Poulan Exhaust Port Advice Needed

[Chris-PA]

I picked up a saw I wanted to repair but it's a hopeless wreck, so I'm trying to salvage the engine. It's a bit rough but I think I will work OK. The saw was a PP315 49cc and I'll probably play with widening the exhaust port, but I'm not sure what to do with it. Like a lot of recent Poulans it has a steel thimble in the port. With that removed it leaves a 0.050" ridge all around the inner opening. I could remove it all but I didn't want to raise or lower the port, just widen it - but I don't want to leave that lip there either. Here's a (poor) picture of what the issue is:

The easy thing to do would be to just take off the ridge all the way around - will this mess up the timing too much? The ridge gets pretty low at the bottom center, so I was considering just removing it on the sides and bottom, but leaving the top intact.

Can anyone offer any recommendations?

 

[Hedgerow]

opcorn:

 

[barneyrb]

Not sure I'd take the ridge out on top or bottom. Top will lower the compression (by how much I don't know) and when you remove the bottom I think (don't know for sure) but that may "freeport" the piston.

 

[blsnelling]

Does no good to remove the steel insert if you leave the ridge, and you don't want to just grind out the ridge. You could end up free-porting the bottom or sides of the port or having way too much exhaust duration. There's a lot more homework to be done before you do anything. Go to the stickies and start learning about porting and degreeing the cylinder.

 

[Chris-PA]

Not sure I'd take the ridge out on top or bottom. Top will lower the compression (by how much I don't know) and when you remove the bottom I think (don't know for sure) but that may "freeport" the piston.

I'm not sure what freeport means - but I am concerned about moving those edges. There is a large curve to the lower edge, maybe if I just don't go below the original edge in the center. But then again they put the shape on it for a reason, and I don't know what it was......

 

[Chris-PA]

Does no good to remove the steel insert if you leave the ridge, and you don't want to just grind out the ridge. You could end up free-porting the bottom or sides of the port or having way too much exhaust duration. There's a lot more homework to be done before you do anything. Go to the stickies and start learning about porting and degreeing the cylinder.

Well I had no interest in messing with the timing at all, just wanted to widen it a bit. But I can't widen it with the insert in there. I suspect that ridge without the insert will be more restrictive than the whole insert would be.

Now I am considering beveling the back of the sides of the insert so I can widen the back of the port - blend it into the modified insert thimble.

 

[Mastermind]

Well I had no interest in messing with the timing at all, just wanted to widen it a bit. But I can't widen it with the insert in there. I suspect that ridge without the insert will be more restrictive than the whole insert would be.

Now I am considering beveling the back of the sides of the insert so I can widen the back of the port - blend it into the modified insert thimble.

Print off a degree wheel and figure out a way to mount it on the crank. A google search for free degree wheel will help you....

Then mount the wheel (I've even used a piece of rubber line to stick over the crank and a bolt). Check total duration by setting the wheel at zero when the piston is at the very top of the port (just cracking open)....turn the crank till the piston go down and back up to the same position.

That number, and the position of the piston relative to the port at BDC and TDC will tell you a lot about what you can do with the port shape.

 

[blsnelling]

Some guys purposely put a drop similar to that on the floor of the exhaust port. I wouldn't worry about it. Just make sure you don't go wider than the piston skirt.

 

[Chris-PA]

Here's what the piston looks like:

Here's where I ended up on the exhaust port:

I wanted to be quite conservative. I decided not to mess with the transfers, as this should flow much better than a slug piston already:

Now I just need to find something to put it in - my 2775 is still out of action as the parts are back ordered at eReplacementParts, so I guess I'll have to wait a bit. I need to look into doing a helicoil on two of the engine mounting bolts anyway - there are threads but not great, and these things have a tendency to loose mounting bolts as it is.

I'd really like to put it in a 141/142 - I think a ported, muffler modded 49cc 142 would be a hoot. But I don't have a scrap one and my 142 runs too well to mess with. I guess there will be a slight delay from here, but it does make a cool paperweight.

 

[Chris-PA]

Well, I did a little more work on the exhaust port, and decided to widen the intake a bit too. I tried to get some pictures, but they did not come out well enough to see much difference from the last ones I took. This is still a conservative porting job - I removed a fair amount of material and smoothed the port a lot (especially the exhaust), but the width is still only at 55% of the piston diameter. I'm going to quit there.

