New stock SBC long block w/ 5hrs break in and compression all over map

[mikeneal]

I recently installed a new longblock SBC ( 5.7L) from large engine distributor ( center state) naps replacement for 5.0GL and it has about 5 hrs on it so no full throttle yet. I changed oil and cut part filter and all looked good. But for grins checked the compression when cold and it's all over the map, ranges from max of 170 to low of 95. I sprayed a very small squirt of wd40 in that one and it rose to 100. The engine vendor recommended checking valve lash at 10 hrs, which I thought was odd since it's hydraulic and roller cam. I "may" hear a funny backfire sound thru exhaust at idle (boat has stock thru prop exhaust) but honestly might be my imagination. Is it possible some valves are slightly tight? Am I over thinking this since it's so new ? I wonder if I can get valve covers off with exhaust in place ( all stock vortex volvo penta drivetrain) . Then decision is to do it messy way now hen running or try to turn it manually. ( has crank mounted sea water pump so that needs to come apart to get to harmonic balancer.

 

[Scott Danforth]

Recheck lash is common. If tight, you could not be sealing the one cylinder

 

[gbeltran]

I would do it the messy way, you can buy those clips that go on the rockers to deflect the oil, but usually at idle I don't get any squirting that much oil. 170 is a good number, 95 is not. If you want to do it the other way, take the plugs out, and you should be able to use the alternator pulley nut to turn the engine via the belt, then you would not have to remove that raw water pump. Don't go crazy, it should move fairly easily, if it doesn't then the raw water pump will have to come off. I still prefer the running method for Chevy small blocks.

 

[mikeneal]

I think I will buy the clips and check valve lash and repeat compression test when warmed up. I wonder if the valve covers can come off with exhaust and riders in place.

 

[jerryjerry05]

The "cough" "backfire" at idle sounds like a stuck valve???

​Do check the lash ASAP it could be keeping a valve open??

I use a heavy material shop rag over the valves if the motors checked when running.

​The lash can be set not running.

Get a remote starter and remove the plugs.

 

[mikeneal]

I read the Interwebs and there is a million opinions as to " best " way to do lash on stock SBC. I have a remote starter switch
From when I set it up to run on a stand prior to install. Do you spin it and adjust them while moving or do you mean bump it and watch the valves and do it one at a time ? I also got a second compression guards to try that just to be sure I don't have something goofy there but I highly doubt it.

The "cough" "backfire" at idle sounds like a stuck valve???

​Do check the lash ASAP it could be keeping a valve open??

I use a heavy material shop rag over the valves if the motors checked when running.

​The lash can be set not running.

Get a remote starter and remove the plugs.

 

[Sunken Ship]

I would express my concern to re-builder ASAP.

 

[mikeneal]

So I got a bit of time tonight after work and borrowed a second compression gauge and pulled all the plugs out ( motor was cold). Everything was 175 - 180 psi in all cylinders. Checked number 2 ( the 90psi with my old gauge Saturday ) and it was fine at 175. Ok, last weekend it was warm from oil change so I started it and let it get warm and checked that one again and still 175 with both gauges. What the heck, maybe my compression gauge is failing and sticky? Super strange. I did mess with idle mixture screws and roughness got a lot better and nearly gone. I guess I will run it a bit longer than do the recommended ten hour valve lash check and redo compression check at that time.

 

[jerryjerry05]

I just bump it till it opens and closes.
​Glad the #s got better.

Makes me wonder???

You remove all the plugs to do the tests?

 

[mikeneal]

I didn't remove all the plugs and pulled the safety lanyard but realized it got power to the coil and halfway tried to start when cranking. Why do you ask?

I just bump it till it opens and closes.
​Glad the #s got better.

Makes me wonder???

You remove all the plugs to do the tests?

 

[jerryjerry05]

The first comp readings were all over and if the plugs aren't all out the readings can be way off..
Also turning over too slow can affect the readings.

Rough idle: Once it starts try spraying starting fluid around the base of the carb and the edges of the intake.
If it makes any difference?? then the gaskets need replacing.

 

[mikeneal]

Some plugs were I a nod some were not during first test. I have the lanyard pulled but realized the coil gets +12v from starter circuit and it actually tried to run sorta a couple times when doing test the first time.