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Re: [Fot] Topeka - TR4 crank pulleys

To: "Dennis DeLap" <yellow-green@sbcglobal.net>, "Bob Kramer"
Subject: Re: [Fot] Topeka - TR4 crank pulleys
From: "Greg Solow" <gregmogdoc@surfnetusa.com>
Date: Wed, 28 Jul 2010 22:57:21 -0700
We have made small diameter crank pulleys in the past that were designed to 
reduce the water pump and generator speeds by about 1/3.  We have never 
found any advantage in using a narrow fan belt or in installing a "damper". 
The engineers that we have consulted with in the past have voiced the 
opinion that a 6 cylinder or a v-8 crank with the rod throws at angles 
relative to one another that are not 180 degrees develops torsional 
vibrations that require a damper, but a crank with throws at 180 degrees 
like our "tractor" engine does not. They have said that a damper on our 
engines is a waste of time and just extra weight and inertia.  Consequently 
we have never installed dampers unless the owner of the engine insisted. 
With a good balance job and rods and pistons as light as we can get them, we 
have had no failures that could be attributed to torsional vibration as long 
as the revs were kept under 7300 rpm.
    The way we have made crank pulleys is to start with a standard hub and 
cut it down and redrill the  holes for the pulley to the smallest diameter 
possible. Then we machined a new pulley to match the new bolt circle. The 
belt groove was then machined to match the standard generator pulley 
profile, but with the inside diameter just larger than the new bolt circle 
that attaches it to the modified hub. This procedure has worked very well 
for us.
    In back to back engine dyno testing , at 6,000 rpm on an engine making 
165 hp, slowing down the water pump by 1/3 was worth about 6 hp at the 
flywheel. The top water hose from the thermostat housing was partly a clear 
glass tube. With the normal water pump speed there are a lot of small water 
bubbles flowing away from the engine. These are caused by cavitation on the 
back side of the water pump impeller. Slowing down the pump dramatically 
reduced the number of air bubbles. This would tend to imply that the water 
pump is operating more efficiently at the slower speed.
    The main reason that we did not go to the narrow belt was that we just 
did not want to go to the trouble of having to change to narrow pullies on 
the generator and water pump. The wide belts have been very reliable and 
operate at a very low tension setting so do not put to much side load on the 
water pump or generator bearings.
                                                                             
                            Greg Solow 
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