Alternator Bracket Problem...Need Help

[Gramp'sGold70K20]

When I installed a new GM 350 Crate engine along with new water pump and alternator I used the old bracket for the alternaor. It looked like the belt wasn't aligned so I spaced it with a couple of washers and used new grade8 bolts. Alignment looked perfect and couldn't detect any vibration. Unfortunately, the lower bolt sheered off in the block. The bracket dropped down and the alternator sliced my powersteering hose. All this happened when I was going about 65m.p.h. getting on the highway. It wasn't a pretty sight. The other belts seem to line up just fine. What have I overlooked and what is a good method to ensure the belts are aligned properly? Is it my new alternator causing the problem? My old Bracket? Where do I start?

[pjmoreland]

I'm thinking that if you have washers between the head and the alternator bracket, the alternator bracket is no longer sitting flat against the head and is not supported very well anymore and the bolts are being overloaded. Instead of just being under a shear load, the bolts are now under a bending load. I don't think it's a good idea to have those washers between the bracket and head. If you absolutely have to space the bracket out, then I'd recommend fabricating a spacer plate of the correct thickness that is the same size as the front of the head so that the bracket is completely supported.

[55454]

Can you post a pic, thats incredible that you sheared a grade eight, I would like to see the lower pully, is it a short set up. It the alt in the first position, closest to the motor. Was this exact same set up on the older motor w/o problems.

Thanks Tommy

[GloryHound]

By adding the washers as spacers you could very well have over engineered it and by using grade 8 bolts you are lucky you did not end up with any damage to your heads as they could have ended up being the weak link. Some times when you start aligning all these belts up perfect while the motor is not being run you can forget about how the centrifical forces can alter alignments. The origional GM engineers were 10 X smarter than I and if they designed a bracket I'll bet it has all the proper alignments for the application. So unless you have peice mealed your bracket set up together or one of your brackets are bent you really should not need any spacers. Something alot of people forget about also is that the different grade bolts all have their proper place. It is not always better to have a higher grade bolt. Sometimes a lower grade bolt is used as a weak link protector to avoid more costly damages. While other times the lower grade bolt is used to allow flex however minor it may be.

[mrein3]

I bought my truck in 1994. Since the day I got it I've had one or the other alternator bracket to head bolts shear off at random. I tried grade 8 bolts too but remember they are more brittle so they will shear quicker than a 5.

I put a new engine in last summer, finishing in the fall. I didn't drive it much over the winter other than across the lake so it didn't really get tested until this summer. And once again I sheared off a bolt.

I finally took off everything from the front of the engine and started it up. The harmonic balancer doesn't wobble.

Then I put on the crank pulleys. They wobbled around like crazy. Upon closer inspection I realized there were washers spacing out the crank pulley. They were there when I bought the truck so I always re-applied them when I worked on it. This time I took them off and cleaned up the back side of the pulley. There is much less wobble but some is still there.

When I put it all back together I didn't use any spacers behind the alternator bracket and I used grade 5 bolts to attach it.

So far so good.

[Gramp'sGold70K20]

All of your answers have been very helpful! I will post some pics on Sunday. I don't even have time to work on it today. I used the original brackets and pulleys from the old engine. I don't remember anything between the head and the bracket on the old engine. I thought it was just a minor difference in the head because it was new. (The old engine was gone before I could compare it). I think I'll do the same thing and start at the balancer and crank pulley for wobble and work my way up. I would like to avoid spacers or fabricating at all costs. Thanks for the info on the bolts. I will go to a grade 5. I'll post progress pictures. I'll double check that bracket and make sure it is not bent too.

[kaycee]

When re-installing 2 pulleys together there is a certain way to mate them there is a hole with a lip that fits into the other pulley that is just a we bit bigger to accept this lip.Hope this is not to confusing the way I explined it.

[Gramp'sGold70K20]

Thanks for that bit of info.

[55454]

Gloryhound,

I totally agree with that, a bolt strength has a correct application, sometimes I wonder when I see a truck full of stainless bolts. I usually look at the lines on the head of the bolt and replace it with the same.

Tommy

[GloryHound]

55454,
I don't think most body bolts have much in the way of stress on them and using stainless is one way to make disassembly a little easier in the future if needed. As for the engine, I would think you would be good to go if you went with a kit from a company with a good rep. They all have their engineers and computer models to run simulations with and I'm sure they put hours of testing into those kits before making them available to the general public. The big thing is don't go to ACE Hardware and try to by new stainless steel motor mount bolts, as these have not been properly tested for that aplication. I work on power plant generators and if I need a new bolt I have to order it through my company. While the customer or owner of the generator may not like the price tag of a couple of hundred bucks for a 1 1/2" X 5" bolt that he says is the same as the one he can get someplace else, the only way my company is going to garantee the unit will work is if they use our bolt. The customer can tell us to use a cheaper one he found, but this gets documented and signed by the customer as a change at his request and releases my company from liability for any damage caused by defects in that part. I know we are not dealing with multi-million dollar generators here, but we are dealing with our pride when we take these trucks for cruises and shows or when we put them to work and pride is something that is hard to put a price tag on.

