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Car Forum / Porsche / Porshe 944 / August 2008'86 951 - Time to do the Timing Belt
OK, I'd like to try changing the timing belt myself in my '86 944 turbo. I've seen the Shop manual. Section 13-2 describes toothed belt tightness for the balance shafts, while 15-1 describes the toothed belt camshaft tightness checks. I don't have the special tool, and the description is pretty weak on changing the belts. Can anyone steer me towards some advice on this. Thanks. clark's garage has a good faq it's not hard, but on your car, you may or may not have the spring tensioner for the timing belt - find that out - if you have the spring tensioner it's easier, but be sure you remove the tensioner, don't try to work the belt around it or you will be very very unhappy (trust me on this one). If you have the manual (no spring) tensioner, you will want to make or buy the wrench to turn the odd sized nut that tensions the belt - set it "about right" based on what the old one felt like, rotate engine by hand and see that all is well and it still feels "about right", then start car and let it idle - if belt flaps, it's too loose, tighten "just a bit". If you hear a whine that sounds like a rootes blower (supercharger), it's too tight, loosen it. > OK, I'd like to try changing the timing belt myself in my '86 944 turbo. > I've seen the Shop manual. Section 13-2 describes toothed belt tightness > for the balance shafts, while 15-1 describes the toothed belt camshaft > tightness checks. I don't have the special tool, and the description is > pretty weak on changing the belts. Can anyone steer me towards some > advice on this. Thanks. ** Posted from http://www.teranews.com ** > clark's garage has a good faq > it's not hard, but on your car, you may or may not have the spring tensioner > for the timing belt - find that out - if you have the spring tensioner it's > easier, but be sure you remove the tensioner, don't try to work the belt > around it or you will be very very unhappy (trust me on this one). Thanks. I found the FAQ at Clark's, and that helped a lot. I also looked for the timing belt and balance belt online. I was surprised to see that the balance belt is about twice as expensive as the timing belt. > If you have the manual (no spring) tensioner, you will want to make or buy > the wrench to turn the odd sized nut that tensions the belt - set it "about [quoted text clipped - 3 lines] > whine that sounds like a rootes blower (supercharger), it's too tight, > loosen it. I suspect I've got the manual (no spring), but that's first on my list to check. Are there any other components I'm likely to need (or should replace) beyond the two belts? I'm at about 150K miles now. > I suspect I've got the manual (no spring), but that's first on my list > to check. Are there any other components I'm likely to need (or should > replace) beyond the two belts? I'm at about 150K miles now. I would recommend you replace all the rollers, particularly !!!! the timing belt tensioning roller. If you see any evidence of an oil leak from the front seal, it is expedient to replace it at the same time - and same for balance shaft seals. Also, inspect water pump - on my 85.5, the original pump started to leak at 90K miles, the replacement pump is still operational and not leaking at over 250K miles balance shaft belt has teeth on both sides - that makes it cost more. Gates makes a tool called "klickit" for testing belt tension - it's cheap, $10 - you can use one of those to build your confidence, but the "whine or flap" test I described is what I do, and it has never failed me. But, remember, if the timing belt breaks, you will damage valves, and it will cost you about $600 in parts plus your labor to remove head and have it fixed. ** Posted from http://www.teranews.com ** I have removed the balance shaft belts on both my 944s. They just rob power and create other problems. How does that affect engine idle smoothness? Can you tell much of a difference? >I have removed the balance shaft belts on both my 944s. They just rob > power and create other problems. there is a significant difference in smoothness - that's why Porsche added them - > How does that affect engine idle smoothness? Can you tell much of a > difference? > >>I have removed the balance shaft belts on both my 944s. They just rob >> power and create other problems. ** Posted from http://www.teranews.com ** > there is a significant difference in smoothness - that's why Porsche added > them - following up - I changed a timing belt and balance shaft belt yesterday - so I did the test with/without and it is clearly obvious at idle that the balance shaft belt is not installed. In fact, when a 944 was my daily driver, I would wait for the balance shaft belt to break as my signal to change both belts - never failed me. ** Posted from http://www.teranews.com ** <I would wait for the balance shaft belt to break as my signal to change both belts > The reason your balance shaft belts broke - is because they weren't tensioned properly. My 1st 944 with 550,000 miles - NEVER broke a belt. My now 87 944 with 250,000 miles also never