What's on your bench today?

[Matthew Arnold]

That sounds like it is low on compression and with the decomp being used, the compression isn't enough for combustion. How is the cutter when it is warm - difficult to start?

 

Perhaps time for new rings or new piston and rings!

 

Cutter is fine when warm and runs absolutely fine when it is up to temp. Had the exhaust off to see the piston and rings and all looked good on that side. Replaced one of the exhaust bolts as one of them had loosened and falllen somwhere along the line.

 

I agree with Spud. It does seem likely that the compression is down due to wear and tear, and is just too low when decompressed as well. Although it is starting fine without the decompressor, if the comp is down you should be noticeing a lack of power in use, and a lag in getting the blade up to speed.

 

If the performance and hot start is OK, then maybe its just a duff decompressor which is not popping up quickly enough after the first fire.

 

In any case a compression check might not be a bad idea if you have a guage.

 

 

Just a duff decompressor luckily. Put the new one on and tried it from cold with no problems. No lack of power and picks up fine when put to full throttle from idle.

[spudulike]

I've got my Husky 51 on the bench and just done compression test. It maxed out at 130 psi which, from reading back in thread, is on the low side of normal. Am I correct?

 

Incidentally, I also checked my Chinese tat and, although it is harder to pull over and appears to have better compression, maxed out at 120.

 

It is a bit low, what gauge have you got and how are you doing the test? I normally put the saw on the "fast idle" start setting and give it 5-6 brisk pulls to get maximum reading. The saw should be cold but be fuelled and pulling fuel through.

 

The first single pull should produce a reading of around half the maximum reading after 5-6 pulls otherwise the ringa are probably suspect.

 

The Chinese saw may have a smaller starter pulley making it feel as though it has more compression.

[Hoggin]

I used a Mac Tools gauge I borrowed from a technician at work. I did the test cold by screwing in the gauge an turning the engine over several times until the pressure stopped climbing. However, it has just dawned on me that the throttle was closed when I did it. Presumably, I need to wire it open?

 

I'll have another go tomorrow afternoon. I'll also have a go at getting the muffler off so that I can have a look at the condition of the piston. It's interesting that you mention the rings because the tech I borrowed the gauge off said something about rings sticking.

 

Thanks.

[spudulike]

I used a Mac Tools gauge I borrowed from a technician at work. I did the test cold by screwing in the gauge an turning the engine over several times until the pressure stopped climbing. However, it has just dawned on me that the throttle was closed when I did it. Presumably, I need to wire it open?

 

I'll have another go tomorrow afternoon. I'll also have a go at getting the muffler off so that I can have a look at the condition of the piston. It's interesting that you mention the rings because the tech I borrowed the gauge off said something about rings sticking.

 

Thanks.

 

Opening the throttle will help you get to the maximum a bit faster but probably wont help you register higher compression.

 

Do yourself a favour and measure a modern low hours saw so you can get a bench mark or ask the owner what he generally gets on good running saws. All gauges are a bit different, some register just a whiff of compression and some register nothing on small engines and only work on cars etc.

 

I have three gauges and all register different amounts but generally stick to using one - typically the Gunson hi gauge and get 150 - 170psi on fresh run in engines with this gauge.

 

Worth getting a benchmark before worrying.

 

The ring could be gummed up but if the saw runs, it is unlikely.

[stokesley]

a 346xp with broken safety catch and 3 ts350s which i should make 2 runners from

[Adamam]

I have this...friend...who took apart a 254xp so as to replace the piston.

 

I...I mean my friend is putting the saw back together, but I...he has a mystery rubber plug with no home.

 

What a fool, eh?

 

Where in heck does my friend's rubber plug fit?

 

I promise to pass the information on, obviously!

 

 

Here is where I'm guessing...my friend is guessing the plug must fit (somewhere):

 

 

Here is the plug:

 

[Rich2484]

Looks like a vibration plug to me!

[Adamam]

Looks like a vibration plug to me!

 

Yeah, but where does it live? I (for the fool is me! Who'd have guessed) can't for the life of me find a corresponding hole!

[Rich2484]

At a guess without look I would have said somewhere with the handles. Are they all on and covered with caps?

[Adamam]

It's not from the front handle I don't reckon. I looks like it should sandwich between the two parts of the case, but I'm buggered if I can see where.