Canyonfrog

I need to do some more diagnosis but this one has me initially stumped. A buddy of mine is sharing a 93 4R for parts with me that he "gave up on" because he said all 3 cylinders on the passenger side had zero compression. I verified behind him, doing the compression test correctly and sure enough all 3 cylinders on the passenger bank are literally at 0 while the drivers side is at 150-160. I pulled the timing cover and so far the pulleys appear to line up for timing and the locator pins appear to be in place, but there's a fibrous debris inside too.

My next step is to pull the valve cover and rotate the engine by hand. The HG appears to be fine with no obvious signs of leakage, but my buddy did report his CAT was "red hot" at one point while it was running. Has anyone else see anything similar to this by chance? I keep coming back to jumped timing or possibly burned valves?

Jimkola

That appears to be belt material. Maybe the inside edge had been rubbing?

Canyonfrog

Yes, that's what I'm thinking. It looks lined up and the cam pulley lips are oriented correctly front and back so I wonder if it's moving when running or if there's an issue further down at the water pump or the crank pulley. The mystery too, is if it's related to the zero compression on all 3 passenger cylinders. My next step is to remove the plenum and then the passenger valve cover and see if there are any clues in there with the camshaft and valves.

scope103

A leak down test could tell whether your issue is with valves open (e.g., valve timing, or a stuck valve) or wrecked rings, or total disaster.

The gadget isn't too expensive, https://www.harborfreight.com/cylind...ter-64918.html but you need an air compressor (which you might need anyway, if working on a donor engine).

The "numbers" from the leak down test won't mean much, but in the process you listen at the exhaust, intake, oil filler, and radiator.

Canyonfrog

Thanks for the detailed advice. Luckily I have a leak down tester and an air compressor, so I'm set there and I'll do just that. If I could identify the rings are good and it's a valve problem I may consider pulling both heads and having them machined/rebuilt and keeping the 3vz in there for now (with a set of headers going back in place of the stock exhaust and cross over) for times sake.

Even after getting the passenger valve cover off, I remain stumped. I almost expected a broken camshaft, but it's fine and rotates just fine (oil looks awesome with no metal in it)


when I turn the engine by hand. The only thing that slightly stands out to me is 5 of the 6 cam lobes are very "shiny" where as one has an oil coating on it. See attached pics, but I'm far from a 3VZE head expert and this is my first time diagnosing something like this with all cylinders on one bank with zero compression. I will look at shim clearances too just in case the shims were put in wrong by someone or they are just too tight, and in that case I'd expect all 3 exhaust valves to be possibly burned?

My buddy mentioned the CAT on this rig "glowing red hot" which to me indicates a lean running condition, so that may be another clue.

coopster

So how did your valve clearances turn out?

Zitoclick

Just IMHO, odds are that banks lifters are adjusted too high to allow the valves to seat and fire the compression stroke. Hence allowing the plug to fire the fuel down into the exhaust and make the cat glow.

Canyonfrog

I put a camera in 2 of those passenger bank cylinders and got a decent view of the horror show for the burned valves in there, so she's put on the back burner for 2 other 3vze engines that won't need the work this one does. I may eventually just pull the heads, have them re-done, inspect the pistons and block and if all is good re-assemble with headers.

Canyonfrog

I'm thinking what you have described is very likely, and caused the mass burned valve issue on that bank. I stopped scoping at 2 cylinders with burned/cracked valves, but I assume cyl 5 is in the same condition as 1 and 3. I'll take the heads to a machine shop (or another spare head I have if one is too far gone) and have them rebuild and spec them, including measuring valve stem length to be sure those exhaust valves aren't too long and causing clearance issues.