question on studs for fan and water pump on a 69 sb 350/350

[Michael L.]

Guys,

I'm trying to bolt together the pulleys, fan, and fan clutch on my 69 sb 350/350 and I have a question on the type of studs used to do this. My fan clutch has the 5/16 coarse threads, while my water pump has the 5/16 fine. According to my AIM studs were used on both of these items, although it appears that the studs used in the fan clutch must have come from the manufacturer already inserted (thanks Terry!) since there is no part number listed there. I have two types of studs I can use: one are the studs that I had refinished with all the rest of the cars hardware, (although I don't know where they came from on the car), and these have 5/16 coarse on one side and fine on the the other. The other studs I bought from one of the vendors, although they were sold as fan clutch studs but since they are 5/16 fine on both sides they don't work for my fan clutch but could work for my waterpump but I'm not sure if they are long enough. For the studs that have two different threads, the unthreaded portion of the stud has me concerned that I won't be able to get the fan tightened correctly because I think the nut MAY bottom out on the threads before reaching proper torque. I attached a pic of the two types of studs. Can anyone enlighten me on what the stud set up was on these cars? Thanks.

Mike

[Mark E.]

Re: question on studs for fan and water pump on a 69 sb 350/350

The stud on the left (with two different threads) connects the W/P hub to the clutch. You shouldn't have any issues with the threads bottoming before the clutch is tight.

I'm probably going to now learn about fan-to-clutch studs. My car currently has bolts installed, but I just checked the AIM and lo and behold, it shows studs and nuts. If studs are "correct" the one on the right in your photo looks about the proper size. But that's a guess.

[Joe L.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Guys,

I'm trying to bolt together the pulleys, fan, and fan clutch on my 69 sb 350/350 and I have a question on the type of studs used to do this. My fan clutch has the 5/16 coarse threads, while my water pump has the 5/16 fine. According to my AIM studs were used on both of these items, although it appears that the studs used in the fan clutch must have come from the manufacturer already inserted (thanks Terry!) since there is no part number listed there. I have two types of studs I can use: one are the studs that I had refinished with all the rest of the cars hardware, (although I don't know where they came from on the car), and these have 5/16 coarse on one side and fine on the the other. The other studs I bought from one of the vendors, although they were sold as fan clutch studs but since they are 5/16 fine on both sides they don't work for my fan clutch but could work for my waterpump but I'm not sure if they are long enough. For the studs that have two different threads, the unthreaded portion of the stud has me concerned that I won't be able to get the fan tightened correctly because I think the nut MAY bottom out on the threads before reaching proper torque. I attached a pic of the two types of studs. Can anyone enlighten me on what the stud set up was on these cars? Thanks.

Mike

Michael------

It's the stud on the left PROVIDING that you know this is an original or replacement water pump to fan clutch stud. That's because these studs were GM 300M material grade (SAE grade 8). Carburetor studs are of a similar configuration but are rarely of SAE grade 8. However, given the phosphate finish on the stud, it's most likely the correct stud.

[Michael L.]

Re: question on studs for fan and water pump on a 69 sb 350/350

OK Joe so can you tell me what type of stud was used on the fan-fan clutch? I do have six of the stud on the left so I can do wp-fan clutch and the short side of the carb but then I need studs for the fan-fan clutch. Remember that the threads on my fan clutch are coarse so the stud on the right won't work on it, but they would work on the wp-fan clutch, I'm just wondering if they might be a little short but they are pretty close to working. I suspect the nut will be able to have full thick bite on them with about a 1/4 inch of thread (4-5 turns) being in the wp flange. Can anyone tell me anything about what type of ztuds are used on the fan-fan clutch? Also keep in mind that I had the studs refinished so not sure we can rely on the finish of the studs for much.

[Mark E.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Remember that the threads on my fan clutch are coarse so the stud on the right won't work on it, but they would work on the wp-fan clutch, I'm just wondering if they might be a little short but they are pretty close to working. I suspect the nut will be able to have full thick bite on them with about a 1/4 inch of thread (4-5 turns) being in the wp flange.

Are you asking if the stud on the right can be used for fastening the clutch to the water pump? The proper studs for this look like the ones on the left, so use those.

[Mark E.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Michael------

It's the stud on the left PROVIDING that you know this is an original or replacement water pump to fan clutch stud. That's because these studs were GM 300M material grade (SAE grade 8). Carburetor studs are of a similar configuration but are rarely of SAE grade 8. However, given the phosphate finish on the stud, it's most likely the correct stud.

Joe,

I've never made that distinction between water pump and carbureator studs before. Thanks for pointing this out.

