11 replies to this topic

[ECG317W]

Hi there,

Could someone please explain to me the procedure to follow when replacing a simplex chain with a duplex one? I understand that modifications to the timing back plate and timing cover need to be made. Also, is there a tensioner for a duplex chain as I can't seem to find one listed on the minispares website?

Thanks you!!

Ben

[WiredbyWilson]

you will need to check the timing does not move during the installation - so mark the crank / cam with timpex or similar (what i did).

there is no duplex tensioner that i know of, they say you do not need one with a duplex kit, but i fitted a std tensioner as a precaution - it comes down to personal preference i believe.

Edited by Wilson1330, 30 September 2009 - 07:45 PM.

[lrostoke]

Behind the bottom sprocket are two bolts, these need to be swapped for countersunk screws, this is where the modification to the back plate comes in, it needs countersinking to accept the screws.
I'm sure I've read some people don't use a tensioner with the duplex, we just refitted the simplex tensior, just checked it on a recent rebuild been on 12 months and no problems.

think chain can catch on outer cover, you just need to hit it with a hammer where it catched.

[Cooperman]

It seems OK to fit the simplex tensioner if you only intend to use medium revs. If regular 6000 rpm or more are envisaged, then don't fit the tensioner. The simplex tensioner bears on both edges of the single chain, but on the duplex it bears only in the centre. I've had one broken tensioner and one that was about to break on duplex chains with simplex tensioners this year alone, but both were on hig-revving engines.

[bmcecosse]

Yes - I too have found a broken up tensioner when used with duplex - don't fit it! In fact - only fit duplex if you are planning fancy high lift cam and strong valve springs. For more reasonable engine mods - a new single chain with tensioner is fine - and much quieter.

[Sherlock]

I never use tensioners with duplex chains, just not necessary & unwise, however, sorry I just have to say this because I only ever post what I've learned from 40 years experience, I fit duplex to make engines quieter, I've never had one noiser than the old clanking simplex.

[bmcecosse]

Yes - the 'old' simplex - but with the tensioner, simplex is fine. Duplex may start off quiet - but soon gets noisy!

[MDMA]

Photos?

[ECG317W]

Thanks very much for all the replies - I won't bother with the tensioner. Am I right in saying that the timing cover will need modifying where the breather is joined on the inside?

[Cooperman]

Yes, you have to remove the semi-circular flange inside the cover by grinding it out or by cutting it out. Also, there is another pressed indent which must be knocked flat from the inside.
It's best to use allen-headed 1/4" unf screws under the sprocket after you countersink the front plate. By the way, don't use a large drill to do the countersinking as the angle is incorrect and the screws can come loose. Used a proper countersinking tool.

[jaydee]

I always wondered..Is it really worth to fit the heavier duplex chain?
I will probably go for a simplex chain in mine, i've found them lighter and reliable too, unless you have a really high revving engine.

[haz]

or if like me you didnt get any csk bolts in your kit you can counterbore the timing plate with a slot drill/end mill/whatever you can lay your hands on and use the origional bolts... requires a pillar drill

check your woodruff keys are a good fit prior to fitament and do a trial fit without them in to check that the two sprockets run true to each other... put a straight edge accross the two. add shim as required.

If you have any trouble sliding them on (they should be a pretty tight fit) just run some scotch brite over the crank tail and inside of the sprockets to remove any slight burrs - careful not to remove too much they must be a good push fit.