Poulan ... what size is my engine?

[Oddjobz]

Yea yeah.....angular momentum, vector, it's actually in newtow/meters blah blah blah.
Your best to not relate the schoolbook physics when looking at practical application.
KISS.....keep it simple stupid!

For the consumer's sake.
Torque is the power that gets things moving/moves against resistance.....ft lbs reflect the amount of force/power that can be developed.

Yes, you are correct....but your argument is pointless when confronting the average consumer.

May the force be with you.......

(I also build computers, networks etc, when someone asks what DNS is, I don't get long winded with things they won't understand,
instead I tell them: It's the phone book for the Internet) K.I.S.S. ....get it?

******

Porting is always a risk.... easiest way to ck for danger.....take the rings off the piston, drop it in the cylinder, scribe a line
at the bottom of the port, pull the piston out and ck the distance to the bottom of the skirt. Note that the piston never reaches
the end of the cylinder when at TDC, so you get a safety margin to boot.

I've always liked to push it to the limits......your play it safe option is perfectly fine......just not for all us dremel happy nuts.

 

[Chris-PA]

Torque is the power that gets things moving

OK, then KISS - Power is the power that gets things moving.

your play it safe option is perfectly fine

Yup, play it safe, that's me. As in a squish modded 42cc Poulan clamshell with a cut cylinder and a relocated crank, pop-up piston, plus a modified crank and filled clamshell cap to reduce case volume and help pump gas up the transfers. http://www.arboristsite.com/community/threads/reducing-squish-on-a-poulan-clamshell.273087/

Even used 3D printed tools:






It's got some porting changes and a bored carb too. I suppose you could mod one further...

 

[Oddjobz]

Ohhh, got a shiver.......that's an awesome one. Squeeeeeeze every last ft lb of 'power' out of that sucker......

 

[Chris-PA]

Ohhh, got a shiver.......that's an awesome one. Squeeeeeeze every last ft lb of 'power' out of that sucker......

They are fun to play with. Sorry for giving you a hard time, I'm glad to see someone else modding them. The darn things run damn well given the humble engine architecture.

 

[Oddjobz]

For the average homeowner they are the perfect saw. They just need to be given access to their full potential.

Just the fact that you can get a dual ring piston puts these saws in a whole new league. Get the vapors flowing
and these saws wake up........I've had great fun modding the 41.1s

If you want to get another quick and easy squeeze of power.......try this. Gives the cylinder a Hemi affect.
Used in pocket bike racing.
I use them in everything in that CJ7 heat range....(sometimes even the CJ6 & 8 can be swapped with these too)

 

[Chris-PA]

For the average homeowner they are the perfect saw. They just need to be given access to their full potential.

Just the fact that you can get a dual ring piston puts these saws in a whole new league. Get the vapors flowing
and these saws wake up........I've had great fun modding the 41.1s

If you want to get another quick and easy squeeze of power.......try this. Gives the cylinder a Hemi affect.
Used in pocket bike racing.
I use them in everything in that CJ7 heat range....(sometimes even the CJ6 & 8 can be swapped with these too)

View attachment 564954 View attachment 564956

Interesting plug.

I bought one of the 2-ring pistons on a lark. It only came with one ring, but I have another - what do you want for $6? It's got a lower piston height though, which puts the squish at 0.050", so I'll have to cut the cylinder even more than I care to. I may use it anyway just to see how it compares. I'll have to get another chassis to put it in though, and I not sure if/when I'm going to get around to building that engine. I might just keep in in case this one fails, although it's holding up well.

Note that the 2-ring pistons are sold for the Partner saws which use the bare aluminum bore/chromed piston. That happens to be the engine I have lying around, but the Poulan Pro engines with plated bores and bare pistons are better from a durability point of view.

 

[Oddjobz]

You can't beat hard chrome plating for durability.... Sadly, once badly scored or cracked the replacement cost of an oem is prohibitive.
The aftermarked P&C with duel rings are under $30 and you can get a 10pk of rings for under $10. I just received a 5pk of pistons I'm
trying out......got 2 sets of P&Cs on the way. Curious to see how the Nikasil Cylinders hold up

There are a few variations of the cylinders....the Jonsered 2137 I have does not have any insert
in the port or ridge either. Different casting number also......but no doubt it is exactly the same engine as the Poulans and Sears I did last week.

 

[Chris-PA]

There are a few variations of the cylinders....the Jonsered 2137 I have does not have any insert
in the port or ridge either. Different casting number also......but no doubt it is exactly the same engine as the Poulans and Sears I did last week.

The later cylinders right before they went to strato are different, with smaller volume transfers and larger combustion chambers, and much different port timing. Some did not have the insert. They used a cat muffler too. Look at the last link I gave above for a build I did one one of these later cylinders - they can be made to run well but are at a disadvantage compared to the earlier ones.

And some of the Jonsered 2137 are actually 46cc, but don't tell anyone as I have not found one yet.

 

[Oddjobz]

This 2137 has the same bore, I'll have to double ck the stroke and top of the jug tomorrow.
Jug is scrap anyway, huge score inside and I'm not going to waste time with epoxy when I have a new jug on the way.

Hmm Jonsered is often doing funny things....I have a 455 (42mm P&C) case that I was able to straight drop a 525 44mm P&C&Crank in since both crank seals
are the same OD. The 525 ended around 1986 when the 455 started. Guess they didn't want to totally re-engineer.

 

[dougand3]

Thanks for info, Oddjobz. The Partner 742 jug is a direct match for a P4128avx. Best price I see for a whole top end is $40. Too much for a saw that sells for $60 as a good runner. Now, if you wanted to learn clamshell rebuilding = small tuition payment.

 

[Chris-PA]

Thanks for info, Oddjobz. The Partner 742 jug is a direct match for a P4128avx. Best price I see for a whole top end is $40. Too much for a saw that sells for $60 as a good runner. Now, if you wanted to learn clamshell rebuilding = small tuition payment.

I find that viewpoint curious. It's a logical way to look at it if you are going to sell it because you have to make money and account for your time. But if you are going to keep and use the saw then shouldn't it just be how much capability you can get for the money spent? If you have a saw with a roached top end it is worthless as a tool. From there, what is the cheapest way to get a capable tool to use? Seems to me it would cost you $40. Add in a little time for some minor mods and you have a very capable tool for most firewood gathering and homeowner uses.

Or you could spend $60 for a "good runner" that will likely be someone else's bundle of problems.

The problem here is in assuming price in $ is a good measure of value.

 

[dougand3]

It's a logical way to look at it if you are going to sell it because you have to make money and account for your time.

My total measure on a trade in non runner. I have plenty of good runners. For someone who has no saws, your point is valid - build a good saw for personal use and learn along the way.

 

[ejs1943]

Sounds like they are varying the stroke with pushrods.

 

[ejs1943]

Sounds like they are varying the stroke with pushrods.

Pushrods in a 2 cycle engine? Explain please