I replaced my water pump on my X-Type 3.0 the other day, and while I was putting the larger pulley back on that drives the belt, I accidentally snapped the head off one of the three bolts holding the pulley to the shaft, right where the threads start. The pulley seemed secure with two out of the three bolts left, so I haven't done anything about that third bolt. I have put about 300 miles on the car since then, and the other two bolts have stayed solid so far, but I'm wondering if it is safe to leave it that way or if I should try to replace that bolt.

I attached a picture of the pulley highlighting which bolt it was.

I'm a college student with limited tool access and financial resources so I'd prefer to leave it if I can, I just don't know if I'm taking too big of a risk.

Any advice is appreciated, Thank You!

 

Luke, in a situation like this, running with only 2 of the bolts is fine under normal situations. Would I be recommending high RPMs? By no means. Part of what goes into how many bolts are needed for a given joint (ie, where the pulley attaches to the water pump) is what is referred to as N+1. Ie, if a joint requires say 4 bolts (N) of a given size to keep things together under normal conditions, then you design the bolt with 5 or more. Running only at 4 will push the bolts to their limits and under unusual conditions, may result in the bolts breaking. So, in this case, you are running on "the edge". Keep things sane and you should be good. Granted, I would also not recommend running a long time this way.

 

I am not sure that it is a good idea to run this way for long. The pulley looks to be plastic. Therefore it flexes much more than a metal one. The N+1 logic breaks down at low numbers. Will something that requires 2 bolts work with 1? Using only 2 bolts on something designed for 3 seems to be pushing it. Getting at the broken off bolt does not seem to be too hard if you remove the battery and it's box. If there is a little bit of the bolt sticking above the flange you might be able to cut a slot with a hack saw or a Dremel tool. Then use a screw driver to back it out. If not, you can get a reverse drill. These are just like ordinary drills but have their twist reversed. You reverse the direction of the drill to use them. Once the drill starts to cut often the snapped off bolt will come out on it's own. Pete.

 

My worry would be the unbalance in the camshaft, I would fix it asap, but would drive the car still and baby it a bit.

 

jagger, the N+1 logic does break down at the extremes. While it is still fairly accurate with 3 bolts, it is meant more for 4-8 bolt applications. I guess you could look at it from a 25% loss aspect too. That may be a bit more realistic and have a broader application. The real answer would be to start looking up the tensile stress charts for various bolts and then figuring out the stresses on the water pump. But that is way beyond what most of us have sitting in our garages. Hence why I use the N+1 rule. Simple, yet will keep you safe in most cases.

 

It is not the bolts that I worry about it is the plastic of the pulley. A very small mount of movement under a bolt on a steel pulley will not wear the surfaces as they jiggle. With plastic rubbing against steel the wear will be much greater. Further, the flexing of the pulley hub with 2 bolts will be much greater than with three. Plastic cannot withstand such flexing like steel can. My point is that such guesses that we all make about the abuse of steel may be way out of line with plastic. Pete.

 

Thank You all for your input. The pulley is actually metal, not plastic, so I am not worried about it breaking. I will try and get that broken bolt out and replace it when I can, and I'll baby it until then. The other 2 bolts have not gotten any looser, and I haven't felt any extra vibration from the unbalance, but I'll keep an eye on it.

 

jagger, if the pulley moves, it is going to snap the other bolts. If you are worried about an imbalance, it is going to trash the whole water pump as the bearings are going to have to give to cause the impeller to move. Now you have a big leak on your hands. Besides, the bolts are in close enough that the loss of a bolt head will not significantly affect the balance as the bolt head's weight is very small to the rotating mass.

Besides, there is a "decent" gap between the impeller and the casing. If the impeller starts hitting the casing, you have much bigger issues. With centrifical design pumps, they need a certain amount of gap to allow for shutoff head flow back and around the impeller. The Navy taught me way too much when it came to how pumps are designed and what certain things can endure. But then, when you are in the middle of the ocean trying to get the nuclear reactor back up and running, you don't want someone just "winging it".

 

Curious as to how the bolt/stud snapped off in the first place?..I would get it fixed soon...

 

If you have a drill, easy-out, and a tap, the job shouldn't take more then 20 minutes, and will get rid of all the dooms day predictions. Finances shouldn't really be taken into account here, nor predicting the future. If there was one more bolt, I would say run with it. Right now you are stressing the large pulley, and it will fatigue to a point where it will break. That belt is tight, as I remember. Financially, you will end up putting more money into the car when the pulley breaks, just by down time, and possible engine damage. Risk and crisis management were my job, before I retired. With only 2 out of 3 bolts holding the pulley on, it is not logical to push a bad hand.......FIX IT......Mike

 

Today I was able to use an easy-out bit to pull it right out and replace it, the whole process didn't take more than a half an hour.

It has been about three weeks since the bolt broke to begin with (I over-tightened it), and since then I have put about 500 miles on the car with no unusual vibrations or irregularities, but I was trying to keep the RPM's as low as possible and baby it.

 

Luke: Glad you were able to replace the broken bolt. College is where many of us first learn how to repair our cars. A thin wallet is a huge motivator, and this forum is an excellent place to learn from others.

Rest assured you did no damage driving ~2 weeks with one broken bolt in the water pump pulley, for two reasons:

1) The pulley bolts don't strain against the tension of the water pump belt. That job is done by the hole in the center of the pulley and the circular flange on the end of the camshaft that mates with it. The bolts simply hold the pulley tightly against the circular flange so the flange can bear most of the load. Lug nuts on wheels serve the same purpose: the weight of the car is supported not by the lug nuts, but by the hole in the center of the wheel mated with the circular flange on the end of the hub.

2) The missing bolt caused an insignificant imbalance in the pulley and camshaft, less than 0.2 pounds / 0.1 kg centripetal force. That's peanuts compared to the constant sideways pull of the water pump belt.

The more important lesson you learned is not to over-tighten bolts, which is particularly easy with small bolts. The JTIS spec for the pulley bolts is only 11 Nm / 8 Ft-Lbs and only 10 Nm / 7 Ft-Lbs for the water pump bolts. That's hand tight. If you don't have a torque wrench, most auto parts stores will lend them. I prefer using a short 1/4 inch socket wrench on these small bolts. If you have only a 3/8 inch socket wrench with a longer handle, grab the handle close to the head when tightening small bolts.

The Internet didn't exist back when many of us learned to repair our first cars. But you have this great advantage, so ask away and the good folks here will help where we can.