How to check compression on a chainsaw

Donny showing compression tester

[@waynetharp]

We have all seen people hang saws by the rope to see if they drop or how slowly drop to judge compression. Every time I see this, I think if a crank bearing was getting bad, it would give the same feeling as good compression. A peek at the cylinder is definitely the best check!👍

[@homp421]

This video proves my point on why compression testers are so important for diagnostics, if someone had justy pulled the muffler and saw the scoring they would say the saw is shot but like donny says the piston is scored but the rings are fine which is what matters so the saw is fine. also there is no way pulling the muffler will tell you that the rings are worn out or that the cylinder is egged out or that chrome plating is worn through on the cylinder. these can only be prompted to check if the compression reads low and the only way to test it is a gauge. anyone who learned 2 stroke theory knows this.

[@ibbylancaster8981]

Donnie, I hope you’re on the mend and are back up and around quickly. A couple of ideas for some videos while you’re laid up would be your views on mix ratios and what mix oils you would recommend. Also the use of the pre mixed fuels. I’ve heard a bunch of bad things about the Tru Fuel brand. My dad always ran 40:1 mix and I have a couple of his old Poulans that look great. Personally, I feel like running a 50:1 mix accelerates the wear over time. I like down in North Carolina and some stores have non ethanol gas, which I religiously use for my mix gas and small engines. Just thinking out loud but I would like to hear your views about it.

[@thebradleysoncatbirdhill6849]

Donny, you have confirmed what has been in my gut for a long time. I've never been one to hang my hat on a compression test. But it is amazing that that is often the deciding point for many people to buy a used saw or not.

[@craigwilson9560]

Donny, great advice. Bought saome great saws thia way. 1 saw i went to buy was an 880. Compression he said was 130 psi. I pulled the muffler and the piston was scored. Showed him what the parts would cost and they deducted that much off. Most dont know tonpull the muffler so this isba great video.

[@db2100]

Great info, thanks. Always wondered what's an acceptable low end number

[@G_Carter]

Very interesting. Thanks, Donny!

[@stusue9733]

Great timing, I was just checking an old saw of mine against a new one and they both came in around 110psi, which I thought was a little low(car guy, first check on a saw). Looks fine on the muffler side I'll keep running it. Thanks

[@davejones3263]

Another great lesson, Thank you Donny

[@donnywalker4691]

Very welcome

[@Brandon.Fischer]

Mr Walker, you’re way further down this road than I am, so I’ll defer to your wisdom, but doesn’t it all matter? When I have a saw in my little hobby saw shop, it always gets a pressure/vac test, piston inspection, compression test, and bore scope. I feel like that is a very inclusive inspection and every point has it’s own tale to tell..

[@brucea550]

That’s the correct way to inspect everything. Not many shops will spend the time, especially on a homeowner saw, but definitely worth doing on a pro saw. Bare minimum I’ll check compression, pull muffler and scope cylinder. Usually an air leak will manifest itself by how the saw idles.

[@edwinhsingmaster9135]

Now I'll have to check my white top, as a comparison. Cheers from Origun, we haven't "gone" anywhere!

[@690_5]

Snow has us stuck in camp the other day. Can’t wait to have enough money to upgrade my 372! Stay safe, everyone.

[@902hand7]

Looking forward to seeing the ol White Top running again with the top end transplant

[@donnywalker4691]

Yes next week thanks

[@jdubya54]

Thanks. Great points

[@MrsSunshine75]

Great video, I got burned on my very first chainsaw that I tried to get goin, little Poulan had 125psi but when it’d get warmed up no power, I was stumped till I learned to pull the muffler, the piston and the ring were scored up real bad!

[@donnywalker4691]

Sorry to hear that

[@Witschor]

@@donnywalker4691what about worm and cold Compression measuring?

[@ronsilva516]

That was informative and please do one thing for me ,,keep the snow I don’t need it right now I still have to to proses a lot of wood in the back yard and bring a nuff on the porch for the winter 😎

[@JoshNoss]

I've seen some ported saws with the base cut that are 200psi+

[@steveriggenbach90]

I agree. Different types of scoring

[@M2theBchainsaws]

Donny, what the idea behind holding the throttle open during the compression test versus not?

