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Bandwidth AbUser
Join Date: Nov 2001
Location: SoCal
Posts: 29,522
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How tight should the MFI drive belt be?
I've started to re-install the engine tin and I replaced the MFI belt with a new OEM belt. Right now the pump is as far as possible away from the pulley on the left cam but the belt still has a fair amount of deflection. Before I tighten everything down, I thought I'd better know how tight the belt needs to be. Thanks!
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Jim R. |
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06-13-2003, 06:45 AM
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Location: Marysville Wa.
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you should be able to twist it 90°, midway between the pulleys, with minor effort, but not with no effort.
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https://www.instagram.com/johnwalker8704 8009 103rd pl ne Marysville Wa 98270 206 637 4071 |
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06-13-2003, 07:28 AM
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Bandwidth AbUser
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Thanks John! I guess my belt is too loose. It looks like I need to open up the slotted holes in the MFI pump base a little bit as I'm up against the stops already.
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Jim R. |
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06-13-2003, 07:36 AM
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Crusty Conservative
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That doesn't sound right. Sure the belt you have is new, and the RIGHT belt??? Maybe you can compare it with others for proper length.
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Bill 69 911 T Targa, 2.4E w/carbs (1985-2001) 70 911 S Coupe, 2nd owner (1989- 2015) 73 911 T Targa, 3.2 Motronic (2001- ) |
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06-13-2003, 07:52 AM
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Bandwidth AbUser
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Bill, it's the same part #, looks the same, and fits no tighter than the old belt.
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Jim R. |
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06-13-2003, 08:35 AM
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maybe the sprockets are worn out.
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06-13-2003, 09:15 AM
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Bandwidth AbUser
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Hmmm. I don't think they're too worn; however. So I've got a dilemma...I was planning on putting the engine back in the car tomorrow AM. If I do, the new belt is as loose (or tight
 ) as the old one. If I run into problems down the road, is it reasonable to replace the sprockets (pulleys) and belt while the engine is in the car, or had I better play it more conservative and order new sprockets and delay putting back in the engine? Thanks for your advice!
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Jim R. |
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06-13-2003, 09:54 AM
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they do seem to hang in there with a somewhat loose belt. you will at least be better off with the new one on there. it may be fine as is. hard to tell from here.
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06-13-2003, 10:30 AM
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Bandwidth AbUser
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That sounds encouraging. Well, here's some pics that may or may not be helpful to evaluate what I'm talking about. Whatd'ya think?
MFI Pump Sprocket:  Cam Sprocket:  Professional hand model showing MFI belt deflection: 
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Jim R. |
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06-13-2003, 11:30 AM
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1970 Porsche 911S 2.2l MFI
