Spark Plug and Compression Test Talk and Evaluations

[Irishman999]

It your burb is not smoking blue I would say just keep an eye open for a set of heads and get all the parts together for a top end rebuild. I see cylinder head sets on CL alot, you could swap the heads in your back yard (assuming its not covered in snow) and all you really need as far as specialty tools is a torque wrench.

 

[89Suburban]

It smokes a little blue when ya first start it but it goes away. I am just going to run it and either locate a replacement motor or replacement SB. In the mean time I will save some cash up for when the time comes to make a move.

 

[RetroC10Sport]

It smokes a little blue when ya first start it but it goes away.

Valve seals.

 

[Irishman999]

Valve seals.

X2! Its really common, mine are bad too. If it does not smoke blue after your engine is at operating temp your bottom end should be fine. A set of rebuilt heads will fix all that crap your experiencing.

 

[GreaseDog]

I've seen many SBC run well under 150psi and work just fine for DD. Is all you work on is new motors? Not saying, 90 is optimal by any stretch, but its doable. IMO the leak down test is a waste at this point. Compression is low, we know the motor has mega miles, so why waste money and time to come up with a leak down tester that is only going to tell us what we already know. Yep, its a tired motor and is in need of a rebuild sooner than later. And his compression may be higher with a shot of oil. So is it really important to know percent of leak down at this point? Kinda moot now. I'd say even IF the heads were redone and new head gaskets, the slightest raise in compression is going to spit the rings into the oil pan. (NOT LITERALLY OF COURSE) And less than 500 miles of use on that patch job, the truck will be blowing blue smoke out the tailpipe too. If it were me, I'd finish the compression test, replace those damaged plugs, clean the others if you don't want to spend the few bucks on new ones since they didn't appear to be that bad. Drive it as is and be putting funds aside for either a used low mileage motor out of a wreck, a crate motor, or rebuild your current motor yourself. But doing that means a week or 2 of downtime. Ordering parts, block and heads in the machine shop etc., then once you got it all gathered up, time to assemble it, where as the crate motor, just swap it. Then, I'd keep that current motor for a builder. Never know if you get another square for cheap wo a motor, or convert a carb motor to TBI etc.

how is a leakdown test a waste? it will tell you precisely where the cylinder pressure is going, and you can fix that component, and be done with it. would you really want to just pull and rebuild and engine that just needed a head gasket? sounds like pissing in the wind to me.

 

[HotRodPC]

how is a leakdown test a waste? it will tell you precisely where the cylinder pressure is going, and you can fix that component, and be done with it. would you really want to just pull and rebuild and engine that just needed a head gasket? sounds like pissing in the wind to me.

As Retro and I already explained, a compression test DRY and note the readings. Do another compression test with a shot of oil in the cylinders. If the compression raises with the oil, then we know the compession is escaping past the rings into the crankcase. If it does NOT increase compression then we know its either valve guides or valve seats or burt valves. Vacuum test will also tell if its burnt valves. Does matter if its a head gasket, cuz no matter what you do, either heads or a complete rering, or rebuild, head gaskets are going to be replaced anyway. Most people don't have a leak down tester, and I don't for the reason, I can diagnose with a compression tester and vacuum guage to the point of knowing if a motor is worth repair or not. We already know valves seals are gone, and possibly vavle guides since he has blue smoke at start up, but it goes away. So the oil rings at this point can be assumed good. If a compression test with oil DOES NOT raise compression, then its safe to assume a valve job just might buy another few thousand miles out of the motor. But, when most heads are redone, they get resurfaced, the valves and guides no longer leak, so compression is higher. Now you raise cylinder pressure from 90PSI to 120-130PSI and the tired rings that were working just fine, now say to hell with it and quit working. The rings are holding 90PSI fine, but how do you know if they are strong enough to hold 120-130PSI??? You don't, but in most cases, it only takes 500-1000 miles and you're now blowing blue smoke and losing compression due to bad rings and back to the initial 90lbs now. So what I am saying, many times a Patch Job as in a valve job is just a waste, where he could leave well enough alone, save funds and just go with a GM crate motor.
So, this doesn't mean you are wrong GD, I do see your point totally, but from experience, I just say the Leak down is not needed, and even if the rings are good now, and valve job is only going to be a short lived patch. And of course its JMO. Anyone else can agree or disagree, or express their own analagy and opinion too.

 

[89Suburban]

Chripes, I feeling better every time I come into this thread.

 

[Old77]

Valve seals.

x3

 

[HotRodPC]

I guess I didn't x3 it when I posted earlier, so I'll just 4x it now. I think your valve seals are bad 89S.

 

[89Suburban]

 

[89Suburban]

x3

Somebody needs to invent a "slap the popcorn out of the smiley's hand" smiley.

 

[RetroC10Sport]

You must be registered for see images attach

 

[HotRodPC]

You must be registered for see images attach

I am thnking that might be popcorn for our African American bruthas. Its in a KFC chicken tub. A whole lotta popcorn nonetheless.

 

[Old77]

Somebody needs to invent a "slap the popcorn out of the smiley's hand" smiley.

quoted for truth!!!

 

[GreaseDog]

As Retro and I already explained, a compression test DRY and note the readings. Do another compression test with a shot of oil in the cylinders. If the compression raises with the oil, then we know the compession is escaping past the rings into the crankcase. If it does NOT increase compression then we know its either valve guides or valve seats or burt valves. Vacuum test will also tell if its burnt valves. Does matter if its a head gasket, cuz no matter what you do, either heads or a complete rering, or rebuild, head gaskets are going to be replaced anyway. Most people don't have a leak down tester, and I don't for the reason, I can diagnose with a compression tester and vacuum guage to the point of knowing if a motor is worth repair or not. We already know valves seals are gone, and possibly vavle guides since he has blue smoke at start up, but it goes away. So the oil rings at this point can be assumed good. If a compression test with oil DOES NOT raise compression, then its safe to assume a valve job just might buy another few thousand miles out of the motor. But, when most heads are redone, they get resurfaced, the valves and guides no longer leak, so compression is higher. Now you raise cylinder pressure from 90PSI to 120-130PSI and the tired rings that were working just fine, now say to hell with it and quit working. The rings are holding 90PSI fine, but how do you know if they are strong enough to hold 120-130PSI??? You don't, but in most cases, it only takes 500-1000 miles and you're now blowing blue smoke and losing compression due to bad rings and back to the initial 90lbs now. So what I am saying, many times a Patch Job as in a valve job is just a waste, where he could leave well enough alone, save funds and just go with a GM crate motor.
So, this doesn't mean you are wrong GD, I do see your point totally, but from experience, I just say the Leak down is not needed, and even if the rings are good now, and valve job is only going to be a short lived patch. And of course its JMO. Anyone else can agree or disagree, or express their own analagy and opinion too.

i prefer to do things once, and know whats wrong with it. bring the cylinder to TDC, install leakdown tester, apply shop air. you now know what is bad, and how bad it is. it will diagnose a lower end problem, a head gasket, and valve to seat seal all in one shot, and tell you how bad it is. i was always told to work smart not hard, if you're running a dry compression test, and a wet compression test, the leakdown tester is already ahead of the game. now throw in a leaky valve or a bown head gasketl, and you have more diagnostic work to do, where the leakdown tester is done.