Replacing the chain tensioner

[raz]

Tomorrow my Stucchi tensioner will arrive and my intention is to mount it along with the properplate and some general maintenance. So, doh, I just realised I may need some special tools. What is the easiest way to replace the tensioner? I will not change the chain but I suppose I must take it off in the process anyway. Any tricks? Could I just go for the cam sprocket, or the oil pump one? Or will I have to pull all three sprockets?

[pete roper]

What makes you think your original tensioner has gone bad?

 

The later model Guzzi tensioners seem to work fine and be long lasting. Quite a few people prefer them to the Stucchi type blade tensioner.

 

Pete

[raz]

What makes you think your original tensioner has gone bad?

 

The later model Guzzi tensioners seem to work fine and be long lasting. Quite a few people prefer them to the Stucchi type blade tensioner.

 

Pete

Bike has 46000 kms on the clock. As I bought it last year and wanted to know and trust it, I had a good look under most covers during winter. The mileage and the fact chain and sprockets look good made me figure they should only be half way to death, tops.

But there is this horrible ringing sound on low rpms. I have dicussed it here and here. It really doesn't sound healthy. The original tensioner is so weak I could probably take it away with no big difference. Maybe it's faulty, I don't know. The punch line is the Stucchi cost way less (€ 15) than a new OEM tensioner (€ 75) or a chain (€ 65), so I figured I'll try it.

[Guest ratchethack]

Raz, I for one will be watching your project here with with keen interest.

 

I've been getting more noticeable symptoms of what I believe is a loose timing chain lately myself (33K miles).

 

Does any of this sound like wot you've been experiencing:

 

The symptoms only show up at steady, low throttle openings. As long as there's load on the motor and even a little throttle, it runs 100% perfectly. But whenever conditions that would cause a loose timing chain to jump and whip, it acts like it's picking up a mis-timed, or more often, an absent signal.

 

Since the signal is taken off the camshaft, I reckon the valve timing is thrown off just enough to conspire with the dropping/mis-timing of a spark signal to cause an occasional backfire, balk, or simply dead miss.

 

When I'm in traffic, it's the worst, and it's startin' to drive me bats. If a wonky tensioner ain't it, I ain't got the first clue wot it is?!

 

Any comment -- Raz and/or Pete?

[raz]

Raz, I for one will be watching your project here with with keen interest.

 

I've been getting more noticeable symptoms of what I believe is a loose timing chain lately myself (33K miles).

 

Does any of this sound like wot you've been experiencing:

 

The symptoms only show up at steady, low throttle openings. As long as there's load on the motor and even a little throttle, it runs 100% perfectly. But whenever conditions that would cause a loose timing chain to jump and whip, it acts like it's picking up a mis-timed, or more often, an absent signal. <_>

 

Since the signal comes from the camshaft, I reckon the valve timing is thrown off just enough to conspire with the dropping/mis-timing of a spark signal to cause an occasional backfire, balk, or simply a missed ignition cycle.

 

When I'm in traffic, it's the worst, and it's startin' to drive me bats. If a wonky tensioner ain't it, I ain't got the first clue wot it is?!

 

Pete?

Spot on, Ratch. It drives me nuts. Clearly the sound originates from the area of the chain and not the clutch. Traffic jam, engage clutch, listen to what could be a ducati clutch on acid. It really sounds like the chain will wear through the timing chest anytime, though I can't see where that could happen, there's plenty of margin. Actually I'm not that sure it's the chain at all, but at €15 (US$ 20) it's the cheapest way to find out. Also, you're right about the mis-timing. This will be interesting. But my original question remains: can I swap the tensioner without tearing the engine to molecules and without buying a set of tools from Rolf?

[callison]

Mine is pretty erratic at idle. Until it tries to run backwards. Then it dies.

[docc]

I'm still not one to answer Raz's question about the mechanics of changing the tensioner, but . . .

