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Duplex Timing Chain


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#1 James Harris

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Posted 05 January 2019 - 05:23 PM

How much slack should there be on the chain with a duplex timing chain with an adjustable vernier pully??

#2 KTS

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Posted 05 January 2019 - 05:45 PM

ideally none as any slack will allow the cam timing (..relative to the crank..) to vary

#3 Moke Spider

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Posted 05 January 2019 - 05:46 PM

When everything is new, and you push on the chain mid-span, I find they only get about 1/8" at most.



#4 James Harris

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Posted 05 January 2019 - 08:02 PM

The engine has only done about 1000 miles from new but iv got quite a bit of slack on the chain. I don't know what is was like from new as I didn't build it. What can be done to solve it?

#5 DeadSquare

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Posted 06 January 2019 - 09:53 AM

The engine has only done about 1000 miles from new but iv got quite a bit of slack on the chain. I don't know what is was like from new as I didn't build it. What can be done to solve it?

 

Replace everything every race.

 

 

Alternatively, reset the vernier now that the chain is run-in, and don't worry about it.



#6 Moke Spider

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Posted 06 January 2019 - 05:03 PM

You'll find from initial assembly there is an initial settling of the chain, or 'bedding in' of the Chain in to the Sprockets, where the slack will increase from that initial amount of around 1/8" to about 1/4" - 3/8" and then usually from here, they don't move much for quite a long while.

 

How much slack have you got in the chain now?



#7 James Harris

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Posted 06 January 2019 - 08:25 PM

I'd say about 6mm ish of movement on the chain.

#8 Cooperman

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Posted 06 January 2019 - 08:48 PM

Most engine builders set the cam timing 2 degrees advanced from nominal. The chain stretches the most during the first 1000 to 1500 miles and then settles down. The stretch gives around 2 degrees of retardation, so cam timing is ideal from around 1500 miles to maybe 5000 to 10000 miles, depending on how hard it is revved.



#9 mk1leg

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Posted 06 January 2019 - 08:55 PM

replace with the Iwis chain its much stronger



#10 James Harris

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Posted 06 January 2019 - 09:57 PM

It's a rally car so is always at high revs.

#11 Moke Spider

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Posted 07 January 2019 - 05:17 AM

I'd say about 6mm ish of movement on the chain.

 

 

It's a rally car so is always at high revs.

 

Ah well,,,,, comes with the territory then, but I wouldn't loose sleep over that much slack at this point in time.

 

Most engine builders set the cam timing 2 degrees advanced from nominal. The chain stretches the most during the first 1000 to 1500 miles and then settles down. The stretch gives around 2 degrees of retardation, so cam timing is ideal from around 1500 miles to maybe 5000 to 10000 miles, depending on how hard it is revved.

 

Yeap, I do this too.



#12 James Harris

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Posted 07 January 2019 - 09:30 PM

Thanks for all your help




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