Setting the timing belt tension

[benl1981]

I'm just about to finally install the timing belt

I've been told a few different way to tension the belt.

Here is what the manual says:

They also mention before this to put the tensioner in with the spring etc. I have a few questions:

1. So - If I rotate the engine twice once everything is in the tensioner spring will provide enough pressure on the belt to set the tension correctly then I just need to tighten it up? IS this CORRECT?

2. Also, with the nissan belt there is markers. Even if you didn't have the cam and crank markers lined up with the v in the piece on the block and marks on the cam cover if you have the all important marks on cam and crank aligned with the belt markers then you are right aren't you. Pretty nice of Nissan to do that.

3. The markers on the old belt did not match the crank and cam centre punched marks...does this mean it was replaced previously at some stage?

Thanks

PS I have found a very good source for the idler and tensioner bearings - $76 for the 2. And they are NSK - i.e. genuine. I have bosted it iin the FAQ

[mabru]

1. YES, tighten it based on what it auto adjust to. Ensure you hold it in place with a hex head wrench when torqueing it down.

2. Yes, the belt marks are a good way to line everything up. To give you an idea, last one I did we were a tooth off on the exhaust cam but couldn't really tell based on looking at the markings on the cam backing plate, but the belt told the tale.

3. No, because of the size difference between the cam and crank sprockets, the marks will move once you start rotating the assembly. Once you get everything setup and running, look at the marks again, they won't line up anymore.

[benl1981]

Thanks Mabru.

Good point in Q3 - silly me that I didn't think of that.

Hopefully get it up and running tomorrow. Just got to buy some loctite.

[mabru]

NP, during the RB26 cams in a RB20 fiasco I must've installed and removed the timing belt and cam gears a hundred times so I'm an expert now.

[GTRgeoff]

Something I discussed with a member recently. It is based on the Engine manual detail. What I didn't see above is the need to remove the plugs to ensure minimum load against turning.

This is a preferred way of ensuring the belt tension is good on the non adjusted side between the exhaust cam wheel and the crank drive pulley. You can do this safely as the belt tension will still be pretty good and shouldn't jump teeth. The tension is then actually set on the belt by using the allen key to bring the adjuster onto the belt with about 20 kg of side tension.

What I do is fit the belt with all marks correct, then fit the harmonic balancer and bolt and tighten slightly to tension the non adjusted side so there is about 5mm deflection on the longest length of belt when wiggled gently, then bring the adjuster in on the other side until there is similar tension that side and nip up the nut.

Too tight on the cam belt and it will sing a bit, too loose and the consequences can be disastrous so the belt should feel firm, not hard or slack. Unfortunately that is the closest I can describe as it would need special tools to determine the tension exactly and the only avoidance is experience.

Find a car recently done that has the cam wheels exposed and feel the tension by grabbing the belt between thumb and forefinger and wiggle slightly. This will give a feel for the right tension.

[benl1981]

Are you talking 5mm in one direction? If I push quite hard on the tensioner side there is about 6mm deflection in one direction. Bit less on the idler side.

I have it back together now but there is still a bit of harshness at low rpm. Whether this is a radiator shroud or something else vibrating. The mechanic thought it was the timing belt hitting the cam cover before. The belt was a lot looser before than it is now though.

Might have to get him to put it one the dyno and have have a look as he loads it up from 1000rpm in 3rd gear.

[GTRgeoff]

Try to get the tension about the same on the tensioner side as the idler and you are about right.