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TR2/3/3A Cyclinder Head work and valve guide issue

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tallguylittlecar

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I got a call from the machine shop today saying that they could not fit the bronze valve guides that I supplied them with. I purchased the conversion set through BPNorthwest. and new 5/16 valves for the head. He says that the outside diameter of the guides in the head are all the same size and the conversion set to go to 5/16 stems are larger for four of them. I know this is due to the way the heads change through the years and is most likely an issue of tr3/4 head vs 4a. When I disassemble my head it had three valve springs and after referencing https://www.tr3a.info/FAQ_heads.htm I believed that I had a late 3B early 4 head. However I am now thinking that I had a later 4A head with three springs installed. Is this likely? The machinist tells me that the OD of all the guides currently in the head is .5

My next question is about he crank. The engine was rebuild somtime in the lat 70's early 80's and the con rod journals are already ground 30. Is there any issue on this engine with grinding the journals to 40 thou.

Any help is much appreciated.

Derek
 
It sounds to me that the guides you got are wrong because thehead is consistently the same. I would just purchase a set of 5/16 cast ironguides or just get one to see if that fits. They only cost a few dollars. I donot know if they changed the actual head other than a high port and low portchange, but I doubt if they changed the casting because they went to a 6cylinder shortly after the 4.
 
Yup, you've got a later head that originally had 5/16" stems. As noted, easier to just buy 4 of the right guides (which are the same as the intake guides). My guess would be that someone previously installed a later head and kept the earlier valve spring setup; but it is possible that the factory made some "crossover" engines.

Whether .040" under is acceptable probably depends on your planned usage. Should be fine for moderate driving, but I've been told not to go smaller than .020" for racing.
 
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