DIY: Serpentine Belt EZ-Tool (<$2) & Routing Topic is solved

[QuirkySwede]

Was at the hardware store looking to make a Serpentine Belt (De-)Tensioner Tool ala serpentine belt tensioner tool but came up with something, easier, cheaper, more compact, and requires no special tools (grinders, drills, etc.) to make nor use other than regular wrenches, crescents, or sockets. Easy enough to make second to wrap up with a old wrench and a used belt and stow with the jack for a little roadtrip breakdown piece of mind.

1. Swing by the local hardware store and pick up a 7/16" - 14 square nut. (Hillman # 3339-H for 70¢ shown). The "14" is the coarse thread pitch. Do not get "20" which is the fine pitch unless it matches the square nut you find. Next, grab a 7/16" - 14, Grade 8, 3/4" long bolt (Hillman # 220172 for 59¢ shown). Note the six lines on the head denoting grade. Last, snag a 7/16" - 14, Grade 8, hex nut (Hillman # 180409 for 45¢ shown). All for $1.74 + tax and no shipping.

SerpBeltEzTool1.JPG (47.69 KiB) Viewed 21820 times

2. Now screw them all together using a pair of crescent wrenches or a 3/4" (19mm), 11/16" (17mm, snug), and 5/8" (16mm). No loctite or extra torque is needed beyond what prevents them from spinning apart as they tighen in use due to the tensioner release being clockwise.

SerpBeltEzTool2.JPG (37.9 KiB) Viewed 21820 times

3. The square tensioner hole measured 19mm across. while the keeper eye holes measured 4.43mm so any strong 5/32", 1/8" or 4mm diameter pin, screw or nail will work, and tying a piece of wire or string to it can be used to lessen the chance of dropping and losing it during installation or removal. There is no risk of the tool slipping through the square hole due to the four bumps. I prefer to screw a 12" crescent wrench, line it up so the handle is around 11:00 (may have to remove turn it 60° to find best angle), pull CW, and slide the pin in. A box end 11/16" or 17mm wrench with some masking tape for retention also works well. Removal is easy, but note your belt routing first! Take a photo! For installation, you may find it helpful to stuff a rag or such under the harmonic balancer on the crankshaft to keep the belt tight against it and in the grooves while routing, just be sure to remove it right after removing the tensioner pin.

SerpBeltEzTool3.JPG (62.39 KiB) Viewed 21820 times

Variations: One could also use a second square nut in place of the 7/16" nut for another 11¢ without worry about whether the edges line up or not, but I prefer the stacked "snowman" look. Whether you have the rounded or sharp edges of the square nut facing out makes no difference in use, other than that I found the rounded facilitates insertion.

ROUTING AND PULLY WRAP COMPARISON

SerpBeltEzTool4.JPG (64.25 KiB) Viewed 21820 times

Type____Crank__PwrStr__Alt.___A/C___Idle
No A/C _ 225° _ 180° __ 90° _ N/A ___ 90°
< 1996 _ 150° _ 230° __ 90° _ 180° _ 180°
> 1996 _ 150° _ 180° _ 170° _ 100° _ 225°
> 2001 _ 160° _ 165° _ 170° _ 220° _ 180°

Notice how Volvo first changed routing to improve grip on the alternator, and later (bottom right) routing regained grip on the A/C reducing the chance of squealing when activated on those 100° F summer days, though that belts backside then runs on the alternator. Other variations may encountered so always check and note routing before removal. One can switch from the "early" to to the "late" setup provided you use the longer belt. Both the picture and table are just to illustrate differences, not a guide for what your particular car should have.

