K Series Cambelt tension

[patibbitts]

My K Series 1600 has a manual adjuster for cambelt tension.

 

I'm about to set the cam timing and would appreciate some advice please.....

 

Q1: Can anyone advise how to set the correct tension on the belt please?

 

Q2: I assume the spring attached to the camber tensioner is NOT used to set the tension - so what's it for?

 

Q3: Torque setting for large tensioner centre fixing bolt, and torque setting for cam tensioner adjuster lock bolt?

 

Q4: How to lock the flywheel to torque up the crankshaft pulley nut to 205NM?

(I used a screwdriver in the ring gear via: the crank sensor appature to remove it)

 

Any help much appreciated.

 

Pat.

[revilla]

The spring is used to set the tension, although it shouldn't be left in place after tensioning. The Spring and the little post it attached so should be removed once the tension as been set to prevent them coming adrift and into the belt.

The large pivot bolt should be 45Nm, the smaller M6 clamp bolt 10Nm.

Once the belt is correctly in place and the timing marks aligned, fit the manual tensioner, leave both bolts slackened by 1 turn to allow the tensioner to move freely. Fit the spring and post. Wind the engine around clockwise two turns steadily until the marks align again (and double check they align correctly). The tensioner should settle to afairly steady position, usually with the small bolt close to the centre of the slot. Carefully tighten the small bolt then the large one making sure the tensioner doesn't move significantly in the process. Then remove the spring and post and put them away for next time.

[revilla]

I posted a suitable crank lock tool on your other thread but it didn't seem to go down well! Works a treat for both removing and refitting.

[revilla]

PS: I picked up this tip on the web somewhere, can't remember where now and never actually tried it:

Crank & Flywheel Locking Peg Design

A steel peg turned to the following dimensions may be inserted into the crankshaft position sensor hole to lock the crankshaft by engaging one of the circular drilled holes in the flywheel which form the sensor trigger pattern.

NB: This method of locking the crankshaft and flywheel will not work with lightened flywheels or early flywheels with a different trigger pattern.

[oilyhands]

With stock cams and valve springs the spring tensioning method may work, but with more aggressive cams and stronger springs kick back from the valve train will be too strong to overcome with the spring. I always set the tension so that the long throw of the belt between the exhaust sprocket and the crank pulley can be turned through 90 degrees.

Bin the spring it is a demon waiting to strike.

Oily

[revilla]

That's interesting to know, thanks Dave.

[revilla]

Would you use the same method on a VVC? I know they used different tensioner springs - was it a slightly lower tension to protect the front mech drive bearing?

[rj]

Wow. Length 28.000mm - I didn't know it was /that/ sensitive.

[revilla]

LOL. As I say I found it on the web - so don't shoot me!

[SM25T]

I have always used the 'twist the long run to 90 degrees' on my VVC.

[revilla]

... and it seems to have lasted!

[Bricol]

The 90 deg twist is specifically frowned on by timing belt manufacturers unless specifically mentioned (by a tiny number of applications) as it does nasty things to the internal fibres.  Take a look at any timing belt manufacturers design and installation information.

So if I see a fitter buggering about with the several hundred quid, carbon reinforced, quite narrow belt I'm using to transmit 55kW at 500rpm with an alternating load, on a new machine design of mine when we build it, I'll be a bit upset ;)  I've got two moveable idler pulleys on that drive to control the belt on and off load.

That said - I've used the technique on various cars, many times, over the last 30 years and  . . . I daren't say anything else :) 

 I guess in most applications they don't have to transmit much power (relatively speaking), just withstand contamination, temp variations, high revs and we usually manage to change them before they get to failure.

With my K-series, using 285H cams, the spring did seem to provide sufficient force to take out the slack (some belt drive designers get really upset over the word "tension" being used ;) ) - the 90 deg twist test reassured me it was okay to lock things up.

[ECR]

Looks like a drawing I did when changing the belt on my Elise (28mm is arbitrary!). I removed the crank sensor and inserted the peg in the hole. Works perfectly!

[patibbitts]

Can't believe it's possible to bend the belt through 90° !!

 

Surely as described, the long run from the exhaust gear to the crankshaft need needs to remain absolutely taught ??

 

Please clarify?

 

[revilla]

I think the reference was to being able to twist the belt about its own axis in the middle of the run by 90 degrees. Having done quite a few by the book using the spring and post I must say I'm slightly mystified too though. The tensioner usually takes up the slack on the non-driven side of the belt. If you've just wound the engine around clockwise the exhaust side will generally be reasonably taut. Is twisting it on that side really enough to pull the cams round and bring the slack to the exhaust side? If the cam pulleys turned freely like an alternator I can see it making sense (so you can check the tension of an alternator belt on a long run anywhere around the belt) but seems prone to error to me on a cam belt with big cams and strong springs?

[patibbitts]

Thanks for the detailed reply, great clarification ta!

 

I see now what was being suggested, by using the 'twist' action, on the long run.

 

Looks like the cam cover is coming off again - sooner than expected!

 

Gents, Many thanks for your assistance on this subject.

 

 

[Bricol]

The "twist" is a bit of a "feel" thing - takes a few to gain confidence in what you are doing, and to judge the force you are exerting to twist it.  

I've done more 16V Lancia engines than K-series - putting 100,000 on each of two integrales with a belt change every 20,000 miles means I did a few.  Lancia have a tool to put a certain loading on an eccentric idler to take the slack out, which is relatively easily duplicated and then you get to feel the force needed to twist.

The K-series sprung idler method didn't feel take enough slack out when I first did it - but doing the twist made me more comfortable with it being okay - relatively mild cams I guess though, so I can understand how the valve train as it loads and unloads could do unfortunate things to the position of the idler - had the same sort of thing happen with changing the three timing chains, two idlers and 6 belt guides inside the Alfa V6 - if you don't watch things very carefully, the last chain very easily jumps a tooth as things move into a more neutrally loaded position if you don't hold things in place . . . and you don't notice until you spend three days jamming it all back in the engine bay and try to start it!