Picking Up 340 Short Block - What to Look For?
not to hijack the thread, but it seems like i see more 68 model year 340s with casting dates of mid summer 67,,i know the 67 casting was correct for 68, but any idea why so many,,(seems like most every) 67 340 castings are all within 2 or 3 weeks time period on june/july?
With the 'new' for '68 engine approaching for the 1968 model year, they needed to have inventory available.
They also needed to run some blocks off the production tooling to evaluate the quality of the tool... Plus if you are going to set up and run the tool, then you may as well run a large batch once you determine that the parts are within sped...
Not to mention that they have to have enough castings available to set up and verify the block machining line... They need to run many blocks through each operation on the block machine line to measure and take data to see where the machining is and to make adjustments to the machining... Since the 340 was brand new for 68, they would have to run a minimum of 30 blocks through every station of the block machine line to measure the parts with the gauges and certify each operation and certify every gauge... You have to run them down the machine line one operation/station at a time from beginning to end... This takes time to do each step along the way...
Plus you need to run some extra blocks through the front of the machine line to make sure you have enough to redo any of the stations further down the line in case you find any out of spec or need to make an adjustment to the machining... After each adjustment you need to run a minimum of 30 parts through the station to get a good idea of where that operation is running in relation to the tolerance spec... Sometimes you target the nominal (middle of the tolerance spec) and sometimes you set them up to one side or the other of the spec to allow for it to wear towards the middle of the spec as the tool wears...
Then you need to machine a bunch of blocks to have for setting up the engine assembly line... You have to back fill an empty line and run them through each station to test the tooling on the engine assembly line...
Then the assembly plant needs enough parts/engines to run their pilot builds... They have a pilot build 6 weeks before production launch (called the PVP build - Pre-Volume Production) to test and verify that all of the tools on the assembly line are capable and ready for production... This is typically 100 - 150 vehicles that are built before production begins... Many of those vehicles are sent to engineering to start running their production verification testing... Every department needs some of the pilot vehicles to verify that their parts are meeting design specs... Engine group, climate control group, engine cooling group, interior group, exterior body group, chassis group, transmission group, vehicle development group, and some are sent to the proving grounds to get miles on them to make sure that there are no problems... They would send some to the Chelsea, MI proving grounds, and some to the Phoenix, AZ proving grounds to start accumulating as many miles as possible before launch to identify if there any problems...
If any problems are found during that testing, then they will hold that particular part of the launch until the design group can identify the problem, come up with a fix, test that the fix will work, and then get the tooling changed to implement that fix... If the production tooling cannot be modified in time, then they may be able to write a temporary deviation (TSA) to launch with a prototype tool until the production tool can be modified and proven for production... Prototype tooling is called "soft tooling" as it is made to run a limited amount of parts before it wears vs the production tool also called "hard tooling" which is harder and made to run many parts over a longer period of time before wearing out... Production tooling is much more durable and made to run more parts over a longer period of time...
PVP builds are supposed to be run of production tooling... If the production tooling is not available then that particular part has to have a deviation written (TSA) and then put on a "hot list" to allow them to run PVP pilot builds off prototype tools...
If they can get a successful PVP pilot run (6 weeks before production launch) they will run a batch of engines to have a bank built up for the assembly plant PVP pilot run and then the production launch... That way the engine plant has completed their launch and the parts will be ready and available for the assembly plant launch... It's better to build them early than to wait until the last minute and have to jump through hoops if a problem arises that could potentially delay the launch...
So that is why you see so many June & July 67 casting blocks as when the foundry has the molds ready, they made a batch run of blocks to run the pilot and launch builds for the engine assembly and vehicle assembly plants... That way they can run a few large batch runs of blocks instead of running smaller batch runs and having to set up the casting line so many times... If you have to do the change over, then run as many as possible to save time later... Then the engine plant can build a bank of engines and have a bank of them ready for the assembly plant launch and start of production...
