Hudson 309742 Cam--not always what it seems

ivanz62

This cam number, 309742, is infamous as the "flat top" or "chain stretcher" 7X cam. Replaced with the "Super 7X" that did not have the problems. I have found two cams with the number 309742 that were ground with a different lobe profile appropriate to hydraulic lifters. The opening and closing "ramps" of a hydraulic lifter grind are different and will not work well at all without the correct lifter style.

So be careful when fitting that 309742 cam you picked up at a swap meet to your solid lifter engine for 7X performance! It is my belief that the hydraulic lifter cam required a larger lobe blank and Hudson just used up the remaining cam blank castings for the 56 engines. That hydraulic lobe won't fit on the earlier blank. I know this from looking for blanks to make re-grinds that have the most material available for more lift than stock. And you can't tell a hydraulic from a mechanical lobe ramp without a sophisticated cam measuring device. But you cam with a pair of calipers or a micrometer measure the lift of the lobe and compare with the specs for lift of the 7X version and the hydraulic version which are quite different. You won't confuse lobe wear with the actual lift. Perhaps someone can post the lift numbers for this thread.

Ivan

[Deleted User]

That's a handy tidbit of information. All my 742's are only fit for regrinding, too worn for using. Thanks for passing your findings on.



Mark

54Hollywood

Ivan:



Thanks for the good information. Here are the cam specs taken from one of Jack's old catalogs.



Model 309742 (7x flat top) cam: Lift .355, Duration 258 degrees

Model 311040 (Super 7x) Super Street cam: Lift .390, Duration 268 degrees.

Model 56 Mechanical cam (Replacement over 56 Hydraulic cam): Lift .376, Duration 254 degrees.



I can't find the specs for either the 306344 or 306344A cams. Perhaps someone else can provide those for reference.



Hope this helps.



Tim in WI

dougson

Here we go with cams again. Interesting to learn that the hydraulic cam in '56's (309742) had different lobe characteristics than the original '54 solid lifter version. That would answer some questions I have posted elsewhere on this forum. However, lift and duration numbers continue to vary. I have a '56 hydraulic cam that came out of my stock '56 engine (with hydraulic lifters). I measured the lobe diameter (closed) and total lift of every lobe using a dial caliper and came up with .375 inches +/- .015 % of total lift. Haven't attempted to measure duration yet. It would be nice to be able to get precise lift and duration characteristics for each and every cam installed in a 308. Also, duration at 50% lift and overlap information would be useful.



Regarding the hydraulic lifters themselves, I can see why they became problematic because the relief tube diameter is so narrow (combined with issues in early oil viscosities and refining) that it would become clogged easily. With proper cleaning and using modern oil they are probably are ok.