Timing Belt Tensioning Help - Can't tell too tight from too loose
10-19-2019, 07:43 PM
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Timing Belt Tensioning Help - Can't tell too tight from too loose
I'm getting closer and closer to finishing the new belts + pump, although I've ran into what is (hopefully) the last obstacle I need advice on. Over the past few weeks I've browsed countless videos and forums about changing the timing and balance belts, and even though the steps are consistent with everyone, I just can't figure out how to tension the belts correctly. Correct me if I'm wrong, but from what I understand the rough, "by hand" rules are:
1. Cam belt - Tension until you can twist it ~90 degrees, and are able to turn the water pump pulley by hand with a little bit of force.
2. Balance belt - Tension until you can twist it by ~100-120 degrees.
(Making sure to turn engine by hand, and check timing marks several times after tensioning).
I know these are slightly vague rules, and as such I went out and bought the Arnnworx 920X v6.1 tensioning tool, with the hope of it at least giving me some reassurance that I'm in the ballpark with the tension. However, after following the instructions, making sure to move the slack to the top, and that the tool isn't hitting anything, I still get readings that say the cam belt is too loose, when my gut tells me it's too tight. Now I understand that what determines if the water pump "twist test" is too tight, depends on how strong the person twisting it is, how grippy your hands are, etc.. But I'm still reluctant to tension it according to what the tool says, because I really don't want to have a belt that's too tight. There is a possibility that the tool is correct, and I'm either doing something wrong or just very weak (I'm also not exactly the strongest person on the planet), although I'm still leaning towards trusting my hand rather than the tool.
Another thing I should point out is, when I move the slack to the top of the cam belt, the water pump becomes very difficult to turn. On the other hand, when the crank pulley is turned clockwise and the slack is removed from the top, I'm able to twist the water pump fairly easily. So to put it simply: if I turn the crank pulley sightly counter clockwise, I'll have loads of slack at the top of the belt, but at the water pump it's pretty much impossible to turn. Obviously this makes sense because I'm taking away the slack at the water pump, but I suppose my problem is I'm unable to determine how much slack there should be (if at all) in the belt when checking the final tension. For example, when you tension your belts and do the "twist tests," do you move any slack on the top of the belt at all?
Maybe I just need to fiddle around with it more, and see if I can get it in a spot where I'm comfortable with. And if it ends up being too loose, I'll probably be able to hear it slapping around and then just re-tension it. I'd also be happy to link videos and/or pictures if that would be of more help, but nonetheless I didn't know if anything I'm saying might ring a bell for someone. Thanks!
1. Cam belt - Tension until you can twist it ~90 degrees, and are able to turn the water pump pulley by hand with a little bit of force.
2. Balance belt - Tension until you can twist it by ~100-120 degrees.
(Making sure to turn engine by hand, and check timing marks several times after tensioning).
I know these are slightly vague rules, and as such I went out and bought the Arnnworx 920X v6.1 tensioning tool, with the hope of it at least giving me some reassurance that I'm in the ballpark with the tension. However, after following the instructions, making sure to move the slack to the top, and that the tool isn't hitting anything, I still get readings that say the cam belt is too loose, when my gut tells me it's too tight. Now I understand that what determines if the water pump "twist test" is too tight, depends on how strong the person twisting it is, how grippy your hands are, etc.. But I'm still reluctant to tension it according to what the tool says, because I really don't want to have a belt that's too tight. There is a possibility that the tool is correct, and I'm either doing something wrong or just very weak (I'm also not exactly the strongest person on the planet), although I'm still leaning towards trusting my hand rather than the tool.
Another thing I should point out is, when I move the slack to the top of the cam belt, the water pump becomes very difficult to turn. On the other hand, when the crank pulley is turned clockwise and the slack is removed from the top, I'm able to twist the water pump fairly easily. So to put it simply: if I turn the crank pulley sightly counter clockwise, I'll have loads of slack at the top of the belt, but at the water pump it's pretty much impossible to turn. Obviously this makes sense because I'm taking away the slack at the water pump, but I suppose my problem is I'm unable to determine how much slack there should be (if at all) in the belt when checking the final tension. For example, when you tension your belts and do the "twist tests," do you move any slack on the top of the belt at all?
Maybe I just need to fiddle around with it more, and see if I can get it in a spot where I'm comfortable with. And if it ends up being too loose, I'll probably be able to hear it slapping around and then just re-tension it. I'd also be happy to link videos and/or pictures if that would be of more help, but nonetheless I didn't know if anything I'm saying might ring a bell for someone. Thanks!
Last edited by AidedGauge; 10-19-2019 at 07:48 PM. Reason: Formatting
10-19-2019, 10:58 PM
#2
I have. 944 turbo, have The Arnworxx tool and have tensioned my belts over a dozen times. Follow those directions precisely, don’t over torque the nuts, and you should be there.
