Can you identify a cam when buying a used motor?

Mac_49

Mac_49

Member
I recently have acquired a flathead that I'm wanting to freshen up....while doing so I was wondering which cam was already in it.
The only markings on the cam are the numbers 55
Didn't know if you could identify cams somehow or not. Any info would be great.
Thanks!!
 
The only way to identify the cam is to profile it. You can take a measurement of how wide the lobe is and how tall the lobe is and subtract the lesser from the larger to give you a ball park on the lift. But you will need to profile to determine exact cam type.
 
Alright then...so when profiling do I measure the widest of the lobe (bottom of pear shape being the widest) and the height (obviously bottom of pear to top or pear)? --> I'm using a pear as a diagram just for reference purpose only
 
Subtracting the two will only give you gross valve lift. You need to measure the cam profile by installing a degree wheel on the engine, setting TDC, then using dummy valves (0 valve lash) check valve lifts at every .050". You will also see the ez spin (compression release) and note it's start and stop. Then you can figure your cam centerlines and make a "best guess" at which cam it most resembles. Note, with much wear at all, it's nearly impossible to determine what cam it was when new. The 30 some cams that are available from Dyno alone (not including their custom grinds for builders) are so very similar that your head will be spinning trying to figure out what a used cam actually is/was. It can surely be narrowed down, but nailing it down it very difficult even for the experienced builder. That's why so may builders will change cams on rebuilds of engines from another builder.
The casting numbers you might see in between the lobes means nothing to the grind -- simply a casting of the core from the casting mold facility.

-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cuts
www.CarlsonMotorsports.com
Celebrating 25 years of service to the karting industry
765-339-4407
bcarlson@CarlsonMotorsports.com
 
From the way it sounds, although still a usable cam, I'd be better off just installing something new instead of trying to "best guess" the cam even through all of that work.
Thank you so much for all of your help and heads up about how difficult it might be even with solid numbers. I appreciate it. Plus...knowing my luck...I'd go through all that work only to find out it's the stock cam which needs changed out anyways lol :rolleyes:
 
You can tell if it's a stock cam pretty easily --
one: by checking the lift (difference between base circle measurement and largest part of the lobe - heel to toe), and
two: by looking closely at the finish of the face of the lobes (factory stock cams are broached and have lines scraped across them, ground cams have a smooth finish and grinding is done lengthwise on the lobes.)
 
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