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DISCUSSION => General Topics => Topic started by: MLM on February 16, 2011, 02:42:13 AM

Title: Difference between pre and post 8/92 M42 engines
Post by: 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.

Title: Difference between pre and post 8/92 M42 engines
Post by: 1998ccc 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 (http://www.318ti.org/forum/showthread.php?p=279232)

Title: Difference between pre and post 8/92 M42 engines
Post by: 1998ccc 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.

Title: Difference between pre and post 8/92 M42 engines
Post by: MLM 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?

Title: Difference between pre and post 8/92 M42 engines
Post by: dsm2002 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.