Last week I provided an overview of air-conditioning retrofit in general, and of what I expected the process to be with my Euro ’79 635CSi in particular. I said that the first and easiest step is to procure and mount the compressor. I also hinted that, for vintage applications, that’s not as easy as it used to be. Here’s why.
The M30 “big six” engines in E3 Bavarias, E9 coupes, E12s, E28s and E34 5 Series, E24 6 Series, and E23 7 Series cars from 1968 through 1994 used several different a/c compressors. If you had a Bavaria or an E9, the compressor was same big, fat York that the 2002 was saddled with, about the size and weight of a lawnmower engine, held to the engine block via a large, heavy bracket with a flat base. Unless you are looking for concours-winning originality, no one in his right mind would choose the York compressor and its bracket for a rejuvenation or a from-scratch installation; the size and weight of the compressor can be dramatically reduced, and the performance improved, by replacing it with a rotary-style Sanden 508 compressor or one of its ubiquitous Chinese-made clones you can buy on eBay for as little as a hundred bucks.
But you need a mounting bracket to attach the compressor to the block.
First, understand that the purpose of a compressor’s mounting bracket is not only to hold the compressor to the block in a location where one of the grooves in its pulleys aligns with the groove in the crankshaft pulley, but also to provide a mechanism to adjust and tighten the belt. On the original York bracket, that function was usually provided by an idler pulley on a little swing arm.
There are two additional ways to take up the slack in the belt. The first is for the bracket to have four slotted holes so that the entire compressor can slide linearly. The second is for the compressor to pivot in an arc about a fixed point and then be tightened in place. With that in mind, you can search eBay for “Sanden compressor bracket” and find two kinds of adapter brackets with flat bases that mount to the flat base of the original York bracket. One kind has four slotted holes, but they’re typically to help align the compressor; they may not provide enough adjustability for belt tightening, and an idler pulley on a short swing-arm may still need to be employed.
The other type of adapter bracket, with two curved tracks, provides the fixed-point-and-pivot approach mentioned above. However, neither of these “bracket-on-a-bracket” (BOAB?) approaches is a great solution, since using two brackets makes things big, heavy, and rife with opportunity for misalignment of the pulleys. By far the better approach is to use a small cast-aluminum mounting bracket specifically designed to mount the Sanden to the M30 block.
When the a/c maintenance needs of M30-equipped cars were in the automotive mainstream, M30/Sanden-specific brackets used to be widely available through WorldPac, eBay, Amazon, and other outlets. They were sold by Air Products Group (APG), part number 0151A, but unfortunately they are simply no longer available. I called APG directly and chased the issue to ground, as they say. APG said that they purchased the brackets from another company who has long since gone out of business. I believe that I bought the last one for sale on Amazon when I resurrected the a/c in the Bavaria a few years back.
(Note that for my 635CSi a/c retrofit, the BOAB approach wasn’t germane, as my car didn’t have a/c to begin with; if it had, it would’ve had a later compressor than a York, and a different bracket. I include the BOAB approach because, overall, the issues of fitting a Sanden compressor to a Bavaria or an E9 are the same as doing it to an E24.)
So the question then becomes how to mount a Sanden 508 compressor to the M30 block when there is no longer any click-and-buy solution to do so. I wrote about this at great length a few years back on the E9Coupe.com forum, and concluded there was no turn-key solution (see https://www.e9coupe.com/forum, which, for years, was where Google immediately went if you typed in “BMW Sanden bracket”).
To be absolutely clear about this, one solution is not to use a Sanden at all, and instead use one of the compressors that BMW used on the M30 that is less objectionable than the boat-anchor York. A number of different compressors were used during the lifetime of the M30 cars. By the late 1980s, the 535i, 635CSi, and 735i all used a fairly compact Bosch Behr compressor, commonly called a “wing cell” compressor. It has four rounded mounting ears and attaches to the block via a fairly compact mounting bracket with a tensioning “tray” on the bottom that acts as the belt-adjustment mechanism, using the same nifty little toothed track-and-gear nut used to tighten the fan belt.
The E30 used this same compressor, although with a different mounting bracket. The Behr Bosch wing-cell compressor is no longer available new, unless you find a NOS one in some dusty corner of a dealership, but there’s absolutely nothing wrong with buying a rebuilt one and its mounting bracket. I believe the Four Seasons part number for the wing-cell with the four rounded ears is 57400. Be absolutely certain that it has four rounded mounting ears and not two rounded ones and two flat ones; that’s a different compressor that uses a different bracket.
For many years, the price of rebuilt 57400s seemed to start at about $350, which, as long as the Sanden adapter brackets were readily available, made the economics clearly in favor of using a new Sanden clone instead of a rebuilt wing-cell. However, some wing-cell rebuilds have been recently appearing on eBay for as low as $160. And, in fact, new Chinese-made knock-offs of the wing-cell compressor are beginning to show up on eBay for about the same price. In candor, had I known that this was an option when I started down my Conditioning The Shark path a few months back, I might have tried out an inexpensive wing-cell rebuild or a clone, but I’ve been using the Chinese-made Sanden knock-offs for quite a while with no problems, so, right or wrong, this was my default path.
