Hi all, so I finally stopped being depressed every time I looked at my broken mini and have started taking it apart. I want to do ground up “restoration” basically on everything in the front end.

It at one point had a rebuild on the head, I am skeptical of all the work done on it at this point, which is why I decided to do it myself. When looking at the head I noticed that the U shaped metal pieces that hold the camshafts down ( a shaft retainer? Collar? I don’t know if these pieces have a name) are not in the order they should be in. I have seen stuff on the past saying they are very important to keep in order, put in where they came out. Now it’s been 6-8k miles on it with them not in order.

so how important is it? When I rebuilt it should I return then to their original positions?

also any tips on parts or “upgrades” to parts in the head would be great.

already planning ARP studs

 

I've torn down three N12 cylinder heads and made a "reassembly" video. All cylinder heads went to a local machine shop for repairs. Some had holes in exhaust valves, some had dropped valve seats, and one head was warped. I got some comments about poor camera angle, so I'm reshooting the video using my current project car. Here's a link to the current reassembly videos. See description for parts 2 & 3.


If you want to find out the technical names for each piece. Go to the realoem . com website and enter the last 7 of your vin; then click on engine. Scroll on down to the cylinder head components to find out their technical names. OBTW, some parts have one name in real OEM, and another in BMW's technical information system (TIS). For example, the real oem calls item 8 in the picture "roller drag levers", but TIS calls them "roller rocker arms".


Also, real OEM calls item 9 "alignment element", but these are actually hydraulic lifters.

Make sure you check these carefully, they should spring back when depressed. Exhaust lifters should measure 1.173". Intake lifters should measure 1.551". If the springs suffer from hysteresis, and your lifters are no longer springing back to the correct height, replace all of them. Rock Auto sells the Melling brand.

The bearing caps you are referring to are critical and are part of the cylinder head; they cannot be ordered separately. See picture. these caps are installed, and a machine line bores the hole; that's why they are numbered. On the exhaust side, you will see the caps numbered 1-4, with number one, going to the front of the engine (timing chain side) or the #1 cylinder. On the intake side, the caps have a paired marking on the eccentric stand shaft supports. If the caps were moved to a different position, changing the original wear pattern, the head is probably no longer serviceable.

 

thank you! I have watched a million videos over and over and feel confident about the tear down. the head has probably like 10k miles on it with the bearing caps in the wrong spots.

 

to add another question to this, could something like mismatched bearing caps be enough to slip timing?

 

No, slipped timing usually results from movement between the crankshaft gear sprocket or a camshaft (intake/exhaust) sprocket and its respective shaft, assuming those parts were correctly installed. However, if the camshaft is not free to rotate, (misalignment, fitment etc) that increases the potential for the driven sprocket to slip on the shaft.

 

so ive been reading other forum posts about this topic (not just here) and have noticed that some people say its okay and but a lot of people say its bad and could end up in failure, but no one seems to elaborate on what issues could go wrong switching caps. so anyone know what potential issues are?

 

gotcha, didn't think so unless the camshafts were like loose or something, just figured id ask.

 

'What could go wrong switching bearing caps?"

As I explained, when the cylinder heads are manufactured, the camshaft bores (bearings) are created by a single machining process. This creates a perfect centerline; the bearing caps are stamped to identify their locations, and then the caps are removed so the camshaft can be installed. Lubricating oil is pumped into the bottom of the bearing to create a hydrodynamic wedge between the rotating camshaft journal and the stationary bearing surface; this wedge keeps the camshafts journals from actually touching the bearing surface (in theory). As with any engine, you are going to get wear between the rotating camshaft journal and the bearing surface. Otherwise known as a wear pattern; using the specified oil, filtration, viscosity, and maintaining the oil (changes) keeps the wear to a minimum. Moving the caps to a location other than is stamped position introduces a different wear pattern on the top of the bearing as compared to the bottom of the bearing; the changed positions of the bearing caps will cause new wear patterns on the camshaft journal. Considering camshafts are low-load, you can probably get away with moving the caps from one location to another in the short-term, but in the long-term you are going to have increased wear. Another potential problem of moving the bearing caps is clearance. Simply saying you can do it doesn't take into account that every engine is different and they develop their own wear patterns. So, on one engine, you may get away with it, but on another, moving the caps may cause the bearing to act like a clamp (no clearance) instead of a bearing (.002"-.005" clearance between the camshaft journal and the bearing. Clear as mud?

 

exactly as clear as mud. So basically lets try to sum this up into layman's terms.

Either the caps will be too loose or to tight if moved, to the point that you get camshaft play or clamping effect in the extremes, did i get that right?

Theoretically, I would assume, in extreme instances, if you are causing different/abnormal wear on a journal you could also be weakening the part, potentially give a point of failure, but I would assume that to be rare.

It also seems to me that if the journals have been moved for at least 10k without issue that that in my situation new wear patterns might've developed and since there is no catastrophic failure yet it might be usable

 

For Toyota there is a cam cap clearance spec using plastigauge but I believe you have to have the valve springs out so no pressure on the cam or possibly at a specific angle there would be little pressure on the cam - don't recall.
Fairly easy measurement but having the factory service manual is a must.

 

I actually just watched a video where they were double checking all tolerances with Plastigauge. And thought I should do that just to check everything
never saw it before that

 

Definitely, I checked the Toyota manual and it places the plastigauge on the top of the cam w/o valves installed so if you have valves installed might be better to place it on the bottom bearing surface. Plastigauge is designed to force the journal to one side for the correct measurement but there is some debate on this, obviously will work on a rod bearing but a cam or crank is not so clear. Anyhow its a confidence measurement, if you perform measurement properly and you are in spec you are good.

I once installed a cap backwards because the arrow was not legible and it was number 1 cap so could not tell the direction - the universe conspired against me on that one. Luckily the cam did not feel right when turning it so I detected it or it would have been an expensive mistake!

This is also a good reason to avoid buying heads on ebay, I know people who have done this and received absolute garbage, entire head spray painted silver including valve springs like thats going to fool someone.

Edit - actually I realized the up/down pressure on the cam depends on whether its a direct cam to valve like early Toyota or rocker arm and anyhow I assume you will have rockers off so no issue there.