Timing Chain Replacement - Tension issue

[ChrisD]

Hi,

I'm replacing the timing chains and tensioners following the RH Camshaft sprocket locating pin interference nut coming loose. I think I have fitted and tensioned the LH chain correctly (although the jackshaft sprocket is more like 5 O'clock rather than just after 3 - I may re-visit that and re-align the distributor). However after fitting and re-tensioning the RH Chain at TDC - I think it looks ok but when I turn the engine through about 180 degrees the lower edge of the chain goes extremely tight against the tensioner and the top edge goes extremely slack. I'm struggling to think what could cause this, as would have expected the number of links between the Camshaft Sprocket and crankshaft sprocket to remain constant.

Any ideas to what may be causing my issue?


Also once you have released a tensioner can you reset it?

Thanks

Chris

PS this is my first attempt at replacing the timing chains.

[ChrisD]

I've just done a quick Google on the tensioner and found a Moss video on it. I was resetting it correctly but didn't realise the tensioner comes out in steps, I thought I was doing something wrong when testing it - it was sticking when pushing it in

Chris

[barkerwilliams]

Chris,

Have you played "hunt the spring" yet? If they release they travel quite a long way.

Alan

[jbuckl]

take the tensioner off.
wind the ratchet piston in against the spring in the plunger.
Use the red plastic setting piece in the tensioner.
refit the tensioner.
Pre load the chain by moving the guides.
remove the setting piece.
push the plunger all the way home to activate it.
check the tension then.
As the cam turns, the tension will be affected slightly in both directions but not dramatically.
even during running the crank & cam speeds are oscillating with every revolution.
consider using new bolts for the tensioner.
measure & buy them from a bolt supplier. (1/4 unf thread & 1.5xd engagement)
Recently bought some from a stag supplier that were too short!

[ChrisD]

Thanks for the replies so far.

Alan yes, I have played 'hunt the spring' - which reminded me to cover the engine with a dust sheet before playing with the tensioners

jbuckl (sorry I don't your name) I followed the procedure you mentioned, the only difference was I inserted a 1mm shim between the tensioner block and chain before adjusting the guide.

I just don't understand why the chain is going tight on the bottom run and slack on the top run I when I turn the engine by the pully.

Chris

[mole42]

Is it possible that the camshaft is out of sync and at one place you have a valve touching a piston? That would increase the tension on the chain quite a lot. You did mention that the jackshaft isn’t lining up according to the marks, that shouldn’t be a problem if the distributor times up correctly but it’s vital that the crank and cam are aligned properly.

[ChrisD]

Thanks Richard. I set TDC and checked the alignment of the camshaft sprockets and camshafts before removing the old chains. The crankshaft is at TDC and the camshaft sprocket and camshaft are aligned with the new chain re-fitted - so I don't think the valve is touching a piston.

[flying farmer]

IIRC due to the firing order there is a point where three valves are opening at once on each bank and at other times the same ones will be closing and driving the cam around, so the variation in tension on the chains is quite significant.
Neil

[ChrisD]

Hi,

Just a quick update.

I spoke to Robsport who were extremely helpful and gave me a few pointers. In the end I replaced the RH Camshaft and Crankshaft sprockets and the camshaft screws. I have now managed to correctly tension the RH chain. I believe there was some unusual wear on the sprockets/screw due to the loose locating pin and camshaft screw.

I also reset the jackshaft and distributor as per the manual. One thing that caught me out was for all four timing marks to realign requires 6 revolutions of the engine, I was just realigning TDC and the Camshaft marks (2 revolutions) and suddenly noticed the Jackshaft wasn't aligned with it's mark.


Thanks to everyone who commented on my post.