Lookin for a answer

New toyota guy here..but not new to mechanics. I've hit a wall and need some suggestions. One owner truck with a 2.4. It has 140000 miles on it. 3 days ago I went to move it and after 2 revolutions of cranking normal something happened then Zero compression. I almost thru up. I pulled valve cover assuming it broke the timing chain. And it was intact. Aligned timing marks and it looked OK. Verified compression and #2 was at 50 and #3 was at 70. Other two around 150. Couldn't see it being a blown head gasket . Oil was spotless. Plugs were spotless too. Did I mention this is a very clean little engine? That's never been abused? So pulling the head was inevitable..the more I dug the more upset I was that I wasn't seeing anything obvious.

 

Here's a couple pics of what I saw tearing it down. Timing marks aligned from what I can see and nothing broke.

 

Plugs look good...no evidence of a head gasket failure either. Truck never ran hot and always ran great too.

 

If you are sure about those compression numbers, then you might as well keep tearing it down. I’d scope it first myself

 

Perform a cylinder leakage test before you pull the head.

 

So I pulled cams and inspected cups and shims. Upon looking further I found this keeper that looked weird . I did scope cylinders maybe to see some witness marks of a valve hit. But no such luck. So I proceeded to pull head. I also should note that I checked valve clearance before pulling cams. Of the 2 cylinders with low compression. Only cylinder 3 had a tight exhaust valve at .009( a .001 out of spec).

 

Cylinders looked good with no ridge and can still see cross hatching although I just visually looked at them. Combustion chambers looked ok too. I was able to merely wipe them clean with a rag and brake clean. Then sprayed brake clean and noticed exhaust valves in those 2 cylinders leaking...ugh...

 

I didn't even think of this honestly.

 

Leakage

 

Cylinders

 

I proceeded to pull pan and removed the timing cover. Nothing broke or out of the ordinary in there. So here is my question...How does this happen to these valves? What am I missing? Can the hydraulic tensioner fail for a moment on start up for it to jump a bit enough to smack valves? Tommorow I will see if my spring compressors will work on this head. So i can remove valves and verify the valves are bent. Until tommorow

 

did you check the valve lash? might just need a valve adjustment.

 

Did you do a leak down? Any head cracks between valves?

Some heads can have the hardened valve seats slowly pound into the heads.
Also what about T chain stretch? A Toyota chain looses color markings when overheated

 

On rare occasions I’ve had engines start and stall (cold start) then spin over with no compression. I usually will hold the pedal to the floor and keep cranking it until it begins to catch. It starts rough but clears out and is fine after.
Usually happens after the engine is cold started, moved then shut off with no warm up. Chrysler had a 2.5L Mitsubishi V6 in the 90’s that would do this quite often. We had a tsb for a PCM flash that helped, but didn’t eliminate the issue. You’d swear the cam belt snapped. Holding the gas to the floor while cranking would clear it out every time.
I recently had a Mazda 2.5 do this at the shop. My only theory is the carbon on the backside of the valves gets dislodged by raw fuel and it comes loose on the next start, causing cylinder leakage. I find it hard to believe all four or six cylinders have carbon holding valves open but I’ve seen stranger things in my career.

 

The #2 and #3 pistons haven't been hit by valves, from what I see.

 

I could see that happening. I don't think this is my issue though.

 

I can't see any indication either.