Thanks Chris
Reducing Squish on a Poulan Clamshell
- Thread starter Chris-PA
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Chris-PA
Where the Wild Things Are
One of the things I wanted to emphasize is that when grinding the bearing pockets you have to go very slow and check often. You are trying to grind a semi-circle freehand after all. I also used the depth gauge on my caliper to measure the distance from the ridge to the bottom of the pocket at the center. This allowed me to make sure I had not gone too far in the middle even before I could use the bearing or the tool I made.
I also wondered if the rubber covered bearings allow the crank to move, especially since I'm reducing the squish and the clearance to the crankshaft counterweights. I don't really think it moves too much though, as the durometer of that rubber is pretty high and it's compressed quite a bit. It probably does damp out really high frequency movement some.
bikemike
loud pipes save lives
Only thing I could think of looking at pics on first page. Possibly slot the skirt where transfer ports are located to help open up more passage way for air fuel mix to get to the transfer ports. Not sure if it would make a difference but my mind was wandering
What did you end up with for squish or what would you recommend it should be?
Chris-PA
Where the Wild Things Are
Yeah, I've seen that done. I should look at the cut away engine and see how that might interact with the other things I've done here. The transfers actually extend down pretty far below the piston at BDC, all the way to the bearing.
I ended up with 0.021". It probably could have been less but given all the hand grinding and the rubber covered bearings I was good with that.
http://www.arboristsite.com/communi...a-poulan-clamshell.273087/page-8#post-5226959
bikemike
loud pipes save lives
Yeah I figured with the width of the crank lobes and narrow passage nearing bdc it looks like it could be a Lil restricted.I honestly can't remember what my 46cc poulan piston looks like but I might practice the squish reduction on my husky 136 and se If I feel confident in my dremel skills to try what you did
this is the saw that still needs more hp runs great and reliable and I mill slabs with it. But want more out of it
this is the saw that still needs more hp runs great and reliable and I mill slabs with it. But want more out of it
I have a 255 poulan pro like the one above I use it for liming after I drop my firewood. I have a question though she kicks back like a mule !`If you don't hang onto the recoil handle tight it will rip the handle through your fingers , hurts like,... well you know. So the timing is off I assume? if I want to fix this which way do I adjust the flywheel? Like if the magnets are lined up with the coil pick up which way would you adjust the flywheel? I really don't know how to ask this intelligently ha ha.
Chris-PA
Where the Wild Things Are
My Poulan 2775 does this too.
In general you would want to retard the spark to make it easier to start, but that is likely to kill the power & throttle response. To retard the timing you would want to rotate it clockwise in relation to the crankshaft (when viewed from the flywheel side). Maybe use better gloves or get one of those giant D handles I see on some saws?
bikemike
loud pipes save lives
I did read up on the naked lady machine that making the air gap of a coil a bigger gap can retard the timing ever so slightly cause it takes that much longer for the magnetic field to make its cycle through the iron plates. I don't know if it would be a noticeable difference in timing
Well I can live with it instead of loosing power. The only real issue is it is hard on the recoil I think.
Hi everyone this is the first time I have put anything on here. I been a long time mechanic on all sorts of different equipment and been into various hi performance hobbies especially tractor pulling so needless to say im never happy leaveing anything I own stock lol and I always enjoy building up something others say is junk into something impressive. I cut wood to heat my garage and I began with a poulan 2900 someone gave me that didnt run that I resurrected. That one poulan turned into a dozen and a few huskeys. I been doing muffler mods and simple improvements that really helped these saws. Raiseing the compression has been in the back of my mind for some time and last night I ran across this thread and what chris did is just what I had been thinking about so reading this gave me the confidence to try it. I took a 42cc craftsman measured the squish at 35 tho I surfaced the jug with a belt sander intended for wood I took it down 40 tho then deepend the bearing journals how chris did and turned the outer portion of the piston down 20 tho to make a dome. I started with 115 psi comp and now have 130 I also ported the exhaust port. Made a test cut tonight and wow what a difference. I now need to grind up an aggressive chain and see what it will really do. Sorry for the long post just wanted to introduce myself and thank everyone here for shareing the great info here and I wanted to share my findings also its good to know others are thinking outside the box like I like to do lol
Chris-PA
Where the Wild Things Are
Cool! I'm glad to see others try it. I know of a couple of others who have ground out the bearing pockets on these through various methods, and they run pretty well.
Chris-PA
Where the Wild Things Are
While I was using this saw today it started acting erratically, revving at idle and all over the place. That turned out to be a loose carb mount block, but while looking for that I happened to notice what looked like arcing marks on the flywheel magnets. I though that was rather odd! So I looked into that further, and polished them off with some Scotchbrite - it was certainly from arcing.
First I figured maybe the coil/module was bad, so I pulled it off. While cleaning it up to put the replacement module in, I realized the metal strap that connects the ignition core lamination to the engine was missing - I had forgotten to put it back when I assembled it last! So in order to fire the plug it had to arc back to the coil lamination in addition to arcing across the plug gap. I'm sure that just did wonderful things to the bearings!
