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Monday, July 22, 2024

Doug's Domain

Doug Vetter, ATP/CFI

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Friday, August 11, 2017

Head Decision

I reported earlier that, although the head had been successfully reworked, Peter had offered to swap my new (and newly reworked) components into a new AMC head for $1100. I asked him to give me a couple days to think about it. In that time I managed to whittle this complex purchase decision down to two questions:

  1. Do I install my reworked original head or buy a new head?

  2. If I buy a new head, should I buy a BMW head or the AMC head?

To answer the first question I had to perform a risk analysis. I was more concerned with the short term risks like defects in manufacturing or servicing which sometimes occur despite best efforts to avoid them, but I also considered fitment issues that might introduce a costly delay or abort of the installation process. The long term risks, which mostly centered around the expected longevity of the parts, were essentially impossible to quantify given how few of these engines are operating with the mileage of my engine and how few AMC heads are in service on these engines. However, all things considered, I ultimately determined buying a new head would result in lower overall project risk.

The second question was a simple matter of cost. Although cam trays are not machined as a set with the head, for some reason BMW only sells the head with cam trays. Which means if you buy a new BMW head you're getting cam trays whether you need them or not. I obviously had plans to buy cams and cam trays, so this policy would not affect me, but for the sake of comparing apples to apples I subtracted the cost of the trays sold individually ($575 list each, $390 my cost) from the cost of the head / trays assembly ($3800 list, $2800 my cost) to arrive at a BMW head price of $2000. That is, of course, almost double the cost of the AMC head, but I was still willing to consider it because to me it represented a lower fitment risk -- BMW parts are guaranteed to work together.

While I did find a thread on bimmerforums showcasing at least one satisfied customer of the AMC head the deciding factor turned out to be Peter's expert opinions on the matter. It's clear Peter has seen all the failure and wear modes of the factory heads so if he says the AMC head is an improvement over the factory head at a reasonable price, I think it's safe to say it is. As a result, I accepted his offer. In return for $1100 and my head he'll send me a new AMC head assembled with my new and restored components. I suppose I could have asked him to return my head as a failsafe of sorts but then I'd have to pay him for the work he performed on the head (yet more $$$) and waste time reselling it later.

At this point the only downside to this decision I can see (aside from the extra cost) is that it will delay shipment by about a week, but that's not a problem because my machinist won't be done before then. As a consequence of this decision I've placed an order for new cams and cam trays from my dealer. I was told these were in Germany so they may take some time getting here. Once mated with the AMC head I'll have, with the exception of the original lower spring plates and Beisan-enhanced VANOS, an entirely new top end.

Engine Bay Cleaning

I spent a few hours cleaning the engine bay yesterday. I began by using compressed air to blow out the dust, dirt, and leaves from within the nooks and crannies surrounding the shock towers. I also used compressed air to blow out the condenser and was amazed at what came flying off / out of it -- tons of sand and other dirt, as well as a bunch of paint that was obviously barely hanging on. I would have preferred to break out the power washer at this point but as the car is tucked far inside the garage that wasn't an option. As a result I was forced to use blue paper towels to pick up the bulk grease on the front subframe and steering rack, and then use towels with a bit of water to clean up the remaining dirt.

As I was examining the engine bay looking for additional places to clean I saw a couple things I didn't like -- first was the heavily rusted pipes on the power steering system. Although oil dripping from the engine the last 100K+ miles kept sections of the pipes free of corrosion the areas near where they connect to the rack are heavily corroded now. This particular rust was not visible from the underside of the vehicle, which explains why I didn't catch it earlier. I also noticed that the A/C condenser was heavily corroded on the sides. Unlike the zinc-plated transmission cooler, the condenser is nothing more than aluminum coated with paint that had long since fractured and fallen off. I could wait to replace these parts but this is clearly the best and easiest time to do this as the systems are already broken down.

During this cleaning process I discovered several areas of rust forming in the engine bay, the result of various harnesses, cables, and pipes rubbing against the paint for 20 years. Fortunately these are mostly a surface phenomenon. To address this I plan to use a roloc disk chucked in my die grinder to remove the rust and smooth out the transition to the surrounding paint. Primer will go on top of that, followed by a base coat that will come from a custom ordered spray can containing my factory color -- Boston Green. On top of that I'll apply a bit of clear as a protective layer and then polish it. While I'm sure this won't match the original engine bay paint perfectly, it will be close enough. After all, this is rust remediation -- not a concours restoration.

Machine Shop Parts Delivery and Labor Quote

A few parts I ordered earlier this week came in. These included parts I delivered to the machinist: the two plugs he'll have to remove to clean the block and 6 OE rod bushings he'll fit to my existing rods. Rich was glad to see the plugs, not only because that meant he wouldn't have to fabricate them, but also because they confirmed the depth of the existing plug (about 5mm) he'll have to drill and thread as required to pull it out of the block.

I fully expected the BMW OE rod bushings to be identical to the original bushings -- a seamless part, bronze in color. The parts that I received, however, had a seam and were silver in color. When I handed them to Rich he said this is what he expected. I brought up the possibility that since BMW doesn't generally produce parts that require machining in the field we might be stuck with whatever clearance that results with the JE pins, but he said that based on his experience these parts should be significantly undersized and therefore easily sized to the JE pins. We shall see.

While standing next to the crank he asked if I had the double-chain sprocket for the front of the crank. I said yes, but not on me. Although he said it is a low profile part and it shouldn't affect the balance that much, he wanted to get that and the damper from me to completely balance the assembly. I promised to bring them to him early next week.

We hadn't spoken about price before this point, as it was mostly pointless to do so. Once he had time to review everything I wanted done he came up with a price of $1200. While this is $200 more than I had budgeted, so far he appears to be attentive and communicating well -- and that negates the slightly higher price in my opinion. His turnaround time of two weeks was also slightly longer than expected, but I knew going in that the summer was his busy season.

Fuel Injectors Removed

Today I removed the fuel injectors from the intake manifold and fuel rail assembly in order to send them to Marren Fuel Injection for reconditioning. I thought this would take a couple minutes but it took closer to 30 as I had to figure out exactly how to extract them without breaking anything expensive or made of unobtainium.

I first removed the two 10mm bolts that secure the metal fuel rail to the intake manifold. I used a flat blade screwdriver to remove the metal clips that tied the top of each injector to the fuel rail and then carefully pried the thin-wire clips that locked the electrical harness connector to each injector. Then it was a pretty simple matter of popping the injectors out.

The injectors are rusty in spots. I'm not sure if Marren will be able to address that but I hope so. I don't think the corrosion will affect operation of the injectors, at least in the short term. Given the price of new injectors and the relative ease with which they can be replaced later, I am not planning to replace them at this time. Of course, if Marren calls me and tells me they are unserviceable for some reason I'll have to source new parts. Fortunately, at first glance Pelican Parts appears to have a Bosch source for around $80 each -- a significant discount from the ~$120 price I'd likely pay at the dealer with my discounts.

Next Up

One of these days I'll finally get around to replacing the hood release hardware. Once that's done I'll jack the car up and get started replacing the fuel lines. Fortunately the hard lines I received for the rear of the vehicle are pre-bent, so it should be relatively easy to install them. The primary challenge will be removal of the fuel tank and replacement of the hoses that lead from the hard lines to the pump and suction units.