View Full Version : Question re: brass plugs in deck of cylinder head.

09-30-2010, 10:03 PM
NOTE: Pix below is NOT my head.

Engine is a 1275.

I had head sealing problems so I decided to lap the valves in an extra head I have and swap the heads with a new gasket. Just a quick swap so I can get some driving in now that the temps will be cooling down. What was happening was the cooling system would get pressurized under heavy loads and it would blow the coolant out. No water in oil.

I pulled the head this evening and when I had the two heads side by side I noticed something about the brass plug in the center of the deck surface. On the original head the plug was recessed about a 1/6th of an inch. On the swap head it was recessed only slightly. There were clear signs that cylinder pressure was leaking across the recess. The recess area intrudes on the cylinder sealing rings on the 1275 as you guys know. The entire center area between the cylinders and the head gasket was very dark. I believe this is my problem area.

Shouldn't the brass plug be flush to the surface? Why would it be recessed? Seen this before? Any way to put it back?

The pix below, which I found with Google, clearly shows the center brass plug.


09-30-2010, 10:38 PM
Lovely head, too nice to bolt down.

09-30-2010, 10:49 PM
Lovely head, too nice to bolt down.

Yeah. Wish I owned it.

10-01-2010, 12:03 AM

I was just wondering where you've been.

10-01-2010, 05:58 AM
I have had 2 heads over the years where the brass plugs recess.
My machine shop removes them, threads the holes, and screws in a new plug.
A basic plumbing fitting and then machines it flat with the surface.

10-01-2010, 08:05 AM
All plugs should be flush with the surface.

This is a common issue on 1275 race heads where the temperatures usually run in the 190-220 range. As a preventive measure, before the head is ported, all brass plugs will be removed and the holes threaded to accept cast iron plugs from "Irontite" (Kwik-way) or soft steel plugs. Brass pipe plugs can be used as well to preserve a "stock" look. The cooling holes can then be re-drilled in the front and rear plugs. If using plumbing type pipe plugs, make sure that the plugs are solid and don't thread the hole too much. The plug needs to be in the head tightly but not bottom out.

Repaired a head a couple months ago for this very same issue.

HTH, Mike Miller

10-01-2010, 09:13 AM
OK. Bummer.

I just want this to run for a while as I get another project ready for sale. Then I can get serious about rebuilding the Midget (Fiat twin cam!). So I think I will risk using the swap head since the recess of the plug on that one is slight.

Thanks for the info!

10-01-2010, 09:16 AM

I was just wondering where you've been.

Who me? I've been quiet lately because I need to concentrate on another car. But I read this forum everyday. I'm filing away info for when I can finally get on the Midget and strip it down. I want a Fiat twin cam and a Fiat 131 5 speed, Miata seats and maybe paint it China blue. I'm pondering the suspension mods. It's gotta be able to endure long, fast drives on PCH.