I set the belts in the middle of the range and do not want the belts too tight as it can affect the life of the water pump and pulleys by wearing out the bearings.
Also be sure to turn the engine by hand (turn the crankshaft) to be certain that you’ve set the timing correctly since this is an interference engine.
If you’ve set the bets too tightly, your belts will whine loudly. You should hear a slight to no whine. If you set it too loose, you might hear belt slap but you risk the belt jumping the sprocket and you could cause the pistons and valves to impact. And at that point you’ll be really upset.
So I’d recommend using the tool according to directions or call Bruce Arnn to check whether you’re using his tool correctly. He is super helpful and a really nice guy. We need more Bruce Arnn’s in this world.
Good luck.
I set the belts in the middle of the range and do not want the belts too tight as it can affect the life of the water pump and pulleys by wearing out the bearings.
Also be sure to turn the engine by hand (turn the crankshaft) to be certain that you’ve set the timing correctly since this is an interference engine.
If you’ve set the bets too tightly, your belts will whine loudly. You should hear a slight to no whine. If you set it too loose, you might hear belt slap but you risk the belt jumping the sprocket and you could cause the pistons and valves to impact. And at that point you’ll be really upset.
So I’d recommend using the tool according to directions or call Bruce Arnn to check whether you’re using his tool correctly. He is super helpful and a really nice guy. We need more Bruce Arnn’s in this world.
Good luck.
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Autobreza (03-18-2023)
10-19-2019, 11:06 PM
#3
Instructor
I don't understand why you are fretting over some arbitrary, rule-of-thumb, belt twisting methods, when you have a brand-new instrument to measure the tension exactly and consistently. All of those "feel" methods are generally inaccurate with the possibility of wide variations in the results, depending on who is doing it. I'll bet that if you got some one with the belt twisting "gift" to tension a belt ten times and then measured each event, that the results would be all over the map.
As to wanting the water pump pulley to slip easily with the belt tensioned, why? if you can easily turn it by hand under tension, then the belt will likely slip on the pump pulley during operation.
Where are you located in Tejas?
As to wanting the water pump pulley to slip easily with the belt tensioned, why? if you can easily turn it by hand under tension, then the belt will likely slip on the pump pulley during operation.
Where are you located in Tejas?
10-22-2019, 12:48 PM
#5
Rennlist Member
Just to be clear up front: I have no intention to undermine the use of the Arnnworx tool and, when I find the stones and need to do it, I will also buy the tool for use on my own car. That said, I am a fan of multiple separate checks on such critical processes. With that as background, and since this is a recent post,I have the following question:
I was watching a samcrac video on his Ferrari rebuild and learned that Gates provides an app that will listen to the resonant frequency of a "twanged" belt as a measure of tension. Based on the frequency which the app hears, it provides feedback on setting the belt tension. Has anyone ever looked into this on their cars? It seems to me that it would be a great, extra layer of security when doing this kind of work. I'll go google to see if Gates even offers this for the 944 but figure I'd throw this up to the more experienced wrenchers.
Again, no intention here to discourage the use of the Arnnworx tool, which gets dang-near universal praise, just looking to see if this is a useful technique.
I was watching a samcrac video on his Ferrari rebuild and learned that Gates provides an app that will listen to the resonant frequency of a "twanged" belt as a measure of tension. Based on the frequency which the app hears, it provides feedback on setting the belt tension. Has anyone ever looked into this on their cars? It seems to me that it would be a great, extra layer of security when doing this kind of work. I'll go google to see if Gates even offers this for the 944 but figure I'd throw this up to the more experienced wrenchers.
Again, no intention here to discourage the use of the Arnnworx tool, which gets dang-near universal praise, just looking to see if this is a useful technique.
10-22-2019, 06:00 PM
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Sorry again for the late reply, although I just finished everything on the car and it seems to be doing great. No flopping noises indicating it's too loose, nor any whining sounds indicating it's too tight. The car idles perfectly and (maybe it's just because I haven't heard it in a while) sounds quieter than it did before.
I think my previous problem was I either wasn't getting the slack moved correctly, or I was missing something in the instructions, but regardless I managed to get a consistent reading on the tool that was within spec and didn't seem too tight. Same story when installing the balance belt, got a good reading on the 920X and it felt very similar to how the previous belt was installed. What I was doing previously was moving all the slack to the top like the instructions said, but it was ending up seemingly way too tight, maybe I was moving it too much and/or was a whole rotation off... I don't know for sure. Like you all were saying having a belt that's too loose is also very bad, as that could cause the valves to impact if the belt jumped, so I wanted to be sure it wasn't too loose either. I made sure to hand crank the engine and check my timing marks several times, all of which were on time and maintained the tension which I verified on the 920X.
I'll keep this thread updated in case anything changes, but everything seems to be fine as of now and the tool has given spot on consistent readings since. Thank you all for the help, and I hope it didn't seem like I was irritated with my 920X or anything, just wanted to see if anyone had similar troubles with getting everything put together/tensioned.
