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compression readings


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are these compression numbers good/normal/acceptable for a freshly rebuilt motor?

n42 block - resurfaced and bored .020

n47 head - resurfaced and valve job

new pistons, rings, etc, but otherwise a stock build


1 170

2 165

3 160

4 155

5 155

6 170

test was done on a cold engine.



Edited by awconroy
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If you're looking for a ball park number, they look like what I just got on my N47/N42 engine, 172-175 across all six. The high numbers anyway. Just tested it about a week ago, trying to diagnose a noise. I drive it daily and it has many miles on it, but it runs very well. It sat for ten years before I got it also.

Your low numbers would be for all of the reasons you mentioned, dry, cold, unseated rings in a slowly spinning engine (one plug at a time). Or because your valves need adjustment. Or both.

Otherwise, it looks like it's ready to start, break-in and go driving.

Edited by Zed Head
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What are you trying to figure out? Who rebuilt the engine, professionals or home garage mechanics? What parts did you use? Were the cylinders honed to match the type of ring used? How badly does it smoke?

Sounds like you're new engine is smoking badly and you're wondering what happened. But you're not giving any details for anyone to offer advice.

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machine work was done by a local machine shop, and i'm almost certain cylinders were honed match the rings.

assembly was done in a home garage.

pistons (ITB?), rings, etc were ordered from Arizona ZCar as a complete kit.

final warm valve adjustment has not been done yet.

i've been sorting out other issues and havent been able to get the car on the road long enough to fully break in the engine. but the initial signs are a little disconcerting.

the smoke doesn't occur when the engine first starts and then clear up like is typical with worn valve guide seals. instead makes a small blue cloud behind the garage when i goose the throttle up to 2 or 3k.

factor in the low-ish compression numbers, and things don't "look right". other than that it fires and runs easily.

i dont expect a diagnosis, but some guidance whether this is all normal for a motor with approx 70 miles on it.

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Blue smoke might be an overly rich mixture. Goosing the throttle is when extra gas gets added. Are you running the stock EFI? Run through the cloud of fumes and smell it. Oil burning smells different than the gasoline of a rich mixture.

And I think break-in time varies depending on the rings used. Chrome rings are noted to take a long time to seat, for example.

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