Author Topic: Difference between pre and post 8/92 M42 engines (Read 3092 times)

MLM · « **on:** February 16, 2011, 02:42:13 AM »

I have been researching cams for a m42 project I have on the go. Catcam for instance offer a number of cams yet only offer pre 8/92 engines.

This got me wondering what are the differences exactly.

So far and yet to be confirmed (this is where i need you guys)

- 6mm valve stems
- Single valve springs
- Piston dish?
- other internal differences?

What else is there to build a good reference guide.

In the ideal world owners of a post 8/92 could "upgrade" to use pre 8/92 parts.

1998ccc · « **Reply #1 on:** February 19, 2011, 04:53:04 PM »

I can share early 7mm info FWIW. I just picked up a 91 e30 short block. I CC'd the piston including valve reliefs. It's ~ 16cc. This makes the factory claimed 10:1 compression ratio quite a bit off. Most manufactures are 0.2 / 0.3 tenths low to allow for carbon buildup but not a full point

Mahle shows less dish on there website for late production pistons. There also is a post on the ti board of ~35cc for a late M42 head vs. ~33 for the early 7mm head.

http://www.318ti.org/forum/showthread.php?p=279232

1998ccc · « **Reply #2 on:** February 19, 2011, 05:00:38 PM »

I can share early 7mm info FWIW. I just picked up a 91 e30 short block. I CC'd the piston including valve reliefs. It's ~ 11cc.

Mahle shows less dish on there website for late production pistons. There also is a post on the ti board of ~35cc for a late M42 head vs. ~33 for the early 7mm head.

MLM · « **Reply #3 on:** February 22, 2011, 03:12:16 PM »

Quote from: 1998ccc;101641

I can share early 7mm info FWIW. I just picked up a 91 e30 short block. I CC'd the piston including valve reliefs. It's ~ 11cc.

Mahle shows less dish on there website for late production pistons. There also is a post on the ti board of ~35cc for a late M42 head vs. ~33 for the early 7mm head.

Interesting, Wonder if late production bottom end (less piston dish) and early head (33cc) would give a higher compression motor?

dsm2002 · « **Reply #4 on:** February 22, 2011, 10:29:10 PM »

I have Catcams 290/275 cams to put in an E30 head. I have also gone for 6mm valves and using Metric Mechanic 6mm guides. I think the main issue with these cams fitting engines to pre 8/92 engines are the retainers and locks. Catcams retainers and locks suit the 7mm valve stems. There are ways to address this.