ridiculous alternator vibration....need help

[Dean Lampe]

I switch to a larger alternator from a 55amp race unit due to inadequate power generation. The new alternator is a denso that I had to modify to case to fit. It is meant to be a serpentine belt alternator with a solid mount top and bottom. I run a gilmer/cog belt set up and the alt. is mounted solid at the bottom and adjustable at the top like a Chevy one wire would be. The problem is that the unit vibrates like crazy. I have checked and recheck the alignment. Could it be that the unit needs a stronger top mount? I can do that but I don't want to mask a problem that will put me on the side of the road. The alt worked fine on the bench test and is charging great.






This is the old alt. but the new one is mounted the same way.

 

[Gregg]

Dean it could be a mounting issue. What is the difference in weight between the two units? May need a stronger mount. I would also check the fit between cog and alternater shaft as well as the shaft by itself. Good luck.

 

[Dean Lampe]

Gregg, I think the pulley and shaft is okay. I spun it pretty hard at the alt. shop with little to no vibration. This alt. is considerably bigger and heavier. It might just be as easy as putting a solid mount on the top. The hiem joints on the current upper mount don't do anything to control vibration. I can build a stronger mount, I just wanted some feed back before a do. If there is a problem that I might not have thought of, I didn't want to use brute force to control it. If you think of anything else, don't hold back!

 

[Rob]

Hey Dean,
I would check the mounted run out of the pulley just to get it off the list. This (for me) would lower the probability of it being an eccentricity related issue (i.e. shaft bend during install, or defective pulley). I would then try to bench evaluate the alt with spinning it at speed and get a sense of the internal balance of the unit. If these seemed to check out OK, then I would rebuild the bracket to eliminate the heim joints. They make it convenient, but only provide longitudinal control and don't offer any stability other than that. My 0.02......

 

[Randy V]

Gilmer belt drives are almost always adjusted too tight... Found this out the hard way by burning up the bearings in a good Peterson oil pump.

Have you tried slackening the belt some?

Also - with a gilmer drive, you need to make sure that your shafts are precisely parallel to each other. Pulling the belt too tight will generally pull something out of an alignment that looked good to begin with..

My $.02 worth..

 

[Jac Mac]

Going by your photos I assume the Alt is driven by the WP which in turn is driven by that single non-tensioned Gilmer belt [ This point might be the problem ]. If there is the slightest amount of runout on the WP / Alt / Crank drives it will transmit into the others. Use a strobe light to 'stop' the belts at various RPM, that might point to where the real problem is. As others pointed out, dont overtighten these belts. Every 'Helpful Harry' that hangs around the TVR tells me the pump belt is too loose, just to freak them out I slide it off the pump drive to prime by hand, then slide it back on- that sends them away shakin their heads.

As an afterthought, try to avoid any 1 to 1 or 2 to 1 belt drive ratios if possible, for example run a 34t on the WP & a 35t on the Alternator-- stops harmonics from repeating/increasing.

 

[Dean Lampe]

I just finished the new bracket and it seems to be holding the vibration down but there seems to be to much even after a bracket upgrade. I was wondering about the tension too. My problem goes the other way. I think the belt is too loose. I am now running one belt around the alt., water pump and crank. There is no longer room for two belts.

When the car is running, and the belts are rotating clockwise, the tension between the crank and the alt. seems REAL loose as the belt tightens up due to the tension created in the alt. and all the slack goes to one place. The belt really flops around in that area. It is a major job to tighten it up much more due to the suspension pickup points. I an less the 3/16's from the frame now. My motor mounts are almost solid so the engine doesn't move but I would hate to be much closer than that. Pulleys are limited in size and availability and the belts come in 2 inch increments at this length.

I can go back to a 28 tooth water pump from a 32 and to a 28 tooth alt. from a 16. That is a net gain of 4 teeth. And a net loss of $185!!!

My next car will be built with all stock, off the shelf parts!

 

[Jac Mac]

One other point, most alternators are overdriven in modern vehicles, your setup appears to be around crank speed only, plus those are 2007 pics.
Also are all your pulleys the correct tooth profile to match the belts- there are many variations out on the market today- not just gilmer, HTD.

FWIW, I personally dont like a toothed drive on an alternator or WP, some minor slippage seems to help in these areas------Nascar also seem to think the same way, most of the pics I have show Vee Belts to W/Pump & Alt.

 

[flatchat(Chris)]

I have to agree with Jac, re:- toothed belts on WP and Alt ---hot rodders like 'em cos they make a sound like a super charger --just a wank off.
Use a single Vee or poly vee only for Alt,WP,AirCon, P/steer and you'll have smiles per miles.
Every (Wannabe) racer boy over here that turns up at the track with a nice shiney "Gilmer drive" (P.O.S) set up is soon in the pits wondering why the alternater has broken something / rattled apart or shredded the belt.

 

[Jim Rosenthal]

It doesn't sound like your alternator is too small at 55amps. This is the size alternator I have on my boat engines, and they work fine. (the 12volt loads on a boat are quite a bit bigger than on a GT40).
What I DO have is multistage regulators. You might look at getting one. The typical regulator which is built into an alternator is a "dumb" single-stage regulator that senses battery state poorly and doesn't do a good job of charging the battery or supplying the car's 12v needs. The only company of which I am aware that builds "smart" regulators is Balmar. These are not race car equipment, but they are programmable, fairly small and light, and can be set for just about any charging curve you can imagine.
Before I fitted these, I had battery charging issues; not any more. The refit involves taking the internal regulator out of the alternator and setting it up for an external regulator. The external regulator can charge flooded, gel or AGM batteries, the charge curve can be customized, etc etc. Most alternators do not perform nearly at their capabilities because they are handicapped by single-stage regulators which waste much of what the alternator can deliver to the battery.

