X-heads vs J-heads: what's the difference??

Swinger 340 said
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I always heard, "never buy a car built on a Monday or Friday". That would mean 40% of cars could be a little off.

Better yet, don't buy the early or end production cars... Mostly the end of the year or model cars...

The first launch cars may have some substitute parts or early prototype parts... The early prototype parts are not so bad as they are to the blueprint for that part, just not made off the production hard tooling, they are made from the soft tooling that made the initial parts for testing to prove them out before production... If the production hard tool is not ready at launch time they will write a temporary substitution for that part to use the soft tool part from the prototype stage that meets the part print until the regular production hard tool is ready and certified... Nothing wrong with that because they make the part the same, but the soft tool wears out faster than the hard tool and is limited on how many parts it is capable of making before wearing out, that's why they have production hard tooling - to handle the long term run for that part...

Now the last one of that model year is the higher risk... At the end of the year as production is ramping down, they may not have as many of that particular part left in stock at the assembly plant... A good example is a fastener (screw or clip)... If that particular part is being phased out and now becoming obsolete for the next year, they may be running short of them in the last week of production... The assembly plant has standard quantities that they order at a time, and if they only need a small portion of the standard quantity, they are not going to order a full order and be left with a bunch of obsolete parts and have to scrap them and eat the cost...

In this case they will look for a substitute part (screw) that will fit the 'hole' and do the job... It can be as simple as a different coating, or slightly longer or shorter, but will still do the job... The design engineer will approve the substitute part and the manufacturing engineer in the assembly plant will write a temporary substitution to authorize using the other part in its place... There is a fastener database listing all of the available fasteners used by the company on all products... They will try to find one that is used in that same assembly plant as it is already in stock, they just have to increase the usage in the database so they don't run out of that one... Second choice is to find one that is used in another 'sister' assembly plant and the production control guys for the plant in need will call the plant that has enough to share and have them ship them to the plant in need... The production control guys have a database and can look at the inventory in all of the other plants to see if they have enough quantity to share...

So it's the last ones off the assembly line that have the higher risk of not being built to the original design and may not be as good as the standard production ones... And us as public are not privy to that information.. Tha's why there's a statement in most of the brochures that the product specifications may change at the manufacturer's discretion...

However the fastener substitution can happen at any time in production if the assembly plant runs short of a particular fastener and has to find a substitute to get by until they can get another batch from the regular supplier.... It could be because someone in production control missed it was running out and did not order it in time, or the supplier is short and can't make anymore before the assembly plant runs out...

They do this because they don't shut down the assembly line if it's not necessary... A typical assembly plant runs about 70 cars per hour average... If the line stops for one minute that is one less car they have to sell... Think of how much money that car lists for, and how much money is lost PER MINUTE the assembly line is stopped... If the line is stopped for a half hour...

Back in the mid 90's if the supplier was responsible for stopping the assembly line they were charged $7000 per minute it was stopped!!! This was to cover the lost product and paying the crew of assembly line workers to stand around waiting for the line to start again... If you are the reason the assembly line stops and they loose thousands of dollars, your *** will be on fire answering to the higher ups or thrown out the door...