Porting the 361 Big Bore

[blsnelling]

Ports look good.

That's good to hear considering it was the first time I really hacked on some transfers.

"Oh where oh where can my circlips be, oh where oh where can they be...."

 

[teacherman]

Brad, you are braver than I. I would like to someday play with a cylinder and piston, but I have no idea what to do. Maybe one of te older 026s can be turned into a hotsaw for practice purposes. Oh by the way, IMPRESSIVE WORK!

 

[Taxmantoo]

beautiful portwork by the way, that cant be easy, i have a hard enough time with intake port of a small block ford....

There's a tradeoff between vertical and horizontal balancing.
For example, let's take one extreme, where the crank is balanced by itself. When you hook up a piston to that crank, you will get a terrible vertical vibration.

Now let's take the other extreme, we'll counterweight the crank until the vertical shake is gone. Now we've got a horizontal shake that's as bad as the vertical shake was in the first example.

The way it works in real life is that the crank counterweights on a single cylinder engine partially balance the piston and connecting rod, striking a compromise between vertical and horizontal shake. If you make the piston lighter without changing anything else, all it does is lessen the vertical shake, no harm in that. If you take weight off both the piston and the counterweight, then both vertical and horizontal vibes go down a bit.

 

[blsnelling]

The bottom line is, it doesn't really matter on a chainsaw. Take a saw like the Dolmar 6400/7300/7900. They're all identical except piston size. Same crank, same everything. Just pistons of three different weights. IMHO, lighter is better when you're looking to turn more RPMs.

 

[timberwolf]

then both vertical and horizontal vibes go down a bit.

Horizantal will go down, but vertical will go up less than it would if piston was left alone, but still more than if the piston was lightened and crank left alone, This as the piston mass is not being fully offset. If the crank is lightened vertical can not be less unless the piston were lightened more than ~ twice that same amount.

I have put some big pistons on smaller saws and going 4-6mm over stock things get shaky. Noticable if you put the saw on a cement floor at idle and it will hop around like a rabbit on 3 cans of Redbull.

 

[FELLNORTH]

hey thanx guys

 

[scotclayshooter]

Awesome work, thanks for all the great tips. I was trying to figure out a way to check skirt clearance, never thought to mark on the piston itself..nice!

Also wasn't sure on the best way to guide/mark inside the cylinder, I tried a pencil, but that wasn't very precise, tape is a good idea too.

I also didn't think about the ring gap.

Any tips on or pics of the cutting tools you're using, looks like some sort of die grinder followed up with some needle files/hand work for smoothing?

Good stuff..

I thought this was a neat idea posted by Timberwolf using a stack of piston rings pushed in with the piston

Have you made up a port map? Thats about the easiest way to keep track of port heights.

As far as getting the height, I like to cut a notch in the center of the port to the height I want then work out to the sides. A stack of used rings can be pushed in with piston to give a reference line also.

 

[blsnelling]

I thought this was a neat idea posted by Timberwolf using a stack of piston rings pushed in with the piston

I didn't use a stack of rings, but I did use the piston to push one of the rings squarely into the bore to help me keep all the transfers square and even. Excellent tip Brian. Thanks.

 

[Wet1]

Yet another excellent writeup on porting Brad! Gotta bump this back TTT...

 

[blsnelling]

Thanks. I was hoping to get the circlip today but did not. I'm anxious to get it running. Instead I spent the day cleaning up my latest acquisition, a 041 Super to go with the 076 Super.

 

[Austin1]

The cylinder is done. This is the first time I did much work to the transfers. I hesitate to even show them. I don't really have the proper tools. I do not have a right-angle grinder. Instead, I had to use a cutoff wheel and a round semi-soft wheel about 1/4" thick. They're not pretty, but it's better than I was afraid they might be. I think they'll flow fine. Notice how I brought the rear transfer back towards the intake more.

How do you get the photo's to work out so good?
I have been up all night working on my 2152 and took some pic's and all I get is a silver blur I have two 100 watt light bulbs above my work bench plus the garage lights. But cant seem to figure out how to turn my flash off unless I go out during daylight I tried the macro setting as well.
Saw is all together but as luck would have it I am out of Oxygen for the torch so the Muffler will have to wait till Monday night.

 

[blsnelling]

I'm using a DSLR. Try backing up a little so that it can focus.

