Can anyone please advise the correct length of the bolts that fasten the oil pan to the crank case?
I bought an oil pan bolt kit from one of the suppliers, and with a gasket in place, it is impossible to tighten down the nut enough to get a cotter key through.
Casting date January 1916 and oil pan has been straightened if that matters.
If you cannot turn the nut far enough, one of two things is wrong. 1. The bolt is not threaded far enough to allow the nut to be tightened. 2. If the threads are long enough, you might need to file off a little of the nut so that when you tighten it, the hole will line up.
I thought of a third possible cause. The hole for the pin is too close to the head of the bolt so that when the nut is tightened all the way, the hole is not exposed.
Hopefully someone might have access to the archives which would give the correct length of bolt, or someone has an original engine which has not had the bolts replaced who could give you more light on the subject.
My choice is, don't use cotter/split pins, just a spring washer.
Bolt up from the bottom of the pan, through the gasket and the block. Next a lock washer then nut. The castellated nuts with a cotter pin look nice but either they fit just right or are too loose or too tight and pull the metal of the pan up, nobody leaves them too loose so they get too tight. This is a "hunt and peck" process where no two are the same unlike a uniform fit with lock washers and an even seal.
The next person to remove the pan will be happy as they will not have to pull cotter keys with wire cutters, have them break off and cut themselves!. You can still use the new oil pan bolt kit, just substitute lock washers for the cotter pins for ease and a uniform torque. If that doesn't look right with castellated nuts with no pin just buy a handful of fine thread nuts and do it easier and better.
The early bolts were 1-1/4" but the ones after 1912 were 1-3/16". Of course some of the crankcase bolts are different, such as the ones used on the pan to front cover and under the starter, both of which have no nuts (1"). I believe that the ones used for most of the black era, after about 1917, are slightly shorter, about 1-5/32".
I used lock washers on my 21 Touring engine rebuild. It made things a little easier. If I remember didn't Ford start using lock washers in late 24? For me they make things easier when you can use them.