Saturday, February 27, 2016

Ducati timing belt replacement, factory tool and cam timing ramblings

I did a 40k service on a 2003 ST4S last week, and given there was a bit of variation in the cranking comp I thought I'd check the cam timing.  With a new pair of Exactfit timing belts tensioned to 11.5 on the old gauge the timing was O: 124/105 and V: 120/108.  The 2003 model year was the first of the Desmoquattro with the adjustable cam pullies that had been fitted to the 2V motors from 2001.  In my experience, the accuracy of the "as delivered" cam timing on these engines is much worse than the old solid pulley engines.  I adjusted the timing to 113/110, advancing all cams between 2 and 11 degrees.

As an aside, when they went to the adjustable pullies on these motors (S4, ST4, S4R, ST4S) they changed the cam numbers (the # stamped on the cam).  I expect this is because the alignment marks on the heads changed to allow for the cam locking tools, and given the pullies were the same as the 2V parts where the marks hadn't changed, they had to change the keyway positions.  Same profiles.

My inspiration for posting this came from a thread I had previously missed on Ducati MS - ST4S running a little strange - about someone who had the belts changed on one of these engines using the full cam and crank locking procedure.  It's quite an interesting thread in terms of both what actually happened and the usual rampant speculation entered into between problem and fix.  I didn't really buy the official explanation either, but reading it again it reads like the shop initially didn't have the right tools, but did it anyway or that the fix was to ignore the tools and set the cam timing as I did above.  Either way, it backs up my view that using the factory tools and method has the potential for a result without any positive apart from being "how it was" and for a whole load of negative.  

There was another thread on Ducati MS I replied to that I outlined my opposition to using the cam and crank locking method for belt changes, so I thought I'd cut and paste that here too.  Only my opinion, of course.

i have never used the factory method of locking crank and cams, for a few reasons i'll try to outline as coherently as possible. and i'll try to cover other related bits as well.

1/ when you lock the cams and crank, the tools used, in combination with the tools locations in the pullies, determine the timing. from memory, the crank locking tool is pretty good. but the cam locking tools and positions thereof were always the issue. when i did some factory training in 2002, the training dept had just set up some 998s for an italian race series. they told us that the factory tools set all the 998s cams about 6 degrees retarded. when we did the timing on them, as a very round rule we used to advance the inlets about 10 degrees and leave the exhausts much where they were, giving the 105/109 we used ish.

i don't think i ever tried setting any of the 2v or 4v desmoquattro motors with the factory tools. ex factory the 800 motors had 5 to 8 degrees retard. s4r/st4s had similar inlet cam inaccuracy, much worse than the fixed pulley st4s motors. from memory the 900 motor was pretty good.

the tools required started to grow with the models, 2005 saw a big cam 749S specific tool with the revised stalling fix timing set in, etc. they were pretty accurate from memory.

so cam locking tool wise, it was a bit of a clustercuss accuracy wise. if the tools gave the same result as the production line, that's fine. inaccurate is ok if it is the same as before. make it worse though and it's an issue. the only way to know the timing is to check and set. most people don't expect to be paying for that as part of a service.

2/ when you have locked everything, you loosen the pulley half screws so the cam outers move. but you have to loosen them a bit to allow them to move freely with belts fitted. when you loosen those screws, it allows the pullies to cock due to the belt tension. so when you tighten them again, the pullies pull up squarely and this increases the belt tension. how much will vary, but following the factory method will introduce error. i don't like that, as it seems kind of pointless to me.

you could fit the belts, tension each correctly with each cylinder at tdc firing individually, then do the cam locking thing. still seems like a great waste of time to me, as you're doing nothing to make the timing more accurate than the factory did. this is the main reason i don't do anything that the factory recommends locking and setting wise. no point imo.

i don't know of any shops that do the factory method. we certainly didn't as an authorised dealership. the importer also never made any point of recommending it. i think, as a service procedure, it's a total waste of time. i might have said that already.

3/ some of the later cams - testa, testa evo, some 659/696/796/1100 - have no timing marks. with experience you can usually know where to set them without tools (except some of the 2v, 696 maybe). or you just mark them in a way that makes sense to you and use those marks to reset. it's pretty easily done. and that's one of the things that's important here - you choose a convention and stick to it and then it works just fine. remove the old belts, fit the new ones, tension and away you go.

4/ the belts themselves can also have an influence. the exactfit belts are a little shorter than the oem belts, due to them being more accurate to the sae tooth form. i think i have back to backed new 900 and 999 belts. the exactfit belts generally advanced the cams 2 degrees.

5/ that's all i can think of, think i might have had something else to say, but i've forgotten now.

My ST3 cam timing and front sprocket post from July 2015 showed other weirdness that can get you too, so possibilities abound for screwing it up no matter how good your intentions are.  The good ol' things you don't know you don't know.

Often you see owners replying to these sort of threads with comments along the line of "I'd expect a dealer to do it by the book".  But the reality is, in some situations, the best thing you can do with the book is hit the owner with it.

1 comment:

Driveparts Direct said...
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