Stuck boss in cast iron compressor cylinder head-help

[peter99]

I'm trying to remove a 75mm diameter course threaded boss on my compressor cylinder head to access the exhaust valve underneath which isn't working. The inlet boss came off reasonably but this one is being a sod. I'm worried any more force will crack the head mounts etc.

The head is on the cylinder block to enable some leverage to be applied but is easily removed.

Have soaked the top of the thread with quality penetrating oil for 2 days, have had a four foot bar on the socket (48mm) with no sucess. Have also warmed the head around the boss and used the same bar on it (although only with a plumbing torch so just hot to the touch, not as hot as say oxy/acet would get it).

I don't have oxy/acet so would have to take the head off the cylinder block to take it to someone which would mean putting the head in a vice which I think could break it when the pressure undoing the boss was applied.

Should I keep soaking/warming (although only lightly)/trying it every day or try something else?

Anybody any advice please? I'm in Yorkshire if anyone knows of anywhere that can help as an alternative.
Thanks in advance, Peter

 

[madkayaker]

ｔｒｙ　ｓｏｃｋｉｎｇ　ｉｎ　ｄｅｓｉａｌ　ｆｏｒ　ａ　ｆｅｗ　ｄａｙｓ　ｔｈａｔ　ｍｉｇｈｔｓｈｉｆｔ　ｉｔ　

 

[peter99]

Madkayaker did you mean diesel or is desial a brand name fluid? tried googling it without success

 

[madkayaker]

ｉ　ｍｅｎｔ　ｄｉｅｓｅｌ　

 

[peter99]

Thanks mate, I might put my head in there with it as I'm dreaming of stuck bosses now

 

[rtbcomp]

Madkayaker - are you using funny characters in your post? IT just comes out as squares on my PC, but obviously Peter can read them!

 

[madkayaker]

ｉｔｓ　ｐｌａｙｉｎｇ　ｓｉｌｌｙ　ｂｕｇｇｅｒｓ　

 

[rtbcomp]

Cheers, MadKayaker - pity I can't read it!

 

[Archie]

To be honest rtb it's lucky you can't.....



Readable on mine but looks pretty weird.

 

[rtbcomp]

To be honest rtb it's lucky you can't.....



Readable on mine but looks pretty weird.

I was wondering whether the Forum God was protecting my sensitive soul

All his other posts are readable - weird.

 

[madkayaker]

is that better

 

[Archie]

Much.

 

[madkayaker]

good. I meant DERV but can't spell!!

 

[MrFluffy]

Tap it gently with a hammer before you try it. Not too fierce or you will crack the casting, but you want a little shock to try and break the corrosion between plug and casting...
If you could get a impact tool on there that'd be beneficial too...

 

[rtbcomp]

is that better

Yup!

 

[madkayaker]

don't know what went wrong there

 

[drivewasher]

Try an air impactgun on the socket you have to shock the threads into releasing. I use this method for all sorts of stuff to stop the thread or bolt breaking.
My 1/2 inch impact wrench has a 4 strenght settng so I start from 1 and work it up the numbers until thread starts to move you will be suprised how much difference it makes

 

[andypocock]

Whip the head off and stick it in the oven for a hour at the highest setting. Once it has cooled enough to handle bolt it back on to hold it firm and have another go.
Works even better if you leave it in the freezer for 24 hours before cooking it.

If the wife doesn't like that idea I'd go with a couple of days soak in a bucket of diesel.

Andy

 

[peter99]

Wouldn't that make it well done on the outside and raw on the inside? would that come under HSE or environmental health?

 

[peter99]

forgot to say the socket is large so is bigger than half inch drive, my impact gun doesn't fit it. brake fluid was recommended too by a mechanic this afternoon.