Chris-PA
Where the Wild Things Are
I did a thread some time ago when I first built this saw (http://www.arboristsite.com/community/threads/building-a-42cc-poulan.231308/), but the pictures are gone now. So is the engine that ended up in it, as it was really a rat and I kept playing with it until I eventually wrecked it. It's been on a shelf for a while, and I finally found part of a used 2001 PP260 saw on eBay with a good engine (well, other than being terribly carboned up). So I thought I'd take some pictures. I'll be trying to combine the best parts as I build it.
This is a 2001 engine, which is different than the final engines they installed before they went strato. This is a shot of the 2001 engine (left) and a 2004 model:
![IMG_6113-800.jpg IMG_6113-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50627-75084cc39911bb7e5afd14fecb93c585.jpg)
The transfers have larger volume and different shrouding at the bottom. The 2004 also has less aggressive timing, smaller ports and the exhaust does not have the steel insert. It also has a cat muffler. Here is the timing map I made of the stock timing:
![42ccPoulanStockTiming.png 42ccPoulanStockTiming.png](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50628-ad5db68df9eafd08668d4d9b51ad0ce9.jpg)
Unfortunately these engines have a large (0.040") squish, probably so couch potatoes don't overexert themselves trying to start it. Since I don't have the means to weld a pop up, I just have to live with it. It means I will not be raising the exhaust, but then 155 is plenty anyway. The intake duration is small, and the case compression angle is too large - I would like it to be around 40deg.
I have had issues increasing the intake on these because of the location of the impulse port right below the intake, and I've made saddle shaped ports and such, but here I decided to just widen the intake, and flatten the lower edge (based on Mastermind's recent comments), and to increase the duration by notching the piston skirt. So both intake and exhaust got widened to 55%, but not intentionally changed in timing. Intake:
![IMG_6130-800.jpg IMG_6130-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50629-b8dcc7a50b4588b1be457c34550d24e3.jpg)
![IMG_6126-800.jpg IMG_6126-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50631-5d6342207ba95512e4599f2055949328.jpg)
Exhaust:
![IMG_6132-800.jpg IMG_6132-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50632-498191667d79cdd764d2fb844acc6560.jpg)
![IMG_6122-800.jpg IMG_6122-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50630-c13058c826a57da1fe4b3bcb759e9d69.jpg)
Then I worked on the piston. I wanted to reduce the blow down to 20deg, but I've never been able to grind the transfers properly. Given the large squish, I decided to try a small bevel on the top of the piston:
![IMG_6133-800.jpg IMG_6133-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50633-0b62fe986d1cbdfd240ffa959d30804c.jpg)
Then I notched the skirt for the intake:
![IMG_6135-800.jpg IMG_6135-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50634-925b12b9e8e099ec53d735cb3673c6cc.jpg)
![IMG_6139-800.jpg IMG_6139-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50635-42dfbe95d25d000b74b5e84e7ad4d93e.jpg)
I had a really clean crank and bottom cap from the 2004 engine, so I used that. The later cap has a groove cast in for better sealing.
![IMG_6140-800.jpg IMG_6140-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50636-1455f2ec5b0005adfefa961926ea8b67.jpg)
This is a 2001 engine, which is different than the final engines they installed before they went strato. This is a shot of the 2001 engine (left) and a 2004 model:
![IMG_6113-800.jpg IMG_6113-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50627-75084cc39911bb7e5afd14fecb93c585.jpg)
The transfers have larger volume and different shrouding at the bottom. The 2004 also has less aggressive timing, smaller ports and the exhaust does not have the steel insert. It also has a cat muffler. Here is the timing map I made of the stock timing:
![42ccPoulanStockTiming.png 42ccPoulanStockTiming.png](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50628-ad5db68df9eafd08668d4d9b51ad0ce9.jpg)
Unfortunately these engines have a large (0.040") squish, probably so couch potatoes don't overexert themselves trying to start it. Since I don't have the means to weld a pop up, I just have to live with it. It means I will not be raising the exhaust, but then 155 is plenty anyway. The intake duration is small, and the case compression angle is too large - I would like it to be around 40deg.
I have had issues increasing the intake on these because of the location of the impulse port right below the intake, and I've made saddle shaped ports and such, but here I decided to just widen the intake, and flatten the lower edge (based on Mastermind's recent comments), and to increase the duration by notching the piston skirt. So both intake and exhaust got widened to 55%, but not intentionally changed in timing. Intake:
![IMG_6130-800.jpg IMG_6130-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50629-b8dcc7a50b4588b1be457c34550d24e3.jpg)
![IMG_6126-800.jpg IMG_6126-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50631-5d6342207ba95512e4599f2055949328.jpg)
Exhaust:
![IMG_6132-800.jpg IMG_6132-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50632-498191667d79cdd764d2fb844acc6560.jpg)
![IMG_6122-800.jpg IMG_6122-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50630-c13058c826a57da1fe4b3bcb759e9d69.jpg)
Then I worked on the piston. I wanted to reduce the blow down to 20deg, but I've never been able to grind the transfers properly. Given the large squish, I decided to try a small bevel on the top of the piston:
![IMG_6133-800.jpg IMG_6133-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50633-0b62fe986d1cbdfd240ffa959d30804c.jpg)
Then I notched the skirt for the intake:
![IMG_6135-800.jpg IMG_6135-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50634-925b12b9e8e099ec53d735cb3673c6cc.jpg)
![IMG_6139-800.jpg IMG_6139-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50635-42dfbe95d25d000b74b5e84e7ad4d93e.jpg)
I had a really clean crank and bottom cap from the 2004 engine, so I used that. The later cap has a groove cast in for better sealing.
![IMG_6140-800.jpg IMG_6140-800.jpg](https://cdn.imagearchive.com/arboristsite/data/attachments/50/50636-1455f2ec5b0005adfefa961926ea8b67.jpg)