[Fot] valve seat crack?

[Steve Yott]

I believe I have answered a similar question previously.  This is a very common problem with cast iron heads and extremely common on Tractor motor heads with cylinder #4 because of excessive heat buildup.

 

The fix is generally easy and the longevity of the fix is dependent on the depth of the crack.  Most shops will first counter bore the intake seat area and fit a new intake seat.  Once this is done they will then counter bore the exhaust seat area and overlap into the new intake seat by just a little.  The new hardened exhaust seat is then installed and a normal machining of the seats is accomplished.   I have done a number of street engines in this manner and the results are normally very good!

 

Steve Yott

 

From: Fot [mailto:fot-bounces at autox.team.net] On Behalf Of Brian Dennis
Sent: Friday, February 19, 2016 2:51 PM
To: FOT List
Subject: [Fot] valve seat crack?

 

I have been told by 2 different machine shops that a hairline crack in the valve seat between intake and exhaust is not a big deal. They both referenced the iron head stock car racers that do it all the time. This is on two GT6 circle B heads I had magnafluxed. I was a little surprised to hear that and just as surprised to hear the same from a second machine shop. Both of these shops do a lot of work on circle track stuff. One I know also does a lot of drag race motors. Both also noted that it is questionable if I was trying to get 100K miles on a road going car but for racing not to worry about it. Check it anytime the head is off. the cracks are in line with a casting line in the valve pocket/port. 

 

Thoughts on that?

 

 I also have an "A" cast head that is not cracked. The B head is supposedly better. I know this came up a couple of months ago but I don't remember the differences between the A head and  the B head.

 

Thanks, Brian

Foster, RI

 

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