So, I got a Detroit 8v71 blower cheap and have started on a project to convert it to suitable for gas then build up a new low compression short block and get it all fitted in my '80.
It turned up, looks a bit grubby, got about 4 layers of different paint on it. It's been stripped down recently and cleaned, but hasn't had any conversion work done on it.
There's several things that you need to do to convert one of these old Detroit blowers to gas:
Fit sealed bearings in the rear instead of the open roller type which have to run in oil.
Fit new dual row bearings in the front
Fit PTFE style shaft seals - GM part 23500533
Triple pin the shafts to the rotors both ends
Machine off the extended shaft at the back of the driven rotor
Plug oil feed and return holes in front cover
Check and adjust rotor clearances as required
Make various blanking and adapter plates.
I started off by stripping it down. Simple job, only thing to be careful of is pulling the gears off the rotors, you need to do both at the same time as they are helical cut. There will be different shims behind the gears, note carefully what's where as it sets the rotor to rotor clearance. Also mark which rotor is which and which end of the case is the front.
Knocked out the old bearings from the covers. The next stop for all the case components is the bead blasters to get all the old paint and crap off them.
This is the bottom of the end plate. The 2 end holes are for through studs, the 3 others in the middle need to be threaded and plugged so that the case retains oil!
These are the replacement bearings - 6305-2RS and 4305 ATN9 double row.
And this is the shaft at the rear of the driven roller that needs to be shortened. It can just be cut with a grinder if you don't have a lathe. Needs to be left long enough to seat in the inner of the new rear bearing (17mm).
Next job is pinning the rotors to the shafts using 6mm or 1/4" dowels. I've got new shaft seals on the way too.