The flywheel is of course connected to the moving portions of the engine, and the plug is connected to the stationary cylinder, so electrical connection needed to be made between the crank/rod/piston assembly and the cylinder. Because the main crank bearings are rubber coated there isn't much connection there. Maybe it arced through the ball bearings and that rubber coating, but more likely it passed through the roller bearings from the crank to the rod to the piston, and then through the ring or piston to the cylinder wall. Anyway, I have no doubt some pitting went on along that path, and I'm not very happy about it - but I didn't put a lot of hours on it since the last rebuild and I'm not pulling it apart now. It's running great.
I am still amazed it ran like that, although I wish it hadn't.
First I figured maybe the coil/module was bad, so I pulled it off. While cleaning it up to put the replacement module in, I realized the metal strap that connects the ignition core lamination to the engine was missing - I had forgotten to put it back when I assembled it last! So in order to fire the plug it had to arc back to the coil lamination in addition to arcing across the plug gap. I'm sure that just did wonderful things to the bearings!
The flywheel is of course connected to the moving portions of the engine, and the plug is connected to the stationary cylinder, so electrical connection needed to be made between the crank/rod/piston assembly and the cylinder. Because the main crank bearings are rubber coated there isn't much connection there. Maybe it arced through the ball bearings and that rubber coating, but more likely it passed through the roller bearings from the crank to the rod to the piston, and then through the ring or piston to the cylinder wall. Anyway, I have no doubt some pitting went on along that path, and I'm not very happy about it - but I didn't put a lot of hours on it since the last rebuild and I'm not pulling it apart now. It's running great.
I am still amazed it ran like that, although I wish it hadn't.
HuskStihl
Chairin'em for the sound
Crazy
yeah, that little grounding strap is easy to miss. you could run a wire from the metal top end to a module mounting screw, like a stihl 029. it's easy to imagine that strap getting lost while you're de-crustifying a dirty saw. and getting it back in is 3-d tetris. i always figured that it wouldn't fire without that strap, amazing. will you need to replace the flywheel or module?
Chris-PA
Where the Wild Things Are
I normally do not remove that strap but I had put helicoil inserts into the plastic case for the ignition screws as well as the recoil, since the threads were starting to strip out. I suspect that may have been when I forgot it.
I did replace the ignition module just to be cautious and because I had another, but I don't think there was anything wrong with it.
Chris-PA
Where the Wild Things Are
It seems to run fine. I decided to make it work:
That's white ash and a 68DL 19" bar with Oregon 91VXL. It's mostly running about 9500rpm, but since it's loaded pretty heavy it varies a bit.
SalahHH83
ArboristSite Lurker
This is awesome, Chris! Great ingenuity! I love projects like this and you've really done a great job with this.
Chris-PA
Where the Wild Things Are
It's been a while since I posted here as I've moved on to other things, but I had to tear this saw apart so I thought I'd stop by and give an update. The main issue was that I just could not keep the bolts for the carb mounting block tight, no matter what I tried they backed off and the carb would get lose. I could always tell because I would have to keep enriching the H and the idle would start creeping up - damned annoying when I'm trying to work!
Eventually I decided the threads must have become loose and polished from so many teardowns, and I had to drill it for some Helicoils so I could use M5 x 0.8 cap screws and LocTite them in. I figured once I had the engine out I'd open it up to see how the JB Weld inserts were holding up.
Here is the cap - it's lost a bit of the thin epoxy in the center (not as much as it appears as I picked a bit more out). It's gotten sort of brown, but seems to be holding up:
Here are the ones I formed in the cylinder - they don't have any screws to reinforce them like the cap does:
I decided to do one more mod while I had it apart - I added some notches in the piston skirt right at the transfer entrance, because the big fat counterweights really block that up at BDC. I've done this on other Poulans since I built this and they worked well. They are 0.125" high and the width of the transfer runner:
Oh, and I did the inserts too:
It also got new bearings and seals since I had some around. It seems to run quite well, and it feels like it might be pulling even better with the transfer notches. Time will tell if the carb stays on.
Anyway, take care and have a happy 2019 - I'll check this thread for a bit but don't plan to stay around too long.
Eventually I decided the threads must have become loose and polished from so many teardowns, and I had to drill it for some Helicoils so I could use M5 x 0.8 cap screws and LocTite them in. I figured once I had the engine out I'd open it up to see how the JB Weld inserts were holding up.
Here is the cap - it's lost a bit of the thin epoxy in the center (not as much as it appears as I picked a bit more out). It's gotten sort of brown, but seems to be holding up:
Here are the ones I formed in the cylinder - they don't have any screws to reinforce them like the cap does:
I decided to do one more mod while I had it apart - I added some notches in the piston skirt right at the transfer entrance, because the big fat counterweights really block that up at BDC. I've done this on other Poulans since I built this and they worked well. They are 0.125" high and the width of the transfer runner:
Oh, and I did the inserts too:
It also got new bearings and seals since I had some around. It seems to run quite well, and it feels like it might be pulling even better with the transfer notches. Time will tell if the carb stays on.
Anyway, take care and have a happy 2019 - I'll check this thread for a bit but don't plan to stay around too long.
