differences in heads Q?

[Don R]

  I bought some sandcast and diecast engine parts recently and while repairing some fin damage I've noticed the very early heads have softer aluminum that bends easily without cracking. This metal appears similar to later heads like the K5 head I repaired that had bent fins with no cracking. In between, there are heads that are more brittle, these fins snap off rather than bend.
  The difference that I can see is, the brittle in between heads have vertical strengthening pins that protrude through the lower fins. The softer metal heads have the pins cast into the fins and are smooth on the underside. I see the protruding pins on 5511, my early k1 and late K1 heads, The non protruding pins on a #500 era sandcast head and K2/K3 and up. These types may have been used at the same time too I don't have any other serial numbers to check.  I have two no center bolt heads that have the protruding pins.

 I have one of each of the two types of heads to use on 2695, I'm not sure which is correct of if either could be OK.

[markb]

The heads from E100, E748 and E1789 are all smooth on the bottom so I assume they are the softer ones. They could all use some straightening. When you straightened fins I assume you used heat? Do you use propane or MAP? How long did you heat before attempting to straighten?
Unless someone can produce one older than E1789 that has the protruding pins I would guess that they changed somewhere between 1789 and 5511.

[Steve Swan]

i've straightened aluminum fins on a number of heads from different makes.  i use map gas, straigh propane does not get the metal hot enough to move the metal.  for the tool, i have flat/smooth jaw pliers.  one set of pliers, the jaws are 1/2" the other set are 3/4".  i ground the serrations of the jaws of the pliers.  i apply heat directly to the fin, when it's too hot to touch the fin is ready to move.  i also heat the jaws of the pliers as the fin tend to cool somewhat quickly.  where i put the pliers on the fin depends on the size and acute angle of the bend.  i  firmly put pressure on the jaws on the fin and  v e r y    s l o w l y  move teh bend to straighten it.  if the fin is hot enough, i can literally feel the metal move, the only way i can think of how to describe what the metal feels like when i moves is like that of hard butter.  my other tip of advice is move the fin a little at a time, reheat as necessary and if the bend is a long one, you may need to move the jaws of your pliers in the area the fin needs to be moved to get the fin in desired alignment.  hope that helps.

Mark, what did you wind up doing with your spoke nipples ?

[Don R]

 I've used a hot air gun on high and propped where it can run for a while. As above, wait until it's too hot to touch, it melts at 1200* but can be worked a little at much lower temps. I use vise grip metal folders with the 3" wide jaws. They help the dips to bend back to level easier.

[markb]

Thanks for the info guys. I have on of those infrared temperature sensors so I can monitor how hot they are. One of these days I'll get to it. 

Steve, I posted on the original spoke nipple thread (or should that be spoke nipple thread thread?). Anyway, should have done that a while ago.

[Don R]

 I actually used a hot air gun, I propped it up where it was aimed and secure and let it cook for a while.