Offy 91ci

220 Bluemax wrote:

Hi all. This is my first post in the auto forum. I'm building a post-war Kurtis Kraft midget race car using the old Monogram midget racer kit, and have some questions about the engine. I'm using the kit engine but with a lot of detail work and alterations to make it appear more like an Offenhauser 91 c.i. engine. One thing I cannot get any info on is where the lower water hose connects to the radiator and the water pump. The second part concerns the T-shaped mechanical device at the back end of the L/H head. I don't know for sure what it is. A line/hose/cable runs forward under the injectors. What is it and where does it goe? Another goes through the firewall, directly behind the device, and another goes to some kind of device on the right side of the firewall. What is this? I would be grateful if some one could help me out. Thanks Jim

Hey Squeakie

Your reply didn't show up.

Jim

220 Bluemax wrote:

Hey Squeakie Your reply didn't show up. Jim

that figures, and it was lengthy at that. So I'll try it again (plus make a couple phone calls to the Offy Gods).

The Offy 91 and the Miller 91 are very similar engines designed by Hy Miller (his real first name was Harry but if you knew him it was "HY"). Upon Hy's death Offy bought the patterns and copyrights.

    The "T fitting" at the rear should be the oil return for the two can towers, and this will go back to the oil pan (I know clear as mud). The oil pan is a dry sump setup with an external gang type oil pump (actually several stages working indipendently of each other). There will be a large oil take mounted somewhere inside the frame as there is no oil stored inside the engine block. There will be at least two oil lines feeding the oil pump from the oil pan, and the output side of the pump will feed the oil tank. OK, now a second line will go from the oil tank to the front oil pump stage, and this will then feed the engine. If it is a later model Offy it may have a three or four gang pump, but the two gang pump is as simple as it gets. If you choose a three gang pump then have one of the pumps feeding the main bearings by itself. A four gang pump will also take the oil to an oil cooler (radiator), and this was common). There'll be lots of hoses by now!

    The line under the injectors depends on it exact location. If it's down by the crankshaft centerline (actually just above it); then it's the main bearing feed line (note some motors used a gun drilled passage to feed the main bearings but this was not well recieved by the users). The fuel injector bodies are constant flow Hilborne or Endrelle, and they all work about the same. There will be a large line feeding all of them with no return line. This line will go to the fuel pump normally mounted on the front end of the crankshaft (also the oil pump and water pump too). These are driven by timing belts (no vee belts on race cars). I've seen the magneto driven off the crank as well, but is not the norm. Don't forget the small air cleaners on the velocity stacks (attached to the fuel injection bodies). The stacks should be about 12" to 18" long.

     It's only been about thirty years since I saw a 91" Offy!

gary

Thanks Gary

I think I've mostly figured it out. The oil tank must be under the seat or tucked up under the firewall. Was the oil pump electric, driven off the mag or mech drive off the engine? Pics I have of midgets show a complicated looking device  on the R/H firewall with a line connecting it to the "T". Not sure what it is but could it be the oil pump? The front of the engine shows the mag and drive housing and a water pump driven off the end of the crankshaft.

This is pretty interesting stuff for me. I've worked on cars(1:1) all my life but never on something like this.

It looks complicated, but probably isn't if you've built a few of these things. I may be trying to get too detailed here because some of the oil lines may not be visible once the car is assembled. If the oil tank is under the seat I will probably just run a couple of lines down each side of the frame.

Jim