[jamis]

Sorry to have to disagree with some of you on the bolt issue and this is just my opinion base on my experience. I think the problem is more the use of washers then the bolt being too hard. I was in the engine machining and building business many years ago and have built hundreds of engines without ever seeing a bolt failure because the bolt was "too hard".
Just because an engineer put a grade 5 bolt there does not mean it is what is best. A lot of the time, cost of production wins over service life. We have a large fleet of Peterbuilt trucks that keep snapping the gearbox bolts. Someone will get hurt or killed one day. None of the engineers can come up with a solution, we have tried every bolt ever made. The problem is in the gearbox not the bolts. But the pride of the engineers wont let them admit it or the bean counters at the factory wont recall them till some one is killed and family sues them.
Here is a little chart to show you the different bolt grades.

[55454]

I do not have any bolt experience but I am truly learning, I also agree that cost plays a role and I was thinking a grade five would break before a grade eight in the same application. I personally would never use stainless on a suspension if I replace a bolt I use the same grade that is there. I think stainless bolts are great and would like to use them more but dont because of lack of knowledge.
I have a 1955 chevy car and someone told me 25 years ago the gear box bolts were a certain grade so they would shear in an accident. I am sure most of you know the factory wheel is made similar to a harpoon. Thats why I was wondering if grade of bolt does matter in some applications. I am a novus at this and any enlightening will be appreciated.

Tommy

[Fred T]

As the chart says, bolts are graded with tensile strength, meaning the load is pulling the length of the bolt. Shear strenght is a different function, which is a load trying to slice across the bolt. Shear calculations require figures for the surrounding structure and materials. Shear strength is generally less than tensile.

Brittleness. The higher the number the more brittle a bolt is. However, the difference in most applications will not cause a problem in most automotive applications.

Use of bolts. Grade 2 is a good grade for most woodworking joints. Grade 5 is a good, all around grade, in automotive applications is the preferred fastener. Grade 8 is usually reserved for high strength applications, with a few places grade 8 are required. The best rule of thumb is to replace a bolt with one of a similar grade.

Stainless steel. If the bolt is an import or is from a hardware store it is should be considered as grade 2. Some US companies are making grade 8 SS bolts. I am not afraid to use the US made bolts, but precautions must be taken to prevent galvanic corrosion and thread galling.

[jamis]

Originally Posted by Fred T

As the chart says, bolts are graded with tensile strength, meaning the load is pulling the length of the bolt. Shear strenght is a different function, which is a load trying to slice across the bolt. Shear calculations require figures for the surrounding structure and materials. Shear strength is generally less than tensile.

True that it is different. The point I was trying to make is the higher the tensile strength the higher the shear strength. This is the formula for shear strength. I should have given this first to show that a grade 8 bolt has more shear strength then a grade 5. The myth that a grade 8 bolt is brittle and will shear before a grade 5 is just plain untrue. Brittle is a relative term. Brittleness in bolts is defined as failure at stresses apparently below the strength of the bolt material with little or no evidence of plastic deformation. Typically, fasteners are not brittle below 180 ksi ultimate tensile strength. Grade 5’s have an ultimate tensile strength of 120 ksi and a grade 8 fastener has an ultimate tensile strength of 150 ksi.

A = Cross-sectional area of the fastener size (since bolt bodies/shanks have circular cross-sections, use area of a circle) = Pi x r2 where R (radius) = .250/2 = .125, therefore A = Pi x (.125)2 = .0491 square inches (in2)

Using a .250-inch diameter grade 8 fastener gives you the following shear capability:

Capability in shear = 91,000 lbs / in2 x .0491 in2 = 4468 lbs


Using the same .250-inch diameter grade 5 fastener results in the following:

Capability in shear = 75,000 lbs / in2 x .0491 in2 = 3683 lbs


Hell no I didnt know these formulas off the top of my head. I had to do some work to find them for you.

[jamis]

Originally Posted by 55454

I have a 1955 chevy car and someone told me 25 years ago the gear box bolts were a certain grade so they would shear in an accident. I am sure most of you know the factory wheel is made similar to a harpoon. Thats why I was wondering if grade of bolt does matter in some applications. I am a novus at this and any enlightening will be appreciated.

