On Wed, 6 Feb 2002, Hugh Fader wrote:
> On the way home from work, I stopped at a machine shop that was highly
> recommended to me. The owner told me that he did not recommend bronze
> guides. Said that cast iron was harder and would last longer under normal
> road use. This is not what I thought. Any opinions?
He's right. But if you are going for performance, the bronze guides are
better because you set them up looser and they expand / contract better at
the higher temperatures of a hopped up motor (e.g. the bronze and iron
guides have different "thermal coefficient(s) of expansion".
If your goal is to build a street motor that'll runn 100K miles or more,
install the cast iron stock guides. If you're building a 14:1 race motor,
then you should be looking at bronze guides.
Note: I have had problems with the iron guides from the various sources.
The holes at the ends measure okay, but the "middles" were slightly wider.
When we looked at them closely, you could see "cut marks" in the bores of
the guides. The amount of variation was not "fixable" with the usual
reaming process. On my street car, I went through 12 intake and 12 exhaust
guides to come up with the 6 of each that I needed.
The timeframe for that exercise was 1999, it's possible that whatever
manufacturing process problem that ocurred then does not exist now, but
several other qualified British car mechanics reported the same results to
me at the time I did that particular valve job.
Moral - pay attention to the parts that you purchase.
> - Hugh
regards,
rml
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