Ok so I had a completely stock ctr swap. My bottom end blew a hole thru the case. When taken apart, the piston on cylinder 4 was beat-up and the rod had snaped. Only that one cylinder was bad. So what i did was put together an ls block with brand new oem p30 pistons and brand new rings. The head was sent to a machine shop where it was supposedly inspected, valves on that cylinder was replaced, .006 was shaved because it had minor warpage, and they guy was supposed to cut the valves in to ensure a proper seal. I got the head back and they said that everything was tested and the head was good to go. So i put in some rocket m22x cams with supertech retainers and springs.


Now the problem is, i put everything together and fired up the motor. compression read 210, 210,210,170. I believe something is not right, but a couple of my friends tell me that its normal because it was a fixed cylinder. The question is, is this true? I am very worried because it is my daily and i really need it. Thanks in advanced

 

You need to do a leakdown test to determine where the pressure is leaking. You should be able to tell is it is the rings, intake valves, or exhaust valves by doing that.

 

Ok. So it is correct that this is not normal right? The numbers should be alot closer?

 

Yeah, #4 is way off. They normally should be within 10% of each other on a good used engine. I'd like to see within 5% on a new build once broken in. You need to do a leakdown test to determine where the air is leaking from. It sounds like you put new pistons and rings in a used block, is that correct? Did you measure the cylinders before installation and did you at least hone them with a dingle ball hone?

 

the block was inspected by a machine shop, hot tanked, honed it and installed the arp rod bolts.

 

i mean used block lol

 

I'm in the same situation right now too. Just finish my first motor build it is a ls-vtec 81.5mm with pr3 pistons, all new rings, new seals, honed, and .005 off the head. My compression came in at 180, 220, 230, 220. Gap all the rings according to manual too, hopefully the rings just needs to seal and not anything else. Crossing fingers...

 

Did you guys heat cycle the motor a few times before taking the compression numbers? Drive around, vary the engine speed and load. Let the car completely cool, and repeat 2-3 times.

 

Motor has not been fired up yet just thought I checked to compression while I crank the motor for oil flow. Plan to have it tow to get tuned and have it first fired up over at the shop.

 

If you have not heat cycled the motor, the rings have not completely seated.

My compression was all over the place when I first assembled my last motor. 30-40% variance if memory is correct. After 50 miles of varying engine speed and load, compression was all within 2-3%.

 

Mine has been heat cycled already. What im worried about is that the one cylinder that was messed up before on the head, is the same one that is off. The other three are very consistent. I guess im going to have to do a leak down to determine whats wrong.

In the meantime, anyone care to help me with my other problem?
https://honda-tech.com/forums/tech-misc-15/ls-vtec-oil-leak-problem-2688156/