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Old 02-23-2021, 05:54 PM   #14
Board Member
Join Date: Jan 2020
Location: Florida

The wide gap among those numbers is troubling.

I recently went through almost the exact same thing. Maybe there's something in my mess that can help you get through yours. You can scroll to the very end for a nutshell list of what I think you should do before sending your head out for machine work.

When I opened up this B20 I saw no detectable wear on the cylinders and found no metal on the drain plug magnet. The oil pressure was good, and the compression was up over 100psi on all four cylinders. There was only one thing that gave me pause ... a couple of the head bolts were really stuck. I had to use a 4ft breaker to get them loose. I bright-sided this and just told myself that they had been in there since 1973, so they really didn't want to leave. With all of this in mind, I decided on a regasket instead of a full rebuild.

After the first start up, I spotted a couple tiny drops of water on the timing cover. I took off the valve cover to do a final torque and there was milky oil. I did the final retorque to 65lb-ft, a few of the bolts POPPED and turned about 90 degrees. Then I had a ways to go before the torque wrench clicked at 65.

stupid harbor freight toque wrench!

Maybe it's not the torque wrench? I definitely chased all head bolt threads, but I did not use a bottoming tap = shame on me. In other words, crud or imperfections in the threads could have given me a false reading during the first two torque cycles. The head might have only been torqued to 40lb-ft for all I know.

WHAT TO CHECK = do a leak down test! You can do this test using the hose from your compression tester or you can score a one-time use crappy LD tester from Amazon or rent one from Autozone.

compressor line pressure set to 100psi
leak down tester zeroed out with line at 30psi
engine cold - cannot start or warm up because of dead battery and I removed the rocker assembly
cyl 1 = 20% - radiator, intake, exhaust, and cyl 2 all quiet. Airflow up through pushrod holes = normal
cyl 2 = 35% - radiator, intake, exhaust, and cyl 1 all quiet. Cyl 3 = very slight whistle
cyl 3 = 25% - radiator, intake, exhaust, and cyl 4 all quiet. Cyl 2 = very slight whistle
cyl 4 = 20% - radiator, intake, exhaust, and cyl 3 all quiet. Airflow up through pushrod holes = normal

I removed the rockers to rotate the piston through its stroke to see if the numbers changed, which would indicate a scratch in the cylinder. I found that the % remained unchanged throughout the stroke, so no major scratches.

Notice #2 & #3. There's a problem there, so the head had to come off.

you can order a machinist straight edge from Summit or Jegs for $50. You can get feeler gauges anywhere. Get a set that goes all the way down to .001.

I got a couple of spots on the deck that showed .0015 gap - same as before. These gaps lined up with the seepage marks above. Luckily, I could not get a .002 to fit, so I now know that the block and head are not compromised. This points toward improper torquing or (worst case) a crack.

NEXT THING TO CHECK = threads - a lot of people will disagree with this one! I was one of them until now.

I'm not proud of this job, but I did take my time and chase all threads with a standard tap when I did the re-gasket. Unfortunately, I didn't use a bottoming tap on the head bolt holes because I didn't have one on hand - shame on me! Here's a pic of the first hole I hit with the bottom tap. That's enough to throw off the torque, especially if each hole is crudded up at the bottom.

Here's a pic of a clean bowl I used to catch all the crud as I re-tapped each bolt hole. That's enough to totally throw off most torque specs, no matter what brand wrench.

Do a leak down test using a rented leak down tester.
Pull the head and check for flatness using a $50 machinist straight edge and feeler gauges.
Use a bottoming tap to clean the bolt holes all the way down.

I hope something in here helps. Best of luck!

Last edited by jrv6a; 02-23-2021 at 06:01 PM..
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