ChasR
RR Helper
motivation
Posts: 10,309
Club RR Member Number: 170
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Aug 31, 2015 17:55:08 GMT
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On many forums you do see people preaching that timing tools must be used or nuns and kittens will die as a result if an alternative method is used without undoing pulleys, like marking things with tippex. OK, maybe not that, but that the engine may be harmed. While I can see how the change in cam timing can effect power and wear (potentially burning out valves etc.) and how in worse cases the valves can be bent why is the timing thrown out on modern engines to affect things this much from simply making up some marks? Is it do with wear in the pulleys, the belt tension varying, different belts being made ever so slightly out or am I missing the picture? Or are the tools simply nonsense. I would have agreed with that notion if I had not seen first hand certain engine go bad through simply having the engine 'tippexed' and the belt changed, even if in theory nothing can go wrong. Surely with the above, changing the belt on a car which has had the cam timing altered via a vernier pulley, a fast road cam etc. can throw things off. To keep things on track here are some photos to show certain issues  .     |
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Last Edit: Aug 31, 2015 17:55:53 GMT by ChasR
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Rich
Club Retro Rides Member
Posts: 6,341 
Club RR Member Number: 160
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Aug 31, 2015 18:28:55 GMT
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The reason is that many cars require the cams to be held because they 'jump' when the belt is removed and it is an easy way of ensuring the belts are easy to fit and quick to change from a manufactures workshop point of view. Many newer marques, renault and ford spring to mind, also have floating crank and often cam pulleys too and removing the crank bolt will allow the timing belt pulley to freewheel on the crank nose, loosing the cam and crank phase enirely. There are certain engines however, that just plain and simple don't need anything more specialist than some tippex.
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ChasR
RR Helper
motivation
Posts: 10,309
Club RR Member Number: 170
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Aug 31, 2015 19:22:22 GMT
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The jumping was a suspicion I had and the fact that on some engines the timing is entirely lost with floating pulleys (on a car with keyed pulleys), but then surely bringing the timing back or holding the teeth with a wedge like the K-Series would be enough to suffice.
I shall attempt to keep the number of questions (hopefully not too silly!) fired out low! The next question why do manufacturers go to the effort of having all of the pulleys freewheeling, and not fixed like the good ol' days?
Furthermore, there are some engines like the Peugeot 306 and Passat PD engines that require the cam pulleys to be loosed upon changing the belt.
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Last Edit: Aug 31, 2015 19:23:44 GMT by ChasR
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Rich
Club Retro Rides Member
Posts: 6,341
Club RR Member Number: 160
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Aug 31, 2015 19:33:51 GMT
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The reason behind freewheeling or vernier pulleys makes for an easier fit timing belt. Zetec engines are a doddle to fit a belt to because you can just lob it on, tension the belt and then torque the pulleys. Same with the PD, you can back the cam pulley round to allow for more slack in the 'tight' side. The PD is also a tuning/fine running thing due to the pump deuce system but that's another kettle of fish altogether..
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Aug 31, 2015 19:35:29 GMT
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Hi, floating or freewheeling pulleys are the ultimate vernier pulley. You time the shafts correctly, then the pulleys are tightened after thebelt is tensioned without regard to manufacturing tolerances of the belt. Its not the first time I've gone to put a belt onto locked pulleys and the belt is loose between them.
Colin
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bortaf
Posted a lot
Posts: 4,549
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Aug 31, 2015 23:37:57 GMT
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Manufacturing tolerences in a nut shell, take the pinto, probably the easyest engine to time without even tippex but i've measured cam pullys before and found up to 3 DEG differance in the keyways.
Had a zetec (early 1.6 with a keyed crank pully) in a Mk6 escort that came in with a hesitation when planting the throttle from under 2000 RPM, owner did a recent WP and belt change but he tippexed the old and new belt as he thought being a keyed crank pully he was ok, after a few hours checking we found the cams were out, locked them with the tools, took the slack out between them and took it up with the tensioner and bingo, no more hesitation, the give away was the cam belt flapping about against the cam cover but other than that it ran fine.
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R.I.P photobucket
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ChasR
RR Helper
motivation
Posts: 10,309
Club RR Member Number: 170
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I guess in some respects I was on the right lines but not quite as I imagined. A 3 degree difference on a keyway? Now that is quite surprising! The belt tension however being affected and throwing the timing out is something I did not bank on at all with the pulleys not being tensioned. It was no the answer I was expecting but it is great to put the idea to rest. As always, cheers for the help and feel free to add on to the thread. Rich I guess the cam timing with PDs is quite finicky due to the injectors being the pump as well? |
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Last Edit: Sept 1, 2015 0:16:09 GMT by ChasR
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Rich
Club Retro Rides Member
Posts: 6,341
Club RR Member Number: 160
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Rich I guess the cam timing with PDs is quite finicky due to the injectors being the pump as well? Not as much as you'd think, the PD injectors are still electronically discharged but it makes a difference to peak injector pressure and the obvious crank to cam phasing also, so can make them run a bit off if it's not 'close enough'. |
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Dez
Club Retro Rides Member
And I won't sit down. And I won't shut up. And most of all I will not grow up.
Posts: 11,790
Club RR Member Number: 34
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cam timing is absolutely critical on PDs, its why a lot of people replace the belt at as little as half intervals, as the small amount of belt stretch present can make a huge difference to the power available and how it is delivered.
another engine that definately requires the correct tools and great care when timing up is the omega v6, not just to get the best out of the engine, but ive seen one done with the 'tippex and molegrips' method that was so far out it wouldnt run! that is largely down to how ridiculously long the belt is and how many pulleys and idlers it has to navigate on its route though. the smallest of errors is greatly compounded by the time its done a trip or two round its route.
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Sept 1, 2015 19:23:41 GMT
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My v6 Omega was running a tooth out on one cam for at least 30000 miles according to its history, it may have gone fractionally better between gearbox and electrical failures afterwards but I would be hard pressed to be sure. It wasn't as bad a job as I was expecting though, certainly easier than a Lexus RX300...
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Also, on some engines there isn't really any other way to hold the cams steady apart from using the proper locking tool.
For example, on older (1980s to about 2003-ish) Subaru EJ series engines, they used to have a nice big hex in the middle of the cams for you to put an open-ended spanner on. When my mate put a new bottom end in his 2004 Liberty GT, he found that the cams are smooth in that area (no hex) and therefore you can't easily hold them in place to undo the cam pulleys. They have variable cam timing on all four cams and there are no holes in the pulleys or anything to hold them in place. The proper factory cam locking tools are therefore the easiest and best way.
We also had a similar experience with an Alfa GTV Twin-Spark 2.0 litre. You really want to have the cam locks for that as well.
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