2 Cycle Engine Assembly 101

[safeT1st]

Here's the situation ;

I have been pulling wrenchs for many years but have little 2 cycle engine assembly experience . I have stripped an old Poulan XXV down to the ground and collected the parts required for a proper rebuild ( restoration) . I have glass beaded and masked the parts in preperation for primer and original paint scheme . My son and I will assembly this saw together as he is in power mechanics and shows an interest and aptitude for this work . I have a few specific questions and would also be interested in any thoughts the members might have .

1) piston pin tight in piston - Heat piston in hot water prior to assembly for slip fit ?

2) Piston pin clip location - appears piston clip grooves will demand gap at bottom ?

3) New cylinder transfer and exhaust ports - any need to lightly dress them to accept new rings ?

4) Oil pump diaphragm - dry ?

5) Assembly fluid - 2 cycle oil , lubriplate ?

6) Run in mix - leaner than normal (meaning more oil) ?

7) Run in procedure ?

If the members could address these questions and offer any other experience or techniques it would be most appreciated . I have put a little more money into this than I care to admit but it is a worthwhile project for my son and I to work together on . If you think about it there are probably more than a 1,000 man years of experience on this topic up here,( and that's just counting Andy ) . What a work force to draw on . Thanks alot and I will post pics as we go .:greenchainsaw:

 

[Bowtie]

Here's the situation ;

I have been pulling wrenchs for many years but have little 2 cycle engine assembly experience . I have stripped an old Poulan XXV down to the ground and collected the parts required for a proper rebuild ( restoration) . I have glass beaded and masked the parts in preperation for primer and original paint scheme . My son and I will assembly this saw together as he is in power mechanics and shows an interest and aptitude for this work . I have a few specific questions and would also be interested in any thoughts the members might have .

1) piston pin tight in piston - Heat piston in hot water prior to assembly for slip fit ?

2) Piston pin clip location - appears piston clip grooves will demand gap at bottom ?

3) New cylinder transfer and exhaust ports - any need to lightly dress them to accept new rings ?

4) Oil pump diaphragm - dry ?

5) Assembly fluid - 2 cycle oil , lubriplate ?

6) Run in mix - leaner than normal (meaning more oil) ?

7) Run in procedure ?

If the members could address these questions and offer any other experience or techniques it would be most appreciated . I have put a little more money into this than I care to admit but it is a worthwhile project for my son and I to work together on . If you think about it there are probably more than a 1,000 man years of experience on this topic up here,( and that's just counting Andy ) . What a work force to draw on . Thanks alot and I will post pics as we go .:greenchainsaw:

1) No heating in anything needed. Just make sure it has 2 cycle oil all over it
2) Not sure on that model
3) There should be a little bevel in the port edges. If there isnt you might want to dress them a little bit with choice tool.
4) Fill it with bar oil and cut wood.
5) 2 cycle oil, I prefer Stihl HP Ultra
6) 50:1, 40:1 if you insist, but not necessary
7) Run in...GO CUT WOOD! Dont let it run out of fuel before refilling!

 

[Lakeside53]

To the original questions:

yes
yes
no
na
mix oil
nope
just use it

 

[safeT1st]

Pics

Thanks for the response guys . Nothing to exciting but here's a few pics .

 

[2many2count]

2 cycle 101

new to site avide vintage poulan fan
1 heat piston
2 no
3 no
4 yes
5 yes
6 a good quality 2 cycle oil stihl or echo preferred 40:1
7 run in normal with the exception of running carb a little richer
question what did you do to inside of cylinder looks chrome plating peeled off?

 

[sleddude5]

1) piston pin tight in piston - Heat piston in hot water prior to assembly for slip fit? I usually just put the piston pin into the fridge the night before assembly, same concept.

2) Piston pin clip location - appears piston clip grooves will demand gap at bottom? In 2 stroke motors, piston circlips should always be installed with the gap at either the bottom or the top of the piston. This helps prevent weakening of the clip tension from the up/down motion of the piston and its resultant forces

3) New cylinder transfer and exhaust ports-any need to lightly dress them to accept new rings? These ports must be chamfered. If not, the ring can catch on the edge of a port which could, in turn, break the ring.

4) Oil pump diaphragm-dry? I don't know.

5) Assembly fluid - 2 cycle oil, lubriplate? Use a good dosage of whatever 2 stroke oil you run in the saw.

6) Run in mix - leaner than normal (meaning more oil)? It is benficial to run a couple tanks of gas through your saw with a higher oil content, such as 40:1 or 32:1. This helps keep plenty lube on the cylinder walls while the rings are breaking in to them.

