Husqvarna 365 compression

[Mr Mower Man]

I've been working with a Husqvarna 365 chainsaw that came in with a damaged cylinder and piston. It would run fine for just a few minutes, and then it would start to struggle and then finally die. When I couldn't get it started anymore, I measured compression, which was 50 lbs., way too low. When I removed the muffler to see the piston, I saw a lot of scoring on it and on the ring. So I found a cylinder/piston assembly from Stens, and bought it because it was easily the best price around on these parts. I also got some replacement crankshaft seals for it, and got it all back together yesterday evening, and it runs terrible. It will idle for a few seconds and die. I can get it started right back up, but it won't idle for very long before it dies again, 10 seconds at the most. And it won't rev up at all. As soon as I open the throttle, it dies instantly. I tried to mess with the carburetor adjustments, but nothing seemed to make any difference. So then I measured the compression. I was only able to get 90 lbs. out of it (Husqvarna compression gauge, air filter removed, throttle completely open, and 4 brisk pulls on the rope). So I removed the muffler to see if I could see anything. Piston and ring looked just fine to me, as it should have, being brand new. I checked the compression again with the muffler off, and I got 95 PSI. I also verified that the cylinder compression relief valve is working properly; I pushed it in at first, and the compression pushed it back out. But honestly, the compression isn't enough that I even need to push it in.

I'm not nearly as good with 2-stroke engines as I am with the other stuff. But I thought that a minimum of 100 PSI was necessary for one of these engines to run at all. And compression was supposed to be at least about 120 PSI anyway, and probably a little higher. Is there anything other than piston/cylinder that affects this upper end compression that I was testing? I'm starting to think the Stens aftermarket cylinder and piston assembly was a mistake. What do you think is going on here?

[KE4AVB]

Hopefully you did oil piston and cylinder with two cycle oil upon assembly and not dry install.

Now the compression actually should be closer to 140 or better with a new piston, ring, and cylinder. Other than piston, ring, and cylinder (PNC) the only thing that affects compression beside the fuel mix is the plug and decompression valve. Even if the decompression was left out it still should have enough compression to run though it will sound funny. Something I did on a 55 a few years ago when they vendor left the dummy plug out of the kit.

To me it sounds like something is amiss with the PNC set . All you can do is take it back a part and inspect the PNC. I kinda suspecting a broken ring.

If I remember that the Stens cylinder is chromed. I don't install too many cylinders either but I haven't had any problems with new PNC kits, be it OEM or AM versions though AM kit are of a lower quality.

[bgsengine]

What I would do before anything else if it has enough compression to start right up easily , would be to check the crankcase vacuum/pressure and make sure I got the seals in properly without damage and that the cylinder jug gasket was installed right, and eliminate any crankcase or pulse hose (where equipped) issues. if that all tested out properly (holds 7 PSI max pressure for 1 minute and 14 inches of vacuum for 1 minute) then I'd use the same tester and test the fuel system/carburetor (pressure and vacuum) to eliminate any fuel system issues, and then a closer look at carburetor. Chances are good you may discover an issue with one of those 2 tests - Also of note, don't matter how many pulls - you want to test compression with throttle wide open, and crank it over until compression tester needle *stops moving* be it 3 pulls or 10 pulls

[KE4AVB]

Agree about the number of pulls can vary but to kinda to give an idea of the normal compression readings. Here I have 359 47mm where the 365 has 48mm. I am getting 130 with throttle closed and using a short rope pull. This is after only 4 pulls. Hand turning the flywheel I got 30 psi.

[Mr Mower Man]

Hopefully you did oil piston and cylinder with two cycle oil upon assembly and not dry install.

I did coat the cylinder and top of the piston with oil, but not 2-cycle oil. Smoked like a freight train when I first started up, but the longer it ran, the less smoke I saw.

What I would do before anything else if it has enough compression to start right up easily , would be to check the crankcase vacuum/pressure and make sure I got the seals in properly without damage and that the cylinder jug gasket was installed right, and eliminate any crankcase or pulse hose (where equipped) issues. if that all tested out properly (holds 7 PSI max pressure for 1 minute and 14 inches of vacuum for 1 minute) then I'd use the same tester and test the fuel system/carburetor (pressure and vacuum) to eliminate any fuel system issues, and then a closer look at carburetor. Chances are good you may discover an issue with one of those 2 tests

What sort of tester would I use for this? I don't believe I have one.

[bgsengine]

What sort of tester would I use for this? I don't believe I have one.

If you go to the forum home page and read the 2-minute drill article I wrote some time back , you will see pictures of the pump. I believe I also made mention of a link to one on Amazon (probably outdated now) but the current echo version of the tester uses a Mightyvac Silverline Elite MV8500 Kit (much cheaper than the original Echo tool I use in the article) - Only thing is that Echo adds in their own adapter (basically a hollow tube tapered on both ends) to create the 91149 Tool kit


Crankcase pressure test is simple enough - block off intake and exhaust ports and plug the impulse hose (if it is there or separated from the intake port somehow) and pump up to 7 PSI *maximum* and wait 1 minute , if pressure holds your crankcase is all fine - if not, spray soap and water around to find the leak. Then pull a vacuum to 14 inches and if that holds too, your crank seals are holding fine , if not then your crank seals are bad.

Carb testing is just as simple - fish out fuel filter, remove it and pressurize to about 7 PSI and see if it leaks down - if it does, move tester to carb inlet nipple and repeat , if no leak then you got leaking fuel lines, if you do have leaks then your carb metering needle is leaking (or a gasket or diaphragm) can also test the purge system and tank vents using the same tool, and as you see in the article, the tool is also very handy in carb service work.

