Air compressor running constantly...bad?

[TipsyMcStagger]

I'm about to change the valve springs on my LS2 (it's on an engine stand). I bought an air adapter hose to keep compressed air in the cylinder in order to keep the valves from dropping.

I have the 30 gallon Morgan compressor from Northern Tool. It's a reconditioned Kobalt unit (the same as discussed in this thread).

As is to be expected, air will escape from the cylinder, so the compressor kicked on very quickly. Unfortunately, it seems air is escaping faster than the compressor can refill the tank, so the motor runs constantly as long as the air is connected to the cylinder.

I don't want to be rushed while doing this job but I don't want to damage my compressor either. I'm thinking it can't be good for the compressor to run constantly. Thoughts?

I might have to switch to the rope-in-the-cylinder method to keep the valves seated.

Tipsy

 

[Brian_B_]

Where is the air going? If you have the cylinder at top dead center..both valves should be closed and no where for the air to go. You may have it on the wrong stroke.

A friend recently did this trying to install a new distributor in his chevy truck. He was on the wrong stroke. My brother and I fixed it, put the distributor in the right general area, hit the key and it was running. Then we adjusted the timing of course.

 

[TipsyMcStagger]

Where is the air going? If you have the cylinder at top dead center..both valves should be closed and no where for the air to go. You may have it on the wrong stroke.

A friend recently did this trying to install a new distributor in his chevy truck. He was on the wrong stroke. My brother and I fixed it, put the distributor in the right general area, hit the key and it was running. Then we adjusted the timing of course.

All of the valves are closed. The air escapes past the rings.

Tipsy

EDIT: Now that I think about, the engine hasn't run in more than a year. Perhaps if I squirt some oil in each cylinder and turn the engine over by hand a few times, the oil will help the rings seal.

 

[nehog]

...
EDIT: Now that I think about, the engine hasn't run in more than a year. Perhaps if I squirt some oil in each cylinder and turn the engine over by hand a few times, the oil will help the rings seal.

Do that, hand crank over the engine a few turns to spread it out.

 

[bochnak]

If the cylinder is at TDC, you should not have more than 10% leakage.

I do leak down test all the time and never have to kick the compressor on. If the rings are leaking that bad, it's time for a rebuild.

 

[Falcon67]

If the cylinder is at TDC, you should not have more than 10% leakage.

I do leak down test all the time and never have to kick the compressor on. If the rings are leaking that bad, it's time for a rebuild.

What he said. If the piston in that cylinder is at BDC on the compression stroke, your exhaust valve is open.

 

[TipsyMcStagger]

Do that, hand crank over the engine a few turns to spread it out.

Oil did the trick. It's still leaking down but much more slowly. About ten minutes before the compressor kicks on.

If the cylinder is at TDC, you should not have more than 10% leakage.

I do leak down test all the time and never have to kick the compressor on. If the rings are leaking that bad, it's time for a rebuild.

It's an LS2 with 71K miles. Every cylinder is leaking down at the same rate (approximately...I'm a bit to busy to sit there with a timer). I'm not too worried about the leak down rate.

What he said. If the piston in that cylinder is at BDC on the compression stroke, your exhaust valve is open.

There are no rockers or puhrods installed. So all of the valves are closed, regardless of piston position. But I've been moving the piston to the top of the bore on each cylinder as a failsafe, just in case a valve were to drop.

Tipsy

 

[BillK]

Tipsy,
I think you will find that with the cylinder at TDC there is no need for the compressor. I am pretty sure the valves can only open a very short distance before hitting the piston so they really cant go anywhere. There are no engines that I can think of where the valve could actually fall far enough to be a problem. I have changed valve springs on probably 50 engines and have never used that setup. Just put the cylinder at tdc and you will be fine. The LS valve stem seal is pretty strong too, it should hold the valve up.

Just my opinion,

 

[TipsyMcStagger]

Tipsy,
I think you will find that with the cylinder at TDC there is no need for the compressor. I am pretty sure the valves can only open a very short distance before hitting the piston so they really cant go anywhere.

Yep...TDC will keep the valve from falling. The air was a belt and suspenders thing.

Got them all done. Came out great

Tipsy

 

[TipsyMcStagger]

I might have to switch to the rope-in-the-cylinder method to keep the valves seated.

Tipsy

Old trick:

Another way of changing spring or seals with the heads on. Thru the plug, stuff rope in the cylinder. Bring the piston up squeezing the rope in the head, rope will prevent valve drop .... I do not need to say leave some rope sticking out of plug hole right?

 

[Uncle Dave]

The nylon rope trick works well. With the piston down a bout half way feed a length of nylon rope into the sparkplug hole. Then run the piston up, the rope compresses, this holds valves closed. Dave

 

[Mr.A]

Dave is correct. Rope trick works best


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[Cyberbear]

As a side note for future reference, all of my compressors came with a 50% duty cycle rating, which the manufacturer says is an industry standard. This translates into me not running the air compressor more than 30 minutes straight in an hour. Otherwise, the maker suggests getting a larger compressor. Like most people I've run my unit non stop when sand blasting, until the motor over heated and the over load kicked out.

 

[TipsyMcStagger]

...all of my compressors came with a 50% duty cycle rating, which the manufacturer says is an industry standard. This translates into me not running the air compressor more than 30 minutes straight in an hour....

Good to know. Thanks.

Tipsy

 

[nmcqueen469]

Glad you got it handled!

Tell me more about the build. Assuming a cam, at least, with those dual springs?

 

[Charles (in GA)]

As a side note for future reference, all of my compressors came with a 50% duty cycle rating, which the manufacturer says is an industry standard. This translates into me not running the air compressor more than 30 minutes straight in an hour. Otherwise, the maker suggests getting a larger compressor. Like most people I've run my unit non stop when sand blasting, until the motor over heated and the over load kicked out.

My large two stage Husky is rated for 100% duty cycle when using synthetic oil.

I don't think 50% is any kind of "industry standard" except for the manufacturer you talked to.

Charles

 

[TipsyMcStagger]

Glad you got it handled!

Tell me more about the build. Assuming a cam, at least, with those dual springs?

The engine is a stock LS2 out of an '06 GTO (71K). I installed a custom grind cam. I also replaced the springs (obviously), oil pump, timing chain and waterpump, just to be safe. I bought it as a complete dropout with the T56, PCM, full harness, pedals and mass air flow sensor.

I'm putting it into an E36 BMW. More info here.

Tipsy

 

[nmcqueen469]

That's a great swap!

I owned an 04 GTO for a few years, and got intimately familiar with the guts of an LSx that way.

 

[TipsyMcStagger]

That's a great swap!

I owned an 04 GTO for a few years, and got intimately familiar with the guts of an LSx that way.

Thanks. They're great engines. Should be fun when it's running.

Tipsy

 

[rodm1]

The nylon rope trick works well. With the piston down a bout half way feed a length of nylon rope into the sparkplug hole. Then run the piston up, the rope compresses, this holds valves closed. Dave

An old spark plug wire works good to.