Belt skpping a rib on crank pulley after smog bypass

putertopia · Nov 7, 2009

Is as the title says. 95 GT, was trying to bypass the smog pump so I bought a 90" belt. 89.5" was too small. Got it on, feels like there's a decent amount of tension on it. Start it, a quick squeal then quiet but the belt pops over a rib on the crank pulley.

I don't typically take what the guys at the local autozone say but they suggested that perhaps my tensioner is going bad, and that could be. I didn't have to use a ratchet on the tensioner to get the original belt off, so I will probably be replacing that. But with a good bit of tension on the belt, should it be causing it to slip over on the crank pulley?

First off, are belts typically directional? This belt doesn't have horizontal crosshatches on it like the original belt does. I've popped it back on the crank but each time I start it it slips over a rib again (towards the motor).

302GTS · Nov 7, 2009

Are you sure it's the correct belt, as dumb as that question may sound?

Also, it could be that your pulleys aren't lining up properly, and you should check that also. Good luck! I'm sure more suggestions will pop up!

revhead347 · Nov 7, 2009

I doubt it's the tensioner. The one think you do have to change when you remove the smog pump is the routing of the belt. It goes around the crank and water pump pulley the opposite from stock. So the belt goes from the bottom of the crank pass the tensioner and to the alternator. The belts are not directional. Some have crosshatches, some do not.

Kurt

HISSIN50 · Nov 8, 2009

Sounds like you have a couple issues. One is a pulley alignment issue. Leave that till later because the tension issue should be handled first. You said you could remove the OEM length belt without using a wrench on the tensioner. That's not normal.

putertopia · Nov 8, 2009

OK well then I guess first thing on the list is a new tensioner. Then I'll try the belt again and see if maybe it's just not too loose to hold on, because today while I was messing with it again, it completely came off the tensioner. The belt sits almost an entire qtr inch further back towards the motor on the tensioner pulley and water pump than when routed normally.

I looked at the pulleys today from above and below by eye and lined them up to eachother and they're almost 100% spot on. If anything were to be off, I'd say the smog pump is slightly pushed out lol.

As soon as I can afford a new tensioner I'll try at this again. Thanks.

HISSIN50 · Nov 8, 2009

A machinist's edge or laser sight is needed to check alignment.

toyman · Nov 8, 2009

putertopia said:
OK well then I guess first thing on the list is a new tensioner. Then I'll try the belt again and see if maybe it's just not too loose to hold on, because today while I was messing with it again, it completely came off the tensioner. The belt sits almost an entire qtr inch further back towards the motor on the tensioner pulley and water pump than when routed normally.

I looked at the pulleys today from above and below by eye and lined them up to eachother and they're almost 100% spot on. If anything were to be off, I'd say the smog pump is slightly pushed out lol.

As soon as I can afford a new tensioner I'll try at this again. Thanks.

Why are you so "gung ho" on the tensioner being the problem? When the belt is off is there resistance when you move the tensioner. If there is it is fine. When the belt is on is the tensioner mark between the out of range markers. What you are describing more closely resembles a pulley alignment or belt length issue.

HISSIN50 · Nov 8, 2009

Richard's points are good ones. The only sentiment that had stuck with me was about the OEM belt came off without a wrench on the tensioner. That made an uh-oh sound in my brain.

I didn't think to ask if the tensioner had been between the hash marks (like Richard wisely suggested). Because people can have issues with loose belts after a smog pump bypass, the scenario he outlined is possible (you might also just need a belt with more tension). It should take a little grunt to get the belt over the final pulley.

putertopia · Nov 8, 2009

The reason I was/am 'gung ho' on the tensioner is because while it does provide resistance, I can take the belt off in less than 3 seconds without a wrench on the tensioner. Given I am a bigger guy, I don't exert more force than needed due to laziness lol. When I went to school for all of this, we mainly focused on the inspection items with some engine/trans swaps here and there and upper end gaskets, steering & suspension, alignments, etc. I have knowledge (and an inspection license that currently means nothing), but I've never worked in an actual everyday garage therefore I lack experience at the age of 20. This is where you guys come in lol. Just trying to build experience...

What's really throwing me off is the fact that if it's routed per stock spec, it's absolutely 100% OK. Belt is 100% on track, no oddities, etc. Tensioner doesn't bounce at idle, but I think it does around 3k RPMs during acceleration and when RPM is slowly increasing around 1400 RPM because I can hear something squeaking and it only sounds like a belt. If I'm remembering the belt direction correctly, isn't the tensioner the right before the crank pulley when routed around the smog pump? That's another thing that pointed to the tensioner for me.