If you follow my link above on the E9 forum, you’ll see that after my original “I don’t see a turnkey solution” sum-up, others commented that folks in the E28 world had been working the same Sanden/M30 bracket problem, and a few enterprising individuals had figured out that there was a way to hang a Sanden 508 from a wing-cell bracket and adjust it via the tensioning tray, albeit with a nightmarish kluge of spacers and angle iron. Then, about three years ago, a gentleman named Will Nolan posted on MyE28.com that he’d developed a pair of adapter brackets that allow the Sanden 508 to be adjusted fairly cleanly and easily via the tensioning tray. The original lengthy post can be found here, which is now the top hit when you search for “BMW Sanden bracket.” Mr. Nolan charges about $50 for the pair of adapter brackets. He can be reached at bimmerbrackets@gmail.com.
So that is the approach I decided to take. You need three main pieces:
• A Sanden 508 compressor, or one of its clones. I bought mine for about $110 from one of the eBay suppliers in Irving, Texas, that I’ve had good luck with. I buy the configuration with small threaded charging fittings on the back of the compressor so I don’t need to splice charging fittings into the hoses.
• The two main pieces of the wing-cell bracket (the cast-aluminum piece that mounts to the block and the tensioning tray that attaches to the bottom of the bracket) from a late M30 car like an ’89 E24 635CSi. A link on Realoem to the parts diagram can be found here: http://www.realoem.com/bmw/enUS/showparts?id=5374-USA-04-1989-E24-BMW-635CSi&diagId=64_0430. The bracket and tray are fairly readily available used on eBay; just don’t confuse the M30 bracket with the shorter, more squared-off M20 bracket—as I did the first time I bought it. If you can get the bracket and tray with all of the bolts that mount the bracket to the block, and the long bolt that holds the tensioning tray to the bracket, and the bolt with the adjuster gear for the toothed track, so much the better. I bought everything as a set from good-guy Richard Aikins, who not only included every mounting bolt and washer to attach the bracket to the block, but color-coded them to their correct locations with pink dots.
• The pair of adapter brackets from Will Nolan.
Be aware that, even with Will’s adapter brackets, there are some issues with this approach. It is not turn-key. First, you have to understand that the purpose of the adapter brackets is not to hang the Sanden from the wing-cell bracket. For that, you need to make two modifications listed below to the wing-cell bracket, and hunt down a bolt and a spacer. The purpose of Will’s adapter brackets is to allow the bottom of the compressor to be attached to the tensioning tray so that it can pivot out and tighten the belt, and it, too, requires bolts and spacers. If you want a turn-key solution, Layne Wylie sells what appears to be a very nicely-engineered solution for about $150. You can find more information about it here. I, however, had already purchased Will’s brackets before I heard about Layne’s. Don’t read any more into it than that.
The first required modification to the wing-cell bracket is enlarging the pivot-bolt hole. The upper through-hole in the wing-cell bracket that forms the main mounting and pivot point for the compressor is sized for a skinny M8 bolt, whereas the mounting holes in the ears of the Sanden are larger, for a 3/8" bolt. Thus you either need to use a skinny M8 bolt and risk the compressor moving around (if you take this approach, a 5/16"-ID/3/8"-OD sleeve available through McMaster-Carr, part number 2868T54, will take up some of the play), or drill out the upper through-hole in the bracket to receive a larger bolt. I found that an M10 bolt is an even better fit to the holes in the Sanden’s ears than a 3/8" bolt, so, wanting to minimize slop and misalignment in the mounting of the compressor, I drilled out the bracket’s upper hole with a 10-mm (0.406") drill. I was initially concerned that since I’m not a machinist and don’t have a milling machine, if I didn’t keep the drill bit absolutely square with the bracket, the hole could wander off at some angle, but looking at the back of the bracket, I could see that much of the drill path was punctuated by open space. This has the effect of centering the bit whenever it enters a new section of a path through metal.
Second, the rear of the bracket needs to be routed out so that the hex head of the M10 (or 3/8-inch) bolt will clear the ridge. It would be nice if you could slide the bolt through the front instead of the rear, but the bolt’s hex head won’t clear the compressor pulley (at least it wouldn’t with my M10 bolt). A Dremel tool with a carbide cutting bit makes routing the needed clearance in the aluminum bracket pretty easy. Make sure that the hex head not only clears the ridge, but that you can get a socket on it.
