Idle roller 928 105 571 00
Idle roller 928 105 571 04
This roller has a simple 6905RS bearing that can be replaced. However the roller is not very expensive.
You need to replace the tensioner pulley which
comes with it's own new bearing that you can't replace without your own shop. Be
aware, this is a pretty vital part of your engine, don't try to save money by
drilling out the rivets and replacing the bearing. Don't !!
All the other T Belt pulley bearings are less crucial can be replaced without your own shop.
About the different versions of the idler pulley: The pump boss of the early 928 is 17mm diameter: The 6303 idler inner diameter is also 17mm;
The S4 and later idler has a 6905 and is 25mm inner diameter
TBelt crank idlers
- 6201 bearings pressed into old shells
TB Idler pulley
-'80 ( early 16v) ...... 6303,
All press into old shells.
These bearings average $7 for top grade double sealed.
Porsche: 928 105 512 12
FEBI BILSTEIN 4442
FEBI BILSTEIN 04442
QUINTON HAZELL QTT247
MS (Motor Service) 320 6124
TRIPLE FIVE 0210-09-06707P
TRIPLE FIVE PBT8109
TRIPLE FIVE TD26103
TRIPLE FIVE Y3452
TRIPLE FIVE MBI-22130
TRIPLE FIVE RKT1821
TRIPLE FIVE 380105
This shows the rollers below the crank at the belt side. The rollers are there to avoid that the belt slips over the crank sprockets when it is loose. Normally it merely touches the belt if at all.
I'm doing the water pump and belt on my
95 GTS and have a question on the lower idler.
One of the carrier holes (the one furthest from the roller bearing) is elongated. This allows the carrier to 'rock' on the 2 spuds that support the carrier. This appears as play at the actual roller but it is the carrier that is not snug on the mounts rather than any roller wear. Was this elongation or 'ovality' in the hole by design? It seems too uniform to be wear!
Interestingly the part no. on mine is 928 105 561 10R and not 928 105 067 01 as per PET.
There are two of these idler roller assemblies, one with one roller and one with two. There was a discussion a year or more ago on Rennlist about the elongated hole and the consensus seemed to be that it was made that way. I can't figure any logical reason for that, except for allowing for sloppiness in the manufacture of the engine, which I don't expect.
What I have done twice when I found this doing the TB/WP job is to locate the exact distance the two pins are apart that this idler rides on and then locate the roller carrier in my mill and mill the elongated hole out large enough to press in an oil-lite bronze bushing and then ream the bushing for a snug fit on the pin. I haven't had one of them apart again to see if the hole is elongating again.
I also replaced the bearings in both of the rollers. They can be sourced at the bearing store and pressed into the rollers. This is also true of the other idler roller on the tensioner arm, but I don't think so as to the larger roller.
The assembly actually comes in 3 versions.
The 928.105.067.00 is the one Mike has, one roller. It is used in 1986-1995
The 928.105.567.00 is used in the 1978-1986 models
And I've seen two-roller versions on cars. My 1988 had one with two rollers. PET does not say this :(
They are both very similar.
One side is loosely attached to the block to allow it to move easily. It goes over two protruding pins at the block and it is attached on one side with a washer and circlip. So no firm attachment. More a holder to prevent slipping off.
It looks to me that the roller is ok. The oval hole is on the circlip-side and probably to allow some expansion of the aluminum block and prevent it from getting stuck.
No worries. Just reuse this. Fix the roller bearing if needed.
1992 Porsche 928 GTS Midnight blue
Pictures taken by Dave.
Keep or delete the
idlers under the crankshaft pulley?
....Porsche engineers didn't put these pieces there because they had extra parts laying around, to use up.
Armchair engineers telling people to remove them are....not very smart.
Regardless of what tensioner design you use, the lower roller helps keep the belt from jumping teeth, if the engine rotates backwards.
Porsche went back and forth between the single roller and the double roller. The GT engines have the double roller. The GTS models went back to the single roller.
With today's slightly thicker factory cam belt (or Gates), you may want to use the single roller, instead of the double roller assembly. (I do.)
The second roller (on the oil pump side) sits closer to the crank gear and can spin all the time. Sounds just like....a small bearing spinning too fast. (Exactly what is happening.)
And because the sound radiates everywhere...and you can't see that roller spinning, you can spend hours trying to figure out what is making that terrible whine.
Ask me why I know this....
Notwithstanding GB's accurate account, as I recall there was a thread where someone posted how the cam belt had jumped several teeth and it was noticed that the lower roller was missing "omitted" by someone who was guided to think it was not needed. The tensioner system works well under normal circumstances but in the [very rare?] event of a backfire the tensioner simply put does nothing in the immediate aftermath. The roller as designed effectively ensures the belt stays in contact with the cam sprocket if there is a tendency to lift off - the word "back-fire" is used for a reason- the engine spins backwards if it fires prematurely/falsely during a start. Whether or not the motor suffered any valve damage I cannot recall - I have a feeling we never read about the outcome! The motor was that of the S4 category [i.e. interference].
That was a classic example of "if one does not understand it do not dick around with it".
IIRC that was the car that rolled back in gear and then the belt jumped teeth on the crank gear.
Another vote to keep it.
I kept mine on this recent timing belt job. The bearing was seized up a little. Donít think the belt ever touched it.
so did the 85-88 come with the single roller then the 89-91 S4/GT had double roller and 92-95 They went back to single roller (assuming same part used on the 85-88)?
I'm pretty sure my 88 has the single roller but canít remember.
Iím in this exact roller spinning situation with a Gates belt (not long life or racing) and yes, its difficult to locate this very annoying noise. My plan was to replace with a genuine Porsche belt but you seem to indicate that Iíll have the same issue with the factory belt. Has this been your recent experience?
I appreciate your response to Kevin, it appears that youíve just saved me from a lot of unproductive work!
Yes, you will have the same problem with a factory belt...Gates makes both on the same equipment.
Simply remove the double roller and saw off the metal bracket just beyond the OD of the second roller. (If you do this carefully, you will end up with a spare roller/bearing.
A quick "touch up" of the sawed end on a grinder or belt sander and you end up with what a single roller looks like, from the factory.
Re-assemble and you are done. And that irritating high speed bearing noise will be gone!
Lower Idler Assembly 83 to 87 - 90 to 95 - Single Roller
Lower Idler Assembly 87 to 90 - Double Roller
Prior to 83 a plastic guide was used. The idler assembly is expensive circa $250.
However we sell the replacement roller bearing for $10.