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Old 04-26-2011, 09:23 AM
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Sbc compression and valve adjustment

hey guys, another question for you. I got a .030 sbc, I just put new rings and rod bearings in. I put my 60cc heads on as they are the only heads I know and have that work at the moment. Did a compression test as follows first and only test so far (so some oil still in cylinders) 1,3,5,7 all ran steady 125 but cylinder 2 and 8 ran about 145 while 4 ran 120 and 6 ran 125. I will be running this again, but is this too much of a difference for 2, 4, 6, 8 cylinders?

Also while turning engine over, exhaust rocker on cylinder two splurges a lot of oil out and also rocker on cylinder 4 does as well. Could this mean it is too loose or tight?

I am having trouble with this firing up. I have previously had it fired up with all the Qjunk set up on it, tore it apart because it had a broken piston. I am just wondering if my timing is that off or if maybe the valves aren't opening or closing enough. But wouldn't the compression test prove that they are?

thanks guys, this is my first tear down and put back together so I am trying to learn all of this by reading. thanks
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Old 04-26-2011, 11:25 AM
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Are you doing the test with the carb at WOT, all plugs out?

You can do a search here for valve adjustment procedures, hydraulic or solid.
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Old 04-26-2011, 11:49 AM
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nova,

I was doing the test with all plugs in minus one with comp gauge, just rolling it over with start button as far as the compression test goes. is that what you meant?

as far as valve adjustment, I have pretty good idea on how it works. I just don't understand why some rockers (in my case 2 of them) splurge more oil
than the rest.

nothing has been adjusted with it running yet. this is all preliminary with just cranking it over.
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Old 04-26-2011, 02:12 PM
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Quote:
Originally Posted by 99 to Life
is that what you meant?
To perform a compression test, you fire the motor and warm it up, shut it down, remove all spark plugs so that the motor can freewheel, wire the carburetor primary throttle plates or throttle body butterfly(ies) wide open so the motor can breathe and disable the ignition so that you don't have a fire.

If I understand you correctly, you have not fired the motor since you got it back together and are performing the test on a cold motor.

I don't see how you're going to learn anything from doing a compression test at this point. The rings are not seated and won't be for several hundred miles. The only thing I see that you're doing is wasting time and wiping all the assembly lube off the cam lobes. The lobes and lifter crowns are lubed by oil splash off the crankshaft and what little oil runs down off the bottom of the cylinder bores. If the crankshaft isn't spinning fast enough to sling oil (like during a compression test), then the cam lobes and lifters are running dry. Bad juju bwana.
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Old 04-26-2011, 05:51 PM
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Well noted on seating the rings then doing compression test.

But in all fairness, I might be new at this but doing a cold compression test
when I got this told me this had bad rings and in my case a broken piston land, so that wasn't a waste of time. also wouldn't doing a compression test regardless of miles be insufficiently getting oil to the cam and lobe base?

The cam I am using was previously used, if it were brand new I wouldn't have tried a compression test before break in and I only turn the engine over twice while putting in a cam and adjusting lifters, trying to get practice getting that right, so I can break in a cam.

I am just not sure if oil gushes out of a rocker if it means too tight or too loose, all the rockers get oil, just two are getting alot more than others.

thanks guys
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