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Bruce Lancaster · 04-25-2013, 04:39 PM

The early 239 rods were the 99A (1939-41) and the 29A, 1942-48...
I do not really know the difference, but I suspect that the difference is actually metallurgical...
During 1941 the Government put many imported or scarce substances on restricted lists as we moved towards war and as many markets were cut off from trade, and made these things usable only for the highest priority goods, like aircraft engines. Several important alloying materials for steel were on the list, and my bet is that Ford changed its steel formula...
Anyway, there are plenty of minor differences in the forgings from different batches and time periods. Here only the "99" and "29" are important to identify the rods. Figuring out what the various suffixes meant would be a good trick, but they are not part of parts number prefixes...I think Ford only meant to sort out the basic model of rod here. 15 and 27 are not Ford prefixes, and I don't think that the 5 or 7 correspond with any engine group...
The caps...that bears some study! I've never even looked there, only being careful to keep caps with their original rods and pointed the right way. Perhaps all caps remained 99 spec? That would NOT be researchable in the parts catalogs, as caps were never sold separately, but parts like that which were never sold by themselves did have part numbers for use within the factory.
So...anyone have a NEW 29A rod hand to look at? I think all the ones I have are rebuilt or used sets.
Perhaps all the caps remained 99 spec, perhaps rebuilders re-machining used rods swapped them...though I believe that Ford's published rebuild standards insisted on maintaining original sets even when resizing.
A new rod, or better yet a sampling of several, should tell the tale.
Damn. Remember when Joblot had crates and barrels full of NOS rods for like $3 each??

04-25-2013, 04:39 PM	#4
Bruce Lancaster Member Emeritus Join Date: May 2010 Location: Madison, NJ Posts: 5,230	Re: Con Rod identification The early 239 rods were the 99A (1939-41) and the 29A, 1942-48... I do not really know the difference, but I suspect that the difference is actually metallurgical... During 1941 the Government put many imported or scarce substances on restricted lists as we moved towards war and as many markets were cut off from trade, and made these things usable only for the highest priority goods, like aircraft engines. Several important alloying materials for steel were on the list, and my bet is that Ford changed its steel formula... Anyway, there are plenty of minor differences in the forgings from different batches and time periods. Here only the "99" and "29" are important to identify the rods. Figuring out what the various suffixes meant would be a good trick, but they are not part of parts number prefixes...I think Ford only meant to sort out the basic model of rod here. 15 and 27 are not Ford prefixes, and I don't think that the 5 or 7 correspond with any engine group... The caps...that bears some study! I've never even looked there, only being careful to keep caps with their original rods and pointed the right way. Perhaps all caps remained 99 spec? That would NOT be researchable in the parts catalogs, as caps were never sold separately, but parts like that which were never sold by themselves did have part numbers for use within the factory. So...anyone have a NEW 29A rod hand to look at? I think all the ones I have are rebuilt or used sets. Perhaps all the caps remained 99 spec, perhaps rebuilders re-machining used rods swapped them...though I believe that Ford's published rebuild standards insisted on maintaining original sets even when resizing. A new rod, or better yet a sampling of several, should tell the tale. Damn. Remember when Joblot had crates and barrels full of NOS rods for like $3 each??