Hi all,
Started an oil change the other day. For some reason my restored K75 seems to be burning oil at a somewhat faster rate than expected. This would have been my first oil change since getting it back together. So I'm letting it warm up and for unremembered reason I was running my hand outside the fuel rail when I felt a pulsating air. So I shoot WD-40 at the throttle bodies and find that it is sucked in on cylinder #1. So after a great deal of feeling around and noting that the engine runs smoother when sucking in the WD-40,  I conclude that my #1 cylinder has an air leak at the Inlet Manifold base.
Inlet Manifold - BMW K75, K100; 11 61 1 460 408 / BMW
Much like the thread on "clean and replace" https://www.k100-forum.com/t14821-clean-and-replace-throttle-bodies-and-plenum
I pull the plenum, and the throttle bodies out of the "Inlet Manifold(s)". The Inlet manifold piece appears to be unbroken/damaged and it was torqued down reasonably (I thought). So I cleaned the whole area using carburetor cleaner. There is some grunge on the metal body which necessitates scraping and multiple cleanings.  The Manifold Inlet itself has two grooves in the base which may have served as part of the seal but they are clean. Now comes my question, I've been advised to put some sealant on the bottom before replacing the Manifold Inlet. Quick trip to the local auto parts store leaves me rather confused. There are numerous choices of products which seem to fall into two categories, gasket makers and gasket sealers. There are at least 3 manufactures and their products differ by temperature range, resistance to oil, water, anti-freeze and color (this latter is apparently a major selling point. So I'm soliciting suggestions as to what product to use. I'd prefer not to purchase on Amazon as that would slow down reassembly as well as I don't like Amazon.  Oh and my location is the USA. I'm leaning toward the temperature range of up to 650F/243.C.  But wondered if the difference between a gasket maker and a gasket sealer would be critical?

I've used silicone gasket maker. I think the difference to sealer is that the sealer is not as thick since it's intended to be spread on a gasket where the gasket maker is intended to replace the gasket and as such probably is a thicker consistency and sets up a little faster with less shrinkage.

The key thing is to put a thin layer of sealant and not to tighten the throttle body down completely until the sealant has a a day to cure. That way you get a better seal and minimize the amount of squeeze out.

jjefferies wrote:I conclude that my #1 cylinder has an air leak at the Inlet Manifold base.
Much like the thread on "clean and replace" https://www.k100-forum.com/t14821-clean-and-replace-throttle-bodies-and-plenum

That rider's throttle body had a leak at what BMW calls the manifold bushing, not the intake manifold. Have you verified that part doesn't have a fine split in it?

Laitch wrote:

jjefferies wrote:I conclude that my #1 cylinder has an air leak at the Inlet Manifold base.
Much like the thread on "clean and replace" https://www.k100-forum.com/t14821-clean-and-replace-throttle-bodies-and-plenum

That rider's throttle body had a leak at what BMW calls the manifold bushing, not the intake manifold. Have you verified that part doesn't have a fine split in it?

Ok, lets make sure we've named the oranges oranges and apples apples.  Starting at the bottom feeding into the engine's head is the "Inlet Manifold", which appears to be rubber and metal. Then mounted on top of this is the throttle body. This is aluminum and holds the butterfly valves which control air flow into the Inlet Manifold and then the engine head. Above the throttle body is the Intake Manifold which connects the throttle body to the Plenum and is made of rubber.

Now what I observed is that if I sprayed WD-40 on the engine head next to the Inlet Manifold of cylinder #1, that the WD-40 immediately disappeared, apparently sucked into the engine. And the engine which has been very rough when cold immediately smoothed out. I had already done the same operation on the other two throttle Inlet Manifolds. In the case of the previous two checks (cylinders 2  & 3) the WD-40 had pooled at the base of the Inlet Manifold and drained aft to spill onto the exhaust. In the case of cylinder #1 the WD-40 immediately disappeared, the engine smoothed out and there was no WD-40 pooling.

The manifold bushing I assume is the bushing where the butterfly valve is controlled. I did not test it as I had what I think is the culprit. When I lifted the "Inlet Manifold" I found stains suggestive that there had been seepage under it. And the throttle body and area were rather dirty by comparison to the other two cylinder manifolds. But as you point out I should and will double check that there aren't any discernible cracks in the throttle body. Thanks for pointing that out.

Point-Seven-five wrote:The key thing is to put a thin layer of sealant and not to tighten the throttle body down completely until the sealant has a a day to cure.  That way you get a better seal and minimize the amount of squeeze out.  