 

[Dean Lampe]

It would be very difficult to switch to v belts at this point. The bolt that holds the pulley stack on the crank is to long to take out with the engine in the car. We went with the gilmer initially to use a smaller diameter WP pulley for clearance at the firewall. I would like to switch it but I can't right now. The alt. is underdrive 2:1 right now. 16 tooth to 32 tooth.

Chris, my set up isn't shiny! Besides, you can be a racerboy and not be dirty.:thumbsup: I like the title "wannabe racerboy". To many people with a gt40 are "waxers". Thats not for me.

Jim, 55 amp just isn't enough for my car. When you add up all the lights, MSD, 3 fans 3 fuel pumps, fuel injection and AC I quickly pass the 55 amp capacity.

Can one of you give me some idea on tension? How much enough for these gilmer belts?

 

[Randy V]

Can one of you give me some idea on tension? How much enough for these gilmer belts?

Hi Dean,

I can guarantee you that you don't need it anywhere near as tight as you would a V-Belt or a timing belt for that matter (the later of which typically has a tensioner pulley to keep in check).. Jac hit it on the head. You should be able to easily slide the belt off and on again when everything is warmed up. There are two different types of Gilmer belt drives, square cut (which I think you have) and radius cut. The former is noisier and lighter, the later being more quiet and requires even less tension because the cogs are deeper also.

Have you tried starting it up for just a minute without the alternator in the circuit to check for vibration? Have you made certain that there is no run-out in the alternator shaft (bent)?

Vibration continued - On my Blown Chevy Nova - I would get a fair amount of vibration just from the belt drive of the blower.. Nothing much could be done about it. Something I had to live with. It was made even worse by the solid motor mounts which I had to have.

 

[Jac Mac]

Sometimes a belt that ' suddenly' starts causing vibration problems with 'snaking' on the slack side from the crank pulley is simply sending a text message of another impending problem, dont panic too much because the 'full english with pictures' version that follows later is quite readable.

 

[Dean Lampe]

Okay, now you have my attention. What am I waiting to see? This isn't a sudden problem. This is a new set up. The old set up worked fine except for the small alt. The belt problem happened when I went to one belt vs two. I can't go back to two because the new alternator is deeper and thus pushes the belt out into alignment with the crank/wp pulley.

What causes the "snaking" because that is exactly what it is doing.

 

[Jac Mac]

As yours is a 'new' setup you wont be able to be sure whether your 'snake' is from belt harmonics etc, or something inside the motor looking for the 'exit' sign. However lets hope that there is nothing internal amiss and concentrate on the belt issue. Since your AC pump has a V belt, get a double groove 4" crank pulley, a double groove WP pulley and a single 3" alt pulley. Now run two V belts--- one goes Crank-Alt-WP, other goes Crank-WP-AC. The 4" crank pulley will keep belt speed down & should give belt clearance desired @ front of radius arm . While you have the motor out see if you can move the oil pump rearwards on the block & shorten the drive snout up a bit--- also check that extension for run out. You also mentioned the use of spherical rod ends as adjusters, however these dont stabilise the Alt like a conventional adjuster strap.
Now I can just about hear you.......Im not takin that ******** motor out again!

I reckon its one of those moments....... you can fix it now, or you can fix it later, but sooner or later............. you WILL have to fix it!! Your Choice.

 

[Rick]

Dean are you using High Quality Rod ends that are "Tight", the ones with Teflon liner? It looks like you have high angularity rod ends currently. Perhaps standard ones would be better. With one belt is it possible the pulses are being transmitted from you A/C compressor, maybe you need to install an idler pulley to dampen the whipping of the belt.

 

[mark b.]

belt is too big/wide to span that width and not flop around without an idler. talk to someone at jones racing, they have thinner cogged belts that are still strong enough, and if you tell them at what rpm your alt. starts putting out juice, what rpm you run, they can tell you what size pulleys to use.

i use one on the jbl and it "snakes" somewhat, but the alt. doesn't notice. your span might be too much, but the guy at jones racing is pretty helpful and could prob steer you in the right direction.

hth

 

[John P]

If the alternator is only secured at the pulley end and not the back end, it will flop around. I can't tell from the photos if it has a rear mount, but if not, it will need one.

 

[Randy V]

.. maybe you need to install an idler pulley to dampen the whipping of the belt.

Dean - If you look at the picture of my blower motor above, you'll see the idler / adjuster pulley. It's on the slack side of the belt.

I do agree with Jac on making sure that your pulleys are not extended out any further than absolutely necessary..

BTW - did you run this combination (recently) without the alternator as I suggested? It's just part of the process of elimination.

I hope you find the right combination for your setup.

 

[Dean Lampe]

There is no way to attach the rear of the alternator. The snaking is gone as I tightened up the belt. I does sound like a supercharger and I didn't notice that before but it was probably always there. The alt. vibrates at idle but not as much as the rpms build although it does have some vibration. The belt is only 3/4 in wide. I will try to shoot a short video for you all to see.