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September 03, 2014, 07:39:17 AM

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Author Topic: Twin timing chain  (Read 526 times)

coinzy

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Twin timing chain
« on: March 10, 2013, 05:29:52 PM »
I just adjusted the chain and noticed it has a slack spot.So it's taught then slack slightly.Do these chains slacken as they warm or the other way around.I'm a little worried that it may overtighten when it comes up to temp.
coinz.

ERC

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Re: Twin timing chain
« Reply #1 on: March 10, 2013, 07:34:13 PM »
If your talking about a 700cc chain due to the age of most of the parts in these you will always havea tight spot. You want it to be loose enough to not bind the motor and not be to loose to slap the case. I'd say by your description you've got it right.    ERC
2-57 Apaches, 2-57 Trailblazers, 60 Chief, 65 Interceptor, 2004 Bullet, 612 Bullet chopped.

barenekd

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Re: Twin timing chain
« Reply #2 on: March 10, 2013, 08:30:55 PM »
Usually slack spots come from worn chains. Is the chain new? If not, the best solution is to get a new one. You don't want to overtighten a chain, so adjust it where it needs to be in the tight section. But beware, a chain with uneven length links, the tight parts vs the slack parts will accelerate the wear on the sprockets.
Bare
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2011 Black Classic G5 (RIP)
I refuse to tiptoe through life only to arrive safely at death
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coinzy

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Re: Twin timing chain
« Reply #3 on: March 10, 2013, 10:04:32 PM »
Thanks guys,i will order a new chain though i believe this one had been replaced in a rebuild,don't think it has done to many miles but can't be sure.Actually what i wanted to know though was do timing chains slacken when going to hot or do they tighten up.I know with these chains if they are adjusted too tight they will "whine",on another note i was just told the flexable nylon quill is a dud,any one else been told this.Apparantly they come with a disclaimer :-[ requiring check every 100 miles.I think i'll go back to the original setup with neoprene rubber quill.
Bike is a '51 500 Twin.
cheers

Arizoni

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Re: Twin timing chain
« Reply #4 on: March 11, 2013, 01:18:47 AM »
I'm just eyeballing an exploded view of a twin and guessing about the distances between the cams and crankshaft so my numbers are not exact.

That said, the aluminum housings will expand more than the chain will when the engine is hot so the distances between the sprockets will become greater.  That will tighten the chain.
The amount of change should be less than a total of .050 for the system so if I were building it I would shoot for a looseness of about  3/4 inch total back and forth  movement on one of the longer spans like between the crankshaft and the exhaust cam.  That would be 3/8" to the right and 3/8" to the left from the untouched chain position.  It might not hurt to even go as much as 1/2" right and 1/2" left with a few pounds of force applied in each direction.

It's better to have it a little loose than too tight.
Not only will it wear the chain if it is too tight but the tight chain will create some very high loads on the camshaft bearings.
Hopefully, someone who has a book that gives factory numbers will tell use what it says.
« Last Edit: March 11, 2013, 01:23:42 AM by Arizoni »
Jim
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1999 Miata 10th Anniversary

ERC

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Re: Twin timing chain
« Reply #5 on: March 11, 2013, 01:39:31 AM »
They  want a 1/4" between the rear cam and timing sprocket. ERC
2-57 Apaches, 2-57 Trailblazers, 60 Chief, 65 Interceptor, 2004 Bullet, 612 Bullet chopped.

Arizoni

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Re: Twin timing chain
« Reply #6 on: March 11, 2013, 03:49:23 AM »
That's kinda weird.
The chain between the rear cam and the crankshaft sprocket goes over the chain tension adjustment sprocket.
The length of the run between the crankshaft sprocket and the adjuster and between the adjuster and the rear (intake) cam is very short.
I wonder if this is why the movement is only 1/4"?
Jim
2011 G5 Deluxe
1999 Miata 10th Anniversary

coinzy

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Re: Twin timing chain
« Reply #7 on: March 11, 2013, 10:05:11 AM »
The manual doesn't mention any slack in the chain,just to tension the chain by moving the adjuster plate in one direction,and not to back off the adjuster.
It actually says "turn the engine until the chain is in it's tightest position and any slack is between the rear cam sprocket and the timing sprocket on the engine shaft."Then adjust the chain.
Soit appears RE weren't concerned with any expansion of the cases affecting chain tension,thanks for your help  ;)

ERC

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Re: Twin timing chain
« Reply #8 on: March 11, 2013, 12:48:04 PM »
In the later manuals they say 1/4".  The early ones don't specify the dimension.  ERC
2-57 Apaches, 2-57 Trailblazers, 60 Chief, 65 Interceptor, 2004 Bullet, 612 Bullet chopped.

coinzy

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Re: Twin timing chain
« Reply #9 on: March 11, 2013, 06:41:22 PM »
Well i've now found another section in the manual,i think it's a photo copy of the handbook.And it states "the chain should be adjusted to the minimum of slackness and it's important that the last movement  of the quadrant before tightening the locking nut should be in the direction which tightens the chain" so thats pretty clear for me now.thanks for your help.
coinz

barenekd

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Re: Twin timing chain
« Reply #10 on: March 11, 2013, 07:17:01 PM »
My book says 1/4" at the tightest part of the chain.
Bare
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coinzy

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Re: Twin timing chain
« Reply #11 on: March 12, 2013, 01:58:46 AM »
I've set it at 3/8" and it's nice and quite at that.coinz.

curtisbelford

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Re: Twin timing chain
« Reply #12 on: March 12, 2013, 04:28:55 AM »
1/4 , 1/2    LOL I like right down the middle 3/8    ;D

Arizoni

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Re: Twin timing chain
« Reply #13 on: March 12, 2013, 04:45:25 AM »
For what it's worth, when I did my calculating I assumed the aluminum crankcase was 200 degrees F hotter than the chain.
That's probably not a realistic value with the true value being more like less than 50 degrees F hotter.  That could explain why my numbers indicated that more slop would be needed.
Jim
2011 G5 Deluxe
1999 Miata 10th Anniversary