Hello,
I have a question about intake air through supercharger.
In parking mode, supercharger clutch does not kick on.
How intake air pass through without supercharger clutch kick on when we start? Is there any space for air flow freely?
I saw supercharger snout rotates slowly without supercharger clutch kick on when starting.
Otherwise, If supercharger rotor is stuck by any reason, starting possible?

 

I am no expert but the SC does not have to rotate fir the engine to run.
There is clearance between the main body bores and the rotors and clearance between the rotor spirals.
The rotors spin due to the air being drawn between these clearances, the rotors are windmilling due to the air passing by them.
You can stop the rotors spinning by stopping the black portion of the clutch carefully and the engine will not hesitate.
If the clearances were not there the SC would be wrecked when the faces touched, this would occur when a bearing or bearings were too worn to maintain the clearances.

 

Is that a gold ceramic thermal coated charge air cooler I see in the lower left corner? Out of curiosity, did you have a leak, and is the reason why you tore down the S.C.? Nice job on the cleanup. A good time to port/gasket match/and polish up the runners, if you haven't already done so.

 

Wow, I think you are an expert!
Thanks a lot.

 

Yes. It is 3-years old speedriven's charge air cooler, not coated but wraped insulation tape. The reason I tore down S.C is oil leakage behind clutch. It's because of old rubber seal at snout. I found bearing is not good also, so I replaced all without snout bearing.(Snout bearing was ok)
Thanks.

 

Great photos, can you tell us how many kilometres the SC has been driven?
I have some photos of the insides of the SC but they are not this clear, well done.
Do you think wrapping the IC is a catch 22 situation? Heat soak is slowed down but will eventually get to be as hot as if it was non wrapped, cooling down will be slowed down in the same manner. Works well at first for a spell then retains heat longer.
Did you paint the SC or fine sandblast it?
Did you use the old clutch bolt or replace it? Remember it must have a hole through it to allow for the expanded hot and blow by air to escape. No hole would lead to oil being forced out along with the air.
I would use a new bolt after all the work you did, I expect you did. You appear to have a good knowledge of these things, my comments are just for others who had not thought of these things and for future record.

 

My car is just over 180,000 km(111,800mile).
I always can see IAT with OBD2 based blutooth display.
I had heat soak when my IC pump was dead.(IAT was 93~94C(200F)). The temp rise was very instant during full acceleration. I thought wrapping IC cooler may delay instant temp rise. I have original hollow pulley bolt.
No sand blasting just washing and SUS spray coated.
Now I am changing headgasket.
I have read many of your helpful writing.^^
Thanks.

 

Not possible, not true Dave. The reason for the hollow in the bolt shank is to prevent someone from over torquing it. Snapping the O.E.M. bolt is better than stripping out the threads of the gear shaft on the S.C. nose! If you have snapped your O.E.M. pulley bolt, or feel that you need to replace your perfectly good O.E.M. bolt, then Rob @ Needswings sells the replacement bolt for you. The bolt he sells is a solid one with no hollow shank, as the O.E.M. hollow bolt is not available new.

 

I believe you are mistaken, bolts that are meant to shear at a predetermined torque have the diameter reduced by a groove, production wise this is cheaper to do than drilling a hole through the centre of the bolt. The position and width of the groove determines where it will shear. A hollow bolt can twist a lot under torsion and where it breaks can be hard to determine each time.
When the temperature of the air inside the gear section rises it will expand and if there is no hole the air will escape through any gap that there is, with no hole in the bolt the air will push past the bearing and oil seal and blow a fine mist of oil.
The oil will be thrown away from the hole in the bolt due to centrifugal force allowing only air and a negligible amount of mist to escape and thus equalize the pressure inside the gear section to the ambient pressure outside the SC.

There has to be some blowback from the rotors as well through the bearings on the ends of the rotors, any positive seal to prevent this would not last long due to the friction caused by the rotation of the rotors. Dynamic seals are used here as well.
Dynamic seals need lubrication, the oil provides this but the surface of the shaft has to have a certain finish on it to provide little wells were the oil can sit, the finish cannot be too rough or it will wear the seal despite the oil. The surface cannot be too polished or there will be nowhere for the oil to sit. The amount of oil we are talking about in a good seal will be hard to see, some of it will get past the seal in minute quantities which over time will show. It is this oil that lubricates the lip of the seal. The viscosity of the oil is important as well, too thin and there will be a lot of leakage, too thick and it will not sit in the wells on the surface.

