Vortec big block questions

[8T7K5]

I've been working on my 99 K2500 Suburban off and on for about a year now. When I bought it, the previous owner had broken a starter bolt in the block. That screwed up the flexplate. Since that needed to be replaced, the starter bolt needed to be drilled out and retapped/helicoiled, the oil pan gasket needed to be replaced, I pulled the engine since all the above are easier with it out of the truck. Prior to me pulling the engine I'd replaced the distributor, plugs, wires, ignition coil, ICM, and injectors as well as the fuel filter and fuel pressure regulator. It had a miss on #s 3 and 4. Pulled those injectors, tested them, and they were fine. Compression was good on all 8.

I've also discovered multiple other issues after pulling it. Leaking rear main, leaking front seal, the oil filter adapter was leaking and apparently rtv was the solution. The balancer needs to be replaced, and after looking at the timing chain it's got quite a bit of slop in it so a new set is on the way. I'm tempted to have it rebuilt or buy a long block but that's not really in the budget at the moment. All that being said, can the bad timing chain cause misfires on specific cylinders? Do I need to look at the valves as a cause of the misfires? I'd like to do a leak down test but it's a ways away from being put back in the truck especially with my limited mechanical abilities. Sorry for the long winded post I'm just trying to give as much background as possible.

 

[Schurkey]

I'd replaced the distributor, plugs, wires, ignition coil, ICM, and injectors as well as the fuel filter and fuel pressure regulator. It had a miss on #s 3 and 4. Pulled those injectors, tested them, and they were fine. Compression was good on all 8.

What were the compression pressure numbers? Has the compression gauge been tested for accuracy?

#4 and #3 are sequential in the firing order. Any chance the plug wires for those two are reversed?

The balancer needs to be replaced,

Why?

can the bad timing chain cause misfires on specific cylinders?

No.

Do I need to look at the valves as a cause of the misfires?

Valves and valve springs. Worth looking at, anyway.

I'd like to do a leak down test but it's a ways away from being put back in the truck especially with my limited mechanical abilities.

Don't need the engine in the truck to perform a leakdown test.

 

[8T7K5]

1-135; 3-125; 5-145; 7-145; 2-135; 4-145; 6-130; 8-130
I checked, double checked, and checked the plug wires again for that. Don't know the accuracy of the tester or if it's been tested itself. Balancer is getting replaced because the rubber is dry rotted and pieces are missing, which is odd considering how oily the lower timing cover is. The previous owner had put a glob of rtv around the crank snout, I'm guessing to fix the leaking front seal. Not knowing the engine didn't have to be in the truck to do a leak down test shows my mechanical incompetence but as soon as the crap weather here clears I'll get that done. What specifically should I look for?

 

[smokymtn65]

with leak down you want the valves closed on that cylinder testing, if its leaking to much second gauge will drop. at the point you determine if air is going past rings, intake, or exhaust valve

 

[Schurkey]

with leak down you want the valves closed on that cylinder testing, if its leaking to much second gauge will drop.

Valves closed, piston at TDC, Exhaust ******. If the piston isn't at TDC, the air pressure from the leakdown tester can push the piston down the hole, turning the crank. It's possible to test with the piston not at TDC, but you have to lock the crank so it can't move. I generally don't bother. Most bore wear is at the top of the cylinder, testing there makes sense.

[Note--the excessive censorship on this site is removing the word "str_oke". That is JUST CRAZY on a site devoted to FOUR STR_OKE ENGINES.]

The second gauge (or the only gauge on a single-gauge tester) always drops, the question is whether it's dropping excessively. The actual cylinder leakage and the INDICATED cylinder leakage vary depending on the tester used, so a simple answer like "10 psi" or "20% leakage" isn't sufficient information--depending on how the tester is manufactured.

