Posted by Gordon Maney on Saturday, November 01, 2003 at 5:51PM :
In Reply to: But Gordon... posted by Eric B. on Saturday, November 01, 2003 at 11:04AM :
When I put the 440 in my W300, it had previously been mated to a Chrysler automatic in a truck. I discovered at that time that there were three different pilot bushings for 440, and was also told by a fellow who had a long history with Chrysler big blocks that there was a version of the 440 crank that was not finish bored for any of these bushings.
If Chrysler makes a bushing for Mr. Taylor’s particular crankshaft, then certainly there is no problem after all, and he is all set. I was replying in the context that the problem was defined, meaning that the hole was too small and there was no bushing available for the existing hole size. I was also speaking partly in reply to the modification of the OD of a bushing with a hacksaw blade, turning the bushing in a drill press.
Yes, the hole in the crank is probably centered, assuming it is bored, and not a feature resulting from the casting (on a cast crank). Initial machining on the crank no doubt supported it between centers, utilizing that hole. The setup may have evolved to some other supporting surface, abandoning the use of that hole. Frank Irons could probably offer some illuminating comment here.
Broadening the discussion beyond this crank, there are cast cranks that have a hole that is not necessarily concentric. An example would be big block Oldsmobile (425, 455) from the 60's and 70's that were originally mated to an automatic transmission. Those were not drilled and there was no bushing available to do that. You had to remove the crank and have the hole machined. The cranks used with manual transmissions were machined to a larger, finished size.
There were people (yes, seriously) who tried boring the A/T cranks with the crank in place in the assembled engine. You can guess the results. A local machine shop, and in this case I am not meaning an automotive machine shop, but an industrial shop, was fascinated to discover (when they machined a bore to accept the manual trans pilot bushing) that the rough, undersize holes in those cranks were not necessarily concentric with finish machined surfaces on that end of the crank. The point being that if you turned the OD of the bushing to get an acceptable interference fit in the rough finished, undersize hole, you were running your new bushing off center some amount.
There was a period of time when a fair number of people were putting 425 and 455 Oldsmobiles in Chevy and GMC trucks, many of which had 4-speeds, and so this was a problem that had to be resolved to allow the installation.
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