When to pressure check a saw?

[MS290man]

I know if you have a saw with a burnt piston you should run a pressure check to make sure the seals are still good but what other symptoms would also lead you to run a pressure check?

 

[exSW]

Usually after it fails a vacuum test.

 

[Spike60]

Finding an elusive air leak before it blows up. Sometimes on a saw that seems impossible to dial in. Sometimes you get one of these and it's best to do the pressure test early and determine if the does or doesn't have a leak. Can save a lot of time in the long run.

 

[Homemade]

Finding an elusive air leak before it blows up. Sometimes on a saw that seems impossible to dial in. Sometimes you get one of these and it's best to do the pressure test early and determine if the does or doesn't have a leak. Can save a lot of time in the long run.

Yep, Impossible to keep dialed in. And slow to idle down. That's a dead giveaway for me.


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[drf256]

Every time I build a saw I do one.

Every time I didn't, I kicked myself for not. Its not that much more work, and far less than the work needed to take the saw apart again to do it right.

 

[PogoInTheWoods]

I try to do a vac/pressure test on a problem saw before completely tearing it down. May save unnecessary disassembly if it's just an impulse line or intake boot and the saw isn't completely fried yet. I always test a case for integrity before bolting much more to it during a rebuild and then again after the intake assembly is in place.

Bear in mind that pressure can occasionally mask a vac leak..., especially at the seals. Think of a seal that holds pressure but leaks vacuum as a one way valve. Works the other way around, too..., usually on the test setup itself if there are several couplers involved, or at the block-offs depending on one's method of choice. Again, think of a one way valve responding differently for vacuum than for pressure. Always check both.

 

[JonCraig]

High idle, can't get it to tune, any time I've had something apart on it, if I'm bored.

 

[brandonstclair20]

I have tried to vacuum test and pressure test many saws and I cannot get a single one to pass and cannot find any leaks with soapy water. Could something be wrong with my mityvac?


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[PogoInTheWoods]

Could something be wrong with my mityvac?

Test it.

 

[brandonstclair20]

Test it.

When I place my thumb on it the gauge reads pressure and vacuum.


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[Fruecrue]

I pressure test most saws.
I got a sweet kit from Dave and like to play with it.
Real easy with the adapters and rubber blank offs.

 

[PogoInTheWoods]

When I place my thumb on it the gauge reads pressure and vacuum.

Then I would say it's fine and you're overlooking something else in your testing method(s). Don't forget decomp buttons and spark plugs as leak sources along with the cylinder base and case seams. Your blockoffs are also obvious places to look for leaks.

 

[brandonstclair20]

Then I would say it's fine and you're overlooking something else in your testing method(s). Don't forget decomp buttons and spark plugs as leak sources along with the cylinder base and case seams. Your blockoffs are also obvious places to look for leaks.

Something must be wrong with my blockoffs.


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[PogoInTheWoods]

What are you using for a test point?

 

[PogoInTheWoods]

Believe it or not, you can use Gorilla tape in a pinch to block off the intake and exhaust if the surfaces are clean enough. Should hold to 6 ~ 8 lbs. of pressure and 12~15 inches of vacuum if you're using a spark plug adapter or impulse line for a test port.

 

[brandonstclair20]

What are you using for a test point?

I have been using the impulse line.


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[Tor R]

It depend
All my 2xx serie saws get new seals, most of the times I dont preasure/vacuum test them afterward.
The saws I've worked most with the last year is 345/346/357/550, I dont trust any of them even with new seal & bearings, 345/346/357 has a *s-wordty intake system while 550 can have leak around the jug foot.

 

[MustangMike]

IMO, gorilla tape works better for Vac than Pressure, but is not reliable enough. Usually bolting something over a tire tube over the exhaust works best (and is easy). I often use a 034 muffler spacer, easy to work with.

I often have trouble getting the intake sealed well.

If the leak is too big to ID with the MityVac, I hook up the bicycle pump to it, jut don't let presser go over 10 lbs. The addl volume helps you find leaks easier. I also sometimes use an automotive stethoscope to hear leaks in hard to reach areas.

Was the only way to ID an intake manifold leak on a MS 250. No other way to access where it was leaking with that stupid cover plate on those saws.

 

[Chainsaw Jim]

If you have a saw with a burnt piston then replace the seals as a rule. They are not designed to withstand the excessive temps of a meltdown. It hardens them a little bit.
The more saws you build the more you notice that strict attention to detail will prevent time loss over troubleshooting.
I never check pressure or vacuum until I'm done reassembling. I think it's a waste of time on a burnt saw because all the parts that can possibly leak should be getting replaced anyways.

 

[backhoelover]

Thought you were a chain guy

I have tried to vacuum test and pressure test many saws and I cannot get a single one to pass and cannot find any leaks with soapy water. Could something be wrong with my mityvac?


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have you check to make sure its not leaking where the bar oil goes? i has one that was leaking, it was not burning the bar oil one of them weird ones! also when you doing a vac test you need to rotate the crank. i had a echo 280e that would only leak when i put the drill to it i think my drill was set on the number 3 speed setting