cyl head

[whitechef]

When I have my head milled to flatten it out do I have to do the top where the cam bearings sit as well?

[datzenmike]

No. And don't remove the cam towers either if you can help it.

[banzai510(hainz)]

only if head was severly warped you would do top and bottom.

 

Try to do just a clean up cut

Dont take the cam towers off if you dont have to but its not the end of the worlld if you do.

 

go to

olddatsuns.com(former 620 tech website)

[ggzilla]

And if it is not warped, don't get it milled. Even when a head gasket blows, it rarely is because it is warped. Nissan specification is up to 4 thousands (0.004) is OK, no need to mill it, it will work fine with a Nissan or other quality gasket. This is for L-series engine. If yours is a racing engine or turbo'd, you may wish to "blueprint" it to a higher spec, say 0.002.

[HRH]

Personally, if ever there's a used head and it doesn't have a mirror finish, I would ALWAYS have it milled. A competent head shop should know, but tell them to make it flat, don't take off any material. They'll do the absolute bare minimum which won't affect your compression ratio or chain tightness.

 

Typically the shims come in .015" if I remember correctly, so if you want a tight chain, do milling for compression in increments of that, for instance, my U67 on the race car was milled .030, but that wasn't for clean-up.

 

As you'll note in the Datsun Bible, which you should own (How to Modify your Nissan/Datsun OHC Engine by Frank Honsowetz) keep it clean! The cleaner the parts, the better chance of sealing and longevity.

 

If you have the block out, I highly suggest taking a knife sanding block, on the fine side, and spray some WD-40 on the block, and work it back and forth across the top of the block. It's too hard to take off a bunch or material, and a standard rectangular sanding block is wider than the L series, so no worries about rounding corners. This will remove the built up crap from years of abuse and will help everything seal nicely.

 

Just remember: An ounce of prevention is worth a pound of cure. Sometimes the shortcuts end up being longcuts.

 

It should look like this:

But it should be a good L head, not this shitty Z20 head. :)

Edited January 18, 2009 by HRH

[HRH]

Here's what the head on the race block looked like prior to installation, note the wavy patterns on the block surface, those were the high spots that were taken care of by patient sanding with the fine grit block.

 

 

If it seems like a lot of work, that's because it is. :)

[datzenmike]

Ahhh my mystery Z20S head.

[whitechef]

Thanks Guys for all the input, I' going to take the head in to a shop and have them check it out. I'll keep you all posted and maybe some pics later. I'd like to keep a record of the whole process of my project. It's a 71 521 with an L20 B out of a later model that sat for 3 years.