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April 3rd, 2008, 01:06 PM   #1
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when is the camchain worn?

ok i want to put this in the doc.

i need to know what a camchain is new over a certain distance? you've all seen how you measure the final drive chain over 18 links and 272mm etc etc.

can someone take a new camchain and do the same over a set distance? we'll use that as a baseline for a 'new' chain?

regards

Taffy
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April 3rd, 2008, 02:28 PM   #2
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RE: when is the camchain worn?

I took a new chain and laid it out on the desk. With the rivet link sitting in one end, the total number of pitches is 64. Based on a pitch length of .375, the overall length equals 24 inches (609.6mm), center to center. A quick check with a tape measure confirms this. A new chain could actually measure a C-hair over 24" due to tolerances.

Out of curiosity I took a piece of #35 roller chain and compared it to the DID chain. Other than the same pitch, there is nothing in common. The DID rollers are larger in diameter and wider.
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April 6th, 2008, 11:54 AM   #3
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RE: when is the camchain worn?

can anyone define when it is worn though?

is there a spec for the wear?

regards

Taffy
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April 6th, 2008, 02:17 PM   #4
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RE: when is the camchain worn?

I went and put a new chain beside my old chain to see how my chain at 40 hours compared to a new one. I can detect no difference even putting both under slight tension and matching pitch for pitch over 24 inches. Now here is the "rest of the story".

The new chain the dealer sent me, part number 81036013100 which is 64 pitches long is not correct for my engine. The part number is correct according to the 2007 550 engine manual, but in the manual it states that chain is 66 pitches. My chain is definitely 66 pitches long, so there is an error in the KTM parts system. The label on the box reads 81036013100 timing chain 64 pitches. This must be a chain for a 450. I suppose the taller 650 engine gets an even longer chain.

Overal length for a 550 = .375 x 66 = 24.750 C-C (628.65 mm)
The 'mounting clearances/wear limits' chart in the repair manual makes no mention of the cam chain.
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April 7th, 2008, 02:37 AM   #5
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for $$$$ sake i used to replace my cam chain when the acct hit full extension , hoping that the tensioner was not at fault due to too much tension , which would rapidly wear the pins and rollers creating the illusion that the chain had '' stretched '' when really it's just wear .
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April 7th, 2008, 11:05 AM   #6
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Overal length for a 550 = .375 x 66 = 24.750 C-C (628.65 mm)

run that by me again keepoing the metric and imperial clearer? i've stuck it in red alert but i'm not clear what you're saying?

regards

Taffy
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April 7th, 2008, 01:59 PM   #7
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Not that I can answer Taff's original question, but to clarify a point, chains do not stretch in service, they wear. The lengthening that people call stretch is just the effect of wear between the pins and bushes. Other wear is between the rollers and bushes, but that does not appear as 'stretch', just floppy rollers. A chain tensioned too tightly will wear prematurely as it is over loaded.

With the steels used in modern chains, they would break after stretching just a very small amount and the loads would be enormous to do this.

Cheers
Steve
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April 7th, 2008, 02:21 PM   #8
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A 550 chain is called up at 66 pitches long (includes the rivet link). Roller chain is called up by pitch. Pitches have almost always been based on imperial measurements. Even looking up metric chain standards results in odd distances like 9.525mm pitch. This is just another way of saying 3/8" pitch. (.375/.03937=9.525mm) Remember that 1mm=.03937 inches.

Chain is made up of inner link assemblies riveted together using pins and outer plates. The number of pitches will always be an even number when you are joining the chain with standard outer plates. The only way to have an odd number is to use an offset link (sometimes called a crank link). The side plates have a dog leg shape and there is one roller attached.

The pitch dimension is the same for all elements, meaning that the rollers which mesh with your sprocket teeth must always be the same distance apart. When we talk about pitch, it really means spacing from one roller centerline to the next roller centerline. Thus 66 pitches will be 66 times 9.525mm = 628.65mm (or 66 times .375 = 24.75 inches). This distance is always "between centers" from the begining to the end of the chain and must include the rivet link so you have the whole chain.

As to tolerances, chain is incredibly demanding because there are so many bits added together. If each pitch was off by only .001", the 550 chain would be out by .066", an amount you would easily notice with old and new side by side.
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April 7th, 2008, 02:31 PM   #9
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yada yada yada

sorry mate, never liked the way you americans put down nimbers and then again the europeans use commas and we use full stops - all for the same measurements.

i got it in the end even if i did have to sit through the 10 commandments as well......

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April 7th, 2008, 03:23 PM   #10
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What is a full stop? I get the 628.65 vs 628,65 thing.
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