Engine/Transmission (1994 - 1998) Head Bolts..are they reusable???

[oldfartnumber6]

I am confused about the reusability of 2nd generation 12 valve (1997) head bolts. My factory manual does not say anything about replacing them but the torque specs ( last step is turn 90 degrees ) sounds like a torque to yield spec. Any experience would be helpful....Thanks

 

[Bob V]

Just turning a bolt an extra amount does not mean it is torque to yield. In a way, it is similar to using bolt stretch to set to fastener to the proper preload, which is more accurate that a torque wrench. There should be a dimension for the old bolt length, if they are longer than that they are stretched and need to be replaced. Some have good luck with the stock bolts, but most will tell you you need studs. ARP are a popular option but there are others. I personally think the stockers get a bad rep and if installed correctly with a retorque that will work fine in most applications. If you need new ones aftermarket studs would probably make the most since.

 

[chipster]

I am confused about the reusability of 2nd generation 12 valve (1997) head bolts. My factory manual does not say anything about replacing them but the torque specs ( last step is turn 90 degrees ) sounds like a torque to yield spec. Any experience would be helpful....Thanks

the head bolts after `90 or so, I forget the exact date, on Cummins engines use the torque ANGLE to set the correct preload. they are NOT (TTY) torque to yield bolts. they are marked with 12.9, tq.+< 90 on top of the bolt head. if they are NOT marked like this, do NOT use the torque angle on them, they will break. you can use the newer bolts in earlier engines with the torque angle spec. after you set the bolts to the primary torque, to settle the gaskets, the final 90 degree will stretch the bolt the required distance. the primary torque is NOT enough to stretch the bolt any measureable amount. it dose not matter what lube, type of torque wrench, how clean the threads are, or any other variables there are. because they know the thread pitch, they know how far the bolt will stretch for a given angle of rotation. cummins bolts are reusable if they are within the free length given in the service manual or the stretch gauge in the gasket set. all engine manufacturers ,these days, use the torque ANGLE, or TTY to tighten all critical fasteners. the TTY WILL STRETCH the fastener beyond its ability to return to its original length. it will hold the load until you loosen it. then you throw it away. usually the new gasket set will come with new bolts or have a warning in BIG letters to get new bolts if they are TTY. if your bolts are within the free length specification, reuse them. if they are right on or longer than specs, replace them. I saw a test by GM. that showed the clamp load on torque angle bolts were always within 3,000 PSI.from bolt to bolt. the clamp load of bolts tightened with a torque wrench would vary 15,000 to 20,000 PSI. from bolt to bolt. depending on how clean, type of lube, type of torque wrench, and the mechanics skill level.

 

[surfbeetle]

Chipster's explanation sounds great to me, I just wanted to add that the added cost of replacement bolts seem negligible compared to the potential problems that can be had if the bolts fail. We had a diesel VW Rabbit years ago that had the engine rebuilt but the shop did not get new head bolts, what a pain that was when the cooling system started to get pressurized and the car overheated due to the stretched bolts.

 

[Joseph Donnelly]

I have reused head bolts over and over. I torque them in steps 30-60-90-115-recheck at 115 to 120. Oil on threads and under shoulders, letting them drain first. You don't want the oil on them, or anything left in the holes to get pushed onto the deck. I checked the angle method about 15 years ago and decided that for used bolts anyway it was not accurate enough. I never had trouble with the above torque sequence, following the factory pattern as to which bolt gets torqued next.

 

[oldfartnumber6]

Gentlemen....Thanks a million for your educational replies....God I love this forum...Again thank you....Oldfartnumber6 AKA George.

 

[ewcmr2]

Cummins head gasket kit comes with stretch gauge. If original bolts are in spec they are reusable. If they have stretched too far it's time for new ones.