Husqvarna 455 Rancher

[lefty]

I have this saw that isn't holding vacuum. Pressure is fine.

I know I can use soapy water and look for bubbles on pressure but am not sure how to locate a vacuum leak. Any advice is appreciated. I'm assuming it's a crank seal? I would think any other leak point would fail in both directions but that's just an assumption at this point.

[KE4AVB]

Boy it been over ten years since I had to replace these seals.

That is about the only area that leak only in one direction. But if you just to verify which seal is the culprit remove the clutch and flywheel. Then turn the saw on each side while pulling a vacuum and place some fuel on the seals the leaking one will draw in the the fuel mix.

Just note you don't just replace one seal. You may have replace both bearings, seals, and gaskets. Just torque screws to standard torque settings.

[lefty]

Thank you.

Any opinion on what an acceptable compression should be on this saw? I'm showing 113 psi. The saw is used by a homeowner to chop firewood.

[bgsengine]

Thank you.

Any opinion on what an acceptable compression should be on this saw? I'm showing 113 psi. The saw is used by a homeowner to chop firewood.

113 PSI is about bare minimum rock bottom number for most any modern 2-stroke. If it has gone far enough that seals are hardening (which is usually why they leak) it has probably experienced extended high heat. I'd probably suggest a new saw for that customer, but if you sell labor on the cheap , might get away with low cost aftermarket parts, but either way likely would need a full tear-down and rebuild, new jug & piston, new seals, full gasket set, plus all the normal maintenance items, and a good cleaning, might serve another 3-5 years depending on maintenance. But for a pro shop - rebuild cost would exceed buying new saw. Of course, could just try and fix the seals (possible to replace them without splitting the crankcase, if you work carefully.) which might help it run another winter (if lucky) but I'd call it throwing good money after bad.

[KE4AVB]

Compression reading does depends on several factors here. First you must be using a compression gauge designed for these small engines with the schrader valve at the cylinder end of the hose. Then reading must be taken with the throttle held wide open, the decompression valve closed, and the cylinder slightly wet with fuel mix as is normally present with good carb and sealed intake system. IF bone dry then the reading will be lower. Leaking decompression valve will lower the reading too. I have found that on my Actron compression gauge that most 2 cycles will only start if above 100 psi minimum with the throttle set at the starting position. Now these saws do have well over 140 psi new; hence, the reason for the decompression valve. I have seen some with 180 psi compression.

Now if the compression is below 100 psi in normal throttle starting position then you are just fighting yourself until until a new PNC set is installed. In the 15 yrs I only seen one saw to start up at 95 psi and that was a Poulan that end up with a new PNC as it failed the in the cut tests. And I do highly recommend anyone repairing these saws to actually use them in wood cutting cookies.

[lefty]

Sorry for the delay. Thanks to all for the info.

Compression release was closed and throttle open. I tested assembled and with the carb off and got similar readings. My tester does have a check valve in the hose.

KE4. Not questioning, but for learning purposes, what is meant by sealed intake system? I will typically hold the throttle open. I typically don't notice a difference between carb on or off but I'd like to do it correctly so I appreciate the info.

I did wet the cylinder with fuel when the carb was off, through the plug hole. Thank you.

[KE4AVB]

Otherwords a sealed intake means all seals and gaskets working as intended which include the crank seals and gaskets as the crankcase is part of the intake system. Some techs forget how a two cycle intake system works.

But with the info provided it does sounds like the PNC is near the end of its life span. It still usable as a home owner saw but not for heavy homeowner used. What I mean by heavy is the cutting of cords and cords of firewood. Personally I would recommend replacing the PNC or a new saw. IF it was my personal saw where labor to repair doesn't count then I would overhaul it. The last saw I rebuilt for myself was a $130 Poulan that costed at the time nearly $100. But it is to note I was upgrading the PNC so if the saw was purchased as build a factory version it would had been a $180 saw at the local retail shops. I had upgraded to a NCC (Nickel Ceramic Coated) cylinder from the plain cylinder and boy did it look rough when i installed it but as the nickel burns off it cleaned up.

And that Husqvarna if the case is in good shape is still worth rebuilding in my opinion but is just my opinion. It is the customer's decision if they want to go that route. Overall costs is always a factor.