LCAM-01XA
Full Access Member
Our IDI's head gaskets appear to be leaking oil out the corners, so it seemed like a good idea to run a compression test before tearing into the thing - you know, to decide whether this engine is worth saving or whether to rebuild a spare one instead. Out the box the HF tester is a well-documented epic fail when it comes to the 10mm adapter IDIs use, but modifying it BDCarillo-style is easy and quick.
Starting with cylinders 1 and 7 as they are piece of cake to get to, gauge showed about 470-480psi - this was surprisingly high as those were the cylinders leaking oil the worst, but whatevs, fire rings must be doing their job well I guess.
With the easy ones done let's move to cylinder #5 - plug comes out np, adapter drops in and tightens np, hose hooks up np, hit the starter (ignition and fuel off) and all hell breaks loose - gauge needle bounces up to like 150psi but immediately drops to zero, and there is a massive hiss (compression leak) coming out of something there. Pull the works out, turns out the adapter got its valve stuck open - replace valve core, verify it works like it should, drop it in, repeat test, same result. Yet another valve core later, still no change in behavior.
OK, just to confirm the tester went **** we hook it up to cylinder #1 - sure enough, zero compression there, valve in adapter gets stuck open immediately and thus the gauge does not record anything.
Fine, tester is dead, major bummer but it is what it is, some numbers is better than no numbers at all. Drop all plugs back in, crank engine again with no fuel, and wouldn't you know, the compression leak hiss is still there!!! *** - aight, pull the plugs again, clean them nice and good, blue loctite on the threads just in case (gotta pull them with the engine hot next time, no biggie), wait a few hours, hit the starter again, SOB the hiss is still there!!! Sounds exactly like what you'd hear if you crank the engine with a plug removed, except all plugs are in and now obviously sealed extra tight.
At this point it's decided that the engine will be started anyways, if it goes **** then so be it - reasoning being the noise wasn't there before the HF tester failed, and there's nothing to a compression test that could cause permanent damage to the engine, so once the engine is running the hiss will surely go away, right? Yeah right - instant light-off after a 10-second glow cycle, the hiss was still there and clearly heard over the clattering of the engine courtesy of the cold advance. Then, after well over a minute pf high idle, IT WENT AWAY! No huffing thru the intake, no hissing, just decent amount of blowby coming thru the CDR but that's normal for this particular engine. 3/4" radiator hose used as a stethoscope with one end near the intake inlet (no air box) and the other against the ear shows nothing but normal whooshing sound of air rushing down the runners. Put air box on, filter in it, drop the top lid and engine vacuum immediately sucks it down tight against the air box - all air noises get much quieter, and of course till no huff or hiss to be heard... Engine got revved to the governor and nothing flew apart, seems like she's all ready and reporting for duty.
So, what do ya'll think happened there? What was that compression leak hiss, and why did it go away shortly while running the engine at high idle? Obviously the HF tester is getting returned, no point in having money tied into the POS if it won't stay working properly even for a single engine's worth of cylinders testing...
Starting with cylinders 1 and 7 as they are piece of cake to get to, gauge showed about 470-480psi - this was surprisingly high as those were the cylinders leaking oil the worst, but whatevs, fire rings must be doing their job well I guess.
With the easy ones done let's move to cylinder #5 - plug comes out np, adapter drops in and tightens np, hose hooks up np, hit the starter (ignition and fuel off) and all hell breaks loose - gauge needle bounces up to like 150psi but immediately drops to zero, and there is a massive hiss (compression leak) coming out of something there. Pull the works out, turns out the adapter got its valve stuck open - replace valve core, verify it works like it should, drop it in, repeat test, same result. Yet another valve core later, still no change in behavior.
OK, just to confirm the tester went **** we hook it up to cylinder #1 - sure enough, zero compression there, valve in adapter gets stuck open immediately and thus the gauge does not record anything.
Fine, tester is dead, major bummer but it is what it is, some numbers is better than no numbers at all. Drop all plugs back in, crank engine again with no fuel, and wouldn't you know, the compression leak hiss is still there!!! *** - aight, pull the plugs again, clean them nice and good, blue loctite on the threads just in case (gotta pull them with the engine hot next time, no biggie), wait a few hours, hit the starter again, SOB the hiss is still there!!! Sounds exactly like what you'd hear if you crank the engine with a plug removed, except all plugs are in and now obviously sealed extra tight.
At this point it's decided that the engine will be started anyways, if it goes **** then so be it - reasoning being the noise wasn't there before the HF tester failed, and there's nothing to a compression test that could cause permanent damage to the engine, so once the engine is running the hiss will surely go away, right? Yeah right - instant light-off after a 10-second glow cycle, the hiss was still there and clearly heard over the clattering of the engine courtesy of the cold advance. Then, after well over a minute pf high idle, IT WENT AWAY! No huffing thru the intake, no hissing, just decent amount of blowby coming thru the CDR but that's normal for this particular engine. 3/4" radiator hose used as a stethoscope with one end near the intake inlet (no air box) and the other against the ear shows nothing but normal whooshing sound of air rushing down the runners. Put air box on, filter in it, drop the top lid and engine vacuum immediately sucks it down tight against the air box - all air noises get much quieter, and of course till no huff or hiss to be heard... Engine got revved to the governor and nothing flew apart, seems like she's all ready and reporting for duty.
So, what do ya'll think happened there? What was that compression leak hiss, and why did it go away shortly while running the engine at high idle? Obviously the HF tester is getting returned, no point in having money tied into the POS if it won't stay working properly even for a single engine's worth of cylinders testing...