The two common ways to determine "excessive" leakage are to
1. Test a bunch of known-good cylinders having similar bore size to the engine in question, to see how that leakdown tester reacts, or
2 Use a "Master Orifice" to "test the tester". A Master Orifice is calibrated to allow a certain amount of leakage, when plugged into the tester, the second gauge drops, and that amount of pressure loss is considered the maximum acceptable leakage. Continental Teledyne makes aircraft engines, the Master Orifice was invented by them. Their Master Orifice is required to test their aircraft engines; but in my opinion it's too "generous", allowing too much leakage for automotive use.

at the point you determine if air is going past rings, intake, or exhaust valve

Listen at the valve cover oil fill cap, intake manifold (throttle body), exhaust manifold or exhaust port, and at the water pump inlet (air escaping past a head gasket or cracked casting--leakage into the water jacket.)

Any whooshing/whistling at the intake or exhaust (valve) means the valve(s) are leaking. Any noise at the water pump means you have internal problems. There's always going to be some noise at the valve cover (leakage past the rings) which is why it's important to have the gauge reading letting you know if the leakage is acceptably low, or unacceptably high.

Acceptable vs. unacceptable leakage past the rings is a matter of degree that includes the intended purpose of the vehicle--is it a highly-tuned racing vehicle, or Little Old Lady's church-and grocery-store appliance.

 

[Donald Mitchell]

Cylinder pressure leakage and a stuck pcv valve will cause a lot of those leaks your fixing too.

 

[smokymtn65]

Had limited time on my reply! LOL

 

[8T7K5]

Valves closed, piston at TDC, Exhaust ******. If the piston isn't at TDC, the air pressure from the leakdown tester can push the piston down the hole, turning the crank. It's possible to test with the piston not at TDC, but you have to lock the crank so it can't move. I generally don't bother. Most bore wear is at the top of the cylinder, testing there makes sense.

[Note--the excessive censorship on this site is removing the word "str_oke". That is JUST CRAZY on a site devoted to FOUR STR_OKE ENGINES.]

The second gauge (or the only gauge on a single-gauge tester) always drops, the question is whether it's dropping excessively. The actual cylinder leakage and the INDICATED cylinder leakage vary depending on the tester used, so a simple answer like "10 psi" or "20% leakage" isn't sufficient information--depending on how the tester is manufactured.

The two common ways to determine "excessive" leakage are to
1. Test a bunch of known-good cylinders having similar bore size to the engine in question, to see how that leakdown tester reacts, or
2 Use a "Master Orifice" to "test the tester". A Master Orifice is calibrated to allow a certain amount of leakage, when plugged into the tester, the second gauge drops, and that amount of pressure loss is considered the maximum acceptable leakage. Continental Teledyne makes aircraft engines, the Master Orifice was invented by them. Their Master Orifice is required to test their aircraft engines; but in my opinion it's too "generous", allowing too much leakage for automotive use.


Listen at the valve cover oil fill cap, intake manifold (throttle body), exhaust manifold or exhaust port, and at the water pump inlet (air escaping past a head gasket or cracked casting--leakage into the water jacket.)

Any whooshing/whistling at the intake or exhaust (valve) means the valve(s) are leaking. Any noise at the water pump means you have internal problems. There's always going to be some noise at the valve cover (leakage past the rings) which is why it's important to have the gauge reading letting you know if the leakage is acceptably low, or unacceptably high.

Acceptable vs. unacceptable leakage past the rings is a matter of degree that includes the intended purpose of the vehicle--is it a highly-tuned racing vehicle, or Little Old Lady's church-and grocery-store appliance.

So if everything else is good, my most likely cause of the 2 misfires will be valves?

 

[Schurkey]

No, but valve issues are worth checking.

 

[8T7K5]

No, but valve issues are worth checking.

Well it looks like I'm going to send the block to the machine shop. I had planned on drilling out a broken starter bolt and putting in a helicoil today but the previous owner screwed it up so bad I can't get the drill bit in straight. Maybe it's time to just have it rebuilt, have the heads redone, and start fresh.