Changing head gasket on 120y

[ltd999]

Hey,

 

I've got a 120y that I just pulled the head off, after it was overheating and losing coolant.

 

I just want to ask some questions.. I have a manual but still like to know.

 

1 - Do I need to change the head bolts? They look fine and aren't damaged. I don't think the head has ever been removed but I could be wrong.

 

2 - I read somewhere about oil ring seals on the block? I didn't see any seals when I was cleaning the block. Does the 120y have these seals or is it just the head gasket itself?

 

3 - I also read about leaving the bit of build up carbon around the top of the bores. I wiped around the top of bores when I was cleaning the block and might have cleaned it up.

 

4 - On the rear cylinder bore it is not smooth to touch as if it has oxidized a little from where the water has come through. Is it ok to use scotchbrite or similar to scuff it up a bit? The other cylinders have honing marks in them still but the rear one doesn't.

 

Thanks in advance :)

 

Cheers!

 

 

[datzenmike]

1/ The head bolts are totally reusable if in good shape.

 

2/ The head will have valve oil seals to control oil getting down the valve stems. With the head off, now is the time to replace them. Worn valve seals allow too much oil down the stem. It's most noticeable as a blue puff of smoke on re starting the engine.

 

3/ Too late to worry about and it will build up again anyway.

 

4/ Clean it, but don't scratch it up. The rings are seated and roughing the walls is unnecessary as the rings will have to re seat over again. They may be worn out and unable to do this.

 

 

Inspect the head for flatness. Aluminum heads can warp from overheating. If the warp is severe enough the gasket will just blow again. The block is much less of a worry. Generally on a 4 cylinder head 0.004" is the maximum. If you can slip a feeler gauge under a straight edge placed diagonally in an X pattern the head should be milled down to true it up.

 

Put the new gasket on dry, with no sealers or dressing.

 

Torque bolts from the middle outward. Not sure how many bolts on the A series but something like this....

 

R A D

7.....8

3.....4

1.....2

5.....6

9....10

 

At least two stages. Up to 20 ft lbs then again in the above sequence to 40 or the finish torque.

[ltd999]

Thanks for your quick response Mike. Just getting head machined but realised it's got m30 and d54 on the new head. Apparently it's off a van? My old one had no numbers on it. Can I use the new head or will I have problems? It's a 74 120y sedan. Cheers!

[datzenmike]

No Idea. A series heads are likely all the same or close, certainly they will all fit.

 

 

Somewhere here there will be an answer to what head you have and if the new one will fit and work properly.

 

http://datsun1200.com/modules/mediawiki/index.php?title=A-series_Cylinder_Heads

 

http://datsun1200.com/modules/mediawiki/index.php?title=Cylinder_Head_Part_Numbers

 

http://datsun1200.com/modules/mediawiki/index.php?title=Cylinder_Heads

[Dguy210]

Pay attention to if the head is a wet or dry intake setup, the intake will need to match the head (dry head is fine on wet intake but not wet head on dry intake). Obviously I'm glossing over port shape and combustion chamber as that is a more a performance vs. it running issue usually.

[ltd999]

Ahh actually it was that site I read it from. It said something about oil galleries being different, I'm not sure if it was for that head though. Is the compression the same for vans and sedans?

Cheers mate

[ltd999]

Hey dguy thanks. Is there a way to tell if wet or dry or should I just go by stamp numbers?

[Dguy210]

Hey dguy thanks. Is there a way to tell if wet or dry or should I just go by stamp numbers?

One gallery is different between a12 and a14. Wet heads have a small oblong coolant passage below and between the intake ports on the head.

[Sierra]

I am still learning how to differentiate between one head and another.

I been using the Datsun 1200 tech wiki in order to educate myself.

http://datsun1200.com/modules/mediawiki/index.php?title=A-series_Cylinder_Heads

 

ID the casting number on the two heads you have and look for them on the website.

They (website) do a great job explaining if its a wet or dry head.

 

Hope this helps.

[datzenmike]

I imagine you can run a dry head as a wet head by drilling two holes and changing to a wet intake. Did this recently on a U67 head L20B.