing my ports? can that be described in more simplistic terms and an example or two maybe? I just want to be right with these junkers before i go hacking at my good 372 cylinder

 

[mdavlee]

I haven't altered the timing on any of mine except lowering the squish. I haven't measured any of them. I've not been touching the roof of the exhaust or anything like that.

 

[joesawer]

I haven't altered the timing on any of mine except lowering the squish. I haven't measured any of them. I've not been touching the roof of the exhaust or anything like that.

You altered the timing by lowering the cylinder.
Imo, There is more power to be had by good timing than by widening the ports and moving the timing the wrong way.

 

[joesawer]

timing my ports? can that be described in more simplistic terms and an example or two maybe? I just want to be right with these junkers before i go hacking at my good 372 cylinder

The piston opening and closing your ports at degrees of rotation is called your timing.
Google two stroke theory and two stroke power tuning and have fun.

 

[nanuk]

but as others have pointed out

it takes quite a bit of vertical to make a difference on the timing...

search for Snelling's info and he's got numbers...

 

[JohnnyBoy1986]

thanks for everyones input, i appreciate it all! i recently ordered a pencil grinder seeing as the dremel wasnt cutting it and a few other opinions seemed to favor this tool and the 9903 dremel carbide cutter. i'll get to work on the junkie cylinder, finish it out, post more pics and if we like what we see then i'll slam for the real deal

 

[AUSSIE1]

thanks for everyones input, i appreciate it all! i recently ordered a pencil grinder seeing as the dremel wasnt cutting it and a few other opinions seemed to favor this tool and the 9903 dremel carbide cutter. i'll get to work on the junkie cylinder, finish it out, post more pics and if we like what we see then i'll slam for the real deal

Those pencil grinders really look the goods if you have a compressor and the price is right.

The only issue I have with the Dremel is it's bulk and the chuck restricts depth.
It certainly removes material without a problem.

I have a bunch of bits but I've settled on that 9903 bit mostly as it gets ports nice and flat and straight and good in the corners.

Just a hint, spray WD40/CRC on your work occasionally to stop your bit from clogging. If you forget and it clogs, just spray on your job and it clears from the bit quickly.

 

[nanuk]

just so I'm getting this right....

Keep the floor, roof and walls as a straight shot to the cyl.

you don't want to see a bell like a trumpet, but more like a highway cone...
straight lines from muff to cylinder wall... except on the roof, you need a bit of curve at the cylinder wall...

am I correct on this?

 

[nanuk]

remember...

good to know, figured as much.
also do i take .075 - .100 towards the piston skirt horizontally? <-> (i would imagine so) and do i take .075 on EACH side of is that a measurement total? For one more i've heard different opinions on raising the exhaust port the thickness of the cylinder gasket... so should i or not? lol

the cylinder/piston my not be symetrical.... remove material only from the sides so that there is still some piston skirt to seal it up after...

the best I've seen that made sense to me...

put the piston on the rod, without rings, and place the cylinder on it... Now with a sharp pencil, trace the port (at the cylinder wall) onto the piston.
the piston will then tell you how much, and where you can remove it.

sometimes you can remove more from one side than the other!

 

[JohnnyBoy1986]

great thats exactly what i did on the first practice cylinder. thanks to all of you guys i think i am on a good track with this whole idea. everything sounds good to me, im just waiting on my pencil grinder and new carbide bit to try her out on junk cylinder #2 and then with a little approval, we'll get her done on the real jug! once again thanks for all your help and support so far

 

[troutfisher]

you want to widen the ports out to about .100 less than the piston skirt width.

on a 372? they are a full circle piston.

 

[mdavlee]

Yes but the skirt tapers to flat sides. They are not just a round circle on the skirt area. That usually will put you right in the neighbor hood of 65-70% of bore width.

 

[AUSSIE1]

Maybe not everybody's cup of tea, but this is how I do it.
The left side not done yet of course in the first pic.

I keep my walls and floor/roof pretty straight but I guess others could do things differently.
It has been mentioned that radiusing the side walls of the exhaust helps scavenge from the transfer sides of the cyl, but something I don't practice personally.
As Nanuk mentioned with the pencil and I grind the pencil down both sides with a curvature to one side. Also I don't think even then the pencil gets right in to the outside so make considerations for that also.

I also think that the inlet doesn't have to be opened as much as the exhaust keeping good velocity.

 

[joesawer]

it takes quite a bit of vertical to make a difference on the timing...

search for Snelling's info and he's got numbers...

A stock 372 has very conservative numbers to begin with. Imo moving them the wrong way but opening the port width is not a very effective way to get more power.
A lot of power can be gained just by improving the numbers and not widening them at all.

 

[Farley9n]

Here's mine....

Here's a peek at the lower transfers. Just got it together and running yesterday and am very pleased with it!.....Bob
http://www.arboristsite.com/attachment.php?attachmentid=124622&stc=1&d=1265730396

 

[blsnelling]

A stock 372 has very conservative numbers to begin with. Imo moving them the wrong way but opening the port width is not a very effective way to get more power.
A lot of power can be gained just by improving the numbers and not widening them at all.

My experience is that stock 372 numbers aren't far off. IMHO, widening the ports is more important than anything else. That's the basis for a woods port. Here's the stock port timing on a 372XP, just measured last week.

Exhaust 101
Transfers 122
Intake 75

However, squish was a huge .042", so removing the gasket brought it down to .025".

 

[blsnelling]

Here's a peek at the lower transfers. Just got it together and running yesterday and am very pleased with it!.....Bob

Here's a little tip for you. Lay your cylinder gasket on the cylinder base, mark it with a scribe, then port match the cylinder to the base using the scribed mark. This takes a lot of blending work, but is worth it.

At the same time, raise the cylinder wall at the transfer intake area up so that it's even with the cylinder base. Then add windows to the piston to look like a Stihl piston. Not only will it add flow, but it will help cool your piston crown.

 

[nanuk]

can you explain this further?

Here's a little tip for you. Lay your cylinder gasket on the cylinder base, mark it with a scribe, then port match the cylinder to the base using the scribed mark. This takes a lot of blending work, but is worth it.

do you mean on the case? or just the cylinder itself?

At the same time, raise the cylinder wall at the transfer intake area up so that it's even with the cylinder base. Then add windows to the piston to look like a Stihl piston. Not only will it add flow, but it will help cool your piston crown.

are you refering to the cylinder wall, just so it does not hang lower into the CrankCase? just even with the Gasket when the cylinder is seated on the case?

thanks.

 

[blsnelling]

Match the cylinder to the gasket. The case already is. You wouldn't want to grind on a case unless it was split and the crank and bearings out.

I'm borrowing some pics from Chevytown13s thread.

As you can see, you'll have to remove part of the cylinder "skirt" to fully port match the transfer intakes. That's fine. You'll be right at the edge of the piston skirt.

Also, raise the cylinder wall as in the cylinder on the right. You'll then have to round over the flat area, as has already been done in the pic above.

 

[dk27]

Then add windows to the piston to look like a Stihl piston. Not only will it add flow

Brad
If possible, could you explain how opening up the piston helps flow?
Thanks