No more valve lash adjustment available?

[TheBirdistheWord]

I'm at the top or "end" of the adjustment on #1 cylinder exhaust valve and the lash is at .007 while hot. All other valves lash are in spec with a bunch more adjustment available in both directions. 

 

Obviously that's not enough clearance, I'm curious what this indicates about the head parts?  This is a rebuilt peanut head with about 10k hard miles on it, am I looking at a another rebuild? What causes this and how can I prevent it in the future?

 

Engine seems to run fine.  

[datzenmike]

The valve is sinking into the seat. This could be just wear or the rebuilder cut them too deep. You can take the pivot post out and thin the adjustment nut which will allow the post to go lower.

 

 

 

 

I used a belt sander and it took some time but thinned it down and the post can now go lower increasing the lash. This is not a fix for a sunken valve but you might get another 20K out of the head.

[thisismatt]

Sunk valve seat

[datzenmike]

You may have to grind some off the bottom of the post as it may hit the bottom of the threaded hole now.

[banzai510(hainz)]

Yup! sunk valve and almost always the exhausted as its the softer seats from the orginal set up.

if truly rebuilt they will use newer iron type seats.  But hope the machinist puts them in good as some fall out if not done right.

 

I think this is less likely on later L20 heads as they used the steel seats cause of the unleaded gas was introduced.

 

 

If doing a performance cam with stronger valve springs to is more likely to happen on a older head with the bronze seats

Edited October 15, 2020 by banzai510(hainz)

[datzenmike]

The lead in the gas lubricated the valve seat faces. Without it they started having to use hardened steel ones.

[Stoffregen Motorsports]

15 hours ago, TheBirdistheWord said:

 I'm curious what this indicates about the head parts?  This is a rebuilt peanut head with about 10k hard miles on it, am I looking at a another rebuild?

Yes, you're looking at a rebuild, but this time use someone else. In the bay area, there are a lot of shops to chose from that know Datsun L motors. I hate to say it, but most machine shops I have ever dealt with are really good at small block Chevys, but don't know jack about imports. Find a Datsun specialist and have a good rebuild done.

 

What is a good rebuild? Obviously you need valve seats, and probably valves too, but a good rebuild will include at least checking the valve springs and retainers, setting the valve lengths, the spring heights and the rocker geometry.  Expect to pay $500 to $1000 for a comprehensive "performance" rebuild. If you want more HP and you've got a bit more of a budget, go for a mild street port job and big valves too.

 

Yes, I am biased because of my years with Rebello, but they would be the best shop to take your head to. I know they get backed up, and if this is a problem for you, you could try Troy Ermish too.