Water pump housing installation-which washers required

[Theo]

I am changing the water pump and water pump housing on my 1966 230SL, no air conditioning. I have the parts that I got at a dealer in Germany, which came with bolts and gaskets, but they did not come with washers. So I would like to know what washer(s) are required.

My question is mainly about  the «cap bolt» (the one with the recessed Allen key indentation in it) at the upper right of the water pump housing attaching the housing to the block. Is any washer required at the back of that cap bolt where it goes into the block. It seems there should be, because the other two mounting bolts are spaced away (albeit very slightly) from the block by the gasket around the water passage. If such a washer is required, does anyone know its dimensions/part number?

[Aaron h]

Yes, a washer is required in this location for all M-127, M-129, and M-130 engines.....with or without air conditioning.   The part number is 621-990-03-40.  It's not a DIN number, so I can't determine the dimensions of the washer.  However, it's very inexpensive to buy new.  It retails for a whopping $1.20. 

[Harry]

Aaron,

It seems that this washer on my housing was "felt or fiber like"?  As a matter of fact, it is still attached to the housing.  Unfortunately, after assembling the engine and filling up the fluids, I had a small but clear coolant leak that appeared to be from the water pump housing, likely bolt 192 in the schematic.  This is a common bolt that clamps half of the sealing face for the coolant passage and the front leg of the heavy bracket for the alternator.  I concluded that perhaps I tightened down the alternator bracket first at the two points on the manifold side of the head, then at this bolt last.  The rigid bracket may have then prevented me from getting bolt 192 tightened enough.

I haven't reassembled yet but I was going to on this premise.  Any thoughts or cautions?

Harry

[wwheeler]

If I remember correctly, the lower gasket on the WP housing makes that mounting surface sit a bit off the head. The washer is there to provide the correct spacing so the housing sits flat evenly when bolted. I do not however remember which bolts on the front side of the engine need to have thread sealant on them, so fluid does not leak around them. There are a couple whether they be for the coolant or oil.   

[Harry]

Wallace - good point on the sealant.  I will be sure that is taken care of.  Just a thread locker?

Harry

[Aaron h]

That's an interesting take on the the thread sealant.  I've never seen anything leak from these bolts, and I've never had one start leaking after replacement of the water pump housing gasket.  Good to know in the event I ever see one leak. 

The original washers were made from a phenolic material, but proved to be useless, as they'd flatten or break when removed.  I don't know when they changed to metal, but they did for good reason.  If coolant is leaking from the water pump housing where it mates to the block it's usually due to pitted surfaces from corrosion, from the housing being cock eyed, and I've also seen some become distorted from the a/c compressor mounting bracket causing distress.  I used to see this a lot on OM621 diesel engines, too, as they had a similar set up for a/c mounting.

And no.  Never use a thread locker in a location such as this.  Use a thread sealant.  The Advance Auto on Asheville Highway has a good selection. 

[wwheeler]

I think I used thread sealant on the bolts that hold the water pump on to the housing. If I remember correctly, those threaded holes go through the housing where the coolant circulates. Thread sealant doesn't hurt anything and if there is any doubt, I use it.

Thread locker is used only for when you do not want the fastener to come apart. Thread sealant is a paste that simply will not allow a fluid to pass through the threads. Here is what I have used -  https://www.permatex.com/products/thread-compounds/thread-sealants/permatex-thread-sealant-with-ptfe/

[Theo]

Thanks for that washer part no. Aaron, much appreciated and also the other very helpful comments.

And what about washers on the usual place directly under the heads of the three bolts mounting the water pump housing to the block? What part no./dimension of washers should I be using there?  When I took off the non-original old pump there were washers there (outer dia. 17mm, inner 9mm), but they appeared to be cheap quality, non-original, severely rusted.  On your diagram, a washer (#205) is shown for the round cap bolt (#197) * , but not for the other lower mounting bolt (#192). Is a different washer required under the head of the round cap bolt than from the other two mounting bolts?

And thanks WWheeler: what you said is indeed what I meant that the gasket around the water passage forcing the pump housing to be ever so slightly away from the block, such that some kind of thin washer is required behind the housing to make the spacing even as between all the 3 mounting bolts. In my case I seem to have lost that washer when taking off the old pump (at that final stage I was getting tired).

And now my last washer question for today: so far, I assume that no washers are required for the 5 bolts (M6x18) mounting the water pump itself onto the water pump housing. My old pump had no washers there, but again its not original. So can you confirm that no washers are used on those 5 bolts?

And just let me mention again that mine is a 1966 230SL with three bolts attaching to the fan pulley just as shown in Aaron’s diagram.



*PS BTW, I said something wrong in my original first post: the round head cap bolt (indented for the Allen key) goes in the lower-most position, not the upper right, because it has to be unscrewed thru the harmonic balancer—hope I have clarified this now.