|Technical note on sizing Schebler Mod...
Post Number: 904
|Posted on Friday, December 21, 2007 - 12:28 pm: ||
The following was sent in by Dick Day:
Technical note on sizing Schebler Model D carburetors.
By Richard A. Day Jr.
There is some confusion determining various sizes of Schebler model D carburetors. The easiest way with a complete carburetor is to simply determine the National Pipe Thread "NPT" size of the Throttle plate. It should be noted that this plate can be mounted either as a side draft or updraft carburetor. The Model D NPT sizes are ½", ¾",1",1-1/4", 1-1/2" and 2". The most common sizes encountered are ¾",1"and 1-1/4".
Note the throat drain on the bowl throat inlet is a small milled slit on the lower face. Do not block this drain with a gasket between the air horn or throttle plate in either the up-draft or side draft application. A cork gasket or O-ring is required at the top of the throat to seal the air gap with the bowl cover. No gasket is used on the bowl rim, the lower face of the bowl or between the cover and the throttle plate or air horn.
When matching up parts from different Model Ds trying to make one good one keep in mind that the bowl internal throat diameter will be approximately the size of the intake air horn, throttle plate and bowl cover junctions with the bowl throat. A bowl with 1" internal throat diameter will require an air horn with 1" internal diameter, throttle plate with 1" internal diameter and cover with 1" internal diameter.
Keep in mind the 1" throttle plate diameter we are talking about is not the pipe-threaded portion, as it would measure approx 1-1/4" diameter. The 1" diameter is the opening where the throttle plate joins the cover throat opening in an updraft configuration or the throat outlet in a side draft application.
The difference in diameter is inside diameter of pipe is only a nominal diameter which is determined by the wall thickness of the pipe. In the case of 1" steel pipe the standard outside diameter is 1.315".
In the case of tubing the diameter is defined as the outside diameter EG. ¼", 5/16", ½" ETC.
In the case of brass pipe its dimensions are similar to steel pipe in order that it will mate with threaded iron pipe fittings. For example 1" diameter seamless brass pipe the outside diameter is approximately 1-5/1/6", whereas the exact outside diameter is 1.315".
There is a related matter that involves Schebler model D Knockoffs and there were a number of them, which look very much like the model D. They also work just as well in low speed antique marine engine applications. These makers include Monarch, Michigan Wheel, Acorn, Generator Valve, and others. Parts from these makers don't however as a general rule mate with the Model D.
There are two that come to mind which for all practical purposes came from the same patterns as the Schebler model D. Schebler ceased manufacturing the Model D in the 1930s. Arcadia and Lunenburg Foundry then manufactured the Model D for many years and some of their parts such as the float valve will fit the Schebler model D. It should be noted most of these two makers products have a rough sand cast, unpolished finish but they work just like the original Model D of Schebler. Schebler stopped polishing the Model D in the early 1930s and left the rough sand cast finish.
One should note that there are two thread sizes found on the Model D gas line hex nut. 16 Thd or 18 Thd so be careful when trying to mate similar parts from different carburetors.
Post Number: 42
|Posted on Friday, December 21, 2007 - 08:07 pm: ||
Thanks Dick & Andrew