Duplex Timing Chains

[sagalout]

Can anyone confirm that the duplex timing chain hasn't got a tensioner , unlike the simplex which has.
Keep seeing the engine bits in the garage but have NO time to get on with it. FRUSTRATING.
Thanks guys

[Cooperman]

Duplex chains don't have a tensioner. Best to time the cam in at about 2 degrees advance from makers nominal to allow for initial chain stratch using either offset woodruff keys or vernier pulleys.

[sagalout]

Thank you Peter, that's what Minispares told me, but I am used to seeing a tensioner in there, as on the other engines I have screwed together.

[miniman]

Strange - I just fitted a duplex vernier chain to my 998 and I refitted the tensioner. Should I take it back off again???

[plotloss]

As a small aside.

Belts or Vernier duplex?

Any strong opinion either way as to best for a perfomance engine?

[Cooperman]

The competition regs I run my Minis to don't allow belts, so I always use a duplex chain ste-up. The disadvantage is that the chains stretch, particularly under sustained high-revs, but the advantage is they never snap and the timing chain rattle tells you when to change them, should you not do so sooner.
One point, when fitting a duplex set-up to a 'tensioner'type single chain engine, make sure you grind away the oil splash flange inside the timing gear cover and make sure that it doesn't hit the chain when you assemble it.

[plotloss]

I was just wondering because apparently they are a lot quieter (not that thats going to be an issue really with a 45 sat effectively in the cabin).

Presumably the belts stretch over time like the chains?

[Cooperman]

No, the belts don't stretch by any discernable amount.
They will snap if not changed regularly, but I guess every 20,000 miles is OK (take manufacturer's advice on this). The big advantage of belts is that they keep the cam timing more accurately.
Got to go and collect my 1330 cc block from which I have just had 0.008" machined from the deck this morning and the new pistons pressed onto the rods. Start final engine assembly this evening if 'er indoors' lets me out to my workshop to play!

[Mr2Mike]

It's quite possible to add the A+ chain tensioner to a duplex chain setup, my last two mini's had this setup with no problems at all.

[Cooperman]

That doesn't really help with keeping the cam timing accurate, as the slack in the chain is always on the chain return to the driven sprocket. It does make it a bit quieter though. I don't know how I'd know the difference in my cars!