KV6 Front Belt Tightness

[Mike Noc]

Originally Posted by xsport

another thought is that its idler or waterpump bearing. Im unclear if you used the timing tools or not. if you didn't and left them static then its possible that there is far too much tension on the belt either side of the waterpump.there are many variables to take into account between belt swops and components used on the job each time. once the two bolts are undone this allows the floating cams to give a much more balanced tension throughout the belts length. if not it puts the bearing under duress.this is one of the reasons I use the tools. many members have done this job without the tools successfully.

Surely with one drive pulley and all the others being driven the tension of the belt pretty much evens out? Of course there will be more tension in the belt runs after the camdrives due to the resistance of the valve springs, but the benefit of using the tools is accuracy of position of the pulleys, and nothing to do with differing belt tension in the runs.

Or am I missing something?

[Lovel]

Originally Posted by Mike Noc

Surely with one drive pulley and all the others being driven the tension of the belt pretty much evens out? Of course there will be more tension in the belt runs after the camdrives due to the resistance of the valve springs, but the benefit of using the tools is accuracy of position of the pulleys, and nothing to do with differing belt tension in the runs.

Or am I missing something?

Additionally to the valve gear position causing differences in belt tension you have the pistons on firing stroke and exhaust which also causes tension and slack on the belt.

[Mike Noc]

Yes there are a few factors governing belt tension on the different runs of the main belt but none that come from whether you use the setting tools or not.

As I see it the good thing about using the tools is that you can set the belt tension independently of the positioning of the cam sprockets, so timing can be spot on.

As for your noisy belt Gary I have come across this before on other engines when timing belts were too tight.

[xsport]

hello gary. I have the suspicion that in an attempt to "fine tune" the rear belts you would have again slackened and readjusted the rear sprockets too much causing extra tension on the belt between the two trying to align the inboard timing marks on the rears. these timing marks can never be accurate as the cams are driven from the top on one bank and from below on the other giving vast differences when at rest due to rear belt play and varying spring tensions directions. I used to do this but now I don't . to me once the tools are in place for timing its fine as it is timing wise and best left alone unless they are obviously out by one tooth. also in rave it tells you to take the loosened sprocket wheels as far as poss outboard to engage the toothing without any stressing of belt or sprocket to engage.im only assuming you have done the " fine tune" my appologies if not. I have done this myself !! I refer to your original post as stating too much tightness on the belt at the pump to sprockets not giving any "turn"as it were and assume the rest of the belt tension was ok ? or have you not checked the rest for tension … cant think of anything else other than I had a pump once (new old stock original) which caused belt whirring as it was fairly tight to turn but still in service now thankfully. all the best xsport

[Lovel]

Originally Posted by xsport

hello gary. I have the suspicion that in an attempt to "fine tune" the rear belts you would have again slackened and readjusted the rear sprockets too much causing extra tension on the belt between the two trying to align the inboard timing marks on the rears. these timing marks can never be accurate as the cams are driven from the top on one bank and from below on the other giving vast differences when at rest due to rear belt play and varying spring tensions directions. I used to do this but now I don't . to me once the tools are in place for timing its fine as it is timing wise and best left alone unless they are obviously out by one tooth. also in rave it tells you to take the loosened sprocket wheels as far as poss outboard to engage the toothing without any stressing of belt or sprocket to engage.im only assuming you have done the " fine tune" my appologies if not. I have done this myself !! I refer to your original post as stating too much tightness on the belt at the pump to sprockets not giving any "turn"as it were and assume the rest of the belt tension was ok ? or have you not checked the rest for tension … cant think of anything else other than I had a pump once (new old stock original) which caused belt whirring as it was fairly tight to turn but still in service now thankfully. all the best xsport

The fine tuning is carried independently of the front belt tension while the front sprocket is loose the cam on each cylinder bank be turned to align the rear sprockets, then tightened up again. Actually I did this engine on the workbench and had a lot of time to play with adjustment trialing the best and worst case timing tolerances before lowering the engine into the car. I have carried out this procedure on another KV6 recently (and others before that) and the belt is less taught and able to twist/move by what I would consider to be reasonable.

[Lovel]

Stripped down the engine back to the timing belt again today and found some interesting things. Intiallly I thought the belt was too tight but it was now found to be relatively loose.

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I found no gap between the tensioner piston and the tensioner roller which is not normal at all. The photo below shows that the piston was fully compressed and the tensioner roller body was contacting the casting of the alloy housing.

Note the indentations on both components.

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I tested the old piston tensioner by squeezing in the vice, but comparing the force required to a new INA tensioner the piston was less, not massively less but it was obviously enough to force the tensioner to bottom out.

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So the engine is now all back together with new belt and tensioner piston and things are nice and quiet again with a nice belt tension. Basically lessons learned are the the piston tensioner can fail enough to allow the roller tensioner to back off even further than it should. Even with the piston fully retracted and the roller tensioner butting up against the housing of the piston tensioner, I don’t think the belt would have jumped a tooth thank goodness.

This engine has done about 140k miles now and was on the original piston tensioner, so next timing belt change you do it might be prudent to change it at the same time as the roller tensioner as it is difficult to judge the force required to push the piston back for reassembly, and only by comparing it against a new piston tensioner in the vice is the only way practically to compare the ratings without some more sophisticated test equipment.

[SD1too]

Originally Posted by Lovel

I found no gap between the tensioner piston and the tensioner roller ...

During my exploratory tests I found that this can happen when the pulley/roller hasn't been set up according to INA's instructions.

Simon

[Lovel]

Originally Posted by SD1too

During my exploratory tests I found that this can happen when the pulley/roller hasn't been set up according to INA's instructions.

Simon

Oh it was set just fine and dandy (following INA procedure to the letter) I have no doubt about that, hence we can eliminate that. When I work on a (or any other engine come to that) KV6 I check, double check and then check again. The bearing was still locked in its original position when I fitted it, as that was my initial suspect when tore down.

The design of the INA piston tensioner for the KV6 would actually tolerate ham fisted persons tbh. The key part that needs to be assembled, adjusted and tightened by a competent person correctly is the roller tensioner bearing, which needs to be free to rotate on its (greased) fulcrum when the 13mm A/F set pin is torqued. Now do they mention that in the INA procedure ? I think not, but I have seen this on one roller tensioner which was binding slightly (this was a non genuine part) so if I followed the INA procedure all would not have been well, as you see the INA procedure although very good does not apply real world assembly techniques and engineering appreciation of tolerances and component fit that have been etched into my mind by journeymen over many years in the field of Engineering.

The culprit was the piston tensioner which although functioning correctly compressed too easily allowing the roller tensioner body to bottom out. There is no recommended test or specifications given for the piston tensioner and one can only check when a new version is compared to the original used piston tensioner fitted to the vehicle.

I repeat. The piston tensioner was at fault and compressed too easily, and hence the recommendation should be to replace at xx miles or age expiry. Basically when you are in there change it, the genuine version can currently be had for £52 if you shop around.

[SD1too]

Gary; just to clear up any possible misunderstanding, I wasn't suggesting that the pulley hadn't been set-up correctly on your particular car, only that I found that this can result in the contact you described and so shouldn't be excluded by readers of this thread in their diagnostic process.

Simon

[sworks]

Did you spot the difference in the piston length from fitting until now through the grommet or did you just pull it apart again?