Comments by "SeanBZA" (@SeanBZA) on "HumbleMechanic"
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They have a steel multipart mould that they blow polystyrene foam into to make the pattern for the block. This pattern is a complete head, fully detailed, so that when sand filled you simply take it and pour in the liquid aluminium and it burns the styrene away so you do not lose fine detail. That allows you to make thousands of patterns and not have any major wear on the master mould, and also the fine detail that you otherwise could not make in a pattern, like straight sides and undercuts, along with complex internal shapes, is easy, as the styrene parts are easy to work with, rigid and detailed.
Might be a half dozen styrene parts finally into the sand, but one assembly, and there is no danger of crumbling blocking parts. Just glue them together with a drop of wood glue on the bonds, and fill with your casting sand, and cure the sand before pouring. Instead of lost wax this is a lost mandrel process, and the detail is fine enough that the actual polystyrene beads detail is impressed into the casting. You can get a really thin wall casting out of this, yet not have many failures due to blow through or incomplete pouring.
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Funny enough by me last time I was looking to change VW CV boots the cost difference between getting just the boot and the clips was only around $3 less than buying the complete CV joint itself, and as a bonus you get a new CV, grease, new nut and about a half hour saved per side. Just undid the nut, lifted the car, took wheel off, then undid the ball joint, tapped the CV loose from hub, popped it out and tapped it off the shaft, then new ready greased CV went on, and 5 minutes later I had it in the hub. Old joint was just scrap then.
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Most of those seals push in, so you remove the casting and press the old ones out, and the new one in. I would say that the cams are assembled using a jig that holds them all in alignment, and the cams and head are heated up to around 150C in an oven, while the shaft is in a liquid nitrogen or dry ice chamber, and then the shaft is aligned with the top casting and pressed into position fast, so that the cams shrink onto the shaft. Not easy to fix, but saves a lot of weight, in not needing any bolts in the upper head, and no chance for misalignment while boring out the bearing holes, though you will need to have very precise control of clearances.
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Worst pain is the heater core, followed by the blend doors, because the entire dash has to come out. While you are there might as well also replace AC evaporator and fan motor, because by now both are pretty close to knackered. While core is cheap, along with the blend door foam, the labour to change them is not, and you run the risk of breaking any one of hundreds of little plastic clips that are now brittle, giving you rattles. When taking apart silicone spray is your friend, lots of it as you go for the clips, so they are at least able to slip off easier. Then replace all foam again, and add more dampening pads as well inside, as the originals are likely now well sad and crumbling.
The good thing is that by me I can get the entire lot as pattern parts, seeing as VW has been consistently the number 1 or 2 seller in the country, with Toyota contending for the other spot, and the VW Golf and variants are well represented in the spare parts market, with pretty much all the vehicle being available as pattern, or OEM from all the local suppliers, who made them for VW to assemble.
Standard joke you only cannot get the VIN plate as aftermarket.
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Bearing races are in general fine to intermingle, if they are from the same manufacturer and the same batch, as they will tend to be all ground to the exact same dimensions. You can even use different batches, but for close tolerance they might be slightly different due to the settings being slightly different between runs, but changing manufacturer is iffy, but still you will get good life out of them. Only with precision bearings will you have to use matched pairs, but if you are using them in a vehicle almost no bearing is in any way going to fall in this category till you are into parts like the AC compressor, and the crank and main bearings.
Fun thing is that VW rear bearing is very commonly used on trailers, so to repack the light duty trailers it is a lot cheaper to go buy the aftermarket VW rear bearing kit instead of the trailer manufacturer kit, and use it instead. Normally the caps will not fit off the bat, so you need to either reuse the old one, or spend a bit of quality time with a hammer to make the new cap shrink to fit the diameter.
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Seen a similar thing on a Ford 1.6 CVH engine, would start, but only run with throttle held near full, and not idle. was looking and wanted to check if there was actually oil in it, so pulled dipstick with engine running. Idle dropped to near normal, with still full throttle, and on removing oil filler, it dropped stone dead. We could have rebuilt it, but instead it was quicker to instead send it to Ford themselves, and get a complete new engine from them in return. Not cheaper, but the engine was needed urgently as otherwise there would be massive delays and lack of critical equipment.
This engine was used to drive a hydraulic pump, and this in turn was a specialised vehicle that there were only a very few of, so a missing one was somewhat of a crisis. Not over revved, as they all had limiters on them ( though often bypassed, so we locked out the throttle plate range instead with a welder, to hold that limiting bolt firmly in place), best we could guess is somebody ran it without oil, or with low oil level, and cooked the bearings and rings, or had not checked coolant, and the engine had overheated. Same end result. Otherwise those engines were pretty robust and gave little issues.
Those VW 2.0 TDI/TSI engines also are the power plant on a lot of fork lift trucks, where they live a very hard life, long idle times, frequent stop starts, hard running when cold, and generally just abused. Amazingly they do survive that quite well. Saw them often at plants, pop that cover and the VW logo is there, while the outside is quite a different logo.
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Bolts are easy, plus the different lengths for steel versus alloy rims are hard to do in a stud form, either they stick out far, or are too short depending on the wheel type. Not much difference from each other, just that bolts at least have the wearing part easier to change, plus broken ones are, because the tension is now off them, are easy to remove, provided you have not left them on for ages to rust fast. Studs on the other hand are a PITA to change, especially when you have no clearance behind to remove them, and have to take a hub apart to do so. Smaller heads as well on them, so smaller diameter possible on the wheel boss, while still having enough strength and fatigue life to last.
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