Intake manifolds

[Westone]

Looks like I am going to being removing the air box, etc, to access the top of the throttle bottles. The rubber boots on top of the TBs, or bushings as BMW calls them, installed on the bike have the crimp style clamps on them, which leads me to believe they are factory installed originals. At ~$9 each it is a no brainer to replace them while in there.

The Intake Manifolds that connect the TBs to the cylinder head however, run $50+ apiece. They have a screw style clamp, but that doesn't necessarily mean they were replaced at some point. I'm debating about spending the money to replace them while I am in there. At 25 years old, I should probably do it. Opinions?

Thanks!

[JamesInCA]

Why are you getting at the top of the TBs?

The intake manifolds are hard plastic, not rubber like the bushings above. If you don't have symptoms of failure and aren't otherwise disassembling those, I'd leave well enough alone.  My daily bike and my parts bike both have screw clamps on the manifolds, BTW. I'd guess that's standard for the part.

If you do disassemble that area, whether you replace the manifolds or not, you'll want to replace the o-ring at the bottom of each manifold.

[Inge K.]

If you do disassemble that area, whether you replace the manifolds or not, you'll want to replace the o-ring at the bottom of each manifold.

Since it's 25 years old...it must be a 2 valve model...which don't have o-rings on the bottom of the manifolds.

[Westone]

@JamesInCA: On advice from a BMW mechanic at the local dealership, going to take a look inside to verify the operation of the valve, remove it and try cleaning the passages w/ compressed air. The online parts fiche does not show an O ring associated with the manifold. Thanks for the info about the plastic construction. Unless visibly damaged I will leave it as is.

@Inge K.: Thanks for the info about no O ring on this model. It is an '88 K75S.

[TIV]

I recommend replacing the manifolds as well as the rubber boots while your in there. If it's a 2 valve there are no rubber rings as Inge pointed out. Two of the old manifolds on mine had cracks and evidence of heat on them where they meet the cylinder head, just a matter of time when they would have started to leak. (It's a pretty hot spot where the plastic and metal meet). I did not see this until after I removed them.

The manifolds have screwed clamps and the rubber boots have crimped clamps. Since this area has moving throttle parts, and is pretty crowded, be careful to replace the clamps and especially the screwed clamps exactly in the same positions as they are now. Draw them up or mark the old ones and use them as reference.

[WayneDW]

when I was in the exact same situation as you a couple of months ago I choose not to replace the manifolds because of the cost.  I may regret my decision, hopefully not soon.

IMO, it really is a question if you can afford them.  If the cost is no concern, replace them because getting all that stuff off and back on is not easy.  If the price is out of reach right now and they aren't leaking, you don't have to but you will eventually need to go back and do it sometime in the future.

[Lawrence]

I too was shocked at the price of those bits.  I inspected mined and found them to be in decent shape, especially for a 1985 model.  I reinstalled them with a very light skin of gasket sealer on the mating surface.  All is well now.   :clap:
I leave enough of my hard-earned money at the BMW dealer....   :eek:

[TIV]

IMO, it really is a question if you can afford them.  If the cost is no concern, replace them because getting all that stuff off and back on is not easy.  If the price is out of reach right now and they aren't leaking, you don't have to but you will eventually need to go back and do it sometime in the future.

I agree with you WayneDW. I did it because I could afford it and as I said, they showed signs of cracking/burning. I also thought: "Maybe itīs a weak point and this is the reason why the O-rings were installed on later models."

[Westone]

Thanks for the input everyone, it helps. Money is an issue right now which is why I am asking about this. However, if they will need replacing at some point down the road, the "While I am in there" factor dictates coming up with the money now. After all, my time and effort is worth something too.

[TIV]

You could take them off and inspect them while you are in there anyway. Then you know what condition they are in, and if they seem to be alright, you can put them back in, with a light smear of gasket sealant.