[zildjian4life218]

I finally got myself a compression tester kit so I can measure cylinder pressure on my engines. I have a newly rebuilt motor with about 15-20 miles on it. 355ci with 5cc flat top pistons. Should be around 10:1 with the vortec heads. The motor still smokes like crazy. How long should it take for the cast rings to set? Cam is a howards 180325-08. Also what would be an appropriate reading on the compression test kit.

[68NovaSS]

I've never had a new rebuild that smoked after two or three minutes of startup, if your cylinders were prepped properly, it should have seated the rings by now. What rings did you use, iron, etc? Different rings require different hone patterns. You might also have valve stem seal problems, were the heads redone? Did you have any difficulties installing the pistons, possibly breaking a ring? Sure they weren't installed upside down? What did you file the end gaps to or what were they when you fitted them?

[zildjian4life218]

Originally Posted by 68NovaSS

I've never had a new rebuild that smoked after two or three minutes of startup, if your cylinders were prepped properly, it should have seated the rings by now. What rings did you use, iron, etc? Different rings require different hone patterns.

Okay well I took it out today and put about 5-10 more miles on it and the smoking during idle has pretty much gone away... there is still some but not enough that it will bother me. When i rev it up or get on it at all it still blows smoke out both exhaust pipes. No WOT passes just having a little fun. The rings are Hastings cheapo rebuilder series.. they were like $18.99 cast rings and my machinist had honed the block. I had like chrome moly rings originally installed and they never sat due to the wrong hone pattern/grit and ended up pulling it apart and having it rehoned and having cast rings put in it.

Originally Posted by 68NovaSS

You might also have valve stem seal problems, were the heads redone? Did you have any difficulties installing the pistons, possibly breaking a ring? Sure they weren't installed upside down? What did you file the end gaps to or what were they when you fitted them?

I rebuild the heads myself.. the guides are fine and they have the little o-ring seals on them. Pistons dropped in fine.. no problems during assembly. I installed the rings according to hastings chart on the side of the box.. one had a bevel and the other had a dot i believe and they both went up if I can remember what the box said. I believe I put the rings at .016" top and .018" second.. If theres any other information you need let me know!

Im still curious about the 120psi reading I got. This seems rather low even for a fresh rebuild. Any ideas what I should be seeing. SCR should be around 10.25:1 and DCR should be around 8.19:1... im not 100% sure about DCR because my cam card got a wet spot right where Intake closing point is so it looks like 50.5 but im not 100% sure.

[S10 Racer]

Originally Posted by zildjian4life218

Okay well I took it out today and put about 5-10 more miles on it and the smoking during idle has pretty much gone away... there is still some but not enough that it will bother me. When i rev it up or get on it at all it still blows smoke out both exhaust pipes. No WOT passes just having a little fun. The rings are Hastings cheapo rebuilder series.. they were like $18.99 cast rings and my machinist had honed the block. I had like chrome moly rings originally installed and they never sat due to the wrong hone pattern/grit and ended up pulling it apart and having it rehoned and having cast rings put in it.



I rebuild the heads myself.. the guides are fine and they have the little o-ring seals on them. Pistons dropped in fine.. no problems during assembly. I installed the rings according to hastings chart on the side of the box.. one had a bevel and the other had a dot i believe and they both went up if I can remember what the box said. I believe I put the rings at .016" top and .018" second.. If theres any other information you need let me know!

Im still curious about the 120psi reading I got. This seems rather low even for a fresh rebuild. Any ideas what I should be seeing. SCR should be around 10.25:1 and DCR should be around 8.19:1... im not 100% sure about DCR because my cam card got a wet spot right where Intake closing point is so it looks like 50.5 but im not 100% sure.

Did you stagger all the ring gaps?

[zildjian4life218]

Originally Posted by S10 Racer

Did you stagger all the ring gaps?