I messed with it more today. I'm about to just give up on the smog pump thing and replace this with a stock belt. I only wanted to bypass the pump because it makes a howling noise when cold, not like it's really going to be a power gain for daily driving.

After the belt pissed me off I just gutted and completely cleaned the interior, went through seven batches of water in the rug washer before not getting black mucky water (previous owners did not know how to clean/keep dirty shoes out), claybared/lightly machine waxxed most of the exterior, did an oil change, converted interior lights to LED, re-routed my temporary amp wiring, figured out that my driver's seat track is indeed toasted, and fixed a few rattles. Still got something accomplished today

Husky44 · Nov 8, 2009

Sounds like you made lemonade out of lemons. Good that you could have a productive day out of one that would be so frustrating.

Here's my lame, non-mechanic's diagnosis:

1) You definitely have a problem with your tensioner that you need to fix. I don't think it's the root cause of your belt jumping, but it's a problem, and it's a simple, and relatively inexpensive fix.

2) Your belt jumping off is an alignment issue. Much like the other post about chewing belts, this could be caused by either pulley alignment, or as I interpret his case, improperly mounted accessories that have a pulley on them (which results in pulley misalignment). Yours isn't as severe, b/c you haven't grenaded a belt yet, but it definitely needs to be resolved, or you will.

My guess is that you've had this problem for a while, but your recent smog bypass exacerbated it by either
a) changing the belt deflection, so that the misalignment of the pulley became more pronounced, (I'd start looking for the culprit at the accessories immediately adjacent to the smog pump location) or
b) the routing change effected your tension enough, that the problem was previously controlled, but now with different routing/tension, it's got enough slack to jump.

But, what do I know???

toyman · Nov 8, 2009

Does this help

http://www.allfordmustangs.com/forums/attachments/94-95-tech/35528d1194203984-1994-mustang-5-0-need-belt-routing-diagram-belt-routing.jpg

m0l0 · Nov 9, 2009

Looks like a pulley aligment problem , its easy to verify just by looking from the Driver side if you have some error on the aligment of the pulleys

toyman · Nov 9, 2009

The 89.5" belt should be the correct size. You mentioned that it was too small. However, you didn't pull back the tensioner to give you the needed slack. The 90" belt just well may be too loose.

putertopia · Nov 10, 2009

I did pull back the tensioner for the 89.5" belt. It was a PITA to do without a very small 3/8" extension, but I just couldnt fit it.

toyman · Nov 10, 2009

putertopia said:
I did pull back the tensioner for the 89.5" belt. It was a PITA to do without a very small 3/8" extension, but I just couldnt fit it.

I didn't think one could move the tensioner without the leverage of a breaker bar. If you did move it like you are suggesting, I would be inclined to think that the internal spring is shot/broken which as mentioned earlier could allow the belt to skip a rib or two.

revhead347 · Nov 10, 2009

toyman said:
I didn't think one could move the tensioner without the leverage of a breaker bar. If you did move it like you are suggesting, I would be inclined to think that the internal spring is shot/broken which as mentioned earlier could allow the belt to skip a rib or two.

You can move it pretty easily with a 3/8" driver, even if it's brand new. That tensioner has a decent range of motion on it. Make sure the ratchet is all the way down by the crank pulley when you put it on, and pull it all the way up as far as you can. You should be able to get an 89.5" belt on there. The other variable in the pulley system is the idler pulley on the top, as well as what under drive pulleys you have. I believe a standard idler pulley is a Dayco 89006. It is not uncommon to mix and match underdrive pulleys to get the desired effect. I use an underdrive alternator and crank pulley, with a stock water pump pulley to get a little more cooling, and better belt clearance. If you can take the belt off with no tools, then it's too long. You need to get a shorter belt on there. If there isn't a belt available between 90.5 and 89.5, you can change the idler pulley to a smaller one. I think the next step down is a Dayco 89003.

Kurt

turbogt · Nov 10, 2009

Mine must be much stiffer than yours.. I could barely move it with a large 1/2" wratchet.. I had to bottom it out all the way, and then force the belt on with a screwdriver, which is why I now think my tensioner is shot because it squeals at startup..

Dino Dino Bambino · Nov 11, 2009

turbogt said:
Mine must be much stiffer than yours..

I wouldn't be so sure about that.

Belt skpping a rib on crank pulley after smog bypass

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