No Compresion in #3

[Mr Raiders]

Okay I just drove my 78 Datsun K/C From Eugene OR to Billings MT. And barely made it. They problem I had the second half of the drive was over heating. When I finally did get ot my destination she was running rough. I described it to my brother in-law like the engine was runnin on 3 cylanders, Well it was only runnin on 3. We pulled the plug wire, Wich is new and still had spark. pulled the plug, also new and it was not in bad shape. The coil, cap, rotor, wires, plugs, Oil, an filter were all replaced before I left. We attached a Compresion tester to the #3 plug hole and got zero compresion, We pulled the valve cover and everything is in place an moving properly. The cams not flat. Were suspecting a hole in the piston or a piston ring is shot. So anyone have this problem or seen this happen? Any suggestions on what to check next? Last time I had something happen to my K/C I was informed to post on here first before just guesing, so i'm trying to head that good advice.

 

Thanks.

 

O and does anyone have an L20b In or around Billings for sale?

Or does anyone know how much they go for?

[nismo dr]

hows the coolant level? could have a blown head gasket, well probably started with a head gasket and the head is probably now warped if you were pushing it while it was overheating

[Mr Raiders]

Coolent lvl was fine the entire drive. I even removed the thermostat half way thru the trip.

 

and ya im affraid I warped the head too. not what I wanted to hear but I kinda figure I did something real bad, instead of something easy to fix.

[banzai510(hainz)]

If you didnt leak any water I wont think you warped a head.

However I loo to see if your valve rocker arm is tight.

 

Look at the #3 intake and exhaust rocker arms closly and see if the lash pad fell out or the rocker while pointing up is very tight It should be slightly loose. adjust if too tight. I do .006intake/.008 exhaust If you cant adjust the ball end(loosen the jam nut and adjust down) then the valve is sinking in the seat and needs to be redone

 

retime your motor. maybe ythats why it was running hot.

 

make sure to renew your anti freeze every 4 years or so.

[Draker]

If you have ZERO compression, I'd start looking for something stuck. Everytime I've seen a bad ring or blown head gasket, I've been able to get some compression reading. Usually around 30psi. If you suspect a ring, put a teaspoon of oil in the spark plug hole and redo the compression test. If you start getting a reading, then it's the rings.

 

 

[datzenmike]

Over tight valve... cant close.

 

Worst case the valve seat fell out and a valve can't close.

[ggzilla]

Worn ring does not cause 0 compression. That's caused by burnt valve or blown gasket. But it is not common to blow the gasket for one cylinder only.

 

What evidence is there that it was overheating?

[Mr Raiders]

Ok, after reading all the posts, I have some idea's now of what to do. I can't get to a garage till next week. As for evidance of over heating, what I mean by that is, when I was on the highway I was at around 220 degree's and hills would be 236 at the highest. Previous to all this I was running at around 185 to 195, and this is at 4500 rpm. I did pull the valve cover and everything looked to be in the right place and nothing was broken or missing. I did not however put a wrench to anything. I will do that. Thanks guys for the information so far, good stuff to look into.

[ggzilla]

It was running hot, but likely did not overheat. The stock 14 psi radiator cap will prevent it from boiling

[racerx]

valve adjustment?

[metalmonkey47]

Check valve lash.

 

 

If you had a hole in the piston, I'd think you'd notice a fairly large amount of blow-by, which you mentioned no symptoms of, but of course I'm no expert so correct me if I'm wrong.

[datzenmike]

Okay I just drove my 78 Datsun K/C From Eugene OR to Billings MT. And barely made it. They problem I had the second half of the drive was over heating. When I finally did get ot my destination she was running rough. I described it to my brother in-law like the engine was runnin on 3 cylanders, Well it was only runnin on 3. We pulled the plug wire, Wich is new and still had spark. pulled the plug, also new and it was not in bad shape. The coil, cap, rotor, wires, plugs, Oil, an filter were all replaced before I left. We attached a Compresion tester to the #3 plug hole and got zero compresion, We pulled the valve cover and everything is in place an moving properly. The cams not flat. Were suspecting a hole in the piston or a piston ring is shot. So anyone have this problem or seen this happen? Any suggestions on what to check next? Last time I had something happen to my K/C I was informed to post on here first before just guesing, so i'm trying to head that good advice.

 

 

 

First, did you test all cylinders for compression?? If not, why did you suspect #3?

Zero compression is difficult to do. Even without rings you would read something.

 

Did you look to see if the valve springs are moving up and down while cranking. Could one be stuck slightly open?

 

Do you have abnormal blow by now???

[ggzilla]

Yes, compression tester is $25 at sears, or borrow one.

[Mr Raiders]

ok, I do have a lot of oil in my air cleaner. My air filter is soaked in oil and I have about half a cup of oil in the bottom of the air cleaner. I'm sure it's getting into my Carb. Also I suspected #3 cause I pulled the plug wires one at a time while the motor was running and they all changed the way the motor ran except #3 when pulled. I did check to see if the valve springs were moving, but not to see if it was sticking open a little, I will have to check that again.