280zwitha383 Posted July 24, 2007 Share Posted July 24, 2007 So I'd like to do a leakdown test on my 383 but I don't have a leakdown tester/gauge. I do have a compression gauge and I'm wondering why I couldn't just use that. I mean the cylinder holds pressure after you build it by cranking the engine and you have the gauge to see what's going on. Why would you need a gauge that hooks up to an air compressor? The other question is: Why does the cylinder not lose its pressure when the exhaust valve opens? I'm sure this is very simple and probably something I should know but it just doesn't make sense. For that matter when the intake valve opens why would the pressure not simply go back into the intake. I'm missing something very basic here. Thanks for any insight. Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted July 24, 2007 Author Share Posted July 24, 2007 After I read a little more about it I realize that I definitely need a leakdown gauge because I need to figure out what percent I am losing and I need to have the cylinders at TDC which of course made sense to me in the first place but it still doesn't make sense how a compression gauge holds pressure. I'm pretty sure it doesn't have a check valve because when you unscrew it from the head it blows out. So.... Quote Link to comment Share on other sites More sharing options...
Daeron Posted July 31, 2007 Share Posted July 31, 2007 the compression tester has a check valve in it. Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted July 31, 2007 Author Share Posted July 31, 2007 Really? Ok. My tools and a few cars are not here at my house so sometimes I have to ask silly stuff that most people would just go out in the garage and look at. Quote Link to comment Share on other sites More sharing options...
Daeron Posted July 31, 2007 Share Posted July 31, 2007 Really? Ok. My tools and a few cars are not here at my house so sometimes I have to ask silly stuff that most people would just go out in the garage and look at. no problem. There are links to making home made leak down checkers if you can get some fittings and a gauge.. and I think a regulator of some sort. Unfortunately, I dont seem to have them bookmarked, but I swear I've seen 'em! Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 31, 2007 Share Posted July 31, 2007 Yes, making a Leakdown tester is not a big deal, regulator, couple of gauges, calibrated orifice, and a sacrificial plug adapter from an old compression tester... But for the cost of one at Harbor Freight, why bother? I have bought several of the 'test' items from HF recently, and generally toss the gauges and replace them at a much higher cost with Ashcroft Mirrored-Gauge or Liquid Filled Units available through local vendors. I trust an Ashcroft that I can send out to be recalibrated occasionally much more than the HF Chinese Gauges. My leakdown tester was originally for Lycoming Engines, and then cruising through Aircraft Spruce one day found an automotive plug adapter, so dug it out of storage and it's been used more and more often recently. Really upset me seeing a Leakdown Tester at Harbor Freight...knowing how much I paid for my unit even 15-20 years ago....it's STILL cheaper today from them. But I digress... Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted August 1, 2007 Author Share Posted August 1, 2007 How much are they at harbor freight? There's a HF in about 20 minutes from me and I really don't mind a little inaccuracy, just a good idea of what's going on would be fine. Oh yeah, in between my first and second post I found this site that describes how to make your own: http://vmaxoutlaw.com/tech/leakdown_tester.htm Quote Link to comment Share on other sites More sharing options...
Daeron Posted August 1, 2007 Share Posted August 1, 2007 http://search.harborfreight.com/cpisearch/web/search.do?keyword=leak-down $30 for the nice one, with a case, $40 for the "crummy" one. (chinese math, gotta love it!) Tony, how much would a pair of reliably accurate gauges cost, ballpark? I am on the fence for that one.. I like accurate instrumentation, but I can make do, soooo.. Quote Link to comment Share on other sites More sharing options...
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