Here's the deal... I had a stock internal LS6 that was super-charged and eventually broke the #7 piston. I decided I'd return the car to stock and fix the damage for the car to be sold. A Toyota mechanic friend (I know, I know) and I tore the engine down and found to top of #7 piston damaged as one would expect, the others including #8 looked good. Since I was not going to mod the car again, I bought a new factory piston and rings for #7 after checking that the block was still good. I had to replace the valves in that cylinder as well, but otherwise the head still looked great. I didn't get to see the engine get reassembled due to my schedule, but my friend is a very good mechanic so I'm sure his work was better than what I likely could have done... although that's obviously not saying much!

After getting the car back together, the engine now has a few issues. First, there seems to be an excessive amount of blow-bye, enough to blow the dipstick out at WOT. It appears the left side of the exhaust is smoking a little, but not real excessively. And lastly, when cold, the engine sounds like it's knocking when revved (this seems to disappear once it warms up). My friend said the rod bearing on #7 looked great and reinstalled it as he saw no need to change it given its condition and low mileage.

I did a compression check on the engine over the weekend to see if that would tell me anything and I was shocked at the results. Numbers 2, 4, 6, and 8 were all exactly 165#. Numbers 1, 3, 5, and 7 were 90#, 100#, 90#, and 120# respectively. FWIW, the two readings at 90# both held the pressure for about 15 minutes while I waited out rain showers. Before #7 went, the compression was 160 to 165 across the board. After I told my mechanic about the entire side being low on compression, he said he has no idea what it could be as he said everything bolts together in a straight forward manor having no adjustments which he could have messed up... you guys would know more about the validity of that statement than I would.

Obviously something isn't right and the engine has to come apart again. Based on the info I provided, does anyone have any ideas regarding what's wrong? I find it very hard to believe the entire left side of the engine was damaged when #7 went, especially since it looked great when we took it apart. Could it be a head gasket issue (new stock gasket) or the way it was installed? What about a cam or rocker issue?

Any insight would be greatly appreciated!

 

Anyone???

 

Since the entire side is bad, perhaps it's a bad head gasket?

Did you replace the rings?

How thoroughly did you check the cylinder walls for scoring?

How many miles on the engine before the rebuild and what kinda boost were you running?

 

Was the #7 cylinder honed for the new rings? The blow by is coming from, compression bypassing around the rings. If the engine has a lot of miles on it ,then the cylinders maybe worn egg shaped and the new rings will not seat right

 

If he didn't "ring it" right that'll cause excessive blow by. Meaning if he didn't rotate the ring openings 180 degrees from each other. If the cylinder walls are hogged out or egged that's another issue. What all was the damage to #7? Those pieces have to go somewhere.

A whole side of an engine with low pressure is the head gasket. Did he reuse the stock gaskets, or the stock head bolts? The bolts are torque to yield, meaning that they cannot be reused. How did he torque the bolts down? There's a torque sequence.