Belt size for HO alt

[shepherd92683]

I've read yes and no on going to a smaller belt size with having an HO alt. I have a Gates micro v 91.5. I don't seem to have any problems with it except my voltage regulator went out (Mechman) and it's currently inbound back to me. Should I keep it how it is or is there some better reasoning to going smaller due to the smaller pulley? What does your experience say?

 

[kickass audio]

I am not sure if mine died from the start or from using a smaller belt to add extra tension on the drive belt which in turn goes to the bearings because I had my rear bearings on my mechman alt literally explode. I went with the belt that the XL version uses as it I believe is an inch smaller. Really it is about the same spot for the tensioner as if you had the stock length belt on with the stock alt so I don't think that is what killed my bearing.

Also don't forget to do your big-3 while you are at it if you haven't done so already.

 

[MAY03LT]

I had to get a smaller one for my mechman. 90 7/8" IIRC. If she aint slipping under load I'd keep it the same.

Kinda off topic but was the reg causing all of your issues?

 

[shepherd92683]

Yes they told me the regulator failed. Did you use the XL wheelbase size May03LT?

 

[MAY03LT]

Yeah that's the one I used.

 

[shepherd92683]

I don't think its slipping, only sounds like a jet engine going down the road at high rpm. At 116k, is the idler pulley something to consider replacing to help in the cause? If so, which one is recommended?

 

[Sparky]

Yeah idlers usually are to blame for that first. Take the belt off and spin pulleys by hand. The one that spins rough like gravel in the bearings is the one that is likely to blame.

 

[shepherd92683]

That's good. I'll check that. It does obly do it with the mechman installed though.

 

[filthyfingers]

Been to NAPA 3 times today. The first belt was much too big for my SWB '02 Envoy compared to the old one. So I took it back and then they offered me "the Trailblazer version". It was too small. So I asked for any belt that was 91.5". They found one that was marked 91 5/8". Can't get it on - no way, no how. Slipped the old one back on in 30 seconds. No sweat. Can't find any numbers on the old one either. Guess I'm shopping for a 92" tomorrow.

I'm done for the day.

 

[filthyfingers]

Finally got the right belt. Gates Micro-V AT 92 1/8" (2340mm). NAPA p/n 25-060915. I thought the "915" in the part number was 91.5" - not necessarily so. The measured size is listed on the back of the sleeve. 13/16"x 92 1/8"

Fits just like the old one. Don't know why the 91 5/8 belt didn't fit. No aftermarket stuff on the loop. (My) problem solved.

 

[shepherd92683]

Good to hear. I'm not installing my alt until next Monday more than likely so I'll have more results at that time.

 

[kickass audio]

Something else to let you guys know, with the mechman alts, they have the smaller diameter pulley (1.75") and from what I learned from them, if you get the engine to rev up high like into 6k rpm, you will have the alt shut off. Now I don't know if that was a command from the PCM to shut it off like how it commands the alt to stay off on cold startups. I talked to Matt at mechman and he said that I really overspun the alt. I had it at 27k rpm for the alternator and they rate them at a max of 18k rpm. I almost never get the engine up in that RPM range but the one day I hammered on the gas to get on the thruway and it got up to 6k rpm and the alt stopped charging for that moment. So for the other users out there, be warned from my issue I learned from and keep your RPM's limited to 4400 engine RPM's. Anything above that and you are exceeding the alternator spin rate they rate them at and are at risk of breaking the bearings and other components from high speed. You could easily correct this with a larger pulley than the 1.75" one they come with, they recommended I use a 2.5" pulley but the issue with that is the output at the lower RPM range would absolutely suck. I opted to keep the 1.75" pulley on the alt and carefully monitor my rpm's when accelerating to prevent it from getting above 4400 RPM engine speed.

 

[filthyfingers]

Good to hear. I'm not installing my alt until next Monday more than likely so I'll have more results at that time.

Good luck let us know how you make out.

 

[shepherd92683]

Something else to let you guys know, with the mechman alts, they have the smaller diameter pulley (1.75") and from what I learned from them, if you get the engine to rev up high like into 6k rpm, you will have the alt shut off. Now I don't know if that was a command from the PCM to shut it off like how it commands the alt to stay off on cold startups. I talked to Matt at mechman and he said that I really overspun the alt. I had it at 27k rpm for the alternator and they rate them at a max of 18k rpm. I almost never get the engine up in that RPM range but the one day I hammered on the gas to get on the thruway and it got up to 6k rpm and the alt stopped charging for that moment. So for the other users out there, be warned from my issue I learned from and keep your RPM's limited to 4400 engine RPM's. Anything above that and you are exceeding the alternator spin rate they rate them at and are at risk of breaking the bearings and other components from high speed. You could easily correct this with a larger pulley than the 1.75" one they come with, they recommended I use a 2.5" pulley but the issue with that is the output at the lower RPM range would absolutely suck. I opted to keep the 1.75" pulley on the alt and carefully monitor my rpm's when accelerating to prevent it from getting above 4400 RPM engine speed.

Mine does the same thing and it drives me nuts.

 

[shepherd92683]

Holy old post, (found this on google searching the topic lol) but I've got more for this same thread! My alternator again failed about 3 weeks ago. I think the culprit was a combination of 2 bad batteries and a high rpm acceleration. The voltage regulator and rotor assembly were bad. They also replaced the pulley they said 'just cause' for free. Parts shipping and free labor was about $100. I reinstalled it this morning and started to get a whine from the belt. It does seem that the pulley is quite smaller than stock. I've been using the OE size but am considering going smaller. The voltage also is dancing from 14.2-15, very inconsistently at idle and driving. The belt tensioner is also a little bouncy, but I don't remember what it looked like with the OE alt on. Is that from the belt slipping?

Talked to Mechman this morning. They recommend going .5-.75" smaller. I'm going to try the .75" shorter and us a Gates 90.75". I'll report back when it's installed.

 

[Ilikemy3s]

Any updates ?