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Tuesday, September 22, 2020

Doug's Domain

Doug Vetter, ATP/CFI

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Thursday August 17, 2017

New Cylinder Head Arrives

A couple days ago I received notification via UPS that my head had shipped from Autohead. Yesterday I received a text from Peter indicating something about the cam carriers and the fact that I should double-check the lifter bores. I called him to clarify what he meant.

I quickly learned that he decided to send me the AMC cam carriers along with the head. I was not aware that AMC even made cam carriers and at no point prior did Peter and I discuss my purchase of anything but a bare head with my components installed, so this was news to me on a couple of fronts. I had to tell him that I had already ordered replacement cams and cam carriers from BMW. I then naturally asked whether there was any way to obtain a credit for the AMC carriers but he said no, because they were sold as a set by AMC and so they would not reimburse him (or me).

When I asked what he meant about checking the lifter bores, he said that he has never sold the AMC carriers to his customers as they typically reuse their BMW parts, so he has no data to indicate whether anyone has successfully used the AMC carriers. So his point was that if I decide to use the AMC carriers I should make sure the cams rotate freely and the lifter bores are of the same size, which I interpreted as "measure everything and calculate the clearances to ensure they are dimensionally equivalent to the BMW parts".

If you're wondering whether I plan to use the AMC carriers, the answer is no. Although I'm reasonably sure AMC wouldn't intentionally sell cam carriers that were incompatible with BMW cams, as they would be quickly laughed, and/or sued out of the industry, I still plan to purchase and install the BMW carriers for a lot of reasons, most of which are related to my aversion to risk for this very costly project. The upside to this decision is that I will be in a position to compare the dimensions between new AMC and BMW carriers and potentially put to rest any concerns about the AMC parts. Why is this important? I want to be able to provide the AMC carriers as an option to anyone who might buy my cams, or I might just want to be able to resell the carriers as new parts by themselves should no one want my cams.

The first thing I noticed when I picked the head up is that it indeed feels heavier than the BMW head. I never weighed my head so I can only take Peter's word for it, but the ten pounds he suggested seems about right. Inspecting the unit I generally liked what I saw. It seems to be a near perfect replica of the BMW head, but I won't try to suggest I am sufficiently experienced with these parts to be able to spot all the differences. If you are thinking of buying the AMC head and wondering about any differences with the BMW head, I recommend you contact Peter, as he's far better qualified to answer that question.

One of the many upsides to buying a new head is that, assuming I take no more than 3-4 thousandths off the deck of the block, I should be able to use the standard thickness BMW head gasket. Yes, the clearances between valves and pistons will be reduced somewhat and the compression will increase slightly as well, but the latter will probably be offset by the significantly larger-than-stock exhaust valve reliefs cut into the JE pistons.

(Image: Marren Fuel Injection report on Bosch injectors)

And speaking of valve reliefs, following a comparison between the stock piston exhaust valve reliefs (which are significantly smaller than the stock intake reliefs) and those of the JE pistons, I'm feeling more justified in complaining to TEP recently that they did not identify the direction of the piston anywhere on the casting. Steve at TEP emailed saying, in effect, "it's obvious...you'll be able to tell". I remain skeptical. The reliefs on the JE pistons look damn near identical to me -- which is clearly not the case for the stock pistons which I expected TEP (and hence JE) to use as a design model.

While I haven't started any concrete analysis of the head I like the view from 10000 feet, so to speak. When I look at the general finish quality and what I'm getting for $1100 I have to say I'm impressed. My purchase of this head was difficult to justify because my original head was found to be serviceable. Had Peter found it to be cracked, however, the decision would have been a lot easier. In that case I would have bought a new head (either AMC or BMW) in a heartbeat, as I don't think welding these heads is a viable fix unless, of course, the goal is to do a bargain-basement repair to prepare the car for sale.

Stay tuned for the measurements on the AMC vs. BMW cam carriers. I probably won't get to the work until I begin the assembly process in a week or two, but I'm sure it will be enlightening.

Fuel Injectors Returned

The fuel injectors were returned from Marren today. It's clear from reading the report that the injectors required service. To begin, the flow rates were all over the place and four of the units failed the spray pattern test. Flushing the units in the reverse direction resulted in the ejection of dirt. After the units were cleaned they passed every test, which is great, since this means I don't need to buy any new injectors at the moment.

From my experience in aviation I can say that roughness, particularly at idle, can be caused by inconsistent fuel flow through injectors of different cylinders. Could some of my roughness have been caused by these dirty injectors? My guess is yes, but I'll never know for sure since I never got around to cleaning them prior to the overhaul. My advice? Send your injectors out for cleaning every 100K miles. It's worth the money.

Next Up

I'll be taking a day off from the project tomorrow as I briefly return to a software project, but I'll be back this weekend, when I'll finally start to dismantle the front of the car as required to remove the support for rust remediation and eventual installation of the new hood latch receptacles.