On the original engine layout the alternator was used to tension the belt that ran around the main crank pulley, water pump and the alternator. Since the alternator has been relocated for my engine placement, a new tensioner must be fabricated for the water pump. I have seen other Mini-4EFTE builds simply lever a belt over just the crankshaft and water pump pulleys without a tensioner, but I was dubious on how much tension this would provide to properly drive the water pump. For the tensioning mechanism, I found a tensioner at an auto wrecker (I can't remember what car it was from) so I could adapt it for my needs.
I purchased the smallest 4PK pulley that my local auto parts store could provide (72mm OD), but this was too large to fit between the other pulleys and subframe tower.
I purchased the smallest 4PK pulley that my local auto parts store could provide (72mm OD), but this was too large to fit between the other pulleys and subframe tower.
I outsourced some work and got a custom pulley machined at a 20% smaller diameter of 58mm OD and used the same bearing size (6201RS) as the pulley I bought at the wreckers. This fitted nicely and seemed like it allowed for some reasonable vertical movement to tension a belt.
The bracket to hold the new tensioner pulley would have to mount to the back of the engine block and share two bolts that the layshaft bracket was using so I had to remove one of the gussets from the layshaft bracket.
The original layshaft bracket design :
One gusset removed :
I wanted the water pump tensioner bracket to be separate and not welded directly to the layshaft bracket. The reason was that if I ever had to remove the upper suspension arm, I could not remove the upper suspension arm bolt (horizontal yellow/gold colour bolt to the left of the silver custom pulley - in the photos above) with the water pump tensioner bracket in the way, and I would have to remove the entire RHS layshaft and driveshaft assembly just to get the upper arm bolt out. Using a separate water pump tensioner bracket, then at worst I would have to remove the water pump pulley (and it's bracket) and the crankshaft pulley. It's all about forward planning.
The new bracket in the position where it would be bolted on top of the layshaft bracket :
The final tensioner bracket design (rear view), made from 6mm steel which allows for approx 30mm of vertical adjustment. In the photo below, there is a custom spacer between the pulley and bracket. I had to make a few spacers of differing widths before getting the alignment with the other pulleys just right.
The bracket in situ. The layshaft bracket is not fitted here so I used some spacers behind the tensioner bracket to simulate the thickness of the layshaft bracket
Note that once the (gold coloured) upper arm nut below is tightened, it will not be so close to the pulley
The final tensioner bracket design (rear view), made from 6mm steel which allows for approx 30mm of vertical adjustment. In the photo below, there is a custom spacer between the pulley and bracket. I had to make a few spacers of differing widths before getting the alignment with the other pulleys just right.
The bracket in situ. The layshaft bracket is not fitted here so I used some spacers behind the tensioner bracket to simulate the thickness of the layshaft bracket
Note that once the (gold coloured) upper arm nut below is tightened, it will not be so close to the pulley
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