I followed your lead and got the gasket maker. The directions call for laying down a then layer, then applying pressure finger tight for an hour, then torquing down the Inlet Manifold and letting sit for 24 hours. Which is what I did. Interestingly finding the appropriate torque pressure in my manuals is a bit of a hassle. Later I find the Inlet Manifold is called a manifold Stubbie in I believe the Clymer's manual and shows the torque as 5 ft lbs. or 7 newtons. After twenty four hours I remount the throttle bodies. But am waiting for EME to send me the 3 hose clamps needed to hold the rubber  Intake Manifold's in. In taking the entire assembly apart you need to cut the lower of the permanent BMW hose clamps and in restoration replace them with  more common screw on hose clamps. None of the major BMW shops in the S.F. Bay Area have the hose clamps in stock. I'm being given to understand this is common for AirHeads and older K bikes. I look at all my spare parts but none of the hose clamps are thin enough to do.

A squiz thru this thread points to suzuki reusable clamps and others.

K100-forum.com » Parts, Accessories and part substitution » Hose clamps. Throttle body, plenum etc

tinyspuds wrote:A squiz thru this thread points to suzuki reusable clamps and others.

K100-forum.com » Parts, Accessories and part substitution » Hose clamps. Throttle body, plenum etc

Ooh, great. And I've already paid for the silly things. I'm just about to go out and ask when they'll be here. Price seems to be falling in the USD $5.00 range. So Suzuki would be right in there.

jjefferies wrote:

Laitch wrote:That rider's throttle body had a leak at what BMW calls the manifold bushing, not the intake manifold. Have you verified that part doesn't have a fine split in it?

Ok, lets make sure we've named the oranges oranges and apples apples.  Starting at the bottom feeding into the engine's head is the "Inlet Manifold", which appears to be rubber and metal. Then mounted on top of this is the throttle body. 

The manifold bushing I assume is the bushing where the butterfly valve is controlled.

There isn't a need to assume. The names aren't being fabricated extemporaneously. Bushing is the label that BMW, rightly or wrongly, gives the rubber connection between the throttle body and the plenum in the parts fiche when ordered by a customer.

Laitch wrote:. Bushing is the label that BMW, rightly or wrongly, gives the rubber connection between the throttle body and the plenum in the parts fiche when ordered by a customer.

Then the opening you are suggesting searching for is in the rubber "bushing" between the throttle body and the plenum. Sorry I don't know where my micro-fiche is. Biggest issue right now is waiting for the hose clamps to be delivered so I can put it all back together.

jjefferies wrote: Sorry I don't know where my micro-fiche is. 

We get to a certain age, misplacing things is a regular part of life. Here, I've got a spare.

Well that was certainly interesting and a taxing afternoon. Hose clamps showed up about 1:30PM as part of a package of items. Checking them it appears that the screw tightened variety that I got from EME which have the same part number as BMW websites are fractionally wider than the original permanent ones. A few moments of panic thinking I had received the wrong ones, but no they are the 46 mm in Diameter as called out on the several websites. Just that they are a b***h to install. Tried to install the plenum with the hose clamps mounted as loosely as possible. No go! Then installed the plenum with the hose clamps open, i.e. screws removed and that worked but getting the screws back in place was a no go. Seems the screws themselves as delivered weren't long enough to allow the clamps to open enough. So I cheated and used screws that were half again the length of the screws delivered. That worked.  All told it took me three and a half hours to get the plenum mounted, hose clamps tightened down and various parts of the air filter system re-installed. The new hose clamps with longer screws have to be carefully positioned to keep various parts from interfering with one another. Finally got the bike back together and cranked it. Started up very sweetly. Took it out for a twenty minute errand/ride to the grocery and it performed as it should.

So thanks for the advice. Not sure what to make of the screws not being long enough to open the hose clamps to their maximum. Maybe it was the supplier but this would be a first for their product not being correct.

jjefferies wrote:The new hose clamps with longer screws have to be carefully positioned to keep various parts from interfering with one another.

Welcome to one of the most common clubs on this forum

Just a final note. After all that I got it back together and it runs a whole lot better. Idle is steady if a tad high at 1500 rpm. I will go and have the throttle bodies synced after the upcoming 49'er rally. I'll ride the red bike up there for that. But otherwise Silver is purring. Thanks for the advice/tips/comments.