Belt Tension Guideline

[colinnwn]

I was getting belt squeal starting up in the morning that would go away within about 15 seconds. I hadn't changed the belts in over 6 years so I figured it was time.

 

I put in new Nissan belts (in addition to an electric radiator fan conversion that I'll do a separate writeup on). Man if you don't have the fan in the way, belt changes on these engines are stupid easy. I don't have a measuring tool to figure out the correct tension. I've read on here it should be pretty tight, but I also didn't want to ruin any of my accessory bearings. I believe the FSM says the A/C belt should flex no more than 9 mm with 22lbs of pressure between pulleys, and the main belt 5 mm. I tried to gauge this by finger and sight. I thought I had the belts overly tight and it turns out I had at least the main belt way loose.

 

For the A/C belt which I haven't been able to test yet, I just used a socket wrench extension and turned the adjusting bolt as much as I could by hand with only the extension.

 

For the main belt I did the same, and then I put the wrench on the extension and gave the adjusting bolt one additional full turn. The first day I had no squeal, the 2nd I had a chirp, the 3rd it was a couple seconds long. I tried putting a few drops of dish soap on the belt on the inside and out. The 4th day it squealed a few seconds longer. So I gave the adjusting bolt a half turn more. For the next 2 days I had very small chirps. I just gave it another half turn, for a total of 2 turns past hand tight, and it looks like that's going to be the perfect tension.

 

Just thought this might help someone

[anyexcuse]

Yes it may! Mine has a squeal for a few seconds after starting it and I need to look into it. Thanks for the info!

[CDN_S4]

Thanks for this, I have the start up squeal too, 2-3 seconds. Sprayed it with belt lubricant but didn't really make a difference. So you're saying tighter made it better...interesting. I was thinking mine were too tight maybe. I'll check back after I tinker around with this a bit.

[kdj]

I'd say it's NOT your belts slipping but your idler pulley squeeling. I thought I had a loose belt till I checked out the idler. When I took the pulley off it would barely turn by hand it was so gummed up. WD40 and compressed air...put it back together and I had no squeel. The belt wasn't the problem.

Edited February 18, 2015 by kdj

[CDN_S4]

^^ good to know!! Did you take it off for that? Or just removed the belt?

[colinnwn]

When I had my belt off I could spin the idler pulley easily. I would expect the squealing to last longer or not stop if the idler was gummed up. Is that not the case?

[Kingman]

Could try taking some fine grit sandpaper to the inside of the pulleys to knock the glaze off. Grippy grippy is no squeaky squeaky.

[kdj]

With mine I thought it was a belt but the adjuster bolt was siezed so that's why I had it all apart, which was a great time to remove all the AC stuff. Who needs AC in Canada? Cleaned up the idler and injected bearing grease into it. Quieter now than before it started squeeeling.

[colinnwn]

I just finished replacing my alternator, and used the same belt from this thread. For the last couple months before the alternator had gone out, I had been getting the occasional startup belt chirp. I had been planning to tighten it up another half turn.

 

But after the alternator replacement, starting from a removed, old but good condition belt - I again hand tightened the tensioner with just the extension, and did one full turn with a wrench. That seemed too loose by pressing on the belt, but I actually didn't try starting it up. I did another half turn, for a total of 1.5 turns, and then the belt felt appropriately tight. There was no chirping on startup.

[colinnwn]

I had to replace my alternator again, and when I did I noticed that the idler pulley turned freely, but it made a light clicking noise. So I replaced it. The engine idles much smoother and quieter. now I couldn't separately detect it from the rest of the engine noise, but the old idler must have been clacking around.

 

It was a Dayton part from Advance Auto Parts. At first I was flustered because the dust cap wouldn't fit on it. But then I read the box closer, and it said the new one had a sealed bearing and discard any old dust cap.

 

I didn't bother removing the AC belt and checking that idler pulley. I guess sometime I will.