Series 3 Hot spot (pre combustion chamber) fitting

I needed to replace the head gasket recently and noticed that the hot spots had some small cracks. I was told that they were not a big issue as they were but I plan to replace them.

I want to know if I can do it on the drive way or will the new hot spots need to be pressed in. Also, does the head have to be skimmed after they are fitted? If the head had been skimmed before will they stand up from the surface?

olsver said:

I needed to replace the head gasket recently and noticed that the hot spots had some small cracks. I was told that they were not a big issue as they were but I plan to replace them.

I want to know if I can do it on the drive way or will the new hot spots need to be pressed in. Also, does the head have to be skimmed after they are fitted? If the head had been skimmed before will they stand up from the surface?

Click to expand...

Small cracks aren't a problem, but if you remove the swirl chambers, you will probably damage them and have to replace. Check carefully for cracks around the swirls, in the head itself.

They are usually fitted with a soft faced mallet, not a press. I have often fitted them outside, no issues.

It is not usually necessary to skim those heads, just clean it up thoroughly, and use a new quality composite gasket. The swirls should protrude slightly from the head, the exact amount should be in the manual.

There is a risk that in takeing the old ones out you enlarge the hole in the head so the new ones are not so tight. A loose chamber is much worse as it moves and wears the head. its a trade off, without seeing the cracks its hard to know. Alarm bells is they look like they are joining up.

rob1miles said:

There is a risk that in takeing the old ones out you enlarge the hole in the head so the new ones are not so tight. A loose chamber is much worse as it moves and wears the head. its a trade off, without seeing the cracks its hard to know. Alarm bells is they look like they are joining up.

Click to expand...

Cracking between the swirl chamber and the valve recess normally means a scrap head.

As you say, if the chambers are in place, and look OK, leave well alone.