Husqvarna 181se cylinder/piston

[cornishman07]

It's a 1983 and it's orange, not an army one. The piston is original with the two thin rings. Never done a vacuum/pressure test before and the half decent testers look expensive! Would be cheaper to just renew the bearings and seals regardless! Any link to a good value vacuum tester that'll do the job without breaking the bank? Can get a compression tester for about a tenner on ebay which looks exactly like a machine mart one. Would this not do the same job or at least confirm compression is ok regardless of any minor leaks? The suggestion something's leaking caused the scoring has got me paranoid now!

[Dan Maynard]

9 hours ago, cornishman07 said:

The suggestion something's leaking caused the scoring has got me paranoid now!

It could be leak but could also be dust through the air filter or even just wear, I guess the thought is that if there is a leak then it'll just score again.

 

I have an ex hire saw that had a small hole under the air filter, wood dust gone through and turn to hard carbon which scored the piston but cylinder ok so I've put a meteor piston in and run fine since. To be fair it started and ran ok on the old piston but bit smokey.

[spudulike]

11 hours ago, Dan Maynard said:

It could be leak but could also be dust through the air filter or even just wear, I guess the thought is that if there is a leak then it'll just score again.

 

I have an ex hire saw that had a small hole under the air filter, wood dust gone through and turn to hard carbon which scored the piston but cylinder ok so I've put a meteor piston in and run fine since. To be fair it started and ran ok on the old piston but bit smokey.

Dust through the air filter usually causes wear to the plating on the inlet side not the exhaust side.

 

[spudulike]

21 hours ago, cornishman07 said:

It's a 1983 and it's orange, not an army one. The piston is original with the two thin rings. Never done a vacuum/pressure test before and the half decent testers look expensive! Would be cheaper to just renew the bearings and seals regardless! Any link to a good value vacuum tester that'll do the job without breaking the bank? Can get a compression tester for about a tenner on ebay which looks exactly like a machine mart one. Would this not do the same job or at least confirm compression is ok regardless of any minor leaks? The suggestion something's leaking caused the scoring has got me paranoid now!

The compression gauge is nothing to do with vac and pressure tests and if you purchase a compression gauge, don't get one for a car, saws need a much more sensitive gauge to measure the compression correctly.

The saw you have is relatively old and old saws can develop air leaks through the crank seals (no need to change the bearings), inlet manifold etc. I believe the 181 manifold is a plastic type one and they can crack hence the test.

The fact the saw has seized means it has happened for a reason. The typical reasons are poor fuel/oil mix, using old fuel/oil mix, issues with fuel delivery such as dirt in the carb, split fuel line etc or the carb high speed screw not being set correctly and the machine over revving or an air leak in the engine.

Doing the leak down test is up to you. It is possible to protect the engine by tuning the carb to run a little richer but any decent engineer would ensure the engine is airtight on rebuilding it. I seem to remember the 181 having a stepped crankshaft making fitting seals an interesting experience for the uninitiated but may be wrong.

 

 

[adw]

The drive side seal is in the pump housing, so yes you need the seal sleeve tool, or a suitable way to smooth the way over the crank step.

[cornishman07]

Thanks for all the replies everyone. I've familiarised myself with the difference between a compression test and pressure/vac test now so thanks for that! I was thinking about detecting leakage around the piston rings which is what I thought a scored cylinder might result in? Also to clarify the saw is a recent acquisition. I gave it a once over and took the exhaust off to look at the piston, which was scored slightly around the exhaust port. Don't know what caused it or when, but it did run fine and wasn't seized. Thanks for the suggestions as to the cause. Looks like a vac test is probably needed 🙄! There's no debris in the crank case and as it's around the exhaust not the intake can't see how it would be debris sucked in? If it was run without oil I suspect there'd be more damage?!

If there's a leaking crank seal how would this lead to scoring the piston? Similarly how would a leaking fuel line lead to the same?

[spudulike]

All fuel AND air should enter the engine through the carb. Your carb will have been set up on this basis. When a crank seal leaks air, it can let extra air in to the engine and this will make the saw run hotter at high revs and also cock up the idle.

A leaking fuel line may show itself as an engine that just lacks power or won't rev out but if the line has a small leak that lets air bubbles in through the line rather than 100% fuel, this will mean that the carb may not supply the correct amount of fuel to the engine causing the engine to run hot and ........BANG!!

It is very possible yours has been just been run on old fuel or the H screw was set lean but, having fixed up more saws than I care to remember, I learnt to do all these checks to ensure returned customer saws worked.

[cornishman07]

Update time;

 

I cleaned the piston and barrel with the intention to just put the saw back together at no cost. After buying three different bits to make an adapter I eventually did do a pressure and vac test and crank seals are good, held 10psi on pressure -10 on vacuum, both held whilst crank rotated. Result!

 

I finally had a bit of free time to rebuild it but when I came to reinstall the piston rings one of them was no longer a piston ring but a piston spiral!!

 

No idea why as each of the three times I got an adapter for the vac test, that didn't fit, both rings were sat on the workbench perfectly fine ready to reassemble! What would cause this?

Anyway, once installed it pinches in the groove and won't move so I assume it's not reusable? Drat!

These are the original thin rings and not available any more so it looks like it's a new piston/cylinder and a ton less in my piggy bank! Double drat! On the plus side looks like the 181 and 188 have the same stroke and 2mm different bore so will be an 88cc monster once done! Might get a 28"bar then!

Also noticed that right where the wires leave the ignition module they've rubbed through the insulation. If I slide heat shrink it won't get right in. A new module is 35 quid so I might just squirt a blob of clear ct1 once assembled and see how it goes? Still not got over the cylinder/piston yet, don't want to ruin my weekend before

it's begun!

[adw]

Those are steel rings, will they not re twist? I confess I have never seen that before.

[cornishman07]

2 hours ago, adw said:

Those are steel rings, will they not re twist? I confess I have never seen that before.

Tried twisting as far as I dare but it just springs back to how it is. I'm tempted to just fit it in the bottom groove and see what happens?! If it damages the piston or cylinder I'm no worse off really.