SERPENTINE BELT LENGTH COMPARISON
Best way to know what best to replace your belt with is measuring the old one and looking for numbering on it. This will provide a rough idea of what was used on which models and when, but verify before purchasing.
125.3cm (49.3") without air conditioning: 9146844, 9146117, 115286, 21.0002, 21.0003, 6PK1256, 6PK1250; 1991-1997 850 w/o A/C, 1997-2005 C70 w/o A/C, 1996-2000 S70 w/o A/C, 1996-1998 S90 w/o A/C, 1996-2000 V70 w/o A/C, 1996-1998 V90 w/o A/C
174.3cm (68.5"): 9186352, 88986809, 94829, 48401, 6PK1743, 5060685, 685K6; 1993-1997 850**, 1998 C70, 1998 S70, 1998 V70
175.2cm (69"): 9458411, 15478, 6PK1755, 6PK1750, 690K6, 685K6; 1997-1998 S90, 1997-1998 V90, 1995**-1997** 960
182.5cm (71.85"): 9458469, 8692141, 30731811, 94824, 6DPK1825; 1999 S70, 1999* S80
184.2cm (72.5"): 9471981, 1841, 30731808, 9471799, 9458376, 124703, 6060724; 1999 C70, 1999-2001 S70, 1999-2006* V70, 1999*-2006 S80, 2000-2003 S40, 2000-2004 V40, 2001-2006* S60, 2003-2006* XC70, 2003-2006* XC90
185.3cm (73"): 9497241, 8627228, 30731809, 6PDK1853, 124709, 15502; 2000-2004 C70, 2000 S70, 2000 V70
* Check Chassis Number
** Use Late Routing (Alt.-Idle-P.S., not A/C-Idle-Alt)
TIP: The belt's length and rib count is often incorporated into aftermarket belts' number:
6PK1755 = 6 ribs 1755mm long
690K6 = 69.0" 6 ribs.

[rspi]

Nice. People need these quick when they need them.

[erikv11]

No need to use grade 8, any grade 5 nuts and bolts will be beyond adequate.

Ah yes, there are dozens of serp belt tensioner solutions out there, each one cheaper and better than the last.

Funny thing is I have actually been using the same one (well, the inverse ...) for many years but don't think I have ever seen it posted. I found an appropriately sized square end bolt in the garage several years ago, so have stuck with it. Except my spare-pieces setup is all metric (19 mm) so hooks up nicely with the wrenches I already have out when I'm working on the car.

funky square end bolt, long washer as a spacer, 19 mm nut

serp tool.jpg (40.12 KiB) Viewed 21810 times

[QuirkySwede]

No need to use grade 8, any grade 5 nuts and bolts will be beyond adequate.
...
my spare-pieces setup is all metric (19 mm) so hooks up nicely with the wrenches I already have out when I'm working on the car.

Agreed about Grade 5 (three marks) though I do like the 8's plating. Grade 2 would likely also work (no marks), but it doesn't take seeing many fail before you pass on them for anything more that light duty. Tool works fine, better actually, with 17mm wrench as 11/16" is 17.45mm but the nut measures 17.17mm and is within a nominal 17mm wrench's actual span.

Curious to see a different angle on your tool. Square-head metric bolts aren't very common around here.

[cn90]

The way I have been doing for 90 cents...

1. Go to hardware store (Home Depot etc.) and the buy the 1-inch plumbing plugs (steel plug), then file opposite sides flat for the adjustable wrench. You can file it with a hand file or with a bench grinder:




2: This is how it works in real life:

[matthew1]

$.90 huh? I've got you beat. $.75, and you get it back

[matthew1]

^ I think this was the first MVS DIY. https://www.matthewsvolvosite.com/serpentine_belt.php

Circa 2001.

[rspi]

LOL, I love it. Get it back.

I had 1 made at the tune of $100. It was $100 for 1 or 20 of them. So I had several of them made and sold the rest to bring down my cost. Like the OP's solution, I like it because it's small and fits in my mini tool box. I paint it yellow so it can be found if dropped and seen, not forgotten.

Before that I was using the plug like cn90 and simply using a pipe wrench.

$.90 huh? I've got you beat. $.75, and you get it back

[QuirkySwede]

I had 1 made at the tune of $100. It was $100 for 1 or 20 of them.

'Round these parts we call that "commitment." You easily win for the most expensive I've seen, but also perhaps for the most catching. Is that color Caution Canary or Racing Yellow?

Point is a lot of nut+bolt combos will work so that even the most tool-less driver can service their serpentine belt on these models in any hardware store parking lot with just a wrench or two and no further modification for a buck or two -- cheap, fast, and easy. Whether you go metric with a M12 x 16mm bolt and a M12 square nut, or the more readily available (U.S.) stuff like above or a 1/2"-13 x 1" square head bolt and a 1/2"-13 nut, just remember anything bigger in diameter than about 10mm and longer than 15mm will bottom out on the 19mm square hole's bumps shown in the third picture.

[cn90]

For those who don't have time (or too lazy lol) to make the tool, there is a seller on ebay who makes the square key for:
* Square key $7.00
* Shipping $5.75
* Total = $12.75

http://www.ebay.com/itm/Volvo-850-V70-S ... 0549445734