7) Run in procedure? Warm saw up very well after the rebuild, let it idle for a few minutes to allow the motor components to equalize in temperature. Then run the saw hard. Keeping the RPM's up during break in is important, here's why...The rings have a small bevel to them, and during installation this bevel should face to the top of the piston, many rings have a mark on them to help designate the top. When the motor is running, the gases from combustion work their way in behind the piston ring and force the ring outward against the cylinder wall. If the RPM's are not high enough while breaking in a motor, the rings will have insufficient pressure exerted on them and you will end up with an underperforming motor with a lot of ring blowby

Jerry C

 

[lesorubcheek]

Are you going to use a new cylinder? The pic you attached looks like the plating is done for. Must have had a catastrophic event like getting really hot.

Dan

 

[drmiller100]

what he said.

you need either a new cylinder or get yours replated, and new piston and rings.

i'd get a new wristpin and wristpin bearing also.

 

[Lakeside53]

I've never seen a new (OEM) cylinder that needed anything done to the ports "chamfer".

 

[Metals406]

I've never seen a new (OEM) cylinder that needed anything done to the ports "chamfer".

Andy, is that jug in the picture garbage? It looks like the plating is mostly gone?

 

[sleddude5]

I've never seen a new (OEM) cylinder that needed anything done to the ports "chamfer".

I'm not saying he needs to chamfer the ports, as a new cylinder should be good to go, but just to make sure that they are.

Jerry C

 

[Lakeside53]

Andy, is that jug in the picture garbage? It looks like the plating is mostly gone?

It look completely shot to me, and the crank shoes "bluing" on the right side...

 

[Modifiedmark]

Just redid one of these last week. Yes the oil pump diaphragm can go on dry. If you have not yet make sure you put a new quad ring on the manual pump also.

Seems the auto oiler don't like to work well if the manual oiler isnt up to snuff.

And like the others said, I hope you dont plan on using that cylinder. Looks like it was bead blasted inside?

 

[safeT1st]

Cylinder Condition

new to site avide vintage poulan fan
1 heat piston
2 no
3 no
4 yes
5 yes
6 a good quality 2 cycle oil stihl or echo preferred 40:1
7 run in normal with the exception of running carb a little richer
question what did you do to inside of cylinder looks chrome plating peeled off?

That's the original cylinder , your guess is as good as mine as to cause of chrome plating sluffing off . I have a brand new P & C and rings . Thanks alot for your answers .

 

[safeT1st]

Should have been more descriptive

Are you going to use a new cylinder? The pic you attached looks like the plating is done for. Must have had a catastrophic event like getting really hot.

Dan

Thanks Dan , Yes I have new parts for complete rebuild .

 

[safeT1st]

Tricks of the trade

Just redid one of these last week. Yes the oil pump diaphragm can go on dry. If you have not yet make sure you put a new quad ring on the manual pump also.

Seems the auto oiler don't like to work well if the manual oiler isnt up to snuff.

And like the others said, I hope you dont plan on using that cylinder. Looks like it was bead blasted inside?

Thanks for the thoughts on the thumb pump . I have the seal for that . Thats how the cylinder was on open up . Pistons bad too . All will be replaced . I've been told that in their day the Poulan XXV was a popular saw for climbers and considered to be a "pro saw" . I think it will be really good to know the guts are good and look after it well .

The input I'm recieving from you guys is terrific . It's almost like a Saturday afternoon and you're all hanging out in my shop (drinking all my beer ).
:greenchainsaw:

 

[safeT1st]

Ready to Assemble

Well , I painted all the parts , de-burred the new cylinder , polished the crank , replaced the case seals and started to re-assemble today . Made an interesting find : I'm replacing the oil inlet valve for the pump ( it's actually a tiny one way check valve and has a little nipple to which the oil supply line connects) . The original nipple broke off the valve at teardown . Any ways I was inspecting the new valve prior to install and found it would not pass air in either direction , messed around with it for sometime and finally had to drive a tiny pin punch down inside it to unseat the check ball which was wedged tight in its bore . Works fine now and I'm sure glad I checked it prior to install . I was cautioned earlier by "modifiedmark " to replace seal ring on manual pump . It's quite clear now that if that seal fails it will allow pressure pump oil to leak past seal and not arrive at bar . Thanks for that heads up . Since I'm there now is there any point in allowing the muffler in picture below to breath a little better ?

 

[safeT1st]

Poulan Bottom End and Oil Pump

G]

 

[safeT1st]

Hope this works

 

[safeT1st]

Getting Closer

I apologize for the effectiveness of the two previous posts . I'm trying to relate the oil pump and bottom end assembly of the little Poulan with pictures . Not being too computer savy it takes a little practice to get the pictures of correct size and order . I'm going to keep trying until I get this right . As you can see I'm doing a complete overhaul of this simple saw and I know that alot of you enjoy the pics .