Loose header bolts
Loose header bolts
(OP)
The bolts that hold a set of headers on a 350 V-8 won't stay tight. I have tried tightening them when the engine is hot and I have tried different grade bolts but they still come loose. Any suggestions?





RE: Loose header bolts
Stock cast iron manifolds are thick and hold the flat machined face well, so no gasket is used. But light headers don't hold, so you may have to try and find a harder gasket.
RE: Loose header bolts
RE: Loose header bolts
I suspect the bolts don't actual back out, the gasket just crushes. If they don't squeeze the gasket, they can easily leak and burn out.
The SMC seems very bad in this regard in those 2 center cylinders-at least in my experience.
RE: Loose header bolts
I am not too up on current American V-8 engines but a long time ago I used a set of special bolts that incorporated small "E" clips to secure them after installation. They worked great. I just don't remember which mfgr. supplied them. I was at "Dougs" last year and all they use are standard socket head capscrews. ???????
On my race engines I use studs and bronze(berillium)(sp) lock nuts when I can get them. SS nuts and spring washers have, on occassion worked but great care and proper anti sieze must be used to keep them from galling and thus becoming impossible to remove.
In addition, as Metalguy points out, as the gasket takes a 'set' it would be a good idea to re tighten the bolts.
Unfortunately, you may end up doing this several times.
Also, the newest headers have 3/8 plate flanges that are less prone to this problem. 1/2 inch plate flanges are available on special order but are difficult to install in some cases.
Rod
RE: Loose header bolts
Blacksmith
RE: Loose header bolts
RE: Loose header bolts
"One of the misunderstood aspects (and I've as guilty of this as anyone!) of bolts is that they should be stressed to about 90% of their yeild strength. This slight deformation helps prevent loosening. If you use too high a grade bolt, you can't get this before you crush the substrate (in this case the header flange) or strip the mating threads"
Good thinking, but I think you'll find that the reason for the high stress it so that any "applied load/stress" will always be less than the preload.
For example, correctly tightened cylinder head bolts do not see a varying load (except slightly) as the cylinder fires. People find that hard to believe, but what happens is that the GASKET sees the varying load, but the bolts "don't know" where all that load comes from, preload or firing loads. The stress on them remains almost constant unless the cyl. pressure/vibration exceeds the preload stress. This is why 2 skinny little bolts and survive while a big con rod fractures via fatigue-even a heat treated strong rod. The rod sees all that variance, but the bolts don't!
RE: Loose header bolts
Blacksmith
RE: Loose header bolts