Timing belt alignment - LotusTalk - The Lotus Cars Community
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post #1 of 17 (permalink) Old 04-24-2019, 06:12 PM Thread Starter
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Timing belt alignment

I am replacing the timing belt and as I turn the crankshaft a few times, I noticed that the belt is tracking towards the firewall too much. Originally, the timing belt would move to the edge of the cam sprockets but never go over the edge. However, since replacing the eccentric bearing and belt, the belt is overhanging by about 0.5cm. I've searched the forums to see what can be adjusted to move the timing belt towards the middle. I saw this post but it didn't outline how to move the belt a significant amount.
https://www.lotustalk.com/#/topics/415673

So is there a trick to adjusting the cam gear or tensioner to get the belt to track towards the middle? Anyone have this issue after installing a Flennor Germany bearing?

Thanks in advance.
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Jim S.
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post #2 of 17 (permalink) Old 04-24-2019, 08:10 PM
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that link didn't work

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post #3 of 17 (permalink) Old 04-25-2019, 03:29 AM
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Does the bearing have a tapered bore which if put on backwards limit how far it goes on? I have seen that with Caterpillar machines.
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post #4 of 17 (permalink) Old 04-25-2019, 04:29 AM
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Flip the belt and see what happens?? Maybe a bad belt??

Tensioner fully tight??

The pulleys are all fixed, so the issue has to be with the tensioner not being square to the travel of the belt.

Jonboy

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post #5 of 17 (permalink) Old 04-25-2019, 04:33 AM
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That belt is too far forward for sure. I have used Flennor bearings a bunch and never had this problem. I would try a "re-set" by slackening the tensioner and slide the belt back to a normal position, re-tension, and hand rotate again to see if anything changes. Other than that the only thing I can think of to check is that seating the bearing into the tensioner eccentric is correct - is is possible you didn't press the eccentric full in to the inner race of the bearing?

Tom Mieczkowski
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post #6 of 17 (permalink) Old 04-25-2019, 07:58 AM Thread Starter
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@Vulcan Grey - link works on Android, but not PC it would seem. Here is the PC link https://www.lotustalk.com/forums/f16...ulleys-415673/

@Jenna'sEspritTurbo - I don't know. I will have to remove it to inspect for a tapered bore (sounds like a stomach parasite)

@Jcslocum - Tensioner is fully tight (108 Hz @ 30deg BTDC). I could try flipping the belt around but the OCD in me won't like having the belt's lettering facing the other direction (j/k).

@mieczkow - Thanks for confirming the new Flennor. I hadn't seen this bearing before and glad to know others had positive experiences with it. I have "reset" the belt at least three times as you have described and it keeps wandering back to the firewall.

I'll pull the tensioner, inspect it and upload photos tonight.

Jim S.
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post #7 of 17 (permalink) Old 04-25-2019, 08:51 AM
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I pressed the bearing on for @Seraph using a hydraulic press. It is fully seated on the hub.

In my experience a walking belt can be due to the head being skimmed when the head wasn't fixtured correctly to hold the cam surfaces parallel to the head surface.
There is a little wiggle room when the cams are bolted to the head, where they could be out of parallel. When I machined my head to fix the tapered issue, I first had to bolt the cams on while verifying parallelism using a dial indicator on a milling machine with a 22" travel. A few thousandths of an inch difference (.007" in my case) end to end will cause the belt to walk. The dowels for the cams do not hold it better than that.

You could try aligning cams a bit at the time of final sealing and tap the turbo side of each cam, towards the other, with a rubber mallet as you tighten them back down. That will angle the cams outward and cause the belt to walk back toward the engine. You'd have to remove, clean, recoat them with the loctite 518 (5188) to reseal them, and do this at the time of final tightening.

It could also be something worn in the pulleys or cam journals, so the belt is pulling them downward.

Travis
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Last edited by Vulcan Grey; 04-25-2019 at 10:37 AM.
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post #8 of 17 (permalink) Old 04-25-2019, 08:57 AM Thread Starter
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Tensioner and bearing pics
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Jim S.
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post #9 of 17 (permalink) Old 04-25-2019, 09:03 AM
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I have had an issue like this, on the one I was doing, the washer behind the crankshaft timing sprocket slipped off of its ledge and wasnt allowing the crank sprocket to seat all the way.

Good luck!! let us know what you find!

T.J.
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post #10 of 17 (permalink) Old 04-25-2019, 09:14 AM Thread Starter
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Good grief. I took a quick work break to pull the tensioner off for pics. Then I'm trying to figure out where all of this red grease is coming from. Turns out I skinned a knuckle and didn't realize it until my finger stuck to my pants.

I'll try giving the cam towers a whack and see what that does.

