How tight should chain be?

[alanscottj]

I have a pull down tensioner like one in the picture. How tight should chain be? I seem to remember someone sayin 6mm (might be sticky's but can't find book). Which do I measure bottom or top chain? At the moment there is no gap between the top chain and the tensioner but the bottom is moving up and down abut an inch. Any thoughts? Many thanks

[Daggs]

You've got an inch of up 'n' down play with the top tensioner pulling down that far !!?
I think the chain is too long mate.

[storkfoot]

There's a lad on here (andychain) who has worked with automotive chains for many years. He reckons that it should be 2 to 3% of the distance from the centre of one sprocket to the other.

It certainly shouldn't be tight to the tensioner.

[rosscla]

You've got an inch of up 'n' down play with the top tensioner pulling down that far !!?
I think the chain is too long mate.

The chain tensioner won't make any difference to the play in the bottom run.

[coaster]

the chain will be tight across the bottom run with the engine under load, the role of the top tensioner is to minimise the whip lash effect on slack on the top section...I believe. 1/2" up and 1/2" down doesn't seem too excessive to me

[HxPaul]

Most Lambretta engine builders say 6mm on the top run,just in front of the chain tensioner.

[alanscottj]

It is definatly tight to the top tensioner so will loosen a bit and aim for the 6mm in front of tensioner.

[Minority]

As Coaster says, the bottom run will be tight under load so make sure it is when you measure the slack (in the top). Either turn the clutch clockwise against the crankshaft on compression or put it in gear and turn the crankshaft bolt anti clockwise. The slack in the bottom is what you get when you back off the throttle e.g. when you change gear and if it is too much the cain will "whip" into the casing (not good). Pretty sure this is why Mr Innocenti fitted a bottom chain guide as well as the tensioner.

[Chris in Margate]

6mm at the top to the left of the front sprocket close to the top tensioner. I use 2 plastic chopsticks! Push the thicker end in and lift and measure the amount of lift with the thicker end of the other one. It's a perfect set of tools and a very accurate measure.

[Daggs]

You've got an inch of up 'n' down play with the top tensioner pulling down that far !!?
I think the chain is too long mate.

The chain tensioner won't make any difference to the play in the bottom run.

Yes I understand that, but that much slack in a chain (tensioner pulled tight and one inch up/down at the bottom) is a pretty good indicator the chain is too long.