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-0.015" Big Block Timing Chain

General engine tech -- Drag Racing to Circle Track

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Kevin Johnson
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Re: -0.015" Big Block Timing Chain

Post by Kevin Johnson » Thu Nov 28, 2019 11:20 am

MadBill wrote:
Thu Nov 28, 2019 12:59 am
Post Script:
Received and installed the 'dash ten' Cloyes chain (identified, as specified, by two copper-colored links) and it fits much tighter on the same sprockets as the new standard chain I removed; just enough slack to compensate for the calculated ~ 0.004" C-C greater expansion of the aluminum block.
:lol: I guess I am just a bit jaded after the GM/Melling high-flow oil pump purchases.
https://www.ustsubaki.com/pdf/the-complete-guide.pdf wrote:...The chain’s wear elongation limit varies according to the number of sprocket
teeth and their shape, as shown in Figure 2.11. Upon calculation, we see that sprockets with large numbers of teeth are very limited in stretch percentage. Smaller sprockets are limited by other harmful effects, such as high vibration and decreasing strength; therefore, in the case of less than 60 teeth, the stretch limit ratio is limited to 1.5 percent (in transmission chain).
The length increase needed to yield the -0.015" spec is far, far less than 1.5 percent.

Cloyes also has a patent on tooth design that would allow stretched chains to operate properly (I know you only purchased the chain for your existing gears):
https://patents.google.com/patent/US5848948A/en wrote:... Specifically, each sprocket tooth 112 is thinned along