[ds968]

Back to my mech's experience, he seems to think very highly of Laso pumps. For whatever that's worth...

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[DaveN]

The last one that went into my previous 944 was a Laso, sold the car with a new pump and one month later, Kaboom. I think it's hit and miss sometimes.

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[retro53]

My new (old) 968 is a '93 with 47K on the odometer (probably true). The timing belt was replaced about three years ago, but the previous owner does not remember whether he brought it back to have it retensioned after the 3000 miles that the mechanic reccommended. Assuming he did not take it back, how important is this. The car seems to be running very well. If the belt should be retensioned, is this something that needs specialized tools?

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[Scott Collins]

retro53,



The 968 timing belt assembly uses a hydraulic tensioner that is not adjustable. I have never re-tensioned a timing belt. I am not sure what you would do... Maybe your mechanic is talking about the balance shaft belt? That one definitely needs to be re-tensioned, and I personally have never waited more that about 300 miles. The balance belt will stretch, especially if it is too tight initially- you would hear pronounced whining from the belt in that case. If it's too loose it can deflect and come into contact with engine components, such as the water pump pulley, which is pretty close to begin with. There is an idler roller located in the center of the longest run of the belt, and the tensioning roller, located at the lowest point on the front of the engine. Both of these are locked down, static, with a 17mm nut. Sorry for this long winded explanation.



You do need a few specialized tools to do this job: flywheel lock (if either belt is being replaced), torque wrench that measures 150ft/lbs to torque the main crank bolt, spanner wrench, and balance shaft sprocket wrench. The spanner and balance shaft sprocket wrenches can be obtained here:



http://www.arnnworx.com/catalog/



Best of luck with the belts. It's one aspect of our cars that needs regular attention and should never be overlooked.



-Scott

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[retro53]

Hi Scott,



Thank you for the quick reply! I checked the service records that came with the car. The work was done in January 2008, and the car had 33K on it. The invoice lists the camshaft timing belt, balance shaft belt, and alternator belt as being replaced. There is a notation under the timing belt that says the timing belt must be retensioned in 2000 miles. Hmm. The car is running great and I don't hear any unusual noises from the engine. Is the procedure for this operation available somewhere in the forum?



John

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[Scott Collins]

John,



PM sent.



-Scott

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[judge]

Well, it's been a bit of a saga, but I finally got my Cab back on the road with the belts and rollers replaced. I've had the car for about 9 months now and the last belt change was in 2005 and about 10,000 kilometers or 6,000 miles ago. I've read all about the need to keep belts up to the car and so it was a job which had to be done. The problems began and ended with US Postal who took TEN F...ING WEEKS to deliver the parts I ordered from Paragon. <img src="/forum/images/smilies/968/mad.gif" class="smilie" alt="" /> After 45 days Paragon were able to start an Insurance claim and I ordered replacements from Type 911 in the UK. Parts duly arrived from the UK in 6 days [!!!] and I booked the job into the local Mercedes dealer.



All goes well until the cam belt tensioner comes out with a leaky seal and we decided to replace it. Ordered the new part from Porsche in Sydney on Friday and they send the wrong part!!! Then Guess what!! I get to work on Tuesday, and there sitting on my desk is the order from Paragon. I called Carol at Paragon and she was great, but the insurance claim is over and it's not worth me sending the parts back for a credit because it'll cost me another $100 in postage!! Anyone in AUS want a new set of belts and rollers?? <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" />



Two more days spent waiting and the job is finished within a couple of hours. So, time from first order to completion - 72 days, time in shop, one week. Cost- enough for two complete sets of parts plus postage x 2, pluss a new tensioner at A$273.21 plus A$539.00 in labour for the belt change and an annual service. BTW the boys at Callaghans in Warrnambool have been great. <img src="/forum/images/smilies/968/clap.gif" class="smilie" alt="" />



Then another guess what - both old belts show no signs of deterioration and very little wear, and all the rollers seem fine. I've read the forums and the accepted wisdom about replacing belts, and I know $1500 or so for a belt job is way cheaper than a new top end or complete motor, but why does there seem to be this vast difference in the apparent wear from one car to another? Are some cars thrashed to death [or raced] and is this the difference - is it just that I'm constrained to drive [reasonably] legally?



Anyway, now I can drive without the fear of coming to a grinding halt and paying a large sum of cash for the privilege of hearing you all say "I told you so.." <img src="/forum/images/smilies/968/968Forums_Rules.gif" class="smilie" alt="" />

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[Cloud9...68]

The problem is that the life of the belts is so unpredictable. Undoubtedly, if you took 100 968s and drove them all fairly similarly until one by one, their belts failed, you'd see a wide, standard bell-shaped distribution, with a small number snapping at around four years or 40K or so miles, and a few going the full ten years. So, where do you place the change interval? At the peak of the distribution (probably at around 5-6 years)? No way! Far too many would snap prior to this time period to be reasonable. You put the interval below the lower tail of the distribution, or about three years in our case, to ensure that virtually nobody ever sees a valve-to-piston encounter of the worst kind. Of course this means most people are throwing away their belts with a lot of life left (thus your very typical observation that your belts appeared to be in great shape), but this the very reasonable price we pay to avoid the possibility of a $5K repair bill.

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[tamathumper]

Keep the belts and rollers, you'll need them in a few years anyway.

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[flash]

i just saw the shot of the pumps - the contours of the chamber seem to be different between all 3



note the recessed area behind the bladed impeller



note the little "bumps" at the bottom of the chamber in both of the lower 2 units



interesting stuff



as for "signs of wear" you can't always see the signs of wear on belts. you would have to do elasticity tests to see the problem. the rubber loses that over time. then, when it finally gets too rigid, it snaps. usually the balance belt first, most often because people fail to retension their belt like they are supposed to. according to the book, it's every other year or 30k miles, whichever is first, though we have found that to be only half as frequent as needed. when that goes, it frequently gets tangled up in the timing belt and snaps that too



so don't feel bad about doing the job. feel smart for avoiding the problem.

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