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Posted By: bobbynudd 51 distributor - Sat May 29 2021 05:08 PM
I have a 1951 gmc 3/4 ton pickup. 228 cu 6. the distributor is loose in the block hole. this movement creates a problem with the point adjustment. do I need a new distributor? is there a bushing that needs to be replaced in the block or on the shaft? the adjusting clamp seems to move with the distributor is there some sort of a problem with the clamp being attached to the vacuum advance ? Also the distributor moves (with the clamp) up and down. Is it improperly seated? Lots of questions any ideas? thanks
Posted By: Jon G Re: 51 distributor - Sat May 29 2021 10:48 PM
You've asked a couple of questions there, Bobby. Let's see what we can say...The 228 distributor (working from memory here as it has been about 40 years since I owned one) is not unlike the 235 distributor. If you look at the way the distributor connects there is a collar with a screw and nut which is tightened around the distributor housing which goes into the block. Then there is another part which couples with that collar and it is held to the block with a bolt. You can adjust timing (advanced or retarded) by loosening that bolt and moving the distributor clockwise or counterclockwise. And the vacuum advance moves the entire distributor clockwise as vacuum increases. There is a picture below...Hope you can see it.

Attached picture knob on distributor.jpg
Posted By: Jon G Re: 51 distributor - Sat May 29 2021 10:51 PM
Oh, sorry...if the distributor moves up and down, I'd guess the collar is loose. The collar and the part which couple with it (including the vacuum advance which is all part of this) should be held fast and kept from moving up/down.
Posted By: buoymaker Re: 51 distributor - Sat May 29 2021 11:38 PM
It sounds like the end of the distributor is not seated properly inside the slot on the oil pump. Sometimes when I install a distributor, I have to raise and lower it several times until it slips in. If that doesn't work, inspect the end of the distributor shaft for burrs and use a flashlight to see if there is anything restricting the slot on the oil pump.
Posted By: 52Carl Re: 51 distributor - Sun May 30 2021 02:45 AM
The collar/clamp which is part of the vacuum advance can be installed at the wrong height. You need to loosen the long bolt which is hard to get to between the backside of the distributor and the block before you drop the distributor in so that that collar/clamp will settle into its proper place. Disregard if you never loosened that bolt while you had it out.
Posted By: bobbynudd Re: 51 distributor - Sun May 30 2021 01:25 PM
Thanks for the help. now I have places to start knowing that it appears the installation is incorrect or the clamp is not attached to the advance correctly
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