Author Topic: Special DT rocker arms  (Read 1956 times)

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Offline Doug

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Special DT rocker arms
« on: 30 Dec 2014 at 04:30 »
Member "BlueSilver" sent in the following images of a special valve rocker for a DT engine. You will note in comparison to a standard DT valve rocker, the push rod arm is shorter. This has the effect of increasing the ratio and hence valve lift.







What is interesting is that it has the standard part number (8530) in the forging. The question is, factory or modified?

If modified, the work appears to have been done long ago and well executed. Report is upon subsequent cleaning the finish all over is very uniform, with no obvious evidence of a weld material.

The argument against it being factory is a different die would be required, and it would then have a different part number, or no part number.

I believe I can see a few locations of weld undercut, or incomplete fill. Here are some close-up views of the short arm.








If there are more of these out there just like this, then it would be more likely it was something the factory made a batch of. Has anyone seen a similar DT valve rocker with a short push rod arm?

-Doug

Offline eddie

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Re: Special DT rocker arms
« Reply #1 on: 30 Dec 2014 at 06:42 »
Doug,
         Could this rocker arm be from a later motor like the F/G31/32 models that had enclosed valve gear? The earlier DT models with open push rods scarcely have enough room for the spark plugs, so spacing the push rods further apart may have been necessary to make room for the tubes.
  Also, from the photos, the arms look to be set at a steeper angle - could that be the result of lifting the pivot point to accommodate the lower half of the rocker box?

  Regards,
               Eddie.

 P.S.    All the best for 2015 - and beyond!!

Offline Doug

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Re: Special DT rocker arms
« Reply #2 on: 30 Dec 2014 at 14:07 »
Eddie,

The F/G31 models and the 1934-35 models uses exactly the same valve rockers as the DT. Or at least on the several F/G engines I have seen and the pair of 1934-35 models that I have.

The sparkplug does indeed just fit between the pushrod tubes, but you will not be using a big, fat Champion spark plug from contemporary Harley Davidson! Also the sparkplug hex lies above (only just) the plane of the pushrods, otherwise getting a socket or wrench on them would be a problem. The enclosed valve models did gain some room because the pushrods run to the head parallel, where as on the DT they converge slightly. The rocker perches are further apart to bring this about.

-Doug