Cylinder Re-hone
 

Just did a rebuild, block work done by a local machine shop, and cylinders #1 and #3 are making a solid 180 PSI compression hot. #2 is at 95 psi and #4 is at 60 psi. Retested wet and the numbers went up to 150 and 120 respectively. She actually runs well with just a bit of a shaky idle, and all the plugs look identical so they are making enough pressure to ignite. I will be performing a leak down test to try to pinpoint where the loss of compression is happening, but I'm pretty sure it's the ring seal. The rebuild has just around 20 miles on it, but from what I've read the moly rings that I used (Hastings), should have sealed by now if they are going to seal. (I checked ring gap, clocked them correctly, and coated the cylinders with some 30 wt dino oil, and used the Joe Gibbs break-in oil) With that few miles on the rebuild, can I just try throwing some new rings on those two pistons, or would it be a better idea to re-hone? If so, what grit stone should I be using? I'm not going to pull the motor again and do another rebuild, if it comes to that then I'm going to say screw it and do a 3rz swap. (hence I'm just going to throw a hail mary and try a re-ring on the affected cylinders)

Just as a bit of back story, about 30,000 miles ago I did the original full rebuild with an engnbldr kit and the rock rings. All the cylinders made weak compression from the beginning. Then #1 fell off to almost nothing recently, prompting the second rebuild.

Have you looked at valve lash clearances??? 20 miles???

.008 intake, .012 exhaust, set hot. And yes...less than 20 miles. For some reason two of the pistons didn't seat correctly. Fresh hone, good crosshatch, break-in done with a conventional break-in oil, 20 minutes at 2,500 RPM.

Well I figured I would close the loop on this thread. Finally got around to doing a leakdown test and found out the exhaust valves on 2 and 4 are ˟˟˟˟ered. TDC, play in the exhaust and intake rockers for the respective cylinder, and air coming out the exhaust pipe. I hereby commend this thread to the archives of Yotatech in hopes that it may help another wayward soul one day.

So, do you think they burned? Did you have head work done at the same time as the lower end rebuild or was the head left alone? Seems sad to Give up on it if you are just a valve job away from a fully rebuilt motor.

I'm not giving up on it, not by a long shot, haha. I just thought this thread had run is course is all. The cylinder head was new from ENGNBLDR the first time I did the rebuild. Not sure why the valves burned, I was always meticulous with the valve lash. I think I'm going to ditch this DNJ cylinder head and cough up the dough for an LCE one.

I'd be curious and I hope you post what you find when you get a closer look at the exhaust valves. Some engines suffer from valve seat recession and that can lead to burnt valves if not caught in time. I'm not familiar with DNJ. Is it Chinese made?

Keep it alive! Let us know how it turns out. Also, I love the stripes on your pickup.

double post

Nothing like a genuine Toyota head casting and OEM exhaust valves.

Nowhere is correct metallurgy more important than in a component that runs at continuous red heat.

I'm sure somebody will correct me if I'm wrong, but I believe it is a Chinese casting that Ted massaged with some of his own parts. I foolishly chucked the original Toyota head when I did the rebuild.

Well, I got the motor all buttoned back up tonight and she runs better than ever with the new head! Super smooth idle (very rough before), and good compression across the board. There was much rejoicing! I don't have a valve spring compressor to really examine the valves (I may rent one), but I do notice the exhaust valves on the old head for cylinders 2 and 4 were more white then for 1 and 3. :dunno:

I did have a hiccup worth mentioning...I learned that when washers spin when tightening a nut for a head stud, bad things happen. I think I had one spin and pull the head bolt threads out of the block. :( After a period of somber mourning and deep reflection, I started looking into helicoil kits, then discovered a thing called Time-Serts. A trip to Amazon, $104, and 3 days later I got my Time-Sert kit and it worked just as advertised. Much stronger than Helicoils and maybe stronger than the original threads. In order to prevent any more washers from spinning, I sanded the bottom of all the washers and cleaned the tops of the...rocker arm towers? Is that what they're called? Anyways, I was very careful torquing the nuts down and noticed a couple more washers try to spin so I immediately would back them off, re-sand/clean, then re-torque.