shredjesse

So I paid a good chunk of change to have a 383 stroker engine built for my corvette. Given my garage is on the other side of the country (I will soon be returning) I was too limited on tools to attempt the job myself.

I got the engine back and installed, and there is now an issue where the belt for the alternator does not have enough tension on it and whines something horribly awful above 2.5k RPM. The shop acknowledged this issue existed and said the current bracket does not allow enough length for adjustability.

I went in to see what is going on, and after fiddling around a bit I noticed I have maybe 1" of adjustability total despite the bracket obviously being cut for more. If I adjust the alternator towards the motor (looser) I distinctly run the alternator into the bottom bracket that mounts onto the exhaust header... and I still have about 4" left on the upper bracket cut out for adjustability... in theory.

This lack of adjustability unfortunately prevents me from going with a shorter length belt, so that is not an option.


Alternator bracket length... may be incorrect bracket.

I noticed online most of the upper brackets I've seen have TWO holes to mount off of the water pump. The upper bracket I have only has a singular hole. I measured my bracket, and it measures out to 13.5" approximately.

Questions:
1- Could some one (or maybe a few people) check the length of their upper bracket and report back please? I'm guessing I've got the wrong length upper bracket and need a longer two hole upper bracket? Mine measures approximately 13.5" as I mention above.

2- I see a lot aftermarket bracket mounting kits. Most of them are low mount kits, or mid mount. I honestly don't know a thing about them. Would any of them potentially work with a 383 engine in a C3 corvette? No power steering or AC if that helps any.




Thanks in advance for any help. This is baffling me, and it really bums me out to have a great motor in this car that creates a migraine inducing screech if you even try and wind it up at all. Hell, I can't even do the speed limit on the highway as is!

shredjesse

I knew some one would suggest that! I wrote this in the description above. I believe you overlooked it, it's a key component to why I believe i have the wrong length upper bracket.

"If I adjust the alternator towards the motor (looser) I distinctly run the alternator into the bottom bracket that mounts onto the exhaust header... "

This means from all the way out, to until the alternator hits the bottom bracket. I have .5-1" of adjustability or so. That is not enough adjustability to go with a smaller belt, as the shop tried to do so before returning the corvette to me.

AzMotorhead

I may be wrong but shouldnt the bracket bolt to the back side of the alterrnator ear?
Also you make no mention of what year your car is
Then again you might be missing other brackets

shredjesse

Valid point! The car is a 1968 C3 Chevy Corvette, with a 383 stroker engine built for it out of the 350 enigne that was in it and it was from the factory a 327 but that engine is long since gone and the frame isn't even original so... not a numbers matching collectors item, heh.


I'm not sure I understand what you're saying about the bracket and where it should mount to. Could you maybe show me a picture?

shredjesse

Here's the best image I could find of a 350 engine that clearly demonstrates their upper alternator bracket setup. Their upper bracket appears notably longer than the one I have in my corvette.

mysixtynine

Maybe a larger diameter pulley on the alternator (under driven) or maybe the waterpump pulley or crank pulleys arent right.

Was this how it was when you had it as a 350? Of course the header mount style is not factory so you deal with issues like this when you use aftermarket stuff.

Maybe jegs or summit can get you something that would make the diameter of the pulley larger resulting in tighter fit to make up the 1/2" u need.

augiedoggy

I recently tried replacing my chromed long upper support that came on my car with a mr gasket one and found it to be too short....
Someone either swapped one of your brackets or you don't have it together right.....this is one of those cases where Googling for images does wonders...

I'll admit with tall valve covers and headers myself I had a hell of a time finding just the right sized belt.... I have about a half inch between the valve cove and alternator and have to loosen the valve cover to move the alternator enough to remove the belt...

shredjesse

Unfortunately, I can barely get the belt on with the alternator as is. Going larger on the pully would make the alternator impossible to get back on. I either need a longer arm, or am missing a bracket...

I looked at the bracket off of the headers. Looks the same as everything I saw online.

I don't have a bracket on the water pump, which is in the image above, but in none of the engine images I've seen online.


I wish I could just roll to a shop and compare these parts, but nobody stocks these since they aren't a wear item!

augiedoggy

The diagram above is misleading... it doesn't show the bracket mounted to the head where it actually goes....its supposed to me showing the brackets floating I believe... I have the same bracket as well as the long arm that mounts through the water pump upper bolt and that's it.... no bracket from the header for my alternator. Mine is a 74 however. Point is nothing should have changed from before the engine rebuild...SBC is SBC... this should be the shops issue to correct unless I'm missing something?

toddalin

OK, assuming that you are using exhaust manifolds that use the two side bolts to hold an "F-bracket" that holds the base of the alternator, I'm betting that the "F-bracket" is incorrect.

The hole in the F-bracket for the bolt that goes through the base of the alternator should not be centered as it is on most aftermarket brackets, and probably some GM pieces. This is what is limiting you from moving in the alternator toward the centerline as the base hits the bracket.

The correct F-bracket sets the hole off center toward the top such that when the alternator is rocked inwards, it does not hit the bracket, or hits it further in.

A no no:



Note how the hole is offset :


But assuming that you just can't get the existing belt quite tight enough using your existing parts, you do have an alternative.

Get some fat washers and place them between the F-bracket and exhaust manifold to move the bottom out a bit more. Movement at the bottom has more impact on the belt tightness than at the top, and this may even swing the top mount in a bit while tightening the belt.

As for the comment on mounting the "J-bar" to the alternator, you should have it mounted to the back rather than the front of the hole that you have it in. Even then, the alternator will sit back a bit from its intended centerline and many of the original J-bars actually had a "crook" in them to compensate to this difference. In other cases, you just end up "tweaking" the bar a bit when the alternator is in the proper position.

shredjesse

Ah ha! This appears to be the case! Where the holes are drilled on the F bracket appears to be completely centered, instead of offset towards the top, hence my alternator is hitting the bracket as I move it inwards.

This is really frustrating because if this issue had happened on my side of the country (where the corvette will eventually live again) I'd have the cutting torch, welder, and everything else I need to just fabricate up a solution to this mess, ugh!

I briefly considered washers on the bottom, but given how snug I am to the end of the adjustability on the alternator, I'm not sure this option would work either.

Kacyc3

I had the same problem, and couldn't check ps fluid with alternator on the car so I said screw it and put late 80's serp setup on the car.

toddalin

No, the washers will shift the bottom of the alternator outwards and this adds tension to the belt. This added tension is relieved by shifting the top of the alternator inward toward the centerline along the J-bar.

So if you couldn't get the belt tight enough, shifting the base out and even leaving the top where it is at the end of its travel on the J-bar will add more tension to your belt.

Stack some washers. Its worth a try and if it works, get some spacers (or the right F-bracket).

shredjesse

I suppose it's $2 at most to try. Sure, I'll give it a go. It's a fair ways off in regards to tension.

If only I had my welder. Adding 2" to this arm would pretty much make it perfect!

shredjesse

Alright! So I tried the washers. I was only able to stack about 1/3" worth of washers in there, and was barely able to get the bolt in. I then used a pry bar to tension the alternator as tight as I could get it, which was the end of the adjuster.

The squeal is now gone at 2.5k, and only exists at 4k and above now... and at that point the engine drowns it out so I think I can live with this until an alternative bracket is built and a smaller belt used.

Has anyone here used the low or mid mount alternator brackets on their C3 with a SBC 350 in it? Any pains or difficulties? Can it be done with the engine in the car?

augiedoggy

this is the bracket that came on my 74....( multicolor plug wires are being replaced sunday.)