Yes. The three oil control rings were placed 120* apart and the two compression rings are 180* across from each other

[cobalt327]

If the cylinders are not round, just honing and fresh rings may never seal well unless there was little wear on the engine to begin with. Was it bored just before the chrome rings were installed?

[RWENUTS]

Did you put the rings in out of the box or did you put square them in the bore and file fit them to the correct gap.
I had a 396 once that someone rebuilt and just put the rings in without checking them. They were 20 over in a 30 over bore.

[zildjian4life218]

Originally Posted by cobalt327

If the cylinders are not round, just honing and fresh rings may never seal well unless there was little wear on the engine to begin with. Was it bored just before the chrome rings were installed?

Yes I had just had the motor bored .030" when the original chrome rings were installed. I checked out of round before I put it back together with the cast rings and it was barely reading on my bore gauge that measures .0005" so I believe the bores are almost perfect.

[zildjian4life218]

Originally Posted by RWENUTS

Did you put the rings in out of the box or did you put square them in the bore and file fit them to the correct gap.
I had a 396 once that someone rebuilt and just put the rings in without checking them. They were 20 over in a 30 over bore.

I filed them to the correct spec according to keith black.

[underdogidi]

personally i would be more inclined to point the finger at your valve seals only because i had a 383 i built that leaked oil down the valves and during high vacume would suck oil off the valves and into the cylinder causing it to smoke when i started it an hammered down, really anytime it drew alot of air. idk about the vortech heads and how they seal the valves but sometimes with o ring seals they can be roled or pinched enough to leak. just my 2 cents...

[F-BIRD'88]

The little o rings will not work very well unless the valve guides are 100%
and the oil shield is installed too.
Even then it is normal for such a engine to puff a bit of blue smoke on start up as some oil does migrate down the valve guide.
This was normal and acceptable back in the day before emissions laws.

The oem GM vortec valve seals do a much better job.
I would get a set and install them on your vortec heads.

The piston rings will seat best by making controlled full power WOT runs.

They will not seat by babying the motor.

As stated there is a possibility you got the wrong rings or installed them upside down or in the wrong groove.

Cranking cylinder pressure should be in the 150-180 PSI range.

120 is low.

Valve/valve seat seal is another source of low compression readings.

[zildjian4life218]

Thank you for all the replies everyone! I guess I need to figure out my next step. I would like to maybe do a cylinder leak down test to find out if its the rings our heads. Can anyone post a link on instructions on how to do a proper leak down test. I will probably do valve seals next weekend. I have a set kicking around somewhere.

[underdogidi]

good deal, and good luch with this. just a little tip that might make it easier for you when you change the valve seals, i have herd rumor but never seen a tool that is basically a spark plug that plugs into your motor and has a chuck for your air compressor, basically it puts pressure into your cylinder and holds the valves up while you remove the springs, obviously you need the spring pullers that grab the spring but it might save you some time if you dont want to pull the heads, i have also herd of ppl sticking a screwdriver into the spark plug hole just so they dont fall all the way down after moving that cylinder to tdc

[zildjian4life218]

Originally Posted by underdogidi

good deal, and good luch with this. just a little tip that might make it easier for you when you change the valve seals, i have herd rumor but never seen a tool that is basically a spark plug that plugs into your motor and has a chuck for your air compressor, basically it puts pressure into your cylinder and holds the valves up while you remove the springs, obviously you need the spring pullers that grab the spring but it might save you some time if you dont want to pull the heads, i have also herd of ppl sticking a screwdriver into the spark plug hole just so they dont fall all the way down after moving that cylinder to tdc

Yup! you can just pound the electrode out of the spark plug and weld on a fitting for an airline.

[cobalt327]

Originally Posted by zildjian4life218

I filed them to the correct spec according to keith black.

Were they the type that uses 0.026"- 0.032" top?

Agreed on the rings possibly butting if it overheated for whatever reason. KB will tell you they can butt- even w/0.060" end gap- if overheated.

Using the small o-ring valve stem seals requires the steel oil shield to be used. X2 on using positive stem seals.