Piston, rings, pot where to start?

[Dan Forsh]

Hi guys,

This is off the track a little, but same discipline. I'm waiting on a Stihl TS360 with poor compression. What I want to know is when do you decide a saw need just rings, or piston and rings or piston, rings and a new pot? Is it sooo obvious or do you start with the cheapest option, rings, and then see how you go on? Is it that its always most likely to be in a certain order, with changing the pot always the last? I take it that you wouldn't keep a piston but change the pot (sorry jug).

As always I value your experience.

 

[NWCS]

pull the muffler and shine a good flashlight in the bore.. look for any scratches, scuffs, or ugly stuff.. if it looks good.. pull the cyl and slap some new rings in.. if not.. ebay allways has a supply of TS350/360 aftermarket cyls and pistons.. the 360 is a bigger setup but will fit either saw (i have a TS350 that will soon have a TS360 piston/cyl for a jump in size) if you need crank seals or gaskets, http://www.bantasaw.com/ has full gasket sets that *include* the crank seals for the TS350/360 and 08S. the PN is 640-287
prices are all in canadian $, but using my visa i have never had a problem ordering or receiving parts from them. visa does the currency conversion for you.

 

[HiOctane]

First,you check the end gap on rings( max .025 i would say ),if over specs,you replace.Piston is replaced if it is scored,seized,or too loose in the pot like you say.On Ts model,the cylinder usually is worn by the dust and sand entering.Check if you feel a ridge where the rings stop travelling in cyl ,sign of seizure and scoring and looking also for the general condition of the nicasil in the bore.

 

[ErrolC]

The Nikasil usually won't wear much without getting scratched and scuffed.."usually"..unless its been through several sets of rings (then check for the wear band/lip, but it will be very subtle)..general rule is if the bore looks clean it'll be fine..

if the piston looks clean of scoring, just check the side clearance of the piston in the bore (just below the bottom ring land) with a feeler guage with the piston at the bottom of the bore. Compare the clearance with the pistons in its usual position i.e exh side against the exh port and the rist pins in line with the crank..meassure clearance under the exh port and compare it to the clearance at 90deg of ea other(under the rist pin) difference should be less than about .001-.002" of the other.. and fit new rings, check their gaps according to manual..the piston and bore wear against the wrist pin will be near nil and will be your std clearance reference..the exh port side will wear most out of round

deglase the bore with 600 grit w&d paper - wet, obliquely around the bore, otherwise the rings could take a long time to bed in and burn or glase

 

[Lakeside53]

pull the muffler and shine a good flashlight in the bore.. look for any scratches, scuffs, or ugly stuff.. if it looks good.. pull the cyl and slap some new rings in.. if not.. ebay allways has a supply of TS350/360 aftermarket cyls and pistons.. the 360 is a bigger setup but will fit either saw (i have a TS350 that will soon have a TS360 piston/cyl for a jump in size) if you need crank seals or gaskets, http://www.bantasaw.com/ has full gasket sets that *include* the crank seals for the TS350/360 and 08S. the PN is 640-287
prices are all in canadian $, but using my visa i have never had a problem ordering or receiving parts from them. visa does the currency conversion for you.

Small point: the TS360 is not a bigger bore. Both the TS350 and TS360 used 47mm pistons, and then for later production, 49mm pistons/cylinders. Obviously, get the 49 if replacing both.

 

[Lakeside53]

Hi guys,

This is off the track a little, but same discipline. I'm waiting on a Stihl TS360 with poor compression. What I want to know is when do you decide a saw need just rings, or piston and rings or piston, rings and a new pot? Is it sooo obvious or do you start with the cheapest option, rings, and then see how you go on? Is it that its always most likely to be in a certain order, with changing the pot always the last? I take it that you wouldn't keep a piston but change the pot (sorry jug).

As always I value your experience.

Check for piston taper. As already pointed out, TS series pistons wear on the inlet side due to injection of concrete or iron dust, and this wears the skirt. More than .004mm at the bottom less than the measurement just below the rings (not the piston top) and it's on the way out. At .008 it will really thunk. If it's still assembled, pull it over with the recoil. The "clack" you hear when the piston rolls over TDC is the piston skirt slapping on the cylinder wall (not the rod bearing as most think). On the other hand, I've seen a bunch of TS with badly slapping pistons run forever, and they still run way after they should be replaced... The 08 motor is really basic and takes a lot of abuse and wear. New rings is often the easiest solution, but do a very LIGHT hone.

 

[West Texas]

Even if the piston shows some wear, I'd squirt some soapy fluid around the gasket, give her a pull and see if there are any bubbles before I tore it apart. Might even want to check the tightness of the bolts holding the cylinder down too? If they are loose then I'd really suspect the gasket.

 

[Lawn Masters]

Well, its standard practice to put a NEW base gasket in whenever replacing rings, or any parts that require the cylinder to be removed. its cheap insurance, plus in some cases, the gasket will have half of it stuck to the crankcase, the other half stuck to the cylinder in which case the gasket will NEED replacment due to tearing in half.

 

[West Texas]

Well Oldsaw, what happened in my case, is I thought it was a piston and ring problem; but, when I replaced the gasket it had a lot of compression and now runs great. That little gasket only cost me $1.80 and that included postage.