broke a belt. I change the belts when the water pump fails or the roller bearings start squeaking. Adjusting those belts based on their flapping or not - is absolutely ridiculous. jolie >> there is a significant difference in smoothness - that's why Porsche >> added them - [quoted text clipped - 6 lines] > > ** Posted from http://www.teranews.com ** as you wish - I am not going to argue with you. I will point out that there is a replacement interval for the belts. Perhaps you have replaced your belts some time in the 550K miles? Well, I discovered that I could replace belts on the scheduled interval, or just wait for the balance shaft belt to fail - typically at about 50% more miles and use that as my signal. If you have driven your 87 for 250,000 miles without ever chaninging a belt, please post that information here. I honestly don't care if you or anyone else believes me - your statement about why the belts break is false, they break due to wear and age. I posted a hint about belts for those who wish to consider it. You are free to disregard it. Much of what you read on the internet is untrue or nonsense. You and anyone else who reads anything on the internet is responsible for decidign what is and is not reasonable and true. Between the 944s I've kept running, I would say there is at least a million miles, maybe more. I've done all my own work since 1985, if you do your own work, perhaps you can post how you set belt tension on a pre 87 car. If you do not do your own work, you are not qualified to discuss the issue. > <I would wait for the balance shaft belt to break as my signal to change > both belts > [quoted text clipped - 19 lines] >> >> ** Posted from http://www.teranews.com ** ** Posted from http://www.teranews.com ** > as you wish - I am not going to argue with you. I will point out that there > is a replacement interval for the belts. Perhaps you have replaced your [quoted text clipped - 40 lines] > > ** Posted fromhttp://www.teranews.com** Dale Carnegie has written a very well received book: How to Win Friends and Influence People. Good reading when inside human society. If you remove the balance shaft belt, start the engine and notice vibration, then you have other problems with the engine. > If you remove the balance shaft belt, start the engine and notice > vibration, then you have other problems with the engine. Odd that you should say that - I would expect that the Porsche litereature would be correct - it explains that the purpose of the balance shaft is to reduce vibration. ** Posted from http://www.teranews.com ** Whenever I changed my 1983 belts, I always used the Porsche <expensive> recommended gauge. I have a friend that owns the gauge and he most generously lets me borrow it. On my 1987, even though I have the gauge available, I found letting the self adjuster do it's thing and that worked great. In my 3/4 million miles of Porsche driving and maintenance, I NEVER had a belt break. I dont really follow Porsche's scheduled maintenance mileage recommendations. I just change the belts (and every other time - the rollers) whenever the water pump fails. I guess if you go that long without changing belts, they better be initially adjusted perfectly - aka the Porsche belt tensioning gauge. joliett ______________ ______________ >> If you remove the balance shaft belt, start the engine and notice >> vibration, then you have other problems with the engine. [quoted text clipped - 4 lines] > > ** Posted from http://www.teranews.com ** I recently changed the timing belt on an Audi TT - it's very much like the porsche timing belt - Audi forgot to change KM to miles in the manual and listed the interval as 120K miles (when it should be 120 K km) - so the belt failed at 80 K miles - the belt did not break, the teeth separated from the belt in one area, with the expected damage to valves. on the 944, as I said, you can drive until the balance shaft belt breaks (and yes, it does break) - and then change both - since the balance shaft belt turns twice as fast as the cam belt, it will fail first, and the increasd vibration is really obvious. Like you, I've never had a timing belt break in something over a million miles - even with my procedure of letting the balance shaft belt break as an "indicator" - I have had a roller fail, with equivalent bad results, so I now change the rollers if there is any suspicion. Oh, and I don't use the expensive tool, I've always set the belts by hand. > Whenever I changed my 1983 belts, I always used the Porsche <expensive> > recommended gauge. I have a friend that owns the gauge and he most [quoted text clipped - 21 lines] >> >> ** Posted from http://www.teranews.com ** ** Posted from http://www.teranews.com ** Oh a TT huh, nice girl's car- did the belt fail after you replaced it - or was it installed by Audi? My friend is one of the most respected and trusted Porsche mechanic and he wouldn't adjust a belt without the Porsche belt adjuster. I also thought I could hand adjust the belt - but it was never correct. That belt has to have zero tension on it - and that's what prevents teeth from breaking off - hence, I never had a broken belt. Well I still have my old trusty 87 944, but I just bought a new 08 VELOCITY YELLOW CORVETTE...what a great supercar so far. GM and the USA should be proud. But it remains to be seen if the car has the greatness of a Porsche. My 30 years and 800,000 miles of driving and maintaining my two 944's myself has been nothing short of spectacular.  