 

If the chain or tensioner were shot couldn't you hook up an induction type timing light and watch a dot on the flywheel jump all over the place? If the dot stays put, it couldn't be the chain or tensioner?

[Guest ratchethack]

If the chain or tensioner were shot couldn't you hook up an induction type timing light and watch a dot on the flywheel jump all over the place? If the dot stays put, it couldn't be the chain or tensioner?

I like it Docc. Now wye didn't I think o' that!?

 

It's been so long since I used a timing light I wonder if I can find mine.

 

More on this later. . .

[Ballabio Bertie]

This may be a dumb question but has no one on this forum tried the timing gear conversion? If not is this a cost issue or do these kits have a bad reputation?I'm new to Guzzi ownership,but gear driven cams seem like a fit and forget option.

[raz]

You are all very welcome to make this a timing gear thread (just not as hostile as the one recently on Guzzi Exchange) but please please answer my question first so I don't spend half a day dismounting half the engine only to find I need some special tool. I have been inside the timing chest so up to that point is no problem. Can I hope to get away with just removing one of the sprockets?

[pete roper]

OK.

 

To answer the questions.

 

1.) As Orson suggested if you stick a strobe on it and watch the timing mark on the flywheel this will give you a pretty good indication of how worn the chain is. If the mark appears to jump about, (A phenomenon known as 'Scatter' then it's a good idea to do something about it.

 

2.) Ypu don't have to remove the engine to do the timing chain. Just pop off the fron't cover and everything is easily acessible.

 

Pete

[Dan M]

I'm still not one to answer Raz's question about the mechanics of changing the tensioner, but . . .

 

If the chain or tensioner were shot couldn't you hook up an induction type timing light and watch a dot on the flywheel jump all over the place? If the dot stays put, it couldn't be the chain or tensioner?

 

 

Right on Docc, Further proof is to increase engine speed to about 2500RPM and watch the movement decrease as the slack is removed from the chain.

[Guest ratchethack]

If the chain or tensioner were shot couldn't you hook up an induction type timing light and watch a dot on the flywheel jump all over the place? If the dot stays put, it couldn't be the chain or tensioner?

Docc, thanks for the suggestion. I just put an inductive strobe on it:

 

1. At steady idle (cold), the flywheel mark is steady as she goes.

 

2. When the motor is warm at idle (evidently providing less drag throughout the valve train due to lower viscosity of the oil), the flywheel mark jumps erratically, off and on, alternately by 4, 5, or 6, maybe as much as 7 mm.

 

Don't know wot "acceptable" scatter is, but I reckon this ain't good.

 

3. Over 3K RPM, it steadies out again, as Dan predicted, (evidently due to the increased drag of the valve train with RPM). When RPMs are on the rise responding to throttle, it's steady as a rock -- exactly as it behaves on the road.

 

Logically, to me this indicates at least some probability -- even liklihood -- of a wonky tensioner.

 

Any and all with anything to add are more'n welcome to comment on this, please.

 

Raz, you still don't have an answer to your Q, but in the meantime, you might try this and see wot you get.

[docc]

I'm pretty sure Pete answered Raz that he could just take off the front cover as in post #11.

 

Ratch' , how may miles on yer 'hack? I've passed the 49,000 mark and still holding a steady idle. Could it be that the tensioners and chains need the 50,000 mile replacement??

 

I don't think it's just the oil that loosens up. All the tensile tolerances in the valvetrain should 'relax' at temperature. Still, the timing mark moving 4-7 mm? That seems like a lot of degrees BTDC.

 

I'm somehow sure you've tightened the timing pick-up and every other simple thing. Does your bike flame out periodically at idle like Nose2winds?

[pete roper]

Damn! Just wrote this out once and then the 'pooter crashed! Don't ya hate that???

 

Lets we'll try and deal with a few misconceptions about the supposed accuracy of the chain drive system. After this we can look at problems and how they may manifest themselves.