[Arkie]

bsengine is right on with his advice. (about one that won't idle, but start up briefly)
pressure/vacuum test first
then if ok
check the fuel system.

You can get more opinions here if desired. Lots of Husky guys hang out here. Just register, post and ask. Sometimes your post gets on pg 2 fast due to other posts and replies get slow so to get back on pg 1 just keep asking ??'s.
http://www.arboristsite.com/community/f ... hainsaw.9/

It should start and run with the your new compression readings if all else is ok. When the rings are seated good you will see very little difference in compression readings with a dry cylinder vs adding little oil into the cylinder on a chainsaw. When doing comp test on a chainsaw pull the rope until the gauge stops going up. (and use a compression gauge designed for small cc engines) Not a automotive gauge. Rotate the crank while watching pressure and if not sealing good check around the bottom of the jug to block seal. (using soap/water/air pressure) sometimes a compression release valve will leak little bit and not upset the running of the saw. (because it's above the piston) Also install a good spark plug. A measley bad spark plug can really make you feel weak after you have re-built all and changed it last and get a good run.

If the fuel lines and pulse line is ok and the carb holds 5 psi pressure on the input you might have a clogged carb. (orifice)

The mityvac MV8500 silverline elite is a good pressure/vacuum tester and can be re-kitted if it goes south. You sometimes see used ones on flea bay but if used one needs a kit the kit costs at least $20. Keep a heads up when using on vacuum and don't let fluids such as brake fluid get sucked into the pump and trash. I sometimes used a piece of felt or cotton in the input line when doing vacuum test as a filter to catch small trash particles before they get into the mityvac pump..
I've used one for years and never had to install a kit, have to clean the little rubber check valve every once in awhile if it draws in trash when doing vacuum and gauge not holding hold vacuum seal.

You can also get some ideas from the above link about cheap pressure gauges, like for example blood pressure bulb pump, etc, but if you work on 2 cycles and piddle around with stuff very much eventually get a Mityvac and don't look back. (very handy for automotive, testing vacuum lines, vacuum diaphragms, bleeding brakes by yourself, to mention a few)

The bulb type inline spark tester also works great for testing for a continuous spark on a erratic chainsaw.

Patience is a good thing when flogging one like you describe.
Sometimes just letting the saw rest and your brain rest for a few days really helps the process.

[Mr Mower Man]

What sort of tester would I use for this? I don't believe I have one.

If you go to the forum home page and read the 2-minute drill article I wrote some time back , you will see pictures of the pump. I believe I also made mention of a link to one on Amazon (probably outdated now) but the current echo version of the tester uses a Mightyvac Silverline Elite MV8500 Kit (much cheaper than the original Echo tool I use in the article) - Only thing is that Echo adds in their own adapter (basically a hollow tube tapered on both ends) to create the 91149 Tool kit


Crankcase pressure test is simple enough - block off intake and exhaust ports and plug the impulse hose (if it is there or separated from the intake port somehow) and pump up to 7 PSI *maximum* and wait 1 minute , if pressure holds your crankcase is all fine - if not, spray soap and water around to find the leak. Then pull a vacuum to 14 inches and if that holds too, your crank seals are holding fine , if not then your crank seals are bad.

Carb testing is just as simple - fish out fuel filter, remove it and pressurize to about 7 PSI and see if it leaks down - if it does, move tester to carb inlet nipple and repeat , if no leak then you got leaking fuel lines, if you do have leaks then your carb metering needle is leaking (or a gasket or diaphragm) can also test the purge system and tank vents using the same tool, and as you see in the article, the tool is also very handy in carb service work.

OK, I think I need to invest in some quality 2-stroke engine tools. I want to get one of these Mightyvac Elite 8500 kits. Elementary question: with the impulse hose blocked, and the exhaust and intake ports blocked, where does the air get into the crankcase? Spark plug hole? And is there a fitting or some adapter in that kit for me to use there? Also, what sort of tool do you recommend to block off the intake and exhaust ports? I think I've see these things before, but I can't remember where. I'd like to find all these things, and rather quickly too. What's the quickest path to these quality tools?

[bgsengine]

Elementary question: with the impulse hose blocked, and the exhaust and intake ports blocked, where does the air get into the crankcase? Spark plug hole? And is there a fitting or some adapter in that kit for me to use there? Also, what sort of tool do you recommend to block off the intake and exhaust ports? I think I've see these things before, but I can't remember where. I'd like to find all these things, and rather quickly too. What's the quickest path to these quality tools?

Oh right I forgot that - Echo has the block off trapezoid (non-permeable rubber) part number 91041 and the 14mm spark plug pressure port 91018 (and if you get any 10mm plug units , there's 91081 10mm adapter) both which go in the spark plug hole and have nipple for the hose to connect to. The 91041 block offs work on most machines unless they have an "oddball" port shape (they are quick since you only have to *loosen* the muffler and carb enough to slip them all the way in and wedge between bolts then just tighten the bolts down - the block off plates from other places (and for the odd-ball shaped ports) you have to physically remove muffler and carburetor to install the plates.

we have all those listed on ebay (I dont list the pressure tester any more since you can just get it much cheaper from Amazon and then use one of the adapters in the kit to hook various pieces of hose together.. Although the hose adapter 91121 can be ordered from an echo dealer too.

[Mr Mower Man]

Thanks everyone. Based on your recommendations, I just ordered a MightyVac Elite 8500 kit, and some other choice pieces from Brian's ebay store. The worst part now is waiting for them to arrive. My customer isn't going to be very happy about waiting either, but I guess that's the price I pay for making sure the job is done right, and not having the right tools already. Investing over $100 in tools doesn't bother me in the least, if they're good quality and I'll have them a long time. Over the long haul, these tools should be worth way more to me than what I paid for them.