by bgsengine » Fri Jul 30, 2021 8:15 pm
I have seen it from time to time- even with short blocks.. but less frequently after I do these things:
1) chase all block threads (a worn tap works nicely, as it doesn't do any cutting, but breaks away carbon and corrosion - preferably a bottoming tap, or grind the taper off a regular tap) until a bolt will fully thread in and bottom out (and make sure the remaining length of bolt is considerably less than the head's thickness)
2) clean all bolt threads (or, I clean them and run them in by hand where they're supposed to go, making sure each bolt will fully thread into the hole it ends up in)
3) make sure head flange where bolt heads seat on are clean and level and have no burrs or raised edges (you can lap them with a flanged head bolt and valve lapping compound if needed)
4) make sure the socket you use has a nice snug fit to the bolt head (if the end of socket is splayed a little like impact sockets , or sockets used for impact duty, can get, they can slip over the aluminum "posts" of the head between fins and give false torque reading)
5) drop bolts in a pan of oil and then remove them and lay em on a clean rag and wrap em up and set aside, so they'll be perfectly oiled when you go to use em (typically I'll have head, block and bolts prepped before even beginning a rebuild or lapping/adxjustment/assembly portion of a valve job, so, they have plenty of time for bolts to "drip dry" into rag and leave a perfect film of oil on everything)
6) wipe bolt heads (not threads) as dry as possible before putting them in (unless specs call for oil on bolt heads, - dry heads vs. oiled heads will affect final torque by as much as 15% - 20%) then assemble and hand tighten (socket in your fingers, no wrench applied - that lets you discover any binding of threads) before snugging them down evenly (quarter to half turn at most usually) and then torque in sequence to specs, eliminates most cases Ive had of "loosening" bolts..
However, due to thermal expansion and gasket quality and consistency of the gasket itself, it is possible for bolts to get loose, after gasket has compressed, parts of it may not recover back the same amount as other parts of gaskets.. So, when I was doing Kohler K series rebuilding/blueprinting (I was doing 3 or 4 of them a day almost every day in our busy season, which is where I got my rep as an engine builder) I'd always go back and re-torque head bolts after initial run-in and cool-down before calling the job complete and turning in my work order. (often, this would be next day, as I would do 3 or 4 builds one day, start and run them in before clocking out, and let them cool overnight, but when it was a rush job, I'd at least wait til it was cool enough that I could hold my palm flat on the head & bolts for several seconds without discomfort - sometimes aided by shop air blowgun blowing through the inlet screen over flywheel)
How poor are they who have not patience. What wound did ever heal, but by degrees? - Iago (Othello Act II, Scene 3)
Some of the items you mentioned I already do, but there were a couple I do not (I will now)