I think my previous problem was I either wasn't getting the slack moved correctly, or I was missing something in the instructions, but regardless I managed to get a consistent reading on the tool that was within spec and didn't seem too tight. Same story when installing the balance belt, got a good reading on the 920X and it felt very similar to how the previous belt was installed. What I was doing previously was moving all the slack to the top like the instructions said, but it was ending up seemingly way too tight, maybe I was moving it too much and/or was a whole rotation off... I don't know for sure. Like you all were saying having a belt that's too loose is also very bad, as that could cause the valves to impact if the belt jumped, so I wanted to be sure it wasn't too loose either. I made sure to hand crank the engine and check my timing marks several times, all of which were on time and maintained the tension which I verified on the 920X.
I'll keep this thread updated in case anything changes, but everything seems to be fine as of now and the tool has given spot on consistent readings since. Thank you all for the help, and I hope it didn't seem like I was irritated with my 920X or anything, just wanted to see if anyone had similar troubles with getting everything put together/tensioned.
10-22-2019, 06:21 PM
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I have. 944 turbo, have The Arnworxx tool and have tensioned my belts over a dozen times. Follow those directions precisely, don’t over torque the nuts, and you should be there.
I set the belts in the middle of the range and do not want the belts too tight as it can affect the life of the water pump and pulleys by wearing out the bearings.
Also be sure to turn the engine by hand (turn the crankshaft) to be certain that you’ve set the timing correctly since this is an interference engine.
If you’ve set the bets too tightly, your belts will whine loudly. You should hear a slight to no whine. If you set it too loose, you might hear belt slap but you risk the belt jumping the sprocket and you could cause the pistons and valves to impact. And at that point you’ll be really upset.
So I’d recommend using the tool according to directions or call Bruce Arnn to check whether you’re using his tool correctly. He is super helpful and a really nice guy. We need more Bruce Arnn’s in this world.
Good luck.
I set the belts in the middle of the range and do not want the belts too tight as it can affect the life of the water pump and pulleys by wearing out the bearings.
Also be sure to turn the engine by hand (turn the crankshaft) to be certain that you’ve set the timing correctly since this is an interference engine.
If you’ve set the bets too tightly, your belts will whine loudly. You should hear a slight to no whine. If you set it too loose, you might hear belt slap but you risk the belt jumping the sprocket and you could cause the pistons and valves to impact. And at that point you’ll be really upset.
So I’d recommend using the tool according to directions or call Bruce Arnn to check whether you’re using his tool correctly. He is super helpful and a really nice guy. We need more Bruce Arnn’s in this world.
Good luck.
I don't understand why you are fretting over some arbitrary, rule-of-thumb, belt twisting methods, when you have a brand-new instrument to measure the tension exactly and consistently. All of those "feel" methods are generally inaccurate with the possibility of wide variations in the results, depending on who is doing it. I'll bet that if you got some one with the belt twisting "gift" to tension a belt ten times and then measured each event, that the results would be all over the map.
As to wanting the water pump pulley to slip easily with the belt tensioned, why? if you can easily turn it by hand under tension, then the belt will likely slip on the pump pulley during operation.
Where are you located in Tejas?
As to wanting the water pump pulley to slip easily with the belt tensioned, why? if you can easily turn it by hand under tension, then the belt will likely slip on the pump pulley during operation.
Where are you located in Tejas?
And I'm located around the Dallas area, I'm very glad it's been cooler outside recently because it's made the process a whole lot easier.
Just to be clear up front: I have no intention to undermine the use of the Arnnworx tool and, when I find the stones and need to do it, I will also buy the tool for use on my own car. That said, I am a fan of multiple separate checks on such critical processes. With that as background, and since this is a recent post,I have the following question:
I was watching a samcrac video on his Ferrari rebuild and learned that Gates provides an app that will listen to the resonant frequency of a "twanged" belt as a measure of tension. Based on the frequency which the app hears, it provides feedback on setting the belt tension. Has anyone ever looked into this on their cars? It seems to me that it would be a great, extra layer of security when doing this kind of work. I'll go google to see if Gates even offers this for the 944 but figure I'd throw this up to the more experienced wrenchers.
Again, no intention here to discourage the use of the Arnnworx tool, which gets dang-near universal praise, just looking to see if this is a useful technique.
I was watching a samcrac video on his Ferrari rebuild and learned that Gates provides an app that will listen to the resonant frequency of a "twanged" belt as a measure of tension. Based on the frequency which the app hears, it provides feedback on setting the belt tension. Has anyone ever looked into this on their cars? It seems to me that it would be a great, extra layer of security when doing this kind of work. I'll go google to see if Gates even offers this for the 944 but figure I'd throw this up to the more experienced wrenchers.
Again, no intention here to discourage the use of the Arnnworx tool, which gets dang-near universal praise, just looking to see if this is a useful technique.