Third, once the bigger bolt can be put through the upper hole in the bracket and the compressor hung from it, you see that the bracket’s upper mounting boss is much smaller than the space between the compressor’s ears, leaving nearly an inch and a quarter of space where the compressor can slide back and forth on the bolt, so some sort of spacer must be used. And, with all that axial play, where should the compressor even go? The enterprising souls in the E28 world found that, if the compressor is slid all the way forward so the back of the bracket’s boss is flush with the compressor’s rear mounting ear, the front pulley of the compressor aligns very well with the crankshaft pulley, so any spacers should go in front of the bracket’s boss, between it and the front mounting ear of the compressor.
Some of the posts on the myE28 forum show the space on the pivot bolt filled up with washers. Perhaps it’s a sign that as I’m getting older, I’m getting less hack-y, but the thought of using that many washers drives me crazy, so I sought out a solution for a spacer. Using calipers, I measured the size of the gap as 1.236", so you either can use a slightly smaller spacer and make up the difference with washers, or a slightly larger spacer and file it down to fit. 1.25" aluminum spacers with a 3/8" hole are readily available on McMaster-Carr (part number 92511A107), but because I’d elected to use an M10 bolt, I needed a spacer with a slightly larger hole (some 3/8" spacers will let a 10-mm bolt through, and others won’t). The actual M10 bolt diameter is 0.386". I wound up ordering a 32-mm-long (1.26") spacer with a 10-mm hole from aluminumspacers.com (part number MAS-19-10-32, $3.04 plus $6 shipping), and filed it down to fit.
I have to say that that spacer is a simple thing of beauty sitting in that gap.
Oh, the length of the pivot bolt: Because I was using metric M10 bolts, I was stuck with metric lengths. The 120-mm bolt (about 4.72", McMaster part number 91287A381) didn’t have quite enough thread length to fit on both a nut and a lock washer, and the 130-mm bolt (91287A383) protruded far enough that I thought it would interfere with the inner groove on the pulley. As it happens, it comes close to the pulley but doesn’t actually hit it, and you put the belt on the outer groove, not the inner one, so 130-mm (5.12") was the right length. If you’re using 3/8" bolts, 5" would be correct.
The adapter brackets also require some “spacing engineering” to get them to sit flush with the rear-facing sides of the tensioning tray. I used one 10-mm washer as a thin spacer between the adapter brackets and the ears of the compressor on the rear-facing side. On the front-facing side, I found some ½"-long spacers at my local hardware store that are sized for a 3/8" hole but fit my 10-mm bolts (the McMaster part number for a spacer that’ll fit both 3/8" and M10 is 93320A315). For the bolts securing the adapter brackets to the compressor, I used 40-mm ones (McMaster part number 94036A641) on the rear ears, and 50-mm ones (94036A651) on the front ears, the extra length needed to accommodate the spacers.
Now that the 8-mm through-bolt with the adjusting-gear nut has to go through not only the adjusting tray but the adapter bracket, it’s a little short. The nut still threads on it, but there’s barely enough room for a lock washer. The original length is 110 mm, so 120-mm would be a better length. Unfortunately, I don’t see any metric carriage bolts on McMaster-Carr longer than 90 mm. The other option is to use spacers to put the adapter bracket on the inside of the adjusting tray rather than on the outside. For now, I’ll just live with the short bolt.
It’s best to test-fit everything (compressor, brackets, adapters, spacers, bolts) on the benchtop and make sure it’s right, then take it partially apart and bolt things onto the block. With this Sanden/wing-cell arrangement, you can simply withdraw the main pivot bolt and spacer, and leave the adapter brackets bolted to the compressor. Bolt the main bracket to the block. If didn’t have a Richard Aikins coding the bracket bolts for you with pink dots as I did, figure out which goes where by trial and error. Compressor brackets experience a fair amount of vibration; I’ve had bolts back out several times, so even when using lock washers, I also now use a dab of Loctite.
Of course, nothing, not even bolting a bracket up to the block, goes according to plan, and as I went to submit this and thought, “You know, a photo of the damn bracket bolted to the damn block is in order,” it turns out that once the bracket is bolted up, the pivot bolt can’t go through the bracket from the back because it hits another mounting boss on the block. And it can’t go through the front because the bolt’s hex head hits the compressor pulley—or at least it does with the M10 bolt I’m using.
I’d say, “Bolt the compressor to the bracket and you’re done with Step One,” but that’s a bit misleading, as you need to deal with oiling the compressor, which may require draining the oil that it came with and replacing it with the oil that’s appropriate for your choice of refrigerant; we’ll cover that in another installment. But getting to the point where you have the bracket bolted up to the block and the compressor either on or ready to go on is a great first chunk of work in an a/c retrofit job.
A great first chunk which I am, apparently, today, denied.
[Next week: The answer to my pivot bolt problem. Then, either the evaporator or the condenser. Whichever gives me less trouble.]—Rob Siegel
Rob’s new book, Ran When Parked: How I Resurrected a Decade-Dead 1972 BMW 2002tii and Road-Tripped it a Thousand Miles Back Home, and How You Can, Too, is now available on Amazon. Or you can order personally inscribed copies through Rob’s website: www.robsiegel.com.
