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| A new Cam Belt Tension Question | Rating: 
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| Posted: 05-15-2006 12:30 pm |
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1st Post |
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Brett Gibson JH5 20497 Member
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Well I thought I would remove the mystery about cam belt tension, the manual shows a belt tension gauge and when it ding's or something, your good to go. So me in my infinate wisdom :>0, go out and buy a belt tension gauge from Mcmaster-Carr so as to remove any doubt I have if I've done the job correct, so I set the belt tension with the old rule of thumb, from the distributor to the cam sprocket you can twist the belt 3/4's to verticle, or there abouts Then I put the belt tension gauge on and take a reading and I get 140 lb's, I go to check against the shop manual and low and behold, it does'nt have a listing on what it should be, I even pulled out some Lotus spec's and a quick search thru the service bulletin's and cant find diddley. Help .................... does anyone know what the belt tension pounds should be ??? I was even thinking that I would bring this gauge along to the Nationals at Springfield in case someone would like to check there tension, actually I could still do that, check a few cars, see what the average is and go from there, humm.... Judson, you rebuild alot of these things, how are you setting tension if you dont mind me asking ??? Any help would be appreciated, Thanks. Brett.
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| Posted: 05-15-2006 01:12 pm |
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2nd Post |
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Judson Manning Member 
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To be honest Brett, it's somewhat of an art based on the unfortunate experience of losing 3 engines to skipped timing belts. Some rules of thumb: 1. Start with the engine cold and using a 3/4" wrench, turn then engine by hand so the belt tension on the crank-to-exhaust sprocket section is at its maximum. 2. When the crank-to-sprocket section is at its tightest, the accessory-to-intake sprocket section should be at its most flexible. Using your thumb and index finger wiggle the belt up and down. It should flex roughly 3/8" to 1/2" in either direction with moderate effort. At the same time, you should be able to twist the crank-to-exhaust sprocket section of the belt 45deg, again with little to moderate effort. 3. When you think you've got it right, start the engine. While the engine is heating up, observe the belt and see if it oscillates up and down (accessory-to-intake section). If any, it should be minor (1/4"). If the belt is too loose it will oscillate far enough to jump teeth on the intake sprocket and trash the engine. 4. Repeat the above procedure when the engine is HOT (not just water temp). Now there should be a significant difference in the accessory-to-intake section tension. Wiggling it this time should only produce 1/2 as much movement. 5. With a new belt, if its too tight, the lettering will wear off quickly if the belt is too tight. 6. It's always a good idea to check/adjust the belt every 3 months and/or 3000miles. The belt itself can last a life-time, but without close attention it can wear, get loose and trash your engine.
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| Posted: 05-15-2006 06:36 pm |
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3rd Post |
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Greg Fletcher Administrator 
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I have an original belt tension service tool and I can tell you from experience, save your money, it's just not a great use of funds. I find the tool mildly interesting from a historical perspective but you are much better off learning to get a feel for it yourself as Judson mentions. If you have not replaced a timing belt before I would think an owner should prefer to rely on their judgement from reading instructions above rather than entrusting belt tension to a mechanical device. It's easy to learn, and not a big deal. Once you've done it a few times and "have the touch", it's like riding a bike- you never forget.
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| Posted: 05-15-2006 07:11 pm |
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4th Post |
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Brett Gibson JH5 20497 Member
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Thanks Judson /Greg for the info. I have changed my belt a couple of times, and I have a tendancy to run it a little on the tight side, but I gradually slacken it off untill the whine goes away, I had'nt thought to much about the long run between the exhaust and crank for checking flex, mostly I'm checking between the inlet and dizzy, thanks for that tip, and also checking every 3000 miles, good info. As for the tool, I kinda like picking up tools here and there and this thing I thought would take the guess work out of setting the JH belt, while not cheap, I do know that it is very accurate, we have some timing belts on power transmission equipment here at work and these gauges work quite well on those. So thats why I thought if someone knew the poundage I could set it for that, then check it out against the suggestion's Judson has kindly provided, to see how they compare. I've seen a few JH's in my time that the belt is so tight that it has polished the cam gears so much that the teeth are rounding off, so I just thought it might be nice to share a tool that "took the guess work out" . Judson, are you going to the nationals, if you are I like to see what poundage reading your engine shows, if not and I dont get a answer to this question, maybe I could send you this tool and you could check it out and see what your readings would be, if your interested that is.
this is the gauge if you want to check it out on the Mcmaster site. Brett.
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| Posted: 05-15-2006 07:17 pm |
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5th Post |
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Brett Gibson JH5 20497 Member
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oops parts # 60275K21 Dial Timing Belt Tension Tester 40 To 180 Pound
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| Posted: 06-16-2006 07:08 pm |
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6th Post |
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Brett Gibson JH5 20497 Member
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Just as a follow up: I took the belt tension gauge to the Nationals in Springfield in the hopes of getting a few readings from JH's, and managed to do so. Result's: 2 cars were running at 80 lbs, 1 at 90 lbs, 1 at 95lbs, mine at 110 lbs and a GT at 130 lbs (w/whine). We adjusted the GT down to 95 - 97 lbs, ( no whine ) Plus we also set a JH to 95 lbs that we attempted to change the timing belt on, but crank bolt would'nt undo. And when I got home I reset mine to 95 lbs. and all seem's well. This is not a scientific study but hey, just some info. all the readings were taken on a cold engine just above the water pump / thermostat housing area. If anyone is having a meet or show and would like to borrow this tool to check a few cars just let me know, all I ask is that it be returned in the condition you recieved it. Thanks Brett.
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| Posted: 06-22-2006 09:06 pm |
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7th Post |
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John Finch Member
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Following is how Tim Engle explained and set up 18309 after bringing it back to life after sitting for 15 years. So far no issues at all. Temp approx 70 degrees f, rotate engine to TDC, Using a Borroughs belt tension gauge we set it to just over 100 pounds knowing the new belt would stretch. We set the gague close to the distributor sprocket. The Lotus guys use the Borroughs gauge all the time. Several models are available so not are all the same. I purchased one on ebay and compared it to Tim's with similar results. My Borroughs is actually labled Robinair # 10240 with mfg by Borroughs, Kalamazoo MI on the dial. The Borroughs for the Lotus 907 is model BT-33-86J according to Tim. John
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