Need information on E31 head/head gasket dimensions

[djwarner]

Oil consumption has been a problem since acquiring my Series I in Aug 2012 (quart every 300 miles). After changing valve guide seals and other checks, I isolated the problem to a leak at the head gasket between #3 and #4 cylinders where the oil galley feeds the cylinder head.

I changed the head gasket with a Felpro. I bought the gasket before opening the engine and discovered there was a Felpro gasket already installed. Flatness was within spec for both the block and head, so I preceded to install the new Felpro only to get the same leak at the same place. The Felpro gasket has thin bead of rubber on one side around the hole for the oil flow and apparently this is still allowing leakage during operation at higher oil pressures.

While reading the Tech Service Bulletins, I found a fix for a similar problem in A12 engines TS72-77.

The fix uses an open rivet (eyelet) to hold an o-ring between the head and block. Apparently the eyelet prevents the collapsing of the o-ring during installation. Trying to do a little reverse engineering, the o-ring will allow the differential thermal growth while accommodating more variation in the head/block gap than a paper gasket.

What makes this solution attractive to me is that otherwise my E31 head holds good idle vacuum and compression. Valve seats were reworked in 2002 but comments with the paperwork say it may not be rebuildable again (due to erosion?).

Before opening the engine again, I would like to gather the needed materials.

I need the diameter of the oil galley hole in the head or block to properly size the eyelet and o-ring. Also, this width and length of the corresponding hole in the head gasket would be helpful.

[madkaw]

I just looked at two of my HGs and there is copper around the hole for the oil feed----yours doesn't have that?

Consider a Nismo gasket from Courtesy--$$$$

That's what I have after a blown felpro on my e-88

[Zed Head]

Looks like you need an o-ring that will fit inside the gasket hole but not clog the port. The oil port is much smaller than the actual headgasket hole, it's tiny. Any standard shape o-ring that fits inside the headgasket hole won't clog the small oil port. I would fit the eyelet and o-ring to the headgasket and not worry about the block or head. And as madkaw suggests, you might not even need an eyelet, the copper crush ring will do the job.

OR, as I've seen recommended, you could just carefully apply some RTV to the oil port area. Do the water passages too while you're at it.

Edited - added a picture from my N42 L28. you can see the oval outline of the copper (in the HG as noted below). The port in the head is big but the orifice determines the flow.

Edited January 31, 2014 by Zed Head

[madkaw]

To be clear-the copper was part of the gasket.

[djwarner]

Having only seen the Felpro gasket, I never knew the OEM form of sealing the passage. The Felpro has a thin bead of rubberlike sealant around the opening as well as around the water passages. Apparently it works quite well with the 13 psig max coolant and prone to problems with 70-100 psig cold oil. At this time I'm looking for a belt and suspenders solution for the next time I pull the head.

Will definitely go with an OEM head gasket but would still appreciate knowing the passage diameter from anyone with and extra head laying around.

[djwarner]

Here is the update on my head gasket oil leak.

Went to Courtesy Nissan for an OEM head gasket but it seemed that the numbers in the parts catalog were no longer available. Unable to find the right part number, the CSR gave me the number to Nissan Motor Sports. The CSR there was quite familiar with 240z's and we were soon able to come up with a NISMO head gasket with 85mm bore and 1.2mm compressed height. The NISMO part number 11044-E4620. Since Nissan Motor Sports do not do retail, I went back to Courtesy and ordered one.

When it finally arrived, I verified it did have the copper crush ring Madkaw mentioned. A quick check showed that it will crush about 0.012" when finally installed. This is much more than the rubber ring imprinted in the Felpro gasket which is a mere 0.002-0.004" thick.

After installation, it appears to have done the trick. While the head was off, I did check flatness of both the head and block. The manual says they should be flat so that they will not accept a 0.004" feeler gauge under a straight edge. My head and block would not accept a 0.002" feeler gage. So it appears the leak was caused by a poor design on the Felpro gasket.

The NISMO gasket was not cheap, especially compared to the Felpro, but it worked fine. And for the cost in blood, sweat, tears, time and money involved in a head gasket replacement, the additional expense of the NISMO is more than justified.

As a "heads up" to my fellow Z car owners, When the Nissan Motor Sports CSR came up with a number, I asked him to verify it was in stock. He replied, "Just checked, we have 43 on hand." So now they have 42 or less. Considering legacy status of our cars, I suspect there may not be another production run. Fore warned is fore armed.