944S2 timing question, can I have done it wrong? - Page 1 - Porsche General - PistonHeads UK

I've just changed the idler wheels and bearings, and had to remove the belt to get to the bearings and idler pulleys, I lined everything up as I had done last year when I changed the belts but when I drive it the car seems to be different somehow and not as willing to rev as it did. When I'm trundling through traffic in a high gear it almost (but not quite) has a hesitance, I've just taken off the front cover and checked the timing marks, with the 'OT' scribe mark directly under the indicator in the flywheel window the mark on the cam sprocket is bang on where it should be so everything to me looks OK and as it should. Is it possible it could be half a tooth out without me realising it?, and if so would it run at all? (though as I said it looks to me to be bang on, I didn't take off the cam timing sprocket or the main pulley) or could I have have I disturbed something?. I'm off to france later on in the week and I don't want it going wrong over there, so any ideas at all would be helpful. Thanks, Andy

Are you sure you've got the balance shafts aligned correctly? Apparantly it's really easy to get them 180° out and this will cause rough running.

Thanks for the idea Andy, I think they are where they are supposed to be, I marked the sprockets and they were lined up back in the same place (and I didn't taker them off the ends) It just feels as though it's not as keen to rev which is why I'm thinking valve timing, I suppose what I'm realy wondering is, is it possible to have the timing out a tooth and get the symptoms I'm seeing or would it be so far away as to not run at all and bend the valves?.... Andy

SilverS2 said: I've just changed the idler wheels and bearings, and had to remove the belt to get to the bearings and idler pulleys, I lined everything up as I had done last year when I changed the belts but when I drive it the car seems to be different somehow and not as willing to rev as it did. When I'm trundling through traffic in a high gear it almost (but not quite) has a hesitance, I've just taken off the front cover and checked the timing marks, with the 'OT' scribe mark directly under the indicator in the flywheel window the mark on the cam sprocket is bang on where it should be so everything to me looks OK and as it should. Is it possible it could be half a tooth out without me realising it?, and if so would it run at all? (though as I said it looks to me to be bang on, I didn't take off the cam timing sprocket or the main pulley) or could I have have I disturbed something?. I'm off to france later on in the week and I don't want it going wrong over there, so any ideas at all would be helpful. Thanks, Andy Hi Andy Yes you got it wrong....you DID check the timing afterwards with a Timing light of course ??? That would tell you instantly if you got it wrong................ If you didnt....take it to a Pro....and get them to put it right...DO NOT drive it..or you may well do MAJOR damage.... I am always amazed at what people who are not qualified will attempt....there are a lot of jobs an amateur can attempt ...BUT a timing belt is NOT one of them... All the best Brett

Brett928S2 said: SilverS2 said: I've just changed the idler wheels and bearings, and had to remove the belt to get to the bearings and idler pulleys, I lined everything up as I had done last year when I changed the belts but when I drive it the car seems to be different somehow and not as willing to rev as it did. When I'm trundling through traffic in a high gear it almost (but not quite) has a hesitance, I've just taken off the front cover and checked the timing marks, with the 'OT' scribe mark directly under the indicator in the flywheel window the mark on the cam sprocket is bang on where it should be so everything to me looks OK and as it should. Is it possible it could be half a tooth out without me realising it?, and if so would it run at all? (though as I said it looks to me to be bang on, I didn't take off the cam timing sprocket or the main pulley) or could I have have I disturbed something?. I'm off to france later on in the week and I don't want it going wrong over there, so any ideas at all would be helpful. Thanks, Andy Hi Andy Yes you got it wrong....you DID check the timing afterwards with a Timing light of course ??? That would tell you instantly if you got it wrong................ If you didnt....take it to a Pro....and get them to put it right...DO NOT drive it..or you may well do MAJOR damage.... I am always amazed at what people who are not qualified will attempt....there are a lot of jobs an amateur can attempt ...BUT a timing belt is NOT one of them... All the best Brett Hmm. Be fair, given the state of the garage trade, the only way to get something done properly is to attempt it yourself.

I did this job a little while ago and iirc the sprockets can be confusing because porsche changed the way they are marked. Either that or/and the shaft can be rotated 180 and the sprocket will still fit. Also, when tensioning the belt I left a little slack in it, just like with an alternator and it's nice and quiet, smooth etc. Boosted.

Well dome for trying to change the belt yourself - it is not rocket science and quite within the scope of most home mechanics with some guts. A new belt is going to be a different length to the old one - shorter and it also will not fit as deep into the sprockets until it has been run for a while - so the actual timing of the cams will be slightly different. This will make the inlet cam (the important one) close a little sooner which results in less top end - so this may be what has happened and if so it should improve with time. Did you check the cam timing marks before removing the old belt as we have come accross some engines that you can time correctly on the inlet cam better if you set the cam belt timing mark one tooth out and cannot actually get it spot on using the original marks - it is rare but can happen (mainly with the 944S to be fair). The washer under the bolt that tightens the cam sprocket to the camshaft can dish oval and when it does it allows the cam timing to creep within the slots made for the adjustment process. Even though you may not have undone the bolt the extra resistance of the new belt may have let it move a little - or it may have moved when the rotor was disconnected. Generally you can get the timing out quite a lot without the valves hitting the pistons - so that should be OK unless you caught a valve while doing the job which a compression check will resolve. If you are concerned about the timing you need to take it to a specialist who will remove the cam cover and time the inlet cam with dial guages on the tappet and piston and he should notice if the washer has dished and if so replace it. The belt may also be too tight slackening it off a bit may help Did you do anything else at the same time? - however simple or innocent - check everything you did again especially the fitting of the distributor housing with those awkward bent screws - they are easy to miss-align! So although you may not have got it quite right - don't be put off by it - and well done again. Baz

