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Re: Engine swap on the C1

Subject: Re: Engine swap on the C1
by BeachBum on 2008/11/25 0:20:48

Quote:

jsup wrote:
That's a fair response. I wonder if shift is typical and if there is an industry accepted tolerance for it, and what that is.

see, I think I am taking a position that the CNC simply exposed the problem, but the problem was a manufacturer defect and should be replaced. Was the tech running the machine slopply, sure, but was that the problem?

Is your position that if the machine was stopped 10 minutes earlier things would be different? Yes, he'd have an undamaged useless head, now what? I don't see how that makes a difference, when does a defect become a defect? (sounds like abortion huh) A factory defect becomes a factory defect when it leaves the factory, at conception.

The mechanism by which it is discovered is irrelevant. But that goes back to my last question...is this a recall type issue? and Is there an industry accepted amount of shift, if so, what is it, and are these out of industry accepted spec? If so, lltrevino has a valid point, if not, then it changes.

Try this.....you buy a tire, it vibrates all the time, you hit a curb. You find out that the tire's belts were shifted from the factory causing not only the vibration, but the accident as well.

Does the tire manufacturer owe you new tires or does the manufacturer tell you to buy more of his twice the price tires since they don't have the belt shifting problem? note, he never denied there was a belt shifting problem.

In response to your questions, on how typical is shift and what is the acceptable amount. I personally do not know the answer to either, but I have heard of shift many times over the years on a variety of cylinder heads, but to what degree and how much is accepted is beyond me. More typical, I also hear of breaking through the wall of the runner, usually by hand porting though, but thats only because most porters do not have 5 axes CNC capability due to the high cost.

In regards to who is at fault on the cylinder head breaking through on the porting, I do have a solid opinion on that, and that is the porters fault, simply because I have an acute understanding of the CNC process, as I teach it. But, I understand what you are saying, the cylinder head was bad, and now it has holes in it.... its still bad. But, this particular cylinder head was usuable as per the poster running it for 2500 miles, and I assume performed well on his original 350 considering I hadn't heard of a performance complaint, but do not know. Thus, what I am saying, he had a functional high performance cylinder head.... and now he doesn't. If it didn't perform from the get-go, it should have been brought to the attention of the manufacturer immediately, not after un-repairable holes had been made.

But, back on the porter breaking through, I can not emphasize enough, that a cylinder head porter has to pay attention to what they are doing and if the cutter is taking off too much material, stop the program and figure out why..... this really, really is CNC machining 101 and very, very common. In fact, I would say over 50% of CNC programs that are executed, are stopped before completion due to a variety of reasons, and then re-started once the problem is solved, with volume production applications being the exception.

Also, we have to consider, the manufacturer of the cylinder head knows nothing about the cnc program that is modifying its port and cannot reasonably warrantee anybody or everybody's cnc program. You have to understand, no two cylinder head porting programs are identical or even close to identical, and also no two cylinder heads are guaranteed to be identical for many reasons, (such as a new version of an existing cylinder head that may have made adjustments to the port that the porter did not, nor could have known about)

I also want to emphasize, in the manufacturing world, and you have to just trust me on this, that the vast majority of the scrap made is 100% directly related to human error.... its a big, big problem and goes back to setting the correct offsets, tool compensation and even machine error compensation in some cases.... plus all CNC machines have error. If they have good reliable Linear Encoders for positional feedback, the error will typically be 5 microns or less guaranteed per meter of travel, which is plenty sufficient for porting cylinder heads, but if they are rotary encoders on the motor, they will typically have considerable backlash error, cross compensation and screw wear error. All of these can be compensated by the CNC, but its on on-going project because all of those variables change with machine use.

But, the blame game really doesn't matter, at the end of the day, we have a fellow racer who has a set of cylinder heads with holes in them and I understand that is very disappointing.

I wish him good luck in finding a resolution.

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