 

Lets first deal with the erroneous idea that chains 'Stretch'. They don't. What happens is that the pins and rollers in the chain wear. The easiest way to see this manifested is to look at the old drive chain off a cahin driven bike and compare it to a new one. If you place them side by side on the bench/floor whatever and try and *bend* them sideways the old chain will Bend* a lot further than the new one. What you are doing is canting the pins over inside the rollers which allows each link to run slightly out of alignemt with the others. The end effect is much the same as stretch but it's important not to confuse the two.

 

OK. So now we need to look at thetining chest and see how the whole sorry business works. From here on I'll be speaking about the engine as viewed from the front.

 

On the right hand side of the timing chest there is a long run of chain thatgoes from the oil pump sprocket, over the tensioner and up to the cam sprocket. It loops over the top of the cam sprocket and then drts right again to circumnavigate the crank sprocket on the right hand side before exiting left again to hook around the left hand side of the oil pump sprocket before once more heading up the RH side of the timing chest.

 

The crank rotates clockwise and the cam is towed round by the chain, but between the crank sprocket and cam sprocket there are only about three links and maybe four pins/rollers. Now given that on anything other than a feathering throttle that four links is always going to be in tension the only thing that will be able to retard the timing is the wear in the pins and rollers. Even assuming a whopping 3 thou clearance betwixt pin and roller with four pins that will give you 1/4 of a mm of increase in *length* of that bit of chain. I can't be bothered to do the sums but 1/4 of a mm at the circumfirence of a 720 degree camwheel is not, I'm sorry to say, going to retard your timing to any noticeable degree. when you are on the over-run it's a different story. Then, unless you have a decent tensioner that will 'Take up the slack' in that long run up the RH side of the case, the chain may well try and 'Bunch up' between the cam sprocket and the crank sprocket but there will still be variable loadings being imposed by the valve train and it is at this point tat the scatter will be most evident when examined with a strobe. The important thing to remember is that unless you are running such a radical cam that your piston to valve clearance is super-critical, And no road-going Guzzi cam is anything like this!) It doesn't matter a tinker's cuss what the valve timing is on the over-run as the engine isn't producing power, exactly the opposite in fact! Certainly if the chain is really badly worn you will eventually damage the sprockets but as far as valve and piston damage is concerned? Don't even think about it!

 

Now the last example, and this I think is probably relevant to Ratch's observations of his bike's behavior, is what is happening on a light or feathering throttle. Here too is a situation where the scatter WILL be apparent. IMHO though the hesitation that he's experiencing is probably much less to do with any variance in cam timing per-se, (Although the observed scatter will prove that the timing is shifting about a bit.) but is Far more likely to be the result of instability in the signal from the 'Phonic Wheel' due to the 'floatation' of the timing due to the slack chain. This may well confuse the ECU so that it periodically says 'F@ck it! and givs up the ghost for a revolution or two until it can get it's bearings again.

 

As has been observed the later model Guzzi tensioner has a pissweak little spring and IMHO it probably won't have the strength to combat the chain-flap on the over-run but I know of CAlis that have done best part of 200,000 miles without replacement of the chain or tensioner so?????????

 

The Valtech/Stucchi type 'Blade' tensioner is in some ways a lot more robust than the Guzzi item. Yes, I know that some people don't like 'em and I know that some people have reported breakages of both blade and spring. I've had one broken spring on dozens I've installed and generally prefer them to the later model Guzzi item but both are a HUGE improvement over the original 'Foot' type tensioner from the early chain drive models. I think like most things both have advantages, both have disadvantages. When the chain or tensioner becomes a problem on my Griso I'll probably install a Valtech type as I think these work better at their true task of tensioning the chain but I certainly have no intention of doing it pre-emptively.

 

As many people know I'm not a fan of any of the available alloy or composite gear sets available for converting to gear drive. I'm not willing to embark on another long and tiresome debate on the subject here. If you want to see how the other half thinks, if somewhat irrationally, go and have a look on the timing gear thread on Guzzi Exchange. I can't be arsed going through all that shit again!

 

Anyway, my

 

Pete