Well, I've been rebuilding engines and working on cars for 20 odd years and have changed loads of timing belts and chains, and never had any problems, so I do have some experience to draw on. I do appreciate that they all have their little traits and quirks though, and that's what has got me thinking there was a chance something just wasn't as it should be..... and with a wealth of knowledge and experience on the forums I thought I find out what others think. Perhaps I should say that the engine was set at TDC whth the timing marks aligned when I started, and nothing was rotated during me changing the idler pulleys and I double checked everything using the procedure from the 'clarkes garage' web page to make sure (I didn't take off any of the major pulleys so all timing marks are as they were) The car does rev out to the redline without any problems and starts, ticks over and runs as it should, as I said it's just there's the hint of hesitation in slow moving traffic and the feeling that it's not as slick and free revving as it was, and I wondered if it's possible to get the timing out half a tooth and get these symptoms, or would it be miles away?, the car just feels a bit different and I'm exploring the possibility that It might not be right. Thanks for the ideas though, it would be interesting to hear if anybody has actually got it wrong in the past and what the outcome was. Thanks for the positive post Baz, you have raised a couple of interesting points, firstly I've noticed that the idler wheel (on the long run between the cam and crank pulley) seems to be deflecting the belt slightly wheras I thought it was 'just touching' before, and that before I did the job the timing marks didn't seem to be as spot on as thet are now, it could be that if for example the idler was a greater diameter than the old one it would have the effect of shortening the belt (which is the original as I changed it last year and was incidentally such a pig to get over the bottom pulley I decided to leave in place rather than risk damaging it), and maight alter the timing subtly as you suggest Baz, I'll have a look at that now..... Andy Edited by SilverS2 on Sunday 15th April 10:36

What did you remove to gain access to the belts? Is the AFM multiplug in fully?

Hi 911 MOT, not sure what that multi plug is but I didn't remove anything electrical at all, just the idlers, I'm off to have a look at the old and new idlers in case they are different diameters, if you let me know whatthe multiplug is I'll give it the once over to check. Cheers, Andy.

Hi I wasnt trying to be negative... You still havent answered the mort important question... DID you put a timing light on it ??????? Baz`s point about dizzy cap alignment is a good point....if that cap is not EXACTLY fitted as intended it will act strangely....make sure the screws are in place and cap is centred and bottomed on the ridge.. All the best Brett

Sorry Brett, no slight intended but no I haven't put a timing light on it, (I haven't used one since my lotus days) I notice that there seems to be adjustment in the position of the rotor arm that would change the ignition timing but I haven't had that off either. I've just checked everything again, and all the marks look as though they line up 100%, I had a vernier on the idler wheels just in case they were a different diameter but they are exactly the same as the old ones so it may well be the cap wasn't positioned correctly. As I said I'm off to sunny France this weekend so a little trip to see Baz at Hartech may be on the cards on the way down if it's just the same when I put it back together. Thanks for all the ideas and tips, Andy

SilverS2 said: I've just changed the idler wheels and bearings, and had to remove the belt to get to the bearings and idler pulleys, I lined everything up as I had done last year when I changed the belts but when I drive it the car seems to be different somehow and not as willing to rev as it did. When I'm trundling through traffic in a high gear it almost (but not quite) has a hesitance, I've just taken off the front cover and checked the timing marks, with the 'OT' scribe mark directly under the indicator in the flywheel window the mark on the cam sprocket is bang on where it should be so everything to me looks OK and as it should. Is it possible it could be half a tooth out without me realising it?, and if so would it run at all? (though as I said it looks to me to be bang on, I didn't take off the cam timing sprocket or the main pulley) or could I have have I disturbed something?. I'm off to france later on in the week and I don't want it going wrong over there, so any ideas at all would be helpful. Thanks, Andy Hello mate. Forget the balance belt / alignment for the time being as they will not affect performance. (assuming its not too tight to break or loose to fall off) If I were you jack the car up and on the clutch housing at the bottom there is a cover held on by 2 17mm bolts - remove this. You will then see a cut out in the housing approx 10mm wide. When at tdc there are 2 marks on the flywheel that will line up in the cut out. Get these perfectly lined up. Now check the cam pulley and see if you are a tooth out. (easier than using the OT mark) Always turn the engine over by hand after in case of misalignment and to get the belts seated correctly - then retension. None of it is rocket science just take care and double check. Rich

Thanks Rich, I've been using the OT mark but I'll certainy have a look underneath at the marks there to see how it lines up. Andy

Brett mentioned using a timing light to verify timing on a 944s2. How is this done? I cannot find any documented procedure. I could create one, but…..