Low Compression on 3L After Full Rebuild Help (1 Viewer)

[mcmarshing]

Hi all,

For the past few months my friend and I have been rebuilding a slightly modified 3L with a CT20 turbo and 2LT exhaust manifold +intercooler in a 1990 LN106 Hilux crew cab. Some time in March the truck broke down while on the highway. After a compression test, the compression numbers for cylinders 1 to 4 respectively were 495 PSI, 455 PSI, 305 PSI (345 PSI with oil), 450PSI. We decided to rebore and rebuild the whole engine after discovering this and got a Terrain Tamer 3L 0.5mm O/S Rebuild kit.

After 4 months we got engine back from the machine shop, and some miscellaneous parts we needed (valve seals, valve exhaust tubes etc. were not part of the rebuild kit and took a month to come in). Put the whole thing together, fired it up, and we got a RPM dependent somewhat metallically sharp "tick tick tick" sound when any gas was applied and the truck could not hold an idle, and just didn't run. The following day we did a compression test out of the recommendation of a friend, and our compression numbers for cylinders 1 to 4 respectively were: 365PSI, 370PSI, 355PSI, 355PSI. After adding 5 eye drop sized droplets of oil into each cylinder, the compression numbers were unchanged.

I called my uncle who's rock solid with Toyota engines (as a disclaimer he did mention he strictly is a petrol straight-6 engine guy) and he suggested that I might need to keep trying to start it to get the temperature of the engine up, and hope the diesel combusts and start breaking in the rings.

Other Background information:
-Valve clearances have been checked and are still good
-Small block stuff is all good (piston diameters, ring gap, groove gaps etc)
-Timing belt is new and timing is all good.
-Main Bearing Journal is 0.025mm U/S instead of 0.05mm, and the clearances are all good.
-Head was properly torqued with new hardware
-Injector is not advanced or retarded, and right at the Toyota match mark for the time being.
-Head Gasket is the thickest head gasket available at (I think it's the F thickness) - came with the rebuild kit, engine could use thinner one if it had to based off of protrusion
-I personally did not assemble the cylinder head. The machine shop did, but based off of their competency and the valve tappet gap being within limits, I assumed that the head was good to go.
-Engine turns over smoothly with no "clanks or dinks" that could indicate valve to piston strikes.

Which all of this leads me to believe: that I need to break this engine in by just forcing combustion (if that's a thing at all), I need a new head gasket, or the machine shop I used goofed up a valve job. That's what I can think of to cause all 4 cylinders to be 100 PSI low, and I'm all ears for any experience or suggestions on the matter. Other things that could be addressed are maybe reconditioning the injectors, but i'm ignoring that for now because that would not contribute to the lack of pressure in each cylinder. Unfortunately, both my friend and I are going back into the military here shortly, and we're desperately trying to get this sucker fired up so my wife or family don't have to deal with a brick of a truck while we are gone.

Located in Utah.

 

[hiluxjeremy]

Weird that it won't idle... Have you gone back and pulled the front cover on a sole mission to verify timing? Note the nice embossed arrow under cam gear.

Some guy in a cave up in canukcistan may have once maybe the one time a little bit had a 3L engine running with a cam timed 180 degrees out.

Only way I know of to seat the rings at this point is to drive it, load the engine as heavily as you possibly can without cooking it. Mind those gauges.

Long shots include fuel quality and delivery path, intake restriction, the ever present spectre of human error, the tendency of the universe towards chaos over order.

Good luck.

 

[GTSSportCoupe]

Are you using a different compression tester? Depending on check valve location, they can read quite differently (as hose volume before check valve adds to cylinder volume).

 

[Dougal]

The consistency in your numbers is encouraging. Could it be the rings just need to seat?

I've never bothered with a compression test before or after a rebuild.

 

[mcmarshing]

Thanks for the responses,

@hiluxjeremy We have verified timing x3 times. We have hand spun the engine at least 40 times at this point too to verify no interference and overall "smoothness" of the engine. Engine spins real smooth.

@GTSSportCoupe I am using the same compression tester. It does have like 16" of hose, but either way it still is the same gauge that read almost 500psi in a few cylinders before the rebuild.

@Dougal Yes the consistency of the numbers and "smoothness" of the engine is encouraging. If there was 1 piston out of whack I would be more concerned.

Update:
So I talked to a few more people, and dug around in some aussie/NZ forums and it looks like it's pretty normal for the compression numbers to be "low" after a rebuild since it takes a few heat cycles and use to get the rings to set. Not to mention, the FSM says that the minimum compression PSI is like 280psi, and I've verified from a friend that there are people out there that have higher mileage healthy engines at the 320PSI-380PSI range.

So, with the simpleness of the engine, and unknown condition of the fuel injectors, I got 4 ebay quality remanufactured ND injectors to just see if something's different and send the original ones to be properly be rebuilt.

Unfortunately... The starter went out right after I re-primed the fuel all the way to the injector pipe union nuts. (I was big sad). We tried jumping it directly from the battery and bypassing the solenoid and the plunger wouldn't plunge into the flywheel to crank (motor kind of just whimsically spun). There's a new cheap starter coming in next week and the plan is to rebuild the old one.

Thankfully though, the "metallic chirping" sound that was RPM dependent has gone away. I feel like it was just maybe air being injected by the injectors since the fuel was not primed all the way to the injectors themselves, and only to the injector pump.

So yeah from my understanding, I'm kind of in a catch 22. I need more heat to get the diesel to ignite, which needs more PSI to get the heat in order for it to ignite, and in order to get higher PSI I need more diesel combust to get the rings to heat up. I had a friend suggest towing it to get it bump started, but I have no desires of really doing that but neither do I want to burn out another starter either haha. So we'll see when we get the new starter if the issue was bad fuel injectors.

 

[chapel gate]

the rings need to bed in then your compression numbers will improve.

it should fire right up once you get fuel up there.

 

[lacalvette]

Some says that a rebuild engine need a big load for seating rings but there is a possibility for creating to much heat…
Idle for a long time on a rebuild engine is not good, new rings creates heat and friction where idling don’t push enough oil for that.
On a big load with a rebuild engine, since rings will have friction and create heat, it will be even worst with a big load…

Too much heat is not good, can do nasty things, even ruine liners, get them loose..
I think of a more progressive way to load a freshly overhauled engine.

Looking good, good luck

 

[mcmarshing]

To close this issue, the main issue for truck not starting was the injector was set to a super low-fuel setting - aka, full throttle at the pedal translated to maybe 1/4 throttle at the actual pump. Just had to mess with the linkages per FSM and truck's good to go. So, if anybody has issues with the truck not starting after a 2L/3L/5L rebuild, make sure to verify the injector pump linkages.

However, I do have other issues with it now that I will just make a whole new thread for. Thank you for all the help.