[@bulkleyoutdoors]

Hey Donny, the new 372xp oe saws (2020+) from overseas are using gilardoni cylinders instead of mahle. What are your thoughts or experiences with gilardoni cylinders? Wondering if its worth waiting to find an older mahle version. Cheers

[@robertdouglas3456]

Pulling the muffler is best!

[@nateolmsted899]

It’s more than an opinion it’s a fact

[@teamflashtv]

Isn't it all about the rings? The Husqvarna workshop manual says to measure ring gap to see if you need new rings, but surely a compression test gives basically the same information assuming the cylinder wall is OK. I measured compression on one of my rebuilds to test if rings actually do bed in after a period of time and increase compression slightly, rather than just trusting someone else's word on it.

[@ericfuller6326]

I had one of those echo testers but it wouldn’t hold psi. Sent it back to the duke.

[@jensenwilliam5434]

Hello Donny.

[@Witschor]

Carbon keeps the Compression up✌️

[@batmantiss]

Good to know

[@stephanied143]

Have a good weekend

[@donnywalker4691]

Thanks you to

[@RyanTitcomb]

I'm looking for nice clutch cover/chainbrake assembly for a beauty old 266se I've got if you know of any Donny!

[@donnywalker4691]

You can get a husky 61 model dude cover with brake

[@robertdancho9671]

Good good and good.

[@garyhenion9459]

Great stuff Think I’m chasing a air leak on my 371, kinda driving me nuts

[@donnywalker4691]

Put some seals in it and check carb boot and cylinder gasket

[@garyhenion9459]

@@donnywalker4691 👍🏻 Thank you for the reply Just seems to be inconsistent, starts decent and seems to idle good but right off idle when hitting the throttle it falls on its face and will die unless you let off the throttle and ease back into it Definitely going to throw some seals into it this winter

[@JoshNoss]

The 585 and 592 are typically pretty low compression from the factory or so I've heard, 155-160psi or so.. may be wrong

[@fabzacres-blackcat]

Less … more like 130-140 psi, actually had one at 128psi but it STIHL pulled like a freight train thru the timber !

[@JoshNoss]

@@fabzacres-blackcat yeah I heard they were very low, was going from memory off a build thread

[@fabzacres-blackcat]

@@JoshNoss that’s how come from the factory - seems to me like they pull pretty g-damn hard in the timber with that supposedly “low compression” … I don’t think high-compression is the be all/end all like some folk believe. A increase to a sweet spot for sure , but 190-225psi is gonna make em puke 🤮 the lower ends prematurely and generate lotsa HEAT! In fact Husqvarna has a dished piston for the 562xp to lower the compression- I see 2 pistons available - there was a guy that commented on me channel that stated there was another cylinder made that reduced the chamber and that’s why they went to the dished/scalloped piston - I cannot find this other cylinder. Maybe Donny can chime in about this and give us the straight goods as to WHY they made the dished piston and IF there is a supposed “other” cylinder with a smaller combustion chamber

[@JoshNoss]

@@fabzacres-blackcat seems that a 562 mark 2 is out overseas, would be interesting to see what they've got going on the inside once they're available here.. my 3 saw are the 592, 572, 550mk2 and I agree about the high compression statement, in these 2 strokes it's not as important as some people think

[@fabzacres-blackcat]

@@JoshNoss mark ii n/a in the states to the best of my knowledge- heard it’s slightly less weight but performance wise no gains … it depends on the saw imho - the g372xp clone I built for a farmer had almost .055 squish so in THAT case it makes sense to use a thinner base gasket or for the machine crowd , machine the squish and the base. For a saw that comes from the FACTORY at .027 - .030 squish I think you’re chasing your tail and it’s not worth

[@kurtsteele5587]

How's Donny

[@chrissirr4036]

hard to pull saws . can you explain causes Chris

[@sawmanbigtreeslayer2360]

No grease on clutch bearing. Total failure of the clutch bearing. I wish I could post pictures but can't. Scored piston. If the saw has been sitting for years it could be dry. No oil on the piston or rings.

[@AA-sk2yi]

😎😎😎👍👍👍

[@DyslexicLunatic]

A chatterbox has limited usefulness. Don't want to watch 7 minutes of video for 30 seconds of useful information. Just me. Others may have time to waste.