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Detroit 1-71 Again

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Bill Tattersall

Member
Hi Guys. A while ago I posted a message on my restoration project of a 1939 Detroit 1-71. Initial start up dumped 2 quarts of oil out the exhaust in 15 seconds. What a mess in my shop. The blower seals need to be replaced. They might not have been changed in 80 years. I have the blower apart and new seals but have a question for any 71 experts out there. There are reference marks on the vane shafts for timing the gears. The markks are actually 1 missing spline on the shaft ends where the gears mount. How do I align these marks?
 
Timing a 71 series blower is done with shims under the two meshing drive gears that are cut on an angle. I have resealed countless blowers and learned early on to MARK everything you remove. Most all the parts are reversible and it can get confusing to figure out what you had when you started. Al
 
Thanks Al. I did as you suggest and carefully identified the shims, gears, etc. and took photos. I was told about the missing splines/timing marks by another person and the missing splines are there. I'm not sure how the position of the gears on the shafts could make a difference, just going by what I was told. Any comment?
 
Not an expert but I rebuilt a 50s era 2-71 once. The new gears had marked teeth for timing. IRRC both dead splines were pointing up when the marks were aligned. The real bear on that job was getting the lobe clearances adjusted. I think I may still have the manual somewhere. I can look later.
 
The gears have precision ground teeth and are a very close fit. Almost zero clearance. Shimming the gears in and out changes the position of the lobes relative to one another. They have to be adjusted so the lobes have some clearance and the leading and trailing clearances are different to allow the clearance to change as the gears wear. Unless the 1 cyl. versions are different, you need two pullers to take the gears off together. Pulling one will bind the rotors. You probably discovered that when you took it apart. I'll scan some of the pages and post them later. May not be exact but they will help you.
 
Hello Bill Tattersall,

I have the manual for a 6 71 series engine. I can right down the procedure for you. May be E-mail would be better. Or you can call me or I you. Timing the lobes is just part of the story. Seals is also the key of a proper rebuilt.

Guido.
 
Thanks Guido but yesterday I came across a 71 series shop manual so I'm good there. New seals were definitely in the works. Luckily they are the same throughout the 71 series. It looks like timing the gears/lobes are going to be the challenge unless, when I put it back together exactly how I took it apart including shims, it is OK without further effort. Keep your fingers crossed for me.
 
Hello Bill,

Looks like you got it covered. Never seen one lunger 71 series. DD school in 1976 had 8v71 we qualified on. Last time I had about 10 71 series blowers apart, was in 1999 with 20 in my diesel class.

Guido.
 
Pay attention to what Mike and Al say, and you need long feeler gauges to reach between the rotors.
 
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