Reduction Drive

Construction Details Finish&Fly Events and Projects Building from Plans Raw Materials Q&A Tools Construction Log

Reduction Drive
Intake Manifold
Engine Mount
Pictures Only



My reduction drive was made by Dave Johnson (Reductions), Winipeg, Canada.  It is a belt drive with a 2.1:1 ratio.  It is pretty heavy at 52lbs.  I elected to use this one for a few reasons:

  1. It is made in Canada
  2. I know at least three people using Dave's redrive with good success.  One of them has been using it for more than 6 years.
  3. Dave produced over 400 of these redrives.  The model he now sells is the fourth generation of his product that evolved over more than a decade.
  4. A belted redrive allows me to simplify the engine installation by keeping the mostly stock intake manifold and by using a carburetor on top of that manifold.
  5. Dave provides a lot of support, not only for his products but he spends a lot of time helping builders to rebuild and convert their engines. 
  6. His redrive is among the cheapest ones on the market.

Dcp01195.jpg (120620 bytes) Dcp01196.jpg (120885 bytes) 

Homebuilding being what it is, errors or issues are to be expected.  And there were some issues with mine that needed to be addressed.  Initially, I was not able to fit the reduction drive on my engine because the dowel pins would not align with my engine bloc. I presume that the assembly might have moved during the milling process. While I was proposed a fix I could apply locally, I preferred to have a unit that I could easily re-install on a different engine bloc if I ever need to do so.   Reductions  replaced the unit without any hesitation.

I sent my re-drive back to him by bus and a totally new one came about a month later.  This one fitted much better (all holes aligned perfectly), but it still had a few minor issues.   On the following pictures, we see the new re-drive (w/o the lower front bearing) installed on my dummy engine to see how it fits.

DCP02098.JPG (93533 bytes) DCP02100.JPG (115225 bytes)

One of the few minor issues is that the material around the lower left bolt has not been milled to a flat surface to allow the bolt head to sit.  I brought it to someone I know who has a milling machine and he quickly corrected this.

The assembly of the re-drive is pretty straight forward and the process is very well explained in Dave's instruction manual.  The first step is to mount the main assembly to the engine.  Once all bolts (except the lower right bolt which attach the starter mounting plate) and the engine dowel pins are set, the bolts are torqued and safety tied.

DCP02105.JPG (111386 bytes) DCP02111.JPG (115149 bytes) DCP02112.JPG (130220 bytes) 

The oil seal holder on my unit is still off-center a little bit (.006"), but the seal appears to fit well.  If it ever causes a problem (like premature oil leaks), I will re-center the seal holder with a centering ring that Dave provided to me and fix it in place with dowel pins. 

I discussed this point with Dave and he was very surprised since his matching process is very exact.  However, upon reflecting on this, he believes that he may not leave enough play for the assembly bolts whose holes are drilled to tight tolerances (on a standard Subaru bell housing, these holes are drilled much larger than they need to be).  The precision fit is to be assured by the dowel pins.  I would bet that future units won't present this problem at all.

And that leaves me with an additional thought... as my mentor says, I spend too much time measuring and not enough progressing... 

DCP02114.JPG (101023 bytes) DCP02115.JPG (92713 bytes) DCP02116.JPG (105785 bytes) DCP02120.JPG (112194 bytes) DCP02106.JPG (81999 bytes)

My own "OUPS!" When I tried to torque the lower right bolt to 19ft-lb, the aluminum spacer for the starter support crushed! :(     That spacer is made from a 5/8" machined aluminum rod.  The wall of the thin portion (which has a outer diameter of .450") is only .049" thick. While I was explained the proper torquing procedure and was offered a replacement part, I decided to go ahead an make a new spacer from a steel rod.  Then, I remembered that I had an old underwater scooter shaft laying in a box in my storage room.  That 1/2" shaft is made of Stainless Steel and is a perfect material for the purpose.   This was the first time I used a lathe and it really makes me appreciate the amount of effort spent in making those parts. 

  DCP02121.JPG (88509 bytes) DCP02122.JPG (94231 bytes) DCP02123.JPG (99021 bytes) DCP02124.JPG (106225 bytes)  

Another of the few minor issues was that the holes in the lower front bearing support were not drilled and tapped as per the instruction manual.  The manual mentions that the holes are pre-drilled to 3/16" and we need to match drill the front plate with these holes, then tap the front plate to 1/4 NC and final drill the front bearing support to 1/4".  On my support, the holes were drilled to 17/64".   

Unfortunately, on that day, Dave was un-reachable, so I followed the advises of a local expert.  I installed the front bearing drilling and tapping the holes in the front plate to 1/4 NC.  Then, I drilled two holes in the bearing support to 5/32" using my press drill.  I matched drilled the plate and enlarged the holes to 3/16".  I inserted two 3/16" by 1-1/4" dowel pins.  These pins now ensure proper alignment of the bearing assembly.

DCP02104.JPG (106529 bytes) DCP02127.JPG (101011 bytes) DCP02128.JPG (113224 bytes)

When I spoke with Dave, later, he approved my installation procedure but he also mentioned it might not have been necessary as this was a result of a change in design.  The new bearing support is better designed to ease the removal and replacement of the bearing assembly.

In the end, the re-drive appears to be a nice unit. I look forward to see it running. I know several people using it for years with great success.  They are all happy with theirs.



Home ] Up ] Construction Details ] Finish&Fly ] Events and Projects ] Building from Plans ] Raw Materials ] Q&A ] Tools ] Construction Log ]
e-Mail me at

Counter reset on August 10, 2000 (4302 visits on main page prior to reset)
Michel Therrien, (c) 1999 - 2003.