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What's the next thing I should look for?

#1

virtual_guy

virtual_guy

I'm at my wit's end. You all led me in the right direction when we found a scored piston. I changed it and the cylinder. Sealed it back up with Loctite 515 and with a coat of oil on the cylinder wall. Compression checked at about 125-130psi. There's a good blue spark and the spark plug is wet.

Won't fire.

The air filter is new. I checked the spark arrester and it was clean, tried to start with the spark arrester off.

Still won't fire.

I checked that the alignment pin on the flywheel is intact and the flywheel is seated on it correctly.

What can I check next other than the direction to a dumpster? Surely I'm close to getting this POS running :LOL:


#2

B

Born2Mow

The next thing you should look for is the engine model number. Since you started a new thread, we can't possibly remember what engine or mower you're talking about. You need to tell us again.

Try some starting fluid or some other spray you know will start engines. See if it will sputter with the spray. If it hits 2 or 3 times, then you know it's the fuel or the fuel delivery system.

Some ideas...
  • Is the fuel in the tank AND the float bowl fresh ??
  • When was the last time you removed the float bowl and looked for water ?


#3

Scrubcadet10

Scrubcadet10

2 smoke engine?
i would check the flywheel key.


#4

cpurvis

cpurvis

Try a known good dry spark plug.


#5

virtual_guy

virtual_guy

Ok ok in my irritation and haste I missed an important point.

It's a Poulan Pro PP5020AV chainsaw.

It has a new carb on it and I checked the flywheel key...a couple times.

I have a new spark plug and the one I pulled out. Both produce good spark as far as I can tell and I've tried both with the same results.

I'm confident with the fuel but I'll check for water. At least it's something to look for.

I don't have any start fluid but that's worth trying.

Thanks!


#6

Hammermechanicman

Hammermechanicman

Ok. Get some real starting fluid. Remove the spark plug and Make sure the spark plug is dry. Spray a VERY small amount of starting fluid into the plug hole. Install plug and try to start it. It should fire a couple times. If it doesn't you have either a spark or compression problem. If it fires spray a small amount into the carb throat and try to start it. If it does not fire you probably have a primary compression (crankcase) problem. You would need to do a pressure and vac test on it. If it fies and runs for a second or so you have a fuel delivery (carb) problem.


#7

B

bertsmobile1

getting rebuilt blue smokes to fire is always problematic
My usual method for obstinate ones is to warm the spark plug up in something else till it is very uncomfortable to hold with a gloved hand
The quickly fit it loosely, say just barely finger tight ( ouch it was hot )
This helps to vapourize the fuel, prevents fuel fouling the plug & allows the engine to be cranked substantially faster .
All of the above make for easier starting.
When it does fire up ( note do not close the choke ) run the engine for a good 5 minutes or so then let it cool down & tighten the spark plug .
Many a Bantam engine required being towed quite a long way in first gear before they gave in a and fired .


#8

G

Gord Baker

bertsmobile1 said:
getting rebuilt blue smokes to fire is always problematic
My usual method for obstinate ones is to warm the spark plug up in something else till it is very uncomfortable to hold with a gloved hand
The quickly fit it loosely, say just barely finger tight ( ouch it was hot )
This helps to vapourize the fuel, prevents fuel fouling the plug & allows the engine to be cranked substantially faster .
All of the above make for easier starting.
When it does fire up ( note do not close the choke ) run the engine for a good 5 minutes or so then let it cool down & tighten the spark plug .
Many a Bantam engine required being towed quite a long way in first gear before they gave in a and fired .
Click to expand...
I always used High Gear to help start a towed vehicle....


#9

K

Kubotafan

virtual_guy said:
It's a Poulan Pro PP5020AV chainsaw.
Click to expand...
Don't they need a lot of poulan and poulan and poulan and poulan and poulan to get started?


#10

M

mechanic mark

What grade of gasoline are you using, if 87 octane it probably will not start. Most chainsaw Operators Manuals state using 91 octane or higher. I use 93 octane gasoline in all outdoor power equipment & my pickup. Read page 9 in Operators Manual concerning fresh 87 octane gas & 40:1 two cycle synthetic oil preferably Poulan brand. If you have a 1 gallon gas container mix 3.2 oz. of Poulan/ Weed Eater Brand 2-cycle synthetic oil with fresh gasoline & just give 93 octane a try. Let us know how it goes, thanks, Mark

Suggestion: When posting in the future start with equipment type, name brand, year, model & serial numbers & any other information you can provide, thanks, Mark


#11

D

Dwstwrt

Are you using fresh fuel? I tried my chainsaw this past fall, fuel & spark—no go. I then took some from tank and lit it with a torch, it was like a candle burning—real slow. New mix and a couple of pulls, good to go!


#12

G

Graeden

Is the safety switch connected? Do you have the On/Stop switch switched to on?

Link to owners manual: https://www.manualslib.com/manual/132533/Poulan-Pro-115153026.html#manual


#13

OzPete

OzPete

virtual_guy said:
I'm at my wit's end. You all led me in the right direction when we found a scored piston. I changed it and the cylinder. Sealed it back up with Loctite 515 and with a coat of oil on the cylinder wall. Compression checked at about 125-130psi. There's a good blue spark and the spark plug is wet.

Won't fire.

The air filter is new. I checked the spark arrester and it was clean, tried to start with the spark arrester off.

Still won't fire.

I checked that the alignment pin on the flywheel is intact and the flywheel is seated on it correctly.

