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I supported Toymods
Location:
I renounced punctuation
Registered:
May 2002
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Re: how a 7m block and head *should* look
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Thu, 25 September 2003 10:03
 
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Chris, whether you need to lap the head at all on a 7M is open to debate. Certainly we have all taken heads from other motors to the machinist had them skimmed and just bolted them on with no other grief. Heck, in my student days I'll confess to just cleaning the surfaces and bolting the head on without any machining (with no probs, although I wouldn't recommend this).
This issue arises with the finicky 7M and its propensity to blow head gaskets. People have looked at a range of things including head bolt tension, head bolt construction, surface irregularities and the head gasket itself. A certain finish is required when using a MHG, ideally quite smooth. Often the machine shops leave quite a 'rough' finish to provide some 'bite' with the fibrous head gaskets, but this is thought to cause problems with a MHG. Therefore it has been recommended that the head be lapped. Of course, you could take your head to a good machinist that understands these things and they will machine the head so that it looks like a mirror (very fine cuts like Ed's).
A glass sheet is traditionally used for lapping. It is poured as a liquid and therefore should form a perfectly flat surface (of course we all know it is extruded nowadays so it is subject to its own imperfections). The premise is that by using one perfectly flat surface, you should be able to make another using some abrasive. That is correct and wrong, as with differing techniques one can make a flat surface OR a spherical surface (definitely not the desired result!).
I can recommend Crankshaft Rebuilders in Nunawading - they did a beautiful job on my head.
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| | Subject | Poster | Date |
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how a 7m block and head *should* look
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ed_ma61 | Wed, 24 September 2003 12:29 |
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Re: how a 7m block and head *should* look (big files)
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gianttomato | Wed, 24 September 2003 12:54 |
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Re: how a 7m block and head *should* look (big files)
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Stenno | Wed, 24 September 2003 13:44 |
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Re: how a 7m block and head *should* look (big files)
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Allan | Wed, 24 September 2003 13:53 |
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Re: how a 7m block and head *should* look (big files)
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Stenno | Wed, 24 September 2003 14:03 |
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Re: how a 7m block and head *should* look (big files)
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gianttomato | Wed, 24 September 2003 14:10 |
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Re: how a 7m block and head *should* look (big files)
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Allan | Wed, 24 September 2003 14:38 |
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Re: how a 7m block and head *should* look
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ed_ma61 | Wed, 24 September 2003 14:42 |
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Re: how a 7m block and head *should* look
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Allan | Wed, 24 September 2003 14:53 |
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Re: how a 7m block and head *should* look
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gianttomato | Wed, 24 September 2003 14:55 |
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Re: how a 7m block and head *should* look
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Allan | Thu, 25 September 2003 00:17 |
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Re: how a 7m block and head *should* look
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Danners | Wed, 24 September 2003 23:31 |
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Re: how a 7m block and head *should* look
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THE WITZL | Thu, 25 September 2003 02:13 |
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Re: how a 7m block and head *should* look
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rob_RA40 | Thu, 25 September 2003 02:25 |
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Re: how a 7m block and head *should* look
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ed_ma61 | Thu, 25 September 2003 02:28 |
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Re: how a 7m block and head *should* look
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Allan | Thu, 25 September 2003 02:38 |
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Re: how a 7m block and head *should* look
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gianttomato | Thu, 25 September 2003 03:47 |
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Re: how a 7m block and head *should* look
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chrisss | Thu, 25 September 2003 09:19 |
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Re: how a 7m block and head *should* look
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gianttomato | Thu, 25 September 2003 10:03 |
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Re: how a 7m block and head *should* look
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ed_ma61 | Thu, 25 September 2003 10:39 |
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Re: how a 7m block and head *should* look
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ed_ma61 | Thu, 25 September 2003 10:42 |
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Re: how a 7m block and head *should* look
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gianttomato | Thu, 25 September 2003 13:36 |
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Re: how a 7m block and head *should* look
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ed_ma61 | Thu, 25 September 2003 13:46 |
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Re: how a 7m block and head *should* look
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gianttomato | Thu, 25 September 2003 13:53 |
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Re: how a 7m block and head *should* look
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Allan | Thu, 25 September 2003 14:04 |
