PK tensioner.... crank idler pullies
11-06-2013, 01:30 PM
#1
Rennlist Member
Thread Starter
PK tensioner.... crank idler pullies
I am installing the PK tensioner on my 87 automatic.
I've heard that the two idler pullies below the crank gear can be left off. Anyone have any comments or suggestions on this one?
The pullies look as if they have never even touched the belt in 150,000km....why are they there?
thanks
John
I've heard that the two idler pullies below the crank gear can be left off. Anyone have any comments or suggestions on this one?
The pullies look as if they have never even touched the belt in 150,000km....why are they there?
thanks
John
11-06-2013, 01:48 PM
#2
There are several different iterations of this set up under the crank gear and I have only found one set that actually felt like it was usable. They all end up having dirt caked on them and have never felt a belt on them. I'm sure there was a reason the geniuses at Porsche put them there, but having said that, I took them off my car and don't see the need to replace them.
Leave them on there if ya wish, it won't make any difference.
Leave them on there if ya wish, it won't make any difference.
11-06-2013, 01:56 PM
#4
A lister on here said that they function to keep the belt tracking in case there's too much slack.
https://rennlist.com/forums/928-foru...de-delete.html
Sean's right. Leave it off or on, your choice, won't hurt. I couldn't get the whole thing out, only the pulley itself so the assembly minus pulley is still on the car. Left off the pulley in case I need to take off the back cam cover again, just have to be creative in how you bend the cover and don't be disappointed it you crack a part of it.
https://rennlist.com/forums/928-foru...de-delete.html
Sean's right. Leave it off or on, your choice, won't hurt. I couldn't get the whole thing out, only the pulley itself so the assembly minus pulley is still on the car. Left off the pulley in case I need to take off the back cam cover again, just have to be creative in how you bend the cover and don't be disappointed it you crack a part of it.
11-06-2013, 02:48 PM
#6
Race Car
Those idlers are a stock belt tensioner band-aid. You can leave them off if you install the PKTensioner. Same with the idler pulley higher up.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
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11-06-2013, 08:39 PM
#9
Interesting posts. Millions were spent on the development of the engine and this included the 1 or 2 idler rollers under the crankshaft drive sprocket/gear.
I replace mine with fully sealed ball bearing years ago at a cost or around $11.00 using the existing belt landing pieces fitted on the OD of the bearings. I like the design to contain any belt flutter and keep full belt contact with the drive sprocket, using the principle of "just in case"! as good risk management, as I believe Porsche engineers are better at designing engines than I.
I replace mine with fully sealed ball bearing years ago at a cost or around $11.00 using the existing belt landing pieces fitted on the OD of the bearings. I like the design to contain any belt flutter and keep full belt contact with the drive sprocket, using the principle of "just in case"! as good risk management, as I believe Porsche engineers are better at designing engines than I.
11-06-2013, 11:33 PM
#10
Race Car
The stock belt tensioning system may have been okay in the '70s, but most definitely not today. You only need to look at the smooth idler pulley that is attempting to stop belt flutter on the toothed portions of the belt (seriously?) to realize that this design by today's standard is embarrassing at best. Have you seen the stock system performing with the belt covers off at various engine temperatures and RPM ranges? When you are changing pretty much the whole belt tensioning system to a modern design, there is no need to contain belt flutter because there shouldn't be any with a real automatic dampener. Also, Porsche engineers are not Gods and every single thing they do is not absolute perfection. Otherwise, there would be no such thing as an automotive recall and there wouldn't be any 928's with ruined thrust bearings and engine blocks after less than 50k miles.
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
11-06-2013, 11:35 PM
#11
Henry Ford designed the Model T after much R&D also. Glad we didn't stop there.
11-07-2013, 05:40 AM
#12
Nordschleife Master
11-07-2013, 10:01 AM
#13
Rennlist Member
My take on this subject..
Based on my experience..
See my post #6
Plus 1
It wasn't the flutter..
In my case on a 1988 S4 engine I had replaced the "outdated design" and replaced it with an automatic dampener, however when the oil pump drive gear came loose from it's shaft (and the TB got slack) I found that the crankshaft pulley's kept the belt on the crankshaft gear. I'm sure it gave me the extra time to keep the belt in place (perhaps a few seconds when I saw the sudden drop in oil pressure) that were needed to shut the engine off without any damage to valves and piston.
I respect everbody's opinion based on my experience they're better on the car than in my parts bin.
A lister on here said that they function to keep the belt tracking in case there's too much slack.
https://rennlist.com/forums/928-foru...de-delete.html
https://rennlist.com/forums/928-foru...de-delete.html
Interesting posts. Millions were spent on the development of the engine and this included the 1 or 2 idler rollers under the crankshaft drive sprocket/gear.
I replace mine with fully sealed ball bearing years ago at a cost or around $11.00 using the existing belt landing pieces fitted on the OD of the bearings. I like the design to contain any belt flutter and keep full belt contact with the drive sprocket, using the principle of "just in case"! as good risk management, as I believe Porsche engineers are better at designing engines than I.
I replace mine with fully sealed ball bearing years ago at a cost or around $11.00 using the existing belt landing pieces fitted on the OD of the bearings. I like the design to contain any belt flutter and keep full belt contact with the drive sprocket, using the principle of "just in case"! as good risk management, as I believe Porsche engineers are better at designing engines than I.
The stock belt tensioning system may have been okay in the '70s, but most definitely not today. You only need to look at the smooth idler pulley that is attempting to stop belt flutter on the toothed portions of the belt (seriously?) to realize that this design by today's standard is embarrassing at best. Have you seen the stock system performing with the belt covers off at various engine temperatures and RPM ranges? When you are changing pretty much the whole belt tensioning system to a modern design, there is no need to contain belt flutter because there shouldn't be any with a real automatic dampener. Also, Porsche engineers are not Gods and every single thing they do is not absolute perfection. Otherwise, there would be no such thing as an automotive recall and there wouldn't be any 928's with ruined thrust bearings and engine blocks after less than 50k miles.
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ftIn my case on a 1988 S4 engine I had replaced the "outdated design" and replaced it with an automatic dampener, however when the oil pump drive gear came loose from it's shaft (and the TB got slack) I found that the crankshaft pulley's kept the belt on the crankshaft gear. I'm sure it gave me the extra time to keep the belt in place (perhaps a few seconds when I saw the sudden drop in oil pressure) that were needed to shut the engine off without any damage to valves and piston.
I respect everbody's opinion based on my experience they're better on the car than in my parts bin.