What can I check next other than the direction to a dumpster? Surely I'm close to getting this POS running :LOL:
Click to expand...
Sounds like its got a crankcase air leak .. which causes a dangerously lean air/fuel mixture .. which is probably what caused your original piston damage (partial seizure). Your scored piston wasn't the cause ... it was the result.
In a two-stroke engine, crankcase integrity (its air-tightness), is critical .. even more critical to the operation of the 'Two-stroke Cycle" than compression in the combustion chamber.
So my guess is a popped (or just worn & leaking), crankshaft seal behind the flywheel or behind the oiler pump on the clutch side.
F.Y.I. - It's considered pointless and particularly poor practice for a small engine mechanic to re-install a cylinder on a 2-stroke engine without performing a crankcase pressure test. In my shop my technicians know that at the outset, after removing the muffler and identifying a scored piston, I insist that they complete the diagnostic process by performing a Crankcase Pressure & Vacuum Test. Pic attached & Search it on Youtube.

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#14

virtual_guy

virtual_guy

OzPete said:
Sounds like its got a crankcase air leak .. which causes a dangerously lean air/fuel mixture .. which is probably what caused your original piston damage (partial seizure). Your scored piston wasn't the cause ... it was the result.
In a two-stroke engine, crankcase integrity (its air-tightness), is critical .. even more critical to the operation of the 'Two-stroke Cycle" than compression in the combustion chamber.
So my guess is a popped (or just worn & leaking), crankshaft seal behind the flywheel or behind the oiler pump on the clutch side.
F.Y.I. - It's considered pointless and particularly poor practice for a small engine mechanic to re-install a cylinder on a 2-stroke engine without performing a crankcase pressure test. In my shop my technicians know that at the outset, after removing the muffler and identifying a scored piston, I insist that they complete the diagnostic process by performing a Crankcase Pressure & Vacuum Test. Pic attached & Search it on Youtube.
Click to expand...
It's been a bit since I checked in here but thank you. Having done some research here and on other sites I had already about reached that conclusion. I'll tear it down again when I get time and see what I can find.


#15

virtual_guy

virtual_guy

So if one or both crank seals is bad, would it not fire at all, even with some starter fluid? Seems like it should still fire with starter fluid put directly into the spark plug opening.

Also, I thought the plastic cylinder inserts were identical but I just figured out they have different part numbers. If I swapped the left and right inserts would it cause this?


#16

R

Rivets

If you just swapped the seals, I would start by getting the proper seals for both sides an install them. This should be done anytime you open a two-cycle crankcase.


#17

B

Born2Mow

virtual_guy said:
So if one or both crank seals is bad, would it not fire at all, even with some starter fluid?
Click to expand...
Without primary compression in the crankcase, the fluid never makes it to the combustion chamber.

That's what the man is telling you.


#18

Hammermechanicman

Hammermechanicman

See post #6
If you have decent SECONDARY (cylinder) compression and spark at proper time if you put a small amout of starting fluid in the spark plug hole. Not carb cleaner or gasoline. It will fire with or without PRIMARY (crankcase) compression. If it won't fire you either have a compression or spark issue. Ignition should be able to jump a 1/4" gap with blue spark. If it does the ignition will run the engine. If it does fire with starting fluid in the cylinder you can move on to possible primary compression issues.


#19

virtual_guy

virtual_guy

Hammermechanicman said:
See post #6
If you have decent SECONDARY (cylinder) compression and spark at proper time if you put a small amout of starting fluid in the spark plug hole. Not carb cleaner or gasoline. It will fire with or without PRIMARY (crankcase) compression. If it won't fire you either have a compression or spark issue. Ignition should be able to jump a 1/4" gap with blue spark. If it does the ignition will run the engine. If it does fire with starting fluid in the cylinder you can move on to possible primary compression issues.
Click to expand...
Thank you. I was sure this was the case and it points to a different issue. I have measured the cylinder compression and it's fine. I put starter fluid into the spark plug hole and it still doesn't fire. I can see spark but it is apparently insufficient. I'll look into that side of it.

Regarding crank case seals, I don't currently have a way to do a pressure test but I'm looking into that.

Thanks everyone.


#20

virtual_guy

virtual_guy

Ok I'm now on to something. In the process of this rebuild I had replaced the flywheel. The new flywheel came in a package that had the right part number on the outside but I failed to notice that it had the wrong part inside. The timing is a full 60 deg off when compared to the old flywheel. While I was a little negligent in not noticing the difference, at least now I have something that explains what I'm seeing.

A new, and hopefully correct, flywheel is on order.


#21

virtual_guy

virtual_guy

New flywheel. Still nothing. I did get it to hit a couple times but can't make it happen again. It's pulling fuel into the top end since the plug gets wet. I see what appears to be good spark.

I don't get it. I'm about to give up. The time an money I've spent on this could have easily bought another. I'd like to say that I learned a lot in the process but clearly not enough. :rolleyes:


#22

S

slomo

mechanic mark said:
Check valve lash & adjust to specs. with engine cold so compression release on camshaft will assist in starting.
Click to expand...
On a chainsaw? Are these 4 strokers now?

slomo


#23

virtual_guy

virtual_guy

Ok so progress has been made in the long saga of my poor chainsaw. I had recently replaced the spark plug so I hadn't really considered that as an issue but on a whim I bought a new on and sure enough it fired up. Sadly it just ran for a bit and died. It also wouldn't fully rev. Carb adjustments did not improve it. I'll go back to the basics of fuel and air now and see if I can figure this out.

Lesson: This probably wasn't worth the effort. :LOL:


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