periodic low/no compression on 357xp

[spudulike]

The ones that screw in to the cylinder are M6 and the ones on the support bracket are M5.

[phirow]

When this happens remove plug and put a drop and I MEAN A DROP of two stroke replace plug if it starts, you have a problem. did you do it yourself? if not take it back to the guy who repaired it.

Has been know just to ring it. but you have to glaze bust the piston if that happened the the piston expands to much losing the compression.

[mattyboy]

given back to my repair man and he is going to change the seals on the crank as he thinks that might be the reason and also going to change the decompression button for a bolt. will wait and see...

[spudulike]

given back to my repair man and he is going to change the seals on the crank as he thinks that might be the reason and also going to change the decompression button for a bolt. will wait and see...

 

The seals will only effect primary compression - that is the compression that happens within the crankcases used for fuel vapor transfer to the top of the cylinder and not secondary compression which is the compression you really feel on the starter cord - the one which we measure through the spark plug hole and is created by the piston travelling between the exhaust port and top dead centre.

 

Even if the seals were completely shot, you would feel no real difference on the starter cord.

 

Sorry to be the bringer of gloom:thumbdown:

[Rich2484]

The only way to test the crank seals are vac and pressure test.

 

The rest is as spud said.

[mattyboy]

thanks for your replies and your time guys.

 

Do you think you can hazard a guess to what it would take to repair?

[spudulike]

thanks for your replies and your time guys.

 

Do you think you can hazard a guess to what it would take to repair?

 

It depends if the issue is really low compression or not, if it is then it will be either a faulty decomp valve, worn piston, worn ring, worn cylinder, worn small end or gudgeon pin piston holes or a possible small seize or gummed up rings.

 

Repair is down to diagnosing the route cause and putting it right, if you get stuck then I am happy to look at it for you and do a good long term repair and ensure the saw is working as it should - I am running a pretty hot 357xp so know them inside out.

 

I hope your tech knows his stuff and gets to the bottom of it but the first thing I would do is to get a compression reading and see if it is good or bad and go from there - very difficult to say how bad it is without seeing it but everything is salvageable:thumbup:

[mattyboy]

Got my saw back from my repair guy and he changed the decompression button for a bolt as i dont find the 357 at all hard to pull to get started.

 

Ive taken some photos of the piston and here they are, it seems fine to me what do your experienced eyes think?

[MATTMOSS]

Doesn't look bad from that pic.

[mattyboy]

another pic of piston