Can the grade of the stud be determined? Does a phosphate finish strongly suggest grade 8? I'm asking because I replaced these studs, but didn't look for a grade 8 specification.

[Michael L.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Are you asking if the stud on the right can be used for fastening the clutch to the water pump? The proper studs for this look like the ones on the left, so use those.

Mark,

No I understood from your and Joe's posts that the one on the left is for the wp-fan clutch. What I'm still asking is what does the fan-fan clutch stud look like?

[Joe L.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Joe,

I've never made that distinction between water pump and carbureator studs before. Thanks for pointing this out.

Can the grade of the stud be determined? Does a phosphate finish strongly suggest grade 8? I'm asking because I replaced these studs, but didn't look for a grade 8 specification.

Mark------

There are no markings I am aware of on the studs to specify material grade. A phosphate finish does imply a grade 8 but it's not a guarantee of it. The only way to know, for sure, is to have studs of a known GM part number or have aftermarket studs of a known material grade. After the studs are separated from the car or separated from their package I don't know of a practical way to determine material grade.

[Joe L.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Mark,

No I understood from your and Joe's posts that the one on the left is for the wp-fan clutch. What I'm still asking is what does the fan-fan clutch stud look like?

Mike-----


The original studs used in the fan clutch for clutch-to-fan blade attachment were supplied to PRODUCTION and SERVICE as part of the fan clutch assembly. They were entirely 5/16-24 thread and, on original clutches, were phosphate finished. Later SERVICE fan clutches often have zinc plated studs. I do not understand why your fan clutch has 5/16-18 threads but I suppose it means its a SERVICE fan clutch of some sort. It does not really matter; no one will ever know what the internal threads are. You'll just need to obtain some studs with different thread on either end.

By the way, I should have mentioned, early 1969's used bolts for attachment of the fan clutch to the waterpump. Just when the change occurred, I don't know. I know that my mid-September, 1969 built car had studs.

Also, when the studs are installed in the waterpump hub, they need to be installed so that 7/8" of the stud is outboard of the hub. That may not be the same thing as running the stud down to the end of the fine threads.

[Michael L.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Joe can you tell me what the studs holding your fan to your fan clutch look like on your 69? Looking to see if they are identical to the wp studs and if not what kind of thread is on the nut side (f/c?) and approx how long do they project out from the fan. If identical to wp studs I would expect them to project out quite a ways past the fan. As always your help would be greatly appreciated.

Mike

[Joe L.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Joe can you tell me what the studs holding your fan to your fan clutch look like on your 69? Looking to see if they are identical to the wp studs and if not what kind of thread is on the nut side (f/c?) and approx how long do they project out from the fan. If identical to wp studs I would expect them to project out quite a ways past the fan. As always your help would be greatly appreciated.

Mike

Mike------


My original fan clutch is stored away in my "used parts" section and difficult to access. I can tell you that they are not identical to the waterpump studs, though. I cannot say what the thread in the fan clutch is as I have never removed these studs. However, I believe that the thread is 5/16-24. I believe that fan clutches of the period typically used fine thread for the internal threads. Like I previously mentioned, it makes no difference as no one can see what thread pitch is (that's why I can't tell you for certain what it is). As I recall, the amount of exposed stud is about 3/4"-7/8".

By the way, if you were to install studs with 5/16-18 thread into your fan clutch and any of those threads could be seen after full installation, then the 5/16-18 end of the studs is too long and needs to be shortened.

[Michael L.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Thanks Joe. As I mentioned my fan clutch is 5/16x18. I spoke with Dan Kirconnel (?sp) who restored my fan clutch and he said the 69's were typically the coarse threads. The wp dual thread studs sounds like they would work given how much exposed threads you recall seeing. Your right the thread size in the fan clutch doesn't matter but i suppose its possible that if originally the studs were a two thread type then the exposed threads would have been 5/16x24 as you recall seeing on yours. I'm thinking I would order wp studs with the two thread types from one of the vendors and see if I can make them work.

Mike

[Joe L.]

Re: question on studs for fan and water pump on a 69 sb 350/350

Thanks Joe. As I mentioned my fan clutch is 5/16x18. I spoke with Dan Kirconnel (?sp) who restored my fan clutch and he said the 69's were typically the coarse threads. The wp dual thread studs sounds like they would work given how much exposed threads you recall seeing. Your right the thread size in the fan clutch doesn't matter but i suppose its possible that if originally the studs were a two thread type then the exposed threads would have been 5/16x24 as you recall seeing on yours. I'm thinking I would order wp studs with the two thread types from one of the vendors and see if I can make them work.

Mike

Mike------


There's no doubt, at all, that the exposed threads are 5/16-24. That's for certain.