2010 455 Rancher low compression/won't start

[CanadianGoldenEagle]

All,

My 455 rancher was working smoothly until just before Christmas then it refused to start after refueling. When checking the compression I'm only getting between 50 and 75psi.

I've used completely fresh gas and replaced the following:

fuel filter
fuel lines
carburetor
spark plug
cylinder head
piston
all gaskets/seals

Could someone please advise what else could be wrong as I'm out of ideas? I'm presently having to resort to my backup 36cc Craftsman (which is not really powerful enough for the trees I'm needing to go through)

Thanks in advance

 

[RedFir Down]

I'd bet stuck piston ring.
I'm not sure why but I've had a dozen or so 455 come in with a stuck ring.

 

[CanadianGoldenEagle]

I'd bet stuck piston ring.
I'm not sure why but I've had a dozen or so 455 come in with a stuck ring.

The new piston came with a brand new ring and so that's been replaced too. The new piston head came with an arrow on the top of it. I've got the arrow pointing towards the intake, as there weren't any instructions with it and the old piston was the original one so no markings.

Could I have put the piston head the wrong way round?

 

[drumbum]

What tester did you use?

 

[irhunter]

The new piston came with a brand new ring and so that's been replaced too. The new piston head came with an arrow on the top of it. I've got the arrow pointing towards the intake, as there weren't any instructions with it and the old piston was the original one so no markings.

Could I have put the piston head the wrong way round?

Yes. You have it in backwards.

BTW, you really should be pressure/vac testing the case before running the saw after pulling the cylinder. Maybe you did that, but didn't mention it. An air leak would not cause your low compression, but it will fry your new piston.

Roy

 

[CanadianGoldenEagle]

What tester did you use?

This one: https://www.amazon.ca/ATP-Compression-Cylinder-Pressure-Adapters/dp/B07GGZY42Q

I did some research into the correct ones for small engines and also searched on Amazon for a Small Engine Compression kit.

 

[irhunter]

It sounds like you may be doing this work without having the shop manual.

I don't have the 455 manual, but the 450 manual clearly shows the arrow points to exhaust.

You can go to the Beg For Manuals thread and ask for the shop manual and IPL for you saw.

Roy

 

[CanadianGoldenEagle]

Yes. You have it in backwards.

BTW, you really should be pressure/vac testing the case before running the saw after pulling the cylinder. Maybe you did that, but didn't mention it. An air leak would not cause your low compression, but it will fry your new piston.

Roy

Thanks irhunter.

The new cylinder case seated correctly on the new gaskets and did seem to form a full seal. I haven't got the ability to do a full test on it to confirm though. I have this one - https://www.amazon.ca/Mityvac-MITMV8500-Silverline-Automotive-Vacuum/dp/B0002SQYUA?th=1 - bookmarked in Amazon ready to purchase if it'll help.

 

[mountainlake]

You have the piston in wrong. the arrow points to the exhaust. Most likely broke the ring already. Steve

 

[irhunter]

Thanks irhunter.

The new cylinder case seated correctly on the new gaskets and did seem to form a full seal. I haven't got the ability to do a full test on it to confirm though. I have this one - https://www.amazon.ca/Mityvac-MITMV8500-Silverline-Automotive-Vacuum/dp/B0002SQYUA?th=1 - bookmarked in Amazon ready to purchase if it'll help.

Cool. That is the right brand and right tool. You may/may not need the full kit.

In any case, you will want to cobble-together block-off plates, and such, to get that tool hooked up to your saw. While all saws should be tested...clamshell saws are especially important to check. And, especially those plastic-bottom Huskys.

Here is a great pressure test vid.



Here is a block-off thread:

https://www.arboristsite.com/threads/show-us-your-pressure-vac-tester-and-block-off-plates.368677/

Roy

 

[atpchas]

I have this one - https://www.amazon.ca/Mityvac-MITMV8500-Silverline-Automotive-Vacuum/dp/B0002SQYUA?th=1 - bookmarked in Amazon ready to purchase if it'll help.

Consider this:
https://www.tooldiscounter.com/prod...e-hand-vacuum-and-pressure-pump-kit-mitmv8500

 

[singinwoodwackr]

The new piston came with a brand new ring and so that's been replaced too. The new piston head came with an arrow on the top of it. I've got the arrow pointing towards the intake, as there weren't any instructions with it and the old piston was the original one so no markings.

Could I have put the piston head the wrong way round?

Arrow goes to exhaust…