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I think I’ll do a compression test next. What’s the best way to determine rings vs. valve damage?
This is a common ASE test question.
Best way is to squirt some oil into the cylinder, not alot mind you. Probably into the glow plug hole. Then you manually turn the engine over to check pressure on a gauge. The oil will help seal the piston rings for this test.
If pressure changes, you can wager the rings are bad. If no change, then can wager the valves/seats are bad.
Best way is to squirt some oil into the cylinder, not alot mind you. Probably into the glow plug hole. Then you manually turn the engine over to check pressure on a gauge. The oil will help seal the piston rings for this test.
If pressure changes, you can wager the rings are bad. If no change, then can wager the valves/seats are bad.
Best way is to squirt some oil into the cylinder, not alot mind you. Probably into the glow plug hole. Then you manually turn the engine over to check pressure on a gauge. The oil will help seal the piston rings for this test.
If pressure changes, you can wager the rings are bad. If no change, then can wager the valves/seats are bad.
This is one way to check.
Cold compression test I was showing 290 to 300psi on number 4. I added about a tablespoon of oil to the cylinder, and compression only went up to 310/315psi. I’ve read where it should jump up significantly if it were bad rings. I’m thinking valve or valve seat damage?
300psi is not awful. Move on to a leak down test, I think that OTC glow plug adapter allows one to attach a leakdown tool there.
I'll look for a leak down tester. I've also heard if I position the piston to TDC and add about 50psi of air through the GP hole, and if I hear/feel air coming leaking into the intake/exhaust, it would indicate valve issues?
Dual gauges, so if you did 100psi into chamber and have 50psi on other, 50% leakdown...bad news. Then you would hear it out the intake, through crankcase, or exhaust.
My oil pan has been leaking in the front and rear, so I decided to just pull the engine anyways. There was no gasket, just RTV. Someone has been into it before, but did the factory use a gasket for the oil pan? I had to extend my hoist to the 1/2 ton setting to reach all the way in, a bit sketchy but it handled the weight fine. I pulled the heads and so far 6 pistons have small cracks, which is fairly normal on these, and I can see valve contact on a few. Nothing on #4 immediately shows a problem, but I'm also not skilled at what exactly I should be looking for. I'll upload some photos later of #4.
Good to know, thank you. Mine had sealant stuck to the pickup tube and some on the screen, so I still think someone was in there prior to my ownership.
What is story with small cracks you observed? Will you do bearings with polished crank?
They are small cracks on the lip or edge of the piston bowls. Internet searches show this is pretty common on the 7.3 so a lot of folks will de-lip them to prevent it.
I don't know what the plan is just yet, either have a local machine shop do the work or get a long block through Kill Devil. Either way, it's going to be a summer of saving pennies before I pull the trigger!
I took a deeper look into things. First, my truck is a 95 but it looks like I have a 97 block, as it has the increased webbing and lobe on the cam for fuel pump.
I also discovered my #4 problems after both pushrods bent. It looks like I have a bent rod. At TDC, 7 of the cylinders rise just above the block deck, but #4 sits just below. How 7 cylinders look at TDC:
How #4 sits at TDC:
The rest are photos of cylinder walls, valve impacts and cracks in the pistons:
What injectors are you running? I'm surprised when mine came from together I didn't have any pistons cracked. After the 1200+ towing for miles years ago I knew they would be a mess and possibly the issue.
Sheesh, worse than I would have thought for ya. :/
Makes sense on the lip, retains excess heat. Big issue back in my 6.4 days with cracked pistons, I never had them others did big time. Total hit and miss, even on basically stock trucks. Solution was Maxxforce 7 slugs that were delipped.
What injectors are you running? I'm surprised when mine came from together I didn't have any pistons cracked. After the 1200+ towing for miles years ago I knew they would be a mess and possibly the issue.
Sadly you have quite a build ahead of you.
I have 180/30's. Since I discovered the block was 97, I'm not sure what kind of life the previous owner(s) gave the truck as I have been pretty careful with ETG's.
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