Hi guys. 

I got my pistons in and mounted the heads on my 390 engine. I was checking compression. Seems like i have some blow by. But i can feel compression on each cylinder. Maybe i got my piston rings set op wrong? I got them set up like this:

Gaps are at least an inch and a half away from each other except on the 3 piece oil ring because the expander is in the middle. Before i installed the pistons i put in compression rings into every cylinder. Gap was within tolerances. 

Let me know what you think. 

Thanks. 

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Gap placement should be fine. From memory there is a top and bottom side of the compression rings.

Hi Jason. 

I forgot to say that the engine isnt build in the car yet. It is currently on its engine stand, breakin in will happen next year if it fires up after i drop in the caddy. After posting the message it occured to me that these engines have hydraulic lifters. There is no oil in them yet so could it be that the valve timing is off because of empty lifters and that the blow by i feel underneath the engine is caused because of that?

Piston rings are mounted as described in the manual that came with them. (top, bottom and oil ring) 

I will check out the break in procedures when its time to install the engine. 

Thanks. 

You are not going to get any accurate compression testing until you fire it up, break-in the engine, and let the rings wear in.  In addition, it is my guess you could cause some damage by just cranking the engine over to get a pre break-in compression reading.  With new rings you will want to run at 1500 rpm for 30 minutes. As noted on the help page this allows the rings to seat against the cylinder walls.

The bigger concern & quesiton is did you follow the proper break-in procedure?  If you need a reference, check out this Help Page entry: Engine Break In Procedures (per Association of Engine Rebuilders)

Remember that compression is checked on a warm engine.

Hi. 

This is my first time building a engine like this. I was a little bit stressing out because it didnt really react like i am used to with 4 or 3 cylinder engines without hydraulic lifters. I will have to wait untill march or maybe april to build in the engine in the caddy due to weather conditions. I will let you know what happens:-) 

Thank you for the info guys! 

Just a heads up --on installing the rocker arms on the 390 and 429 engines
Some of the best engine builders ( ?) have put them on backwards preventing correct oil flow on a new rebuilt engine
A really bad thing to happen to a new rebuilt engine

You will need to use a tool down the dist shaft to pump the first oil thru the engine before the first start up

There is a Search engine on the top right of the home page or the Help Section that should contain the details on that

The rings on these engine are a very very hard metal that will take more time to seat for that reason
Oil consumtion will be higher for a while due to that
You will need to seat the rings with a few thousand miles before you will get a good compression reading
Conventional oil used first will help that happen over a full syn oil that will take longer to seat the metal parts
You need to fire up the engine and get it to run up to 1000 RPMs ASAP to have the parts seat correctly
Then hold it over 1000 RPMs for a period of time
All engine bolts should be retorqued after the first few run ups bringing the engine to operating temp each time

Having a new fresh engine has to be a highlight of any restoration project

Enjoy or your doing it wrong

My own opinion is it takes 10,000 miles to break in a new engine on all cars
Working out the --Bugs that all new builds will have ( oil leaks - carb jetting etc ) will be the next step in the project after the engine is running

Enjoy

As Jason suggests 1500 Rpms for 30 min will do the trick on the first run up

Enjoy

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