I recently installed a new longblock SBC ( 5.7L) from large engine distributor ( center state) 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 and it's all over the map, ranges from max of 170 to low of 95. ( done cold) 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 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 when running or try to turn it manually. ( has crank mounted sea water pump so that needs to come apart to get to harmonic balancer. I haven't adjusted valves on anything in about a decade.

Been a ton of years now that modern moly rings and modern honing operations makes ring break in unbelievably quick.

The days of hoping for weeks that you're chrome rings break in are long gone.

Yes, it could be your valves not sealing. You can bring cyl's to tdc and do leak down to see if you here air coming out of exhaust or intake.

A new long block from a reputable place should have a warrantym before you turn a wrench, make sure it has a legit warranty and that your wrench turning isnt voiding it,,,,'

'Next if you have a legit warranty have that take care of your problems.

Maybe do a leak down test and see where you're losing air. Could be a valve is adjusted to tight,

Are you sure this is a new longblock not a reman ? Who sold the longblock to you ?

It was new long block for sure, not reman. I bought it from center state exchange and in theory has a 1 yr warranty but I don't think it covers any labor.

My statement was not in regards to labor coverage. It was to possibly help you avoid a situation where they say the warranty is now void because you messed with it....

if it fails a basic diagnostic tests and its under warranty, its their deal.

Warm it up and do another compression test.

I think I will attempt to remove valve covers and run it and do valve adjustment ( may buy the mr gasket defector things to reduce mess). And then do a compression test repeat. If still sucks then maybe buy a leak down tester at harbor freight.

Like phragle said though you may at the very least consider contacting center state before doing anything. At least at that point they can document your phone call and inconsistencies in compression an may have you check/set valve lash before sending engine back. They may even have local approved repair facilities through out the country for warranty work also. Phone call would be advised for sure. In regards to adjusting your rocker arms the old fashion way isn't what I would recommend however that's your choice. There are a few different ways you can successfully do it just as quick. Rather than covering the different methods do a quick internet search and maybe choose one that works for you. For years many would set half of them at #1 tdc and the other half at #6 tdc. It's quick and simple. Basically the old chiltons method. You'd be fine doing this way on a stock engine.