The pistons rings in the engine ride on a very thin layer of oil, again the surface finish of the bores and the oil viscosity are critical in keeping the oil in place.

There is a post by Rudy some years back now that explains the reason for the hole, I just added a little more detail as I see it, maybe a little too much detail.

Feel free to point out any errors, I can take it as I am a big boy now. 😉

 

Damn Dave, that's a lot of technical info.there. All good and compelling points. Not that you have any errors in your above post, but as a layman, I just don't see how any air,mist can escape to anywhere. There's no hole at the bottom of the threaded gear shaft hole, is there? No. And there's no hole in the head of bolt; how can it escape? What is the travel path? Is it traveling up through the threads? My position on this matter is based on my recollection from this very debate several years back, along with Rob @ Needswings stated opinion on this matter. I see now, that initially and for quite some time, Rob didn't have the hollow bolt, but now he is offering it. You can buy the inexpensive solid bolt, or pay $18. +sh. for the hollow bolt. I would think that if the solid bolt was detrimental to our S.C.'s, that Rob would not offer the solid bolt?
Do I believe you, or Rob our XF guru? Check out Needswings.com / SRT6 / Supercharger/ SC pulley bolt

 

The first photo shows the shaft for the pulley on the extreme right and the second photo shows the hole in the other end of the shaft where the gear is attached.
The first picture is not too clear but you can see the hole on one end and vaguely the six driving pins on the other. The second photo is upside down.

 

FYI

 

More great photos, these are the definitive photos of the SC on this forum.
Thanks.

 

Great pictures, but they still don't explain how the hollow bolt does any kind of venting of air "to escape", as you say. You didn't answer any of the questions; as though we are to figure it all out from the pic.'s? Are you telling me that Rob at Needswings got it wrong? How does a hollow bolt that leads to nowhere work? Trying to figure out your theory here Dave.

 

A picture is worth a thousand words, you can see both ends of the shaft and each end has the hole. The driving disk with the six driving pins in it uses the six pins to drive the plate with six holes in it. There is a gap between the disks and the air moves through this gap.

 

I never thought I'd see the inside of our supercharger, yet here I am.

And there it is.

 

Again, great pic.'s, but still doesn't explain how the hollow bolt has anything to do with that. And again, is Rob wrong about this? If you are right, then Rob got it wrong; Right? See his explanation of the SC pulley bolt @ Needswings.com.

 

Either he is right or Rudy and myself are right.
When you have gears rotating at high speed an aerosol of the oil will be formed at the same time the air in the SC gear housing will expand with heat. You do not want that aerosol mixing with the hot air escaping through the bearings and seals at the front of the SC as this will soon deplete the oil. You basically just want the expanded air to escape and the minimum of oil.
The photo shows the hole in the shaft from both ends, with a hole in the bolt why wouldn’t the expanded air and the cooler air later pass through the whole to bring the air pressure inside the gearbox back to the ambient air pressure?
I made the wrong assumption way back and I got this reply from Rudy. Ironically you replied to Rudy’s post immediately after his post and did not disagree then.
CLiCK

 

I regret that I did not give air pressure to snout hole.
I already fabricated supercharger and installed.
Hope someone test it later~~~^^

Mercedes should have reason to design this hollow bolt which is weak than solid. (Preventing overtightening could be done by more easy and cheep method)
I saw that the length of the hollow bolt is abnormally shorter than depth of snout thread, that means there shoule be popose of connecting bolt hole and snout hole.

 

FWIW, I have the hollow bolt. Rob just told me that they have been using the solid bolts for the past decade without issues. I stand on my belief that a hollow bolt with no pinhole at the top, does absolutely nothing. The bolt simply doesn't vent. Except for the hole at the end of the bolt threads, it's an enclosed chamber that measures in minimal c.c.'s As Spock would say, "Highly Illogical".