Balance shaft belt tensioning

[BennSport]

@CarBot , is there a good way to check balance shaft belt tension on an early 944 without specialty tools?

[CarBot]

, is there a good way to check balance shaft belt tension on an early 944 without specialty tools?

On an early 944 you can get it close without the factory tension gauge, but it’s more of a “good enough to drive” check than a precise setup.

The most practical method is the twist check on the longest straight run of the balance belt (usually the upper run you can access at the front). With moderate finger pressure you should be able to twist it to about 90 degrees, not much more. If it twists easily past 90 it’s too loose; if you can barely get it to 90 it’s too tight.

After you set it, rotate the engine by hand at the crank two full turns clockwise, recheck the twist, and listen/feel for anything binding. Then recheck again after a short heat cycle or a few drives, because new belts relax a bit. Too tight is what you really want to avoid on these since it can get noisy and it’s hard on the balance shaft bearings and front end components.

If you tell me whether it’s a fresh belt or an existing belt you’re checking, and roughly how many miles since it was last tensioned, I can suggest how conservative to be with the “90 degree” feel.

[BennSport]

@CarBot On an existing belt that’s been driven around 2000 miles since new, how conservative should I be with the 90 degree test?

[CarBot]

On an existing belt that’s been driven around 2000 miles since new, how conservative should I be with the 90 degree test?

At 2000 miles the belt has mostly done its initial stretch, so you can be a bit less conservative than you would on a brand new install, but I’d still bias slightly toward “not too tight.”

With the 90 degree twist check, aim for “just about 90 degrees with moderate finger pressure” rather than “barely reaches 90.” If it only twists, say, 60–70 degrees with a normal pinch-and-twist, that’s usually a sign it’s on the tight side. If it goes past 90 easily to 120+ degrees, it’s likely loose.

A couple practical tells on an existing belt: if you’re hearing a pronounced whine that rises with RPM from the front of the engine, that often correlates with over-tension. If you’re getting slapping/flutter at idle or on decel, that points more to under-tension.

If you want a sanity check without special tools, do the twist test in the same spot with the engine cold, then again fully warm after a drive (careful around the fans). You’re looking for it to still feel reasonable and not go obviously loose when hot.

If you can share which tensioner setup you have (early eccentric/manual vs spring tensioner) and whether you’re hearing any whine or slap, I can steer you a little tighter or looser.

[BennSport]

@CarBot its on an early style eccentric roller, and I’m hearing a whine. Does the idler roller also affect the whine?

[CarBot]

its on an early style eccentric roller, and I’m hearing a whine. Does the idler roller also affect the whine?

Yes. On the early eccentric setup, a front-end whine can come from belt tension, but it can also come from any of the rollers themselves, including the balance belt idler and tensioner rollers, and even the timing belt rollers if the sound is hard to localize.

The idler roller can absolutely whine if its bearing is dry or starting to pit. A too-tight belt loads the bearings and can make a marginal roller get loud fast, so the two issues often show up together.

A quick way to separate “tension whine” from “bad roller whine” is to back the balance belt tension off slightly and see if the pitch/volume changes noticeably. If the whine drops a lot with a small tension reduction, it was likely over-tensioned. If it doesn’t change much, suspect a roller bearing.

If you can safely do it, pull the upper front covers and use a mechanic’s stethoscope or a long screwdriver to your ear and probe the roller studs/housings while it’s idling. A bad roller will usually be very obvious compared to the others. Also, with the engine off and belts relaxed, spin the rollers by hand; any roughness, notchiness, or “dry” sound is a replace-now sign. Don’t rely on “no play” alone, because they can be noisy before they get loose.

If the whine is new after your last tension check, I’d slightly loosen the balance belt to the “just reaches 90 degrees” feel cold and re-evaluate. If it still whines, I’d plan on replacing the suspect roller(s) sooner rather than later. If you tell me whether the timing belt was done at the same time and whether the whine changes with RPM instantly or only when warm, that helps narrow which component is singing.