Setting the correct .005" preload on a girdle

[Turboholic87]

I understand that the engine girdle needs about .005" preload on it for propper fiitup. Does this mean the gap between the girdle and the pan rail with the main studs tightened down or before everything is tightened down. The cat girdle instructions are useless and none of the threads are clear on this.

Thanks,

 

[pacecarta]

I understand that the engine girdle needs about .005" preload on it for propper fiitup. Does this mean the gap between the girdle and the pan rail with the main studs tightened down or before everything is tightened down. The cat girdle instructions are useless and none of the threads are clear on this.

Thanks,

the gap between the girdle and the pan rail with the main studs tightened down

 

[bison]

The clearance will vary a little side to side and it needs to be .004-.005 torqued down at the mains. You may need to mill the girdle on one side to correct the variance side to side since the factory block machining is not very consistent. This is common practice these days to get a very consistent clearance around the block to achieve equal pre-load when the studs are torqued down.

 

[Turboholic87]

From a bolted joint perspective if you leave a gap between the plate and the side rails most of the dynamic loading is absorbed by the bolt and not the abutment. Plus you have a prying action on the bolt. I think that is why so many people are having issues with some of the studs failing. Why not leave a very small gap say .001" so there is minimal loading on the studs? Has anyone ever tried this? I guess I just don't get why you need a gap there in the first place.

 

[ijames]

You want a gap that gets pulled down tight when you tighten the rail studs (or bolts) so that you are sure that the girdle is somewhere between neutral and acting like a spring pushing down on the main caps. If the rail was high and you tightened it down you would actually have the girdle pulling up on the caps and doing harm, not good. I think the 0.005" is just to make sure the girdle is slightly higher than the rail; I don't think there is actually much spring force involved. As for the loading on the bolt, the gap is eliminated when the rail studs are tightened, so while I'm sure the clamp force is reduced by the initial gap, again I don't think the spring force is that much so I don't think the clamp force is really lessened significantly.