Help with 4.3L Timing Mark?

[nigel]

I'm trying to set the timing on my 1998 2bbl 4.3L 190hp carb engines but can't find the timing mark scale - all I have is a tab with a notch in it. There is no scale on the damper either - just one very thin line.

What do the notch and line indicate, if I align them? TDC? Or are they positioned so that aligning them gives the correct timing - i.e. 10deg BTDC?

Does anyone know if Merc have changed the timing spec for these engines? - I heard that many engines have had their timing changed to 4deg TDC from 8deg to compensate for rough fuel quality.

Whilst I'm writing - The centre bolt on my damper appeared loose so I tightened it up as high as I could - about 50lb ft - without clamping the engine to stop it rotating. But would you expect this bolt to move anyway relative to the crank as part of the damper's normal operation?

Many thanks in advance for any help you can give!

Cheers,

Nigel.

 

[SR Tech]

On the tab you should see several notches, the biggest one being a recess 0deg.

They count all points on the tab, protruding and recessed.

Notches to the left of 0deg are BTDC; goes to 12deg

Notches to the right of 0deg are ATDC;only goes to 6deg

You may need to take a wire brush to the tab to see the numbers, and it actually says "before" and "after" on there.

Your motor is specd at 8deg Before, If you don't like how it runs drop it to 6deg Before.

Mark your line on the balancer, and on the tab at the number you want with white out. Makes it much easier to see with the timing light.

Good Luck:thumbsup:

 

[nigel]

Thanks for this. Should all engines from all years have a scale on then? - The tab is smooth with just one big notch in it, in the middle. As this is the only mark I guess this would indicate TDC when aligned with the line on the damper?

Looking at the damper, it seems some of the paint has come off in a very orderly/square manner - maybe somone in the past has stuck a timing scale label on there and its dropped off - taking the paint underneath with it..

Cheers for your help,

Nigel.

 

[SR Tech]

Some do have the scale on the balancer, its normally just a sticker, and you line it up with the point on the tab. Sounds like you did at one point.

If you don't have the scale on your tab then you need a new sticker for the balancer. The thin line is 0deg when you go and line up the sticker.

 

[nigel]

Excellent. Many thanks!