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Engine Pressure 1977 Datsun 620

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Just started my old 1977 Datsun 620 that has been garaged for the last 15 years with 30,000 miles on the truck.

Pulled plugs oiled cylinder walls, changed oil, new battery, flushed new antifreeze, fresh gas started up runs great but ......

I noticed when I started the engine I didn't screw the oil cap back in the valve cover, probably a good thing because their is

a lot of internal pressure commming out of the valve cover oil fill hole. Can't figure out what is causing this pressure,

can't believe it's blow-back with the engine at only 30,000 miles. I removed the plugs and soaked the cylinders with Rislone

added some oil and turned the engine over before starting to lube things after setting for 15 years. I can't believe compression

is getting by the rings. This engine is original with all the smog still on it. Any ideas appreciated.

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Takes some time for everything to "hydrate" I guess you could say. My truck smoked like a bitch when I got it and had pressure at the oil cap. Then after an oil change it quit smoking after 45 minutes running. My last project, a 74 ford supervan with a 302, overheated and burned up the valve guide seals. Fixed it with a bottle of some kind of Lucas brand seal conditioner put directly into the oil. No more blowby.

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OIl fill hole?


Most people dont run the motor with the cap off as there is a lobe there that will spray oil.


anyways there is the vent tube up top but air come out that also unless you have a stock valve cover and have the stock hose to route to the valve cover.

If you hava weber DGV the bottom of the DGV aircleaner will have a hole and there is a plastic angle that coems in the kitso you can route a rubber hose from the valve cover vent tube to the lower carb aircleaner.


otherwise I dont thin you have a proplem.


One way to tell bad blow by is pull the lower hose from the crank case and it will stink really bad at idle(blows out) when reved up (it will suck in)



I say just run it for awhile

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Drive it. Nothing you can do now but drive it and see if it improves. Gotta watch out for those cylinder lubricant, mystery oil treatments or what ever. Carbon plays an important role in sealing in compression on older motors. That Rislone may have washed away or loosened any carbon on the piston tops or around the rings. Keep driving, it may seal up in a few thousand miles.

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