I decided to make custom size dowel pins, only about .010 larger than the stock 5/16” (.3125) holes in the GMC blower case. I did this so I would not have to open up the dowel holes to the next standard size, which is 3/8”, in case I made a mistake in setting clearances, or if I ever had to move things around in the future. This is just my personal preference, and is in no way a superior method over using standard size dowel pins. This just gives more options for oversize pins in the future.
The pins are made from O-1, letter “P” (.323” diameter) size drill rod, purchased from McMaster Carr. The part number for the rod that I used is 8893K225 and it is very inexpensive at $6.49 for a 3’ section. If you are a professional machinist and are reading this, you might be thinking “O-1 is not hard enough, or close tolerance enough to use for dowel pins.” Well, if this were a precision steel die, or a part for an aerospace application, that might be true. However, this is not the Space Shuttle. It is a cast aluminum blower case where a very hard pin surface is completely unnecessary to prevent galling during installation. Also, these pins are exclusively for static alignment during assembly and they are under no appreciable shear load while the blower is in operation. The 10 end plate bolts bear all of the shear loads. The only thing that these pins must do is stay put in the bearing plates, and allow for a slip fit into the blower case, and for the front cover.
Size “P” reamers can be obtained from any tooling supplier and I was able to get mine off of Amazon for under $5.00, as an add on item. In the end, the select fit item was the dowel pin, the cheapest part of the assembly. Any errors that I would make would be confined to this 10 cent part, and I could always cut another one from my 3’ long rod if I had a clearance or size problem. Although slightly oversize reamers (.3235) can be obtained, they are not as common as standard "P" size reamers and they are more expensive than the standard size reamers. This was another reason why I decided to select fit my pins by using the emery to reduce the blower case section of the pin by about .0005 for my slip fit. If I did this all the time, the $35 oversize reamer would be in my tool box, but for a "one time only" type of job, I elected to reduce the case end of the pins instead.
================================================
Disclaimer: This video series is not intended to be an exhaustive “How to do it” tutorial on how to rebuild a 6-71 blower for Gasoline use. Rather, it is meant to be a “How I did it” journal of one of many projects that I undertake in my home workshop, using hobbyist equipment and methods. If you attempt to duplicate any of these methods, you do so at your own risk. Therefore, I will not be held liable for any incidental or consequential damages as a result of trying to duplicate these methods.
Sources for clearances and tear down/assembly details referenced the Detroit Diesel assembly manual, with additional details referenced from the SA Design book “A Do-it-yourself guide to: Street Supercharging” by Pat Ganahl, ISBN 0-931472-17-2. If you are not an experienced mechanic/machinist, do not attempt to replicate this work. Take your Blower to a professional Blower builder.
Негізгі бет Автокөліктер мен көлік құралдары My 6-71 Blower rebuild, Part 13: Installing oversize dowel pins.
Пікірлер: 21