tightening engine screws
 

I asked in the Glow Engine forums opinions about using a torque screwdriver to tighten engine screws. I was given a link to a site that suggest the following torque for head and cranckase screws. I would like to know if these values are ok for OS engines. I accidentally stripped some engine screws and would like to avoid that in the future.

Screw Size-------Torque

2.0 m ---- ------ 5-7 in-lb
2-56 ---- -------6-8 in-lb
2.5 mm ---------8-10 in-lb
4-40 -------------12-14 in-lb
3.0 mm ----------13-15 in-lb
5-40--------------14-16 in-lb
6-32 --------------17-21 in-lb
4.0 mm ----------20-24 in-lb
8-32 -------------22-26 in-lb

And Glow Plug : 20-24 in-lb ( slightly more in high rpm applications)


Thank you

RE: tightening engine screws
 

We'd not be able to state whether those numbers are correct. We've never seen any brand of engine that we serviced, except some of the gassers, where there was a specification by the manufacturer, and we've services quite a number of engine brands over the years.

RE: tightening engine screws
 

Bax, any idea why this is the case? Is it say, the metal changing over time?

RE: tightening engine screws
 

Why what is the case? Your question isn't clear.

The bolt holes usually strip because the bolts have been over-tightened at some time. Add to this an overheat, and the aluminum of the crankcase can be bonded to the threads of the bolt. With the weakening caused by over-tightening, and the heat, the aluminum can strip out the next time the bolt's removed.

Overheating can also help stripping because an overheat will overstretch the steel bolts. When the engine cools, the head's loose. If the head bolts are tightened when the engine's still warm, they'll be loose again when the engine cools. They wind up being repeatedly torqued a bit too much to prevent loosening, and the holes strip out as a result.