Yall may already know this but it was new information for me and maybe it will help someone.
I upgraded my oil pump plugs with a set of aftermarket ones back in the spring and all was fine until I had to park the bike for the entire month of July due to rain almost every day (that’s right, I don’t ride in the rain if I don’t have to). When I finally got a chance to ride, the bike sumped like a mother on crank up. I know that a lot of folks say this is normal but this bike has not sumped even a little bit since the top end rebuild and it sumped only rarely before that.
I ordered a new ball and spring from J&P and this is where I first realized that there might be something weird with my 1980 oil pump. J&P does not list a check valve spring for 1977 thru 1980 so I ordered the 1981 and up spring and a new ball. After talking to a member here, I now realize that the chances of a steel ball going bad before an aluminum seat is slim to none but I ordered it anyway.
New spring and ball arrived so I clamped the supply hose and pulled the old stuff out with a pencil magnet. Got most of the old oil out of the check valve seat and spritzed some brake cleaner in there JIC there was a bit of trash. Dropped new ball in but noticed that the new spring was longer than my old spring by .337 inches. Put my old spring back in and ordered the 1976 and earlier spring.
Received the new spring and installed it but the bike was still sumping like a pig after sitting for more than a couple of days. I don’t know why but I figured that I would check the spring recess hole in my new aftermarket plug and compare it to my old stock plug. The stock plug spring recess hole has a depth of .358 and the new aftermarket plug recess is .564. All measurements taken by a nonmachinist on an analog vernier but you can get the gist of what I am saying. I put my old stock plug and the early spring in the bike and let it sit for 8 days. Cranked it up yesterday and not a drop of sumping. So here is what I deduced after doing some reading.
1966 to 1972
Check ball spring 26363-36
Check ball plug 26362-36
1973 to 1980
Check ball spring 26363-36 (length 1.626 inches)
Or 26262-80 (length 1.963 inches)
Check ball plug 26362-36 (spring recess hole depth .358 inches)
Or 26263-80 (spring recess hole depth .564 inches)
1981 to 1985
Check ball spring 26262-80
Check ball plug 26263-80
There are 2 different check ball part numbers also but I don’t know the differences in them (HD-8866 or HD-8873). Both are basically 3/8 ball bearings as far as I know.
My 1980 oil pump could have either the early spring and plug or the late spring and plug but if you use a -36 spring, you must use the -36 plug. Likewise, if you use the -80 spring, you must use the -80 plug.
So back in the spring I had installed a -80 style plug on a pump with a -36 spring and I was not getting the correct check ball seat pressure (the -36 spring is .337 shorter than the -80 spring).
So, if you have a 1973 to 1980 oil pump, insure that you don’t mix and match dash numbers like I did.