Help with my 620....please.

[BagelsAndDatsuns]

So I have a 73 620 with an L20b engine from a 75 in it. It overheated and the water pump went. I replace d the pump and was suprised to see that I was getting alot of white smoke, than relized the radiator was empty...everytime the thermostat gets to temp and pops open the engine sucks a full 2 gallons of water into the engine. I took off the head and everything looks ok, the gasket was in decent shape, no blowouts. the Head is not warped and if the block is imperfect it is by as little as one mm. I ordered new gaskets and intent on finishing the job but I have to say that I'm not confident that It's gonna fix anything. I mean how could that small of a space being emptying the whole radiatr worth of water into the engine in a matter or 3 or 4 minutes. Does this mean that theres a crack in the block inbetween the water and oil passages??? Is my truck asking for the junk yard? any ideas as to what could be wrong would be a great help. Thanks.

 

Dave

[ggzilla]

Sounds like a blown head gasket. They usually look OK.

 

Checking for leaks is easily done before you remove the head, and not easy with it off.

 

The truck overheating does not cause the water pump to go bad. But a bad water pump causes the engine to overheat, which in turn causes the head to lift up and blow the seal. In worst cases the head will warp more than allowable.

 

Be sure to check the head for flatness before putting back on.

[BagelsAndDatsuns]

cool, I was expected the head gasket to look all chewed up and have spaces torn in between the water and oil passages. I guess I can go into the replacement and reassembly with more confidence.

 

Thank you sir.

[ggzilla]

Check surface flatness yourself. Most do not need head skimming (head milling). Use a straightedge (I use a quality level) and a .004 inch feeler gauge. It is allowed to be up to .004 but I rarely see that much even after overheating and blown gaskets. Normal is .002 inch per the Datsun factory service manual.

 

Every shop I've ever talked to says "oh that's not right, you got to mill 'em every time or you'll warp the gasket ... and it's only $ to do it - it's cheap insurance". What a bunch of baloney -- as if the factory doesn't know anything. It is more important to get the block and head scraped clean (no old-gasket residue) and get the oil off the surface before putting the new gasket on. I use a little starting fluid (ether) to get the oil off. Torque the bolts in pattern to the correct torque steps (use a torque wrench) and it'll be just fine - if the flatness is in spec.

[red13]

also when you fill it up burp the engine.  Leave the radiator cap off and let the bubbles come till the subside.

[datzenmike]

There are only two places even close on the head where oil and water could meet. The oil feed hole up from the block, but at 40 PSI it's doubtful water can force it's way in. The other is the oil return drain hole at the rear. Very unlikely oil can get near it. Water get's into the oil in the form of steam or small droplets being pushed past the rings from a gasket leak into a cylinder.

 

Look at the dip stick. If two gallons of water got into the block the oil will be floating over the top of the stick.

 

If there is a large amount of water in the oil, remove the water pump and look in the timing cover cavity. A hole here from corrosion will drain into the block.

[Figbuck]

I'm with Mike on this. There ain't two gallons of water in the crankcase... it went out the exhaust... you blew the gasket. Hope you didn't mess up any rings. Look for the cylinder that was pumping the coolant. It you ran it for a while, you might see weirdness on the wall where it forced it into the oil rings or something. Or not.

 

 

B & D... homie... where are the OICS?

[datzenmike]

The cylinder with the steam cleaned piston top and spotless combustion chamber is the one.

[BagelsAndDatsuns]

hahahaha, you are right, there is one cylinder that I thought was oddly clean. I'm stoked that the gasket is most likely the fix for my problem, I love my 620!!. I won't be getting to this until thursday or friday. But I'll tell ya'll how it goes. Thank you.

[izzo]

Another thing.  Clean the head bolt holes out GOOD. Don't half ass it.  Get them bitches clean clean clean.  You'll get a proper torque reading this way.  I use a small wire brush on my head bolts, then dip my finger in oil and run it around the threads.  Not enough to make a drip come off the bolt, just enough to slightly lube it.  A dried out head bolt hole, and a dry rusty head bolt will drag causing a bad reading, too.

[Z-train]

While a clean hole is great,oiling the bolt will change the torque value.