Intake Valves Dont Completely Close

[JCat]

I've seen the valve stems get bent (on a Chevy 327) cause someone messed up the plug wires and firing order.

 

[BubbaFL]

I put air in the sparkplug and I can feel air going through the intake valve.

Some leakage is normal - the cylinders aren't going to be perfectly airtight. You need to do a leakdown test.

If you don't have a dedicated tester, you can make one out of a normal compression test kit (the screw-in kind) and an air compressor w/ tank and regulator:

- Set the cylinder at TDC

- Take the schrader valve out of the compression tester and screw it in the spark plug hole.

- Set the regulator at 100 PSI (any number will work, but using 100 makes the math easy)

- Charge up the compressor

- Connect the air hose from your compressor to the compression tester, and read the PSI on the regulator (hose side).

- If it's stable at 90 or more, you're in good shape

 

[First_Explorer]

Update

Thank you all for your input. I will take another look at my timing.

"What was the condition of the timing chains, guides and tensioners when you disassembled the engine?"

My left cassette and primary tensioners went out and a piece of the plastic was wedged between the primary chain and the crankshaft sprocket, which siezed the engine. All the chains were intact, could the primary chain be too streched to reuse?

Is it possible the intake valves were bent without chain breakage?

I have not tried a leakdown test, I did try to do a compression test and I could not get any compression reading. The engine is on a stand and I had cranked the engine, The engine did not feel as though it was building pressure either. I cranked for a good constant minute or two.

 

[BubbaFL]

I have not tried a leakdown test, I did try to do a compression test and I could not get any compression reading. The engine is on a stand and I had cranked the engine, The engine did not feel as though it was building pressure either. I cranked for a good constant minute or two.

Compression test won't work on a stand (at least not with the 4.0 SOHC, no idea about other motors) - been there, tried that.

Do an improvised leakdown test; if you get 90% or better readings, put it back together and try to run it - or do a compression test once the engine is back in the vehicle.

 

[First_Explorer]

"Compression test won't work on a stand (at least not with the 4.0 SOHC, no idea about other motors) - been there, tried that. "

That is very refreshing information, as getting no compression was making me think the worst. I will try the leakdown test.

 

[First_Explorer]

Problem Solved

I preformed the leakdown test, set engine at TDC and air was just rushing through the intake valves. My compressor couldn't keep up with the amount of air it was losing.

After this I decided it was time to pull the head.

You can see the marks where both the intake and exhaust valves hit the piston.

This is after the head was pulled off. This is the amount of light coming through the bent valves.

"Closed"

So this poses a question, should I continue to rebuild this engine, or just replace it. The engine has about 100k on it. I can purchase a 2000 sohc 4.0l from a wrecking yard for $500 with a 90 day warranty, then install the new timing gear set I purchased for this engine, along with all the other parts.

 

[JCat]

IMO - replace it. Once you have internal parts smacking into each other it increases the odds of future problems.

 

[Dono]

Id be concerned about piston/connecting rod/connecting rod bearings also. Sorry. This is not good news

 

[SoNic67]

Valve stems bended?

...

You can see the marks where both the intake and exhaust valves hit the piston.

Sorry, I thought so.
So, the 4.0L it is an interference engine... :thumbdwn:

 

[colintrax]

I don't feel like reading everyone's posts, so sorry if it's been mentioned. But why not check them? Feeler gauges are cheap, and shims aren't real expensive. Every motor needs valve adjustments, just did my dirt bike, time to do my mom's Civic hybrid, and the riding mower.
"tight" valves won't close all the way


*nevermind, just saw were you said the valves hit the piston. Guess the timing chain jumped.

 

[BubbaFL]

So this poses a question, should I continue to rebuild this engine, or just replace it.

For the price of a used engine plus a new timing kit, I'd look for a V8 donor truck instead, or just part out what you've got and buy a V8 truck.

 

[Dono]

RIP. Another explorer down for the count.
Never good news.

 

[2000StreetRod]

salvage engine

. . .
So this poses a question, should I continue to rebuild this engine, or just replace it. The engine has about 100k on it. I can purchase a 2000 sohc 4.0l from a wrecking yard for $500 with a 90 day warranty, then install the new timing gear set I purchased for this engine, along with all the other parts.

The SOHC V6 is a fairly expensive engine to rebuild. The valve/piston collisions may require some machine work on the heads. Using a salvage engine may enable you to do all the work yourself and save labor costs. The 2000 engine will have a returnless fuel system and does not support the 1997 variable induction system. You'll probably end up just using the 2000 long block. I suggest that you take the heads to a machine shop and ask for a repair estimate. A special tool is required to compress the valves and the valves are not cheap. The heads may need new valve guides. The pistons may not be reliable after striking the valves. The rods could be bent. I think the salvage engine is a safer prospect.