6 replies to this topic

[Dusky]

Hi!

 

Should a duplex be fitted on a performance engine( 998 cooper head/544 cm)? I currently have a simplex with a tensioner

 

And where do you guys buy your woodruf keys? Would be handy to have some laying around if I change to duplex, don't want to wait for another week after 'measuring' my cam timing, again IF i change to duplex... Or would the timing be more or less the same as my current ( simplex) setup?

 

Does anyone know how acurate the minispares standard duplex kits are ? I should time my cam @ 110°.

Edited by Dusky, 20 November 2014 - 07:44 AM.

[Spider]

For a road going Mini, I always fit a duplex timing chain kit regards of what the engine is. The tensoner though designed for a simplex set up works equally as well with the duplex chain.

 

I buy my off-set keys from Mini Spares or you could try the veriner set up from Mini Speed, these are quite good, though all of them are a little on the expensive side especially when compared to off-set keys.

 

I've found the dulex sprockets from Mini Spares as good as originals, they will usually get you within 6 degrees of spec or better, hence then need for the off-set keys.

 

Again for road going cars, I usually tend to set the Cam Timing about 2 - 4 degrees advanced from that recommended by the cam grinder, this is a personal choice. I do this to make the engine more responsive at lower revs but they do loose out a little at the upper revs.

[Ethel]

Duplex, no tensioner for me. The tensioner is a tad narrow for the duplex, so bad things could happen when it wears down. There are also low stretch simplex chains now, but I've no experience of them.

[Dusky]

And is the duplex worthwile? What's the difference between my current simplex tensioned with a duplex?

Its to fit on a ( hopefully?!) 60-65 bhp engine

[jaydee]

Simplex with iwix chain

Lower weight and no stretch issues.

[Spider]

Chain stretch, or lack of is only one part of it, the other being spocket wear.

 

 

Duplex, no tensioner for me. The tensioner is a tad narrow for the duplex, so bad things could happen when it wears down. There are also low stretch simplex chains now, but I've no experience of them.

 

 

Fair enough, but I have to say, I've never worn one out. My missus car would have done over 200 000 km.

[Cooperman]

A 998 with a 544 cam will need to be revving to around 6700 rpm to work at its best. These revs are certainly a bit high for a simplex chain and a duplex will stretch at only 50% of the simplex. So for those revs a duplex is really vital.

As for tensioners, it seems a personal choice. I have had experience of 2 duplex set-ups with a tensioner where pad disintegration had either happened or was about to happen. Both were on similar high-revving units (regular use of over 6500 rpm) and on lower revving engines they are probably fine..

As for cam timing, I usually time mine in at 2 degrees advanced from nominal to allow for initial chain stretch and I know many other engine builders who do the same. I once checked and the timing had reduced by 1 degree after 1500 miles, so 2 degs will give best performance between chain replacements.

For the OP, with that cam and thus high revs, the chain and really the engine will need regular stripping and re-building anyway, so it's no real big issue not having a tensioner.