I also decided the ring needed replacing, so I bought a piston kit. It will be interesting to see if the one they supply me will have the cast cutouts or will be a solid slug. I only really need the ring, so if it's a slug I won't use the piston. Naturally it's backordered, as PP315's are not very common.

Here's another question: Which flywheel should I use?

The PP315 flywheel has the straight fins, while the newer 2775 one has the curved. I had planned on using the PP315 wheel until I noticed the fin difference. The weight is the same. I'm sure it doesn't really matter, but there's always a reason to use one or the other.

 

[Hedgerow]

Use the 2775 flywheel as long as the timing is right...

 

[Mastermind]

Just be sure the timing is the same on both flywheels.

You can advance the ignition timing about 1/4" CCW at the outside diameter of the flywheel. That wakes those little saws up a bit

 

[Chris-PA]

Thanks! I forgot to mention that the keyway and magnet positioning appears to be identical, but I want to verify that more accurately. What is the best way to advance the timing - modify the coil mounting?

 

[Mastermind]

Thanks! I forgot to mention that the keyway and magnet positioning appears to be identical, but I want to verify that more accurately. What is the best way to advance the timing - modify the coil mounting?

File the key inside the flywheel. Just go about .015 - .020 I like to check it on the outside edge of the flywheel.......about 1/4" of advance is all that you want. Be sure the flywheel moves counter clockwise.

 

[Hedgerow]

Thanks! I forgot to mention that the keyway and magnet positioning appears to be identical, but I want to verify that more accurately. What is the best way to advance the timing - modify the coil mounting?

Depends on the model... The best way I've found so far is to remove about a third of the key, and advance the flywheel. Though I have physically "moved" the coil... I have also had a moved coil get eaten by the flywheel cause it came loose... :msp_thumbdn:

 

[Chris-PA]

It turns out the two were not the same timing - the 2775 wheel is 0.090" more advanced at the edge, or 3deg. On the other hand there is about 3deg of slop in each, so I don't know if that is intentional or just production variation. I thinned the key on the 2775 wheel to get another 3deg, so the now the 2775 wheel is 6deg more advanced than the PP315 wheel. But then I never ran the PP315 and it's only 3deg advanced over the 46cc 2775 I know. Bah. I'll have to think a bit as to whether I'll go any farther. It would be hard to do too much with the coil, as I'd need a fairly large movement out there.

 

[Chris-PA]

Well, I got it back together and it runs! The piston kit I ordered from OrderTree never came in, but Sears coughed up a ring which was all I really needed. Out with the old, in with the older - 46cc on right, in perfect shape so it will be oiled and bagged:

Mildly ported 49cc engine installed:

Now it has a cool blue scoop:

Exhaust port:

New oil pump:

I used high strength hex head cap screws with blue Loktite, and helicoils at all four corners of the mounting bolts. I don't want to lose the mounting bolts again!

The timing was advanced about 3 degrees over the 46cc motor and 6 degrees over the PP315 49cc motor (which I never ran). I could see from looking in the intake port that the 46cc piston is a simple round slug type with just a relief in the skirt, unlike the 49cc piston.

It fired right up and sure seems to run nice no load and sounds nasty - I'm looking forward to running it in wood as soon as I can. I don't know the compression yet, as I only have one of those old press-in gauges with the tapered rubber tip, and it's hard to hold it in while pulling it!

 

[Hedgerow]

Just make sure you're running plenty of fuel through it for the first few tanks... Tune it again after a while, and do it when it's warm... I've found it's more accurate that way...
Looks like you're having fun...

 

[Bluefish]

Do you have a light source in the cylinder when you took those pics? They look great! Russ

 

[Chris-PA]

Just make sure you're running plenty of fuel through it for the first few tanks... Tune it again after a while, and do it when it's warm... I've found it's more accurate that way...
Looks like you're having fun...

Yup, I always keep and adjusting tool with me and I'll be cautious for a while. I'm hoping it holds together and that the ring seats properly.

Do you have a light source in the cylinder when you took those pics? They look great! Russ

The blue light is from the plutonium coating on the cylinder for extra power!

Actually it's just an LED flashlight shining in the bottom of the cylinder, and it didn't really look that blue. The o.ther ones were just flash on the shiny bits