Jim S.
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post #11 of 17 (permalink) Old 04-25-2019, 09:24 AM
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Confirm the washer for the crank pulley is installed and is the correct orientation and that it is seated properly, then look from there in the direction of rotation how does it run on the tensioner? is it off to the front there too? then the aux pulley? then the intake and ex pulley. If any of the pulleys were removed (say for a green dot upgrade) confirm they are all seated correctly. There is also a ring on the aux/oil pump pulley that if not seated correctly can allow the pulley to 'move'.
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post #12 of 17 (permalink) Old 04-25-2019, 02:44 PM
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it's been years since I did replaced the bearing...can't the sleeve go on the bearing either way? the sleeve may have a slight taper from wear and is on backwards from previous
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post #13 of 17 (permalink) Old 04-25-2019, 04:24 PM Thread Starter
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This might be part of my problem. The washer behind the crankshaft pulley does not sit flush on the crankshaft pulley gear. It is slightly too small. A new washer is ordered and on it's way. Now I twiddle thumbs looking at the car for the weekend.
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Last edited by Seraph; 04-27-2019 at 06:00 PM. Reason: Wrong washer description
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post #14 of 17 (permalink) Old 04-25-2019, 04:32 PM Thread Starter
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I have looked at the bearing from both sides and there doesn't appear to be any tapered edges to indicate the bearing requires a certain direction installing the eccentric.

Jim S.
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post #15 of 17 (permalink) Old 05-02-2019, 11:41 AM Thread Starter
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@Twasak! wins. The washer didn't properly fit over the lip of the crankshaft pulley gear. I installed a new washer and the belt appears to be tracking to its usual position (about 0.2cm of gear to spare on the front side). I have only cranked the engine half a dozen turns but looks good so far.
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post #16 of 17 (permalink) Old 05-02-2019, 02:35 PM
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I'm late to this discussion. Sorry if this is too little too late.

The washer on the crank sprocket doesn't sit flush. It should solidly engage the 'ledge', but it's thicker than the ledge is deep, so it will stand proud. That way it is pinched by the sprocket when everything is tightened down, and clamped securely in place.

The washer isn't flat... it's curved/ domed backwards such that it's outer perimeter leans back torward the engine. The rear face of the V-belt pulley is curved forward, and the washer is curved backward. Between the two, they form a funnel that guides the belt onto the crank sprocket. That is the feature that locates where the timing belt tracks, presuming all else is also correct/ straight.

If the washer is installed backwards, such that it curves forward over the sprocket's space, then it will push the timing belt forward. Once it's track is set 'forward', the belt will ride forward on all the sprockets. Flip the washer over so that it curves backwards toward the engine, then the belt should track noramlly.

*~*~*~*
All that presumes everything else is correct.

All the pivot axis are supposed to be parallel... crank, tensioner bearing, auxiliary shaft, and cam shafts. If something happens to cause one axis to be out of parallel, like the tensioner mounting stud is bent, then the axis will coverge toward some point. Whether they converge forward or backwards, the belt will track 'off the cone' toward the convergence point.

907s and early 910s used a spring-loaded, semi-automatic tensioner. It was articulated, and the 'hinge' could wear. When it got sloppy, the moving side of the tensioner would flop off-axis toward the most-worn side of the hinge. The bearing itself wasn't tapered, but it was running at an angle to the plane of the belt, and the belt would run off the 'taper'... forward or backward as chance would have it. Later spring loaded tensioners (all 910) have plastic bushings in the hinge pivots, and they should be replaced everytime the tensioner bearing is replaced. The bushings are cheap. If the tensioner is apart for any reason, replace the bushings.

One possibility that Travis mentioned is when a warped head it milled to flatten it. If an unknowing shop simply mills the bottom flat without also making certain the bottom is perfectly parallel to the cam bores, then the cams will be off-axis when the 'wedge head' is installed. That's a whole 'nother' topic, but it is absolutely NOT correct to simply mill a warped head !!

Everything about the tensioner bearing/ roller is straight and cylindrical. No tapers anywhere. And they're hardened steel, so it's very unlikely that they will wear to a taper.

The cam and auxiliary pulleys are also made without any tapers. They're aluminum and hard annodized with a dark olive drab to black color. If the outside perimeter (the teeth) are bright, shiny metal, then the annodizing has worn off. In that case, the raw aluminum will wear quickly, so replace the pulley. If a shiny pulley is wearing, then it's likely it will wear at something other than perfectly straight, and the belt will run off center in the direction of any taper.

Any pulley that has a raised edge around the front or rear is bad... replace it. It doesn't have a 'raised' edge, it's the center that has been worn down. If a pulley is worn enough to show edges, trash it.... whether the belt is tracking straight or not.

Regards,
Tim Engel
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post #17 of 17 (permalink) Old 05-06-2019, 08:28 PM Thread Starter
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@Esprit2
Thanks Tim for your sage advice.

It seems that after the engine ran for about 60 seconds the timing belt moved back to the front and overhung by about 4mm. No new leaks at least.

I tried installing the old belt and it still hanging off the front pulleys too.

The cam pulleys are still in good shape. The anodizing is still on them and no worn spots.

I am at a loss on what I should try next. I suppose I could try reinstalling the eccentric into the old bearing and see if that has any affect, but I'll need to go buy or borrow a hydraulic press.

Any other ideas before taking the engine cams & cam journals out?

Jim S.
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