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It's rings. Valve seals don't cause low compression. Time for a refresh.
Define rich on cold start? Its typical for stock ECU speed density to cold start in the 11.0-12.0 range to make it run ok. It doesn't hurt anything.
The AFR gauge will sit at 10.0 (the lowest it'll read) sometimes bouncing up to 11. On a built motor with forged internals could the tolerance be a littler looser in anticipation of making more power? In that case, might my compression test be ok? I'm going to perform a leak down test once I can get my hands on the requisite tools
- What was the reason for the rebuild?
-What kind of cams are in that engine?
-Was the cylinder head rebuilt too or just the shortblock?
- Previous owner said the original engine threw a rod, a used block was acquired and overbored .020
- I should know that, but I don't. How could I find out? [EDIT: Cams are stock, texted previous owner]
- I've attached a picture of the build receipt that details the work done prior to purchase
Last edited by MIVEC_IX; Feb 23, 2020 at 07:06 PM.
Also... how can an engine built 15k miles ago already require a rebuild? Improper assembly? Improper break in?
It's not break in. The best way to break in an engine is moderate boost levels with lots of vacuum pulls. You want to take advantage of the fresh crosshatching on the cylinder walls while you can to sand the piston rings into the cylinder wall for a better seal.
I was hoping they weren't stock cams because there are some cams that cause low compression readings naturally. Your currently tested compression is too low, but compression isn't the real problem. The real problem is that the oil you are burning will lower your fuels octane rating and cause unpredictable knock, which could blow your motor again.
To answer your question though, this is caused by either parts failure or improper assembly. I wouldn't go back to the shop who built it either because they or their machine shop is doing something wrong. There are a lot of places to make mistakes when assembling 4G6x's. If the piston to wall clearance, ring gaps, and cylinder health (bore, crosshatching, ovaling, tapper) were all within spec, then your engine would not burn oil. If your cylinder head is straight, valves, valve guides, and valve stem seals are good, then the shortblock needs a rebuild.
Also it looks like they probably gave you an evo 8 block since the receipt says "drill and tap for mivec." Nothing wrong with that part if done right.
I'm in agreement that something is up given oil consumption and pooling in the dishes.
Compression tests should be done with the engine at or near operating temp for a few reasons. One being that if you're comparing to the spec in the service manual, those values are HOT values. Another being thermal expansion and the lack of seal when the engine is cold. Especially if that engine is using 2618 alloy pistons...it's gonna be on the looser side when cold.
Even if assembly was spot on, it's nearly worthless if the machine work was botched.
Some of these numbers are high enough that I'm wondering if I did it correctly. I made sure the engine was warm prior to the test. I'm wondering if the oil within the cylinder is helping seal the chamber and showing values that are better than what's really happening?
Some of these numbers are high enough that I'm wondering if I did it correctly. I made sure the engine was warm prior to the test. I'm wondering if the oil within the cylinder is helping seal the chamber and showing values that are better than what's really happening?
I would address the pig rich at cold start . Thats unacceptable. Its not doing the engine any good by fueling the oil down or causing a poor ring seal.
13.5-14.0 on cold start with cams is where most people shoot for cold start/idle.