Tommy

Yes Tommy if a bolt is ment to fail with a certain force then it should NOT be replaced with a harder bolt. I lot of service manuel indicate these bolts as LOW SHEAR meaning that a low tensile strength is recomended. There are a few that I know of like the shear bolts on bushhog mowers. I never heard of the gear box bolts on the 55, but that makes good sense in that situation.

[cdowns]

back to the original question, sounds like your water pump pulley isn't sitting down correctly on the flange of the water pump// i've been using aircraft grade stainless for mounting altenators for over 40years never had a problem with them

[Gramp'sGold70K20]

Wow! Great info on bolts! I believe I will go back to the bolt for the proper applicaion in this case. Sorry I forgot my camera when I went to the shop.

Pulled everything off and found a little wobble in the harmonic balancer and lower crank pulley. I purchased a new balancer. I think I am going to replace the crank pulley. cdowns, thanks for your insight regarding the water pump pulley. I will make sure it is seated properly during the install. Plan to replace it as well.

Any suggestions on a pulley setup? I can't seem to find the 4 groove pulley that I have on my engine. Is there a reason for the 4 groove pulley system or can I convert it to a 3 groove pulley system?

My job takes me out of town until next Sunday, so it looks like the truck will have to wait. At least I'll have my computer with me to look at this sight!

[pjmoreland]

One thing that mrein3 mentioned in his post awhile back about his alternator bracket bolts snapping was that it was a whole lot more difficult to drill a snapped off grade 8 bolt out of the head than a grade 5.

[55454]

Thanks for any info directed towards me, The 55 thing may be a myth I can always look at the bolts and post the grade.

Going back to the question, I have never seen a pully with four rows on something older than 72, do you guys think this can be throwing off the alignment. I have seen an a/c,p/s, alt, 67-68 and possibly 69 with the three slot cast pully on the water pump, and four postions on the bottom with no pully in the second postion from the engine. Could the alignment be off because of that pully?

Thanks Tommy

[cdowns]

4groove isn't needed use 3groove if you have ac///also what type alt bracket are you using?? this pic of the bracket for a 71-2 with the stock short water pump maybe it was used in other years also but i'm not sure of when

[mrein3]

Originally Posted by pjmoreland

One thing that mrein3 mentioned in his post awhile back about his alternator bracket bolts snapping was that it was a whole lot more difficult to drill a snapped off grade 8 bolt out of the head than a grade 5.

This is true, an 8 is harder to drill than a 5. But remember the bolt in the head holding that bracket isn't bottomed out so it usually comes out with a flat blade screwdriver. This last time I used my smallest easy out. When I was drilling with the small drill bit I noticed the hunk of bolt started to turn in. When you see this happen you know it is coming out easy.

When I worked my way through college at the local repair shop my boss was able to get "left hand drill bits". Those things rock for taking out broken fasteners. You put your drill in reverse and start drilling. Most of the time the broken bolt walks out when the bit catches a burr. If it doesn't you just use the hole you made for an easy-out.

Anybody know where I can get my hands on a left-hand drill bit?

[55454]

That would be 69-72 truck, I dont know if he has the 68 below or late 69 above I guess pics would tell all. The three pully will work with this altenator bracket. On the parts board some one had the same problem. The early 69,68,67 have a different set-up. Gramps you may have mixed pully's thats why I asked how did it work previously.

Also is the balancer back all the way, can you measure from the timing cover to the edge the balancer on both, oh well I will wait for pic's. Can some on post a pic of the correct set-up for 1970. Is the balancer for a internally balanced motor or externally.

EDIT: a small block 400 is external also 454, balancer and flywheel are not the same as 396,350,402, etc..

Tommy

[GMC AMI]

Sounds like the crate motor has a long waterpump and your brackets are for the short
original waterpump.

[Gramp'sGold70K20]

Everyone has been very helpful so far. I really wish I was in town to post some pictures!

cdowns (#16): I measured my water pump and it is 5 7/8 from the back to the front flange. I assume this is a short pump.

cdowns (#20): The bracket in that post looks exactly like mine.

mrein3 (#21): I used a small punch to mark my drill point. when I started to drill the bolt started to turn in. It came right out with an easy out. I hardly drilled a hole at all. I got pretty lucky. I will ask our aircraft mechanics if they know where to get those left hand drill bits.

55454 (#22): I never had this problem on the old engine. The new motor hasn't been in for more than 4 months. The other belts for the a/c and p/s looked like they lined up pretty well, but I was adjusting the tension maybe once a month. I didn't give it much thought because it was a new engine and all new belts. I figured they were just stretching a bit. Also, when you ask if the harmonic balancer is back all the way. How far is all the way back? I thought is was pressed on all the way, but maybe not. There is 1/2" space between the timing cover and the balancer. How close should it be? I will make sure it is the correct distance with the new one. A picture of the this might be helpfull too.