New member new saw

[pinhead]

Just ordered a vac pump off eBay I have been after one for a while anyway so will vac test it looks easy enough 

Also ordered a tacho to tune with just incase my ear is rubbish 

 

Spud 

What causes the poor compression is it ring seal issues or poor combustion chamber shape and or port timing 

 

[pinhead]

Bit of an update got the saw torn down

First thing I found was a split fuel pipe in the tank near the filter so that could have been the cause of irratic running before 

and my vac pump arrived so I vac tested it really struggled with seal on the intake boot but when I got that sealed it held vac fine 

So I took the cylinder off and it all became apparent what had happened 

The wire lock on the clutch side had failed and the pin had slid to the side making a nice gouge in the cylinder the resulting bits of metal were mainly attached to the spark plug and melted around the combustion chamber surprisingly the piston was not too bad all considered but had some scoring on the exhaust side and the second ring land was damaged slightly  

The bottom end bearings felt fine so I flushed the crankcase out with brake cleaner and compressed air until it came clean and then ran some light oil in and turned it over to make sure everything had some lube for first start 

 

I decided to put the piston and cylinder on that I had bought its farmertech brand it may be rubbish but it is an easy enough swap if I decide to put a genuine one on in the future 

And thats it for now waiting for new pipes and everything before i get any further with it 

[spudulike]

On ‎04‎/‎11‎/‎2017 at 03:35, pinhead said:

Just ordered a vac pump off eBay I have been after one for a while anyway so will vac test it looks easy enough 

Also ordered a tacho to tune with just incase my ear is rubbish 

 

Spud 

What causes the poor compression is it ring seal issues or poor combustion chamber shape and or port timing 

 

Poor compression......... scores in the bore, scores on the rings, scores on the piston, worn piston skirts, worn bore, worn rings, holed or cracked piston crown, saw has nipped piston, broken ring, poor cylinder/piston manufacture, too much squish clearance, saw not run in well, carbon build up causing stuck ring.....I am sure there may be more!

[pinhead]

I specifically ment the aftermarket pots not just general cause 

I did notice when I eyballed the 2 side by side the transfer ports were smaller on the farmertech pot but the inlet and exhaust looked less restrictive

[bmp01]

Was the cylinder and piston assy a genuine part - the one that failed?  Not often you see that. .... 

 

After market circlips and rings on the other hand are less reliable,  some builders substitute these parts with genuine ones.

Personally i don't like circlips with those extra "grab here" features on them - the extra wire mass is subject to the same accelerations as the rest on the piston and that means there more likely to move / fret / break. 

 

 

[spudulike]

7 hours ago, pinhead said:

I specifically ment the aftermarket pots not just general cause 

I did notice when I eyballed the 2 side by side the transfer ports were smaller on the farmertech pot but the inlet and exhaust looked less restrictive

Usually poor piston to bore clearance and greater squish. Usually just a poor piston to bore fit lowers it significantly. The compression is unaffected by the transfers and the only port to effect it is the height of the exhaust port as compression is made as the piston clears the top of the exhaust port and heads up to TDC.

[pinhead]

Managed another hour or so last night on the saw and its nearly back together 

 

When I stripped the carb the mesh filter was full of saw dust completely blocked how it ran I don't know 

Any how theory is now is its leaned out and either over reved causing it to fail or nipped a bit with the heat and the broken bit of ring has wiped out the retaining clip for the piston pin 

Sawdust has come from taking in unfiltered fuel due to fuel pipe split 

 

The other thing I have noticed is that it has more compression than before but that could change when it has run a bit 

 

Just waiting for an oil to bar pipe that did not come with the other bits then that side can go together and I can try it out 

[pinhead]

Got it all finished and I have got something wrong the saw wont start at all 

So I poured some petrol on the filter and it ran a bit but wouldn't catch

I noticed that the fuel pipe was slightly kinked so I played with that a load and think it's ok now bit still won't run 

It fires on the choke and then runs for a shirt time on fast idle but dies 

My thoughts are starved of fuel but I cannot work out why changing the mixture screws changes nothing 

So now if I choke it it starts a bit runs longer than it should I think for choke 

Then flick to fast idle and again runs for a few seconds and dies you can repeat this time and again and it just does the same 

Is it something that I have possibly got wrong with the carb build or do I need to keep investigating the fuel pipe 

[Stubby]

4 minutes ago, pinhead said:

Got it all finished and I have got something wrong the saw wont start at all 

So I poured some petrol on the filter and it ran a bit but wouldn't catch

I noticed that the fuel pipe was slightly kinked so I played with that a load and think it's ok now bit still won't run 

It fires on the choke and then runs for a shirt time on fast idle but dies 

My thoughts are starved of fuel but I cannot work out why changing the mixture screws changes nothing 

So now if I choke it it starts a bit runs longer than it should I think for choke 

Then flick to fast idle and again runs for a few seconds and dies you can repeat this time and again and it just does the same 

Is it something that I have possibly got wrong with the carb build or do I need to keep investigating the fuel pipe 

Spud ...............................

[billpierce]

Look at an exploded carb diagram for this saw. Check you put back together ok. Gaskets in the right order etc. H and l screw 1 full turn out from fully in.