Signaturejoliett ______________ ______________ >I recently changed the timing belt on an Audi TT - it's very much like the >porsche timing belt - Audi forgot to change KM to miles in the manual and [quoted text clipped - 39 lines] > > ** Posted from http://www.teranews.com ** the TT had the original factory belt you can believe or not. and, quite frankly, your statement "the belt has to have zero tension on it" is absolute complete utter nonsense. What do you think that $650 gauge measures if it isn't belt tension? In fact it is physically impossible for the belt to have zero tension on it, even if you are holding it in your hand not installed in the car. I am sure your friend is an excellent and trusted mechanic. If he is also technically knowlegable, have him explain to you about belt tension. Or, you can read for yourself in the SAE handbook, or in the Porsche manual, or in a myriad of other technical publications. Normally I would ignore this, but if others were to believe the "zero tension" statement, they would put their car at serious risk of damage - you may do what you want with your car, but others should be extremely cautious if they elect to follow your tension number. > Oh a TT huh, nice girl's car- did the belt fail after you replaced it - or > was it installed by Audi? [quoted text clipped - 12 lines] > My 30 years and 800,000 miles of driving and maintaining my two 944's > myself has been nothing short of spectacular. ** Posted from http://www.teranews.com ** Porsche specs says to adjust the drive and balance belts to USED BELT 2.7 +-.3 or NEW BELT 4 +-.3 (humm units arent available - so it's specific to Porsche's expensive gauge) - which is pretty darn close to zero tension. The idea is such that the teeth aren't supposed to be pulled one way or the other from too much tension or too little tension. They are supposed to sit in the sprocket without very little tension. Too loose and you skip a sprocket and possible valve damage - too tight and you break a tooth and possibly the belt. Again - take it is you will, 800K miles of Porsche driving and maintenance myself - with NEVER a belt broken. Also, I didn't adhere to the scheduled mileage recommendations for belt changes either...not that I recommend that to anyone...I only changed the belts when servicing the water pump - or when I had oil leaking into the rollers and belts through shaft bearing seals - so sometimes I would say I went 100K miles without belt changing. I bet it was using that expensive Porsche belt adjusting tool that kept my belts in such great unbroken shape. I think - not sure - that most Porsche clubs have one to lend. Anyway -- I think the 944 - especially the 1983 944 - was perhaps the best and most reliable car ever built. And thank you Mr. Noble for your invaluable forum participation. joliett ______________ ______________ > the TT had the original factory belt you can believe or not. > [quoted text clipped - 32 lines] > > ** Posted from http://www.teranews.com ** > Porsche specs says to adjust the drive and balance belts to USED BELT 2.7 > +-.3 or NEW BELT 4 +-.3 (humm units arent available - so it's specific to [quoted text clipped - 4 lines] > skip a sprocket and possible valve damage - too tight and you break a > tooth and possibly the belt. Whoopee - we agree. Belt requires SOME tension - amount not specified in manual. Of course using the gauge is safe. What I was pointing out is that if you dont' have the gauge, you can do it without the gauge, and I was pointing out a convenient artifact of the design, in that the balance shaft belt can pretty much be depended on to fail first. You can tell too tight vs too loose by inspection - too tight and you get a VERY distinctive whine from overloaded bearings. Too loose and the belt flaps visibly. 87 and later have a spring tensioner for timing belt, so you can compare tension on the balance belt to the timing belt with your finger or a GATES "Clickit" tool if you need to. But, my recent Audi experience suggests another caution - the belt DID NOT break, and on that car the belt is tensioned automatically by a hydraulically damped spring loaded roller. The failure mode was separation of 4 to 6 teeth. This is probably age related. The audi belt is under more load (due to 24 valves and dual cams) than 944s (well, S model excluded) but the failure mode could certainly happen - so to avoid $$ repair, I suggest you do not want to wait for a water pump failure to change belts. On my 85.5, with around 300K miles now, the water pump failed at 90K, replaced it (and belts) and that was it - same water pump is on the car as I put on at 90K. That is way too long to expect critical belts to last. (and no, I don't drive it, I gave it to my brother) ** Posted from http://www.teranews.com ** |
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