Chainsaw compression testing???

[Arkie]

Homelite chainsaw XL2 automatic. Exact model number glue on sticker is gone.

Do not know the history of this saw, was given too me because they could not get it started.
Has good ignition spark. will start sometimes and briefly run when engine completely cold sometimes after several pulls of the rope.
After it dies it won't even produce a pop even if carb throat is primed. New spark plug.
Looking thru the muffler port the cylinder looks shiny and the piston and one ring looks ok, ring not stuck, muffler screen clean.
Compression checks 25 PSI after several pulls of the starter rope. Add spoonful of 10W motor oil thru spark plug hole and compression will go the 125-150 in 2 pulls of rope. Is this a sign of worn out ring/cylinder on a 2 cycle chainsaw engine?

Main reason I ask is when doing a compression comparison test on a super 2 (block looks same as the XL2Auto in question) that starts and runs strong and the compression dry test is only 50psi max and a old Stihl 026 that starts and runs good at 75psi max. (dry test means no oil added to the cylinder during these PSI tests) Compression indicates that these two good running saws should be junked due to compression too weak.
I did not even bother trying to do a crankcase vac/pressure test after seeing the compression increase after adding oil to the cylinder! (I'm thinking the XL2 cylinder is worn out even thou it looks shiny and good thru the muffler port)
The saw is headed for the spare parts box!

Need your humble opinion: I'm new to checking chainsaw compressions

[KE4AVB]

Yep it time for a rebuild. As far 2 cycle compression it usually takes 100 psi for most to even hit. Of course this is with of whatever amount 2 cycle fuel mix gets sucked in from carburetor.

Also need to check your compression gauge as it normally 100 psi as above on my gauges for one to even think of starting. I have replaced several Poulan 42 cc cylinders that had 95 psi that would not start even with direct prime.

[KE4AVB]

Btw is this one a little top handle version with plastic housing?

[Arkie]

Btw is this one a little top handle version with plastic housing?

No. Its the better pot metal aluminum housings.
Why do you ask about plastic Homelite housing types?

[Arkie]

Yep it time for a rebuild. As far 2 cycle compression it usually takes 100 psi for most to even hit. Of course this is with of whatever amount 2 cycle fuel mix gets sucked in from carburetor.

Also need to check your compression gauge as it normally 100 psi as above on my gauges for one to even think of starting. I have replaced several Poulan 42 cc cylinders that had 95 psi that would not start even with direct prime.

I tried with two different gauges and also took the gauge to my air compressor and compared psi readings and all was right on PSI wise.
I also made a hose to the gauge as short as possible like 6 inches and compared the readings using a 18 inch hose and all readings still same. Reason I did this hose length comparison is I read on this forum awhile back that false max compression gauge readings might result when checking some 2 cycle engines if the hose is too long due to volume of the cylinder vs gauge hose volume.
Appears too me that some engines will run ok with low compression while others won't and the chainsaws compression of used saws might be an indicator of saws that may not last very much longer or have been used a lot already.

I just now thought that the Stihl 026AV may have a compression release mechanism when cranking with the throttle held open???(it was only reading 75 PSI and starts and runs great)

Also the XL2auto saw when picked up by the pull rope allows the rope to extract without much compression breakover.

The other 2 saws won't allow the rope to extract using the weight of the saw only.

[bgsengine]

Also the XL2auto saw when picked up by the pull rope allows the rope to extract without much compression breakover.

.

Sounds like stuck rings . although *SOME* of those old Homelites did have an automatic compression release (looks much like the manual oiler on some saws) that activated by the recoil starter but them'd have linkages hooked to the starter housing. Ive only ever seen one.

[KE4AVB]

As long you have not change the scharder valve it should not be a problem but if you have or do in the future remember these are not same as those used in in inner tube and tire stems. Those in the tire systems are design to be depress physically and have heavier hold springs.

I just now thought that the Stihl 026AV may have a compression release mechanism when cranking with the throttle held open???(it was only reading 75 PSI and starts and runs great)

Same type as the Husqvarna have if it is equipped with one and it would loacated on top near the muffler; otherwise there will probably be bolt plug

[Arkie]

Also the XL2auto saw when picked up by the pull rope allows the rope to extract without much compression breakover.

.

Sounds like stuck rings . although *SOME* of those old Homelites did have an automatic compression release (looks much like the manual oiler on some saws) that activated by the recoil starter but them'd have linkages hooked to the starter housing. Ive only ever seen one.

This little bitty Homelite XL2 Auto don't have a compression release. I have a larger Homelite EZ Auto that has the manual compression release and it starts easily when the release is manually activated.. I don't know how much the release actually reduces the compression when cranking.

The piston only has one ring.

[KE4AVB]

Arkie is this what the saw looks like? If so most of the parts are NLA. I got one that I restored; had another but had compression problems and parted it out. The saw actually very handy doing brush work. It can be dangerous since it doesn't have a chain brake.

It was very picky about it carburetor settings. I suspect it was the wear and abuse the previous owner did to it. I could get it to run prefect and go back a week or so and have problems but now it is just as reliable as the rest of my personal saws.

[Arkie]

Arkie is this what the saw looks like? If so most of the parts are NLA. I got one that I restored; had another but had compression problems and parted it out. The saw actually very handy doing brush work. It can be dangerous since it doesn't have a chain brake.

It was very picky about it carburetor settings. I suspect it was the wear and abuse the previous owner did to it. I could get it to run prefect and go back a week or so and have problems but now it is just as reliable as the rest of my personal saws.

Looks about like your pic.
I have couple more of the little homelites that are super 2 and they all look about same. I carry a super 2 on a ATV or in vec for clearing or cleaning small stuff out of roads and ATV trails. Both of the others I have went thru them with carb kits, fuel lines, chain oilers, etc and they start and run good. One of them that runs good indicates 50 psi max when I compared the compression to the bad saw and it looks almost new. I found it in trash and installed a carb kit and fuel lines. The XL2Auto that has 25 psi looks like same block and the super 2's. When I placeed spoonful of 10W motor oil in the spark plug hole the compression goes from 25 max to 150 psi on the bad saw. Do not see any compression release on any of them.
I can still find several parts for the little fellers, (carb kits, duck bills, oilers, fuel lines, chains, sprockets, etc.=) but have to be careful because they are the disposable types.
I just laid the XL2Auto with low compression back for spare parts. Has good clean carb, fuel and oil tanks, magneto, recoil, etc.

I have a Homelite Super EZ that has the manual compression release and don't know how much it reduces the crank compression but it starts easily using the manual compression release.

From what I have seen some 2 cycles will start and run ok with low compression (below 80-100psi) and others just won't go?????