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Engine Specific Info and Questions => IDI Engine => Topic started by: bajacalal on August 12, 2014, 05:46:53 pm
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Does this belt tension look ok? I thought "you should be able to twist the belt 90 degrees" and this looks like less.
http://vimeo.com/103267313 (http://vimeo.com/103267313)
It seemed tight to me, but I barely even moved the tensioner when I tightened it. With the other belts I've installed you had to move it maybe 1/4 turn but this was barely even 1/8 turn to get it to this point, it was maybe one finger's worth of a gentle pull. So I can't believe it would be too tight. This is also a different brand of belt than the Contitech I used before, it seems a lot more rigid and thick even without being tensioned than the Contitechs were. This was after 10 minutes of the engine being run, it was tighter before that.
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I believe the seat of the pants measurement for belt tightness is not 90*, but 45; it looks like you're about spot on from the video. I haven't put it on yet, but I also bought a Mitsuboshi belt, and I agree that it does seem to be made of slightly stiffer rubber than the Contitech belts.
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That belt is tighter than I put them on. Bentley says to use gauge so I would defer to that. IM shaft and IP bushings like the looser side of things on the 45 to 90 twist scale.
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When I was still running my 1.6 I would go as loose as I could without belt flap between the pump and cam pulley. The 'sweet spot' is very close to that "45 degree twist" - less tension and the belt will be flapping. Once the belt is stable you should be good to go. As was mentioned above, an overly tight TB will cause quite a bit of damage to your intermediate shaft bearings and your injection pump input shaft bushing.
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Wthout a belt gauge, that's the approach I take also -just tight enough so it does not flop. I have heard that if you make the belt too tight, it will sing
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Atleast its not as tight as I have seen on some used cars :)
Just curious for those that do their own belt, do you use the tool on the tensioner?
I don't and I think that stops me from making them too tight.
I move the tensioner to get the slack out with minimal force and then find myself exerting a little extra to nudge it and hold while I tighten the bolt up.
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I try to get 90 degrees with the twist scale. Bentley says use gauge so I will not endorse twist scale and hillbilly it up. FWIW I have seen guys that ran engines from the junk yard that the tensioner was loose and the belt flopping with no valve contact. I don't think there is enough play if it is timed correctly to get valve contact if it is way too loose.
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A flapping belt isn't going to cause valve contact on its own if everything stays in place, but it will dramatically increase the chances of skipping a tooth.
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Here's the Bentley:
(http://img.photobucket.com/albums/v55/dedfrog/belt_zps65d5e537.jpg)
I feel like physical strength could influence the "twist by hand" method however.
A bodybuilders twist and my feeble-handed twist are probably a lot different haha.
I weigh 130 lbs and probably can't bench much more than that.
I went out and twisted my belt and it is about 60°-70° I'd say.
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Another somewhat subjective test that is a little more accurate than the twist is to do the following. Hook the four fingertips of both hands over the edge of the belt on the cam or injection pump and give it a decent yank towards you. You should be able to pull it a small amount (1/8" or so). If you can't budge it at all, it is too tight. If it slides easily it is too loose. IMO it is a good idea to get either the belt tension tool and do a couple to spec so you know what the right tension is or to feel the tension on a new properly tensioned late AAZ or AHU/1Z with the automatic tensioner. The early AAZ and 1.6 should be tensioned similarly.
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To follow up I checked on it and completely loosened the tensioner and then re-tensioned it like shown in the Bentley as far as how far up to pull up the tool and it seemed to be about the same amount of tension but the belt feels looser now than in the video, you can turn it a little more and you get a little bit of I guess lateral deflection if you want to call it that (pulling it forward) so I think it's good... The Mitsuboshi belt is definitely stiffer than the old Continental ones and a little thicker too I think so they do behave differently.
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The direction of the wrench when properly tensioned will change slightly from one engine to the next.
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I lost my tensioner nut, drove aroud for over a week wondering why it ran so bad at low revs.
When i pulled the cover the belt was only halfway on, but on the right tooth...
After this incident i've been less scared of not thigtening the belt enaugh, and more scared of not thightening the nut enaugh. Locktite is also a good help...
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Now you have me scared. I am sure my belt is on the loose side , as it "flops" a bit. OTOH, I have been running these cars for 20 years now and never skipped a tooth or wore out an intermediate shaft bearing or pump prematurely.
After re-reading the passage in the manual above I see it reads "between the injection pump sprocket and the CRANKSHAFT sprocket"...can you even twist it there? (that can't be right...the picture shows pump to cam sprocket)
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That appears to be a typo in that version of the bentley
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Wow that could really be a typo in that Bentley manual .
I have the equivalent VW tension gauge (looks exactly like it) and the reading is taken halfway between Cam Sprock and Inj Sprock.
I'm so overboard with my belt/timing parameters that I even count the belt cogs to verify centered. lol
The tool (new in package) was not too expensive on eBay and very gratifying to know you REALLY have it right. Maybe by genetic coincidence, my comfort level hits the range most every time without re-adjusting.
Still consider it a highly valuable tool for doing the belts and still check them all each time. Belt, bearings and seals life/wear are less stress in the back of my mind after buying the tension measuring tool some years ago.