 

[Martinm210]

FYI,

Here is a good link someone pointed me toward.

This is a good couple of pages on cylinder mapping, only difference is we only have to work from the bottom and don't have as many ports to work with.

http://www.macdizzy.com/cylinder_map.htm

He does point out here when measuring port area, that it's not necessarily the opening along the cylinder wall that's important so much as the area of the port running along the channel:

http://www.macdizzy.com/cylinder_map2.htm

This would indicate the importance of opening back into the channels as best as we can.

Anyhow, I thought it was a pretty cool idea how he left the port map taped into a cylinder, then stuck the piston down in there and measured the port width at the angles they come in using the flaps of paper to simulate the angles.

The only bad part is that in the end he used software to do some calculations on the port areas to predict performance. I havn't searched very hard, but it would be great if there were some freeware tools for this to play with.

 

[Austin1]

I'm using a DSLR. Try backing up a little so that it can focus.

I am using a little pocket camera fuji 340, I found my manual so now I know how to turn the flash off as all the little syboils on the camera are worn off. I had wanted to show how easy the transfers were to get at on this saw, it's the same as my 2159.I was able to take pics of things that were dull in colour but taking pics of metallic shiny objects were impossible

 

[Martinm210]

I am using a little pocket camera fuji 340, I found my manual so now I know how to turn the flash off as all the little syboils on the camera are worn off. I had wanted to show how easy the transfers were to get at on this saw, it's the same as my 2159.I was able to take pics of things that were dull in colour but taking pics of metallic shiny objects were impossible

Yeah, uou just need to stick some sort of bright light to light everything up consistently. It's dynamic range that you're fighting. A camera can only capture something on the order of 5 stops worth of dynamic range, when the visible eye can see up to 12 stops worth (completely black to white). This is why people use flash in bright outdoor conditions, it's to fill in the dark spots the camera has trouble capturing.

In the case of macro or close up type shot. Shiny objects are always tricky, but even more of a problem is the flash. Most cameras struggle metering flash appropriately for anything closer than a few feet away, and shiny objects are just simply hard to avoid overexposure on with flash.

A DSLR and using a raw program to correct for overexposure can usually help with this. It gives you about a 1 stop cushion to capture information either way that would otherwise be lost.

Anyhow good stuff here on the porting, some great general guidlines.

 

[parrisw]

Yeah, uou just need to stick some sort of bright light to light everything up consistently. It's dynamic range that you're fighting. A camera can only capture something on the order of 5 stops worth of dynamic range, when the visible eye can see up to 12 stops worth (completely black to white). This is why people use flash in bright outdoor conditions, it's to fill in the dark spots the camera has trouble capturing.

In the case of macro or close up type shot. Shiny objects are always tricky, but even more of a problem is the flash. Most cameras struggle metering flash appropriately for anything closer than a few feet away, and shiny objects are just simply hard to avoid overexposure on with flash.

A DSLR and using a raw program to correct for overexposure can usually help with this. It gives you about a 1 stop cushion to capture information either way that would otherwise be lost.

Anyhow good stuff here on the porting, some great general guidlines.

Good write up. This is what makes these good to have. But are kinda spendy.

 

[blsnelling]

I would so love to have a ring flash!!!!!!!!!!!!!!!

 

[parrisw]

I would so love to have a ring flash!!!!!!!!!!!!!!!

Yup, they sure are nice. But then you need a nice Macro lens to go with it, which is also kinda spendy!!!! I've already got too much invested into my DSLR, ahhh, whats another $1000

 

[blsnelling]

I take 99.9% of my pics with a 24-105L IS lens. That's 90% of the picture quality right there. Good light is always a challenge. I really should get a good macro lens for all the closeup shots I'm always taking. The big DSLR sensor fights you though with a much more shallow field of view. A guy really needs to use a tripod and small aperature to get good pics of the work we do.

 

[Urbicide]

How do you get the photo's to work out so good?
I have been up all night working on my 2152 and took some pic's and all I get is a silver blur I have two 100 watt light bulbs above my work bench plus the garage lights. But cant seem to figure out how to turn my flash off unless I go out during daylight I tried the macro setting as well.
Saw is all together but as luck would have it I am out of Oxygen for the torch so the Muffler will have to wait till Monday night.

How about a piece of electrical tape over the flash?