Hello all,

Brought my P79 head into a shop yesterday to have some work done. I'm having new SI valves, guides, springs, retainers installed and shave the head 0.080".

I asked my machinist if he can get the stem heights the same from exhaust/intake. He told me that they are going to be whatever height they end up at because of the new guides and valves. To get all the heights the same it would require all new seats, which he quoted as 2k+ job alone.

I've been given advice on 2 schools of thoughts here from his experience from 2 different professional builders.

1. All stem heights should be the same and there should be a zero variance on all valves in order to have the same size lash pad.

2. It is common to have different stem heights when taking it in for a valve job/guide replacement and you should see varying heights as intake and exhaust valves are different heights. As long as you have the correct size lash pads and the wipe patterns are centered, having different installed heights does not matter.

Just curious what everyone elses thoughts are on this?

Also, have any of you brought in a head to have new guides/valves installed and had success with stem heights recutting the existing seat or are new valve seats required?

Thanks!

Have you read datsungarage p79 modification? You shave 80 off, shim cam towers 80 higher and use the valves from the N head.

https://datsunzgarage.us/p79/

Never mind! Coffee kicked in. 3 outer and only 2 inner shims.

I read back through that and this doesn't make sense. Diseazed do you know how many valve spring washers Eiji uses? I don't know him like you do and kinda scared to call and ask a bunch of questions until I am actually ready to do mine. I know he's a busy man.

Because .080" longer valves are now in the head the springs must be shimmed up to from the bottom to retain the same spring tension. The washers are hardened steel and are there to prevent galling of the aluminum head...don't get them from the hardware store. The stock head came with only one shim under each per spring is exactly .040" in thickness. So just add 2 more under each outer spring (total fo three) and you can achieve the desired increase of .080". Washers used to be available at MSA and were inexpensive.

The single stock washer under the inner spring is also .040" thick. But you can only add a total of 2 washers under the valve seal instead of 3, as it won't let the valve seal lock-ring seat properly. The inner spring is more of a "helper" spring and won't be adversely affected, I've had no problems using only 2 washers here and I rev my engine to 7,300.

Edited 2 hours ago2 hr by siteunseen