The BSA A7-A10 Forum

Technical (topic titles must be descriptive) => A7 & A10 Engine => Topic started by: RichardL on 13.02. 2021 16:21

Title: Crankcase Studs
Post by: RichardL on 13.02. 2021 16:21
Maybe not worthy of a tech topic, but moderately interesting, maybe.

After shaviing the upper front mounts to a hair over 3" separation, figured I was about ready to mount the engine. Slow down there, boy! How are you going to clamp the crankcase between the rear mounting plates if the two in-between crankcase mounting studs are sticking up above the plane of the plate landing zone? (Fortunately, realized this before I had the engine in my arms.) Are the new stainless studs not installed to the depth of the 5/16"-18 threads? Are the studs too long? Neither, so what is it? Turns out, the manufacturer was short about two-and-a-half 5/16"-18 threads. Now what? (New paragraph for breath.)

"So," he asks himself, "do I own a American Standard die that will work for this?" I don't own a lot of dies and was pessimistic. Searched the normal spot. Nothing. Searched an unlikely spot, EUREKA! There it was, siiting in the die handle. Would it spin onto the stud thread? Yep (but you knew that). Figured an 1/8" of non-Whitworth thread wouldn't hurt anything. Ran a test on an old stud (one that holds crankcase halves together  *smile*). That worked, so, on to the stainless, for which I had no threading experience. A bit surprised that it  felt about the same as the carbon steel.

To end the story, it worked. YAY. Another surprise was how critical is the length of those studs and the threading.

RIchard L.
Title: Re: Crankcase Studs
Post by: berger on 13.02. 2021 17:34
i have had some bad results when extending an existing thread on stainless bolts, sometimes the die would dig deep leaving one part of the bolt having a shallow thread. I did use plenty of cutting compound. now I open up a split die to just start a shallow thread then increase the pressure on the die to cut a bit deeper, it takes time but this method cuts the thread evenly. don't ask why some of my threading ended up sort of one sided because I am not an engineer , perhaps the real engineers will know.
Title: Re: Crankcase Studs
Post by: RichardL on 13.02. 2021 19:20

Thanks for your comments, after reading them I was thinking of posting a picture of the threads,  but decided I didn't want to remove the studs again. Getting them installed involved creating thin nuts to run them down, otherwise there wasn't  enough thread available to double-nut. I did look at the thread under magnification and saw no alarming difference. Nevertheless, I gently ran a thread file over the whole thread. Unfortunately, I didn't have the luxury of a split die to consider.

Richard L.
Title: Re: Crankcase Studs
Post by: RichardL on 13.02. 2021 19:44
Oh, another thing about removing and reinstalling these studs. The length of thread I ended up with was not a precise factory value, the perfect installed depth had to be checked and rechecked to be sure the protrusion on either end of the stud did not hit the mounting plates.

Richard L