Minimum chainsaw compression for starting and running.

Treestuff
Shop deals on ebay
Rugged made
Arborist Forum

Help Support Arborist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Rx7man said:
I have an old homelite XL12, it feels like it's got no compression (I didn't bother checking it), but it starts up with about 3 pulls every time... doesn't make much power in the cut though... it's funny how some saws with low compression seem to do surprisingly well, while others just quit if they have less than 140psi
Click to expand...
your right as rain, I've got a Poulan Pro that doesn't have enough compression to blow paper towels out of the spark plug hole but I've used it for the last 2years its runs perfect for cutting wood up to 8 inches in diameter
 
pioneerguy600 said:
I have seen that more on the older all magnesium chainsaws, for the most part they had longer stroke and heavier flywheels plus they had points and condenser+ coil ignition systems that made a fatter blue spark when pulled over. The newer saws with electronic ign modules seem to produce a weaker spark when just pulling them over with the recoil.
Click to expand...
the newer saws with the electronic ignition can produce a blue spark by cleaning the coil and magneto and gauging them with a sheet of writing paper folded in half, most companies require them to be set with 0.10 of air gap which is about what a piece of paper folded in half is hope this helps
 
Anthony Pillois said:
the newer saws with the electronic ignition can produce a blue spark by cleaning the coil and magneto and gauging them with a sheet of writing paper folded in half, most companies require them to be set with 0.10 of air gap which is about what a piece of paper folded in half is hope this helps
Click to expand...

More commonly a business card is used these days to set the air gap between the module and flywheel as common card stock is in the .010 - .012 range. The modern electronic modules make less spark at lower rpm like when being pulled over with the recoil, they certainly make adequate spark to start the engine.
 
I seen this post has come alive and also that I failed to report back the latest about the little homelite super 2 saw that would not start with low compression.
I had two of them little homelites just alike one ran great and this one no go. I set the problem saw back thinking I would keep it as a parts saw and few days or weeks later later picked it up cold and it fired and briefy ran cold and when I tried a prime and it flooded with no pop, let it sit 24 hrs and it would briefly run again when cold. I swapped the two carbs and the problem was the carb. A kit and good cleaning in a ultrasonic would not fix the bad carb. (and I'm usually good and repairing sall carbs but this one would not come around)
I located a ebay carb and both saws are running and cutting great one with 80-90 lbs compression and piston and cylinder looks good and it starts easily.
Summary: Bad carb would briefly allow saw to run if saw set for about 10-24 hours then would flood the crankcase/engine.
 
Okie said:
I seen this post has come alive and also that I failed to report back the latest about the little homelite super 2 saw that would not start with low compression.
I had two of them little homelites just alike one ran great and this one no go. I set the problem saw back thinking I would keep it as a parts saw and few days or weeks later later picked it up cold and it fired and briefy ran cold and when I tried a prime and it flooded with no pop, let it sit 24 hrs and it would briefly run again when cold. I swapped the two carbs and the problem was the carb. A kit and good cleaning in a ultrasonic would not fix the bad carb. (and I'm usually good and repairing sall carbs but this one would not come around)
I located a ebay carb and both saws are running and cutting great one with 80-90 lbs compression and piston and cylinder looks good and it starts easily.
Summary: Bad carb would briefly allow saw to run if saw set for about 10-24 hours then would flood the crankcase/engine.
Click to expand...
okay the only thing that would cause the gas to go into the crankcase is the needle jet not sealing properly, as you know that's a easy fix
 
undee70ss said:
Normal compression pressures for Homelite saws. Taken from a Homelite training manual.

View attachment 618297
Click to expand...
I agree that's what it should be under normal circumstances but a saw can run with considerable less compression you just have to tinker with them I've been repairing small engines for over 40 years and in most cases low compression usually means you are going to use it under less of a load
 
undee70ss.

Thanks for posting the normal training manual compressions for Homelite chainsaws. I saved it too my Homelite computer reference file and also printed it off for my shop file.

But I've seen several saws (when all else is ok) that will start easily, run strong and cut ok when the compression is below the recommended per the book (taking the reading with a accurate gauge) If I see the piston and/or cylinder is scored I don't bother trying to save the existing. I've seen some EZ Homelites that run real good with 135 lbs compression for example. Even if compression is real good I take a peek at the piston/cylinder to see if any cancer is inside. (and is usually the first thing I check)

I've got an old good running 30 year old 028 Stihl with a 16 inch bar that I use every season for firewood and when checking compression it should not even start or run. (probably would not pull a 20 inch chain but does real good with a 16 inch aggressive cut chain)

Sometimes a guy will get pleasantly surprised how good a saw operates when compression is low, therefore I do take compression readings with a grain of salt. (and I do not trust the picture of very high compression readings I see on ebay of saws for sale) Too much puffing and buying a used as is chainsaw on-line is in the same category as buying a pig in a poke.;)
 
Okie said:
undee70ss.

Thanks for posting the normal training manual compressions for Homelite chainsaws. I saved it too my Homelite computer reference file and also printed it off for my shop file.

But I've seen several saws (when all else is ok) that will start easily, run strong and cut ok when the compression is below the recommended per the book (taking the reading with a accurate gauge) If I see the piston and/or cylinder is scored I don't bother trying to save the existing. I've seen some EZ Homelites that run real good with 135 lbs compression for example. Even if compression is real good I take a peek at the piston/cylinder to see if any cancer is inside. (and is usually the first thing I check)

I've got an old good running 30 year old 028 Stihl with a 16 inch bar that I use every season for firewood and when checking compression it should not even start or run. (probably would not pull a 20 inch chain but does real good with a 16 inch aggressive cut chain)

Sometimes a guy will get pleasantly surprised how good a saw operates when compression is low, therefore I do take compression readings with a grain of salt. (and I do not trust the picture of very high compression readings I see on ebay of saws for sale) Too much puffing and buying a used as is chainsaw on-line is in the same category as buying a pig in a poke.;)
Click to expand...
I am doing a video for utube tomorrow using a Mac 1010 with 150 ppsi compression and a Poulan pro 5020av with less than 50 ppsi compression not even enough to blow paper towels out of the spark plug hole and yet I have used it for 2 years I hope y'all check it out tomorrow afternoon
 
Rx7man said:
I have an old homelite XL12, it feels like it's got no compression (I didn't bother checking it), but it starts up with about 3 pulls every time... doesn't make much power in the cut though... it's funny how some saws with low compression seem to do surprisingly well, while others just quit if they have less than 140psi
Click to expand...

I was going to post this also as my old XL12 is much the same. Now I'm kind of curious so may put the gauge on it just to see what it really is.


Sent from my iPad using Tapatalk
 
alderman said:
I was going to post this also as my old XL12 is much the same. Now I'm kind of curious so may put the gauge on it just to see what it really is.


Sent from my iPad using Tapatalk
Click to expand...
i plan on posting a easy to understand comparison on compression between a Mac1010 and a Poulan Pro 5020av the Mac 1010 has 150 lbs of compression and the Poulan only has 30 lbs of compression and after all the research the Poulan isnt suppose to run but after tomorrow people will see low compression isn't the end of the road for the saw
 
I generally go with 110+ is good, 100-110 is maybe weak depending on the saw, and 100-90 is probably bad, 90- is definitely something wrong. But always do a muffler check too
 

Similar threads

G
Husqvarna 240 still won’t start!
Replies
9
Views
609
Northerner
Northerner
T
McCulloch 10-10A no start
Replies
1
Views
174
irhunter
irhunter
K
Poulan 2000 rebuild not starting cold
Replies
15
Views
869
EchovsStihl63
EchovsStihl63
M
Homelite chainsaw woes
Replies
8
Views
882
OnlyHomelites
OnlyHomelites
Bart01
Jonsereds 49sp does not start
2
Replies
34
Views
2K
Cantdog
Cantdog

Latest posts

Back
Top