What's on your bench today?

[spudulike]

Got a 372XP in with a well buggered piston. The saw has been fitted with an aftermarket kit and looks generally low hours.

 

From the damage, it looks like the ring broke and caught on the lower exhaust port on the downward stroke that smashed the top off the crown of the piston. The strange thing was the ports and bore have zero damage.

 

I have flushed the lower crankcase to get rid of the aluminium bits - after a bit if a scare, the bearings feel fine - a big notch in one area cleared after a flush out.

 

A new Meteor piston has been fitted on the aftermarket kit and the exhaust port has been re-beveled to ensure the ring doesn't snag again.

[spudulike]

Got the 395XP back with the spark plug insert that had blown out - it was aluminium and looks like it had split:thumbdown:

 

First operation was to ream out the hole - forget those cheap reamers - HSS hand reamer used here to prepare the hole for the tap.

 

Taps - a taper and bottoming tap in the picture - you start with the taper and finish with the bottoming one but in this instance - the thread was good with using the taper only so just used this tap. No need to clean the thread and make the insert looser than is necessary. Taps HSS again!

 

Picture of the finished thread - good, clean and deep - ready to receive the insert.

 

The insert is carbon steel so is damn hard and is held in with thread lock - high temperature thread lock:thumbup:

 

The cylinder was warmed four times with a plumbers lamp before refitting, running, cooling and checking the plug for tightness again.

 

This time, the repair should be a good one:thumbup:

[GardenKit]

I did a bit of research on this a while ago, Steve, but read that carbon steel inserts should not be used in aluminium heads.

 

There seem to be two reasons

 

1, Steel dissipates heat slower than Aluminium, so the plug cannot cool quick enough and may overheat.

2, Aluminium expands about 2.5 times faster than steel, so the insert becomes slack quickly,

 

I was put off using steel because of this. It seems that Anodized aluminium inserts should be used.

 

I have never done either so cannot comment from experience, but will be interested to hear your results.

 

Barrie

[Eddy_t]

Are you sure about the heat dissipation Barrie? I've always found ally retains heat much longer than steel

 

 

Sent using Arbtalk Mobile App

[Mull]

Are you sure about the heat dissipation Barrie? I've always found ally retains heat much longer than steel

 

 

Sent using Arbtalk Mobile App

 

 

Ally not as dense as steel, so surely can't retain heat as long?

I may be wrong.

[GardenKit]

Yes Eddy, Aluminium has a greater thermal conductivity than steel. In other words, it absorbs heat faster.

[Mull]

Yes Eddy, Aluminium has a greater thermal conductivity than steel. In other words, it absorbs heat faster.

 

 

And loses it quicker.

[GardenKit]

Ally not as dense as steel, so surely can't retain heat as long?

I may be wrong.

Thats right, a lump of steel will retain its heat much longer than a lump of ally.

[Mull]

Are you sure about the heat dissipation Barrie? I've always found ally retains heat much longer than steel

Sent using Arbtalk Mobile App

 

 

In which situation did you find alloy retaining heat longer than steel eddy?

[Eddy_t]

In which situation did you find alloy retaining heat longer than steel eddy?

 

 

Hedgecutter bearing and gear changes, fabrication of various parts, likewise I found quenching of ally quite ineffective compared to that of steel.

 

 

Sent using Arbtalk Mobile App