Damaged muffler and cylinder

[Muddy42]

Old 1980s Husqvarna 50 Rancher (with the white top)

 

Whilst I am waiting for the replacement piston to arrive, I have stripped the saw back, cleaned and then reassembled to pressure/vacuum test.  I ended up having to submerge the saw in a bucket of water to diagnose the exact location of an air leak.  The crank seals are good but air is escaping where this plastic impulse line pokes into the cylinder (see photo highlighted in red). To be clear this is the original MAHLE OEM cylinder and plastic intake partition.  The plastic is a bit discoloured but seems sound, I think air is simply escaping round the side where it meets the cylinder.

 

Is there some kind of liquid rubber sealant that I should use here to fix this? There was some rubber goo on here and the rubber intake boot when I took them apart.

 

Thanks

Edited April 24, 2023 by Muddy42

[spudulike]

There should be a silicone sealing sleeve that pushes in to the cylinder and that bit you have marked pushes in to this. This part can split and it is usually best to replace.

I have used nitryle fuel pipe rather than the silicone part as it works, is far cheaper and is stronger although silicone does have a higher temperature ceiling - choice is yours.

You can seal with a smear of liquid gasket just don't use too much and block the impulse. 

The rubber intake manifold can sometimes leak as well and may benefit from a smear of liquid gasket or replacement.

Make sure you put plenty of WD40 on your clutch if it was still in place when you "bathed" it.

[Muddy42]

2 hours ago, spudulike said:

There should be a silicone sealing sleeve that pushes in to the cylinder and that bit you have marked pushes in to this. This part can split and it is usually best to replace.

I have used nitryle fuel pipe rather than the silicone part as it works, is far cheaper and is stronger although silicone does have a higher temperature ceiling - choice is yours.

You can seal with a smear of liquid gasket just don't use too much and block the impulse. 

The rubber intake manifold can sometimes leak as well and may benefit from a smear of liquid gasket or replacement.

Make sure you put plenty of WD40 on your clutch if it was still in place when you "bathed" it.

Thank you. I hadn't noticed the silicone sleeve until now. I thought it was just part of the cylinder. Mine actually seems sound, but I will investigate sealing it or replacing it with a pipe that has a slightly narrower bore.

 

Edited April 24, 2023 by Muddy42

[Muddy42]

@openspaceman  @Stubby

 

I have rebuilt the top end but am now having issues with air leaks! Specifically the diagonal carburettor screw that holds the throttle and butterfly in.  I have taken the whole screw out and cleaned it, but with no improvement.  See video below. Is there a way to fix this?

 

 

[Muddy42]

Sorry ignore me! The saw holds pressure and vacuum when sealed behind the carb with a piece of rubber.

 

[spudulike]

Doh

[Muddy42]

I wasn't thinking properly!  I'm just waiting for a new muffler to arrive and then we'll see if it fires up.  Compression doesn't feel amazing (by hand on the starter cord) with the new piston, but I'm hoping that's just excess oil or lack of a break in period.

[spudulike]

The excess oil in the bore will usually give insanely higher compression as it seals the piston to bore nicely.

I take it the piston was the correct diameter?

[Muddy42]

19 hours ago, spudulike said:

The excess oil in the bore will usually give insanely higher compression as it seals the piston to bore nicely.

I take it the piston was the correct diameter?

 

Yes 44mm.  I don't have a compression tester.  So I'll just see if it starts.

 

[spudulike]

When you cleaned the transfer off, you didn't rub up and down the bore excessively in one area did you? This can cause a very shallow cavity that can knock off compression. It is better to get rid of most of it with chemical and rubbing around the bore.

Try running it, if the compression is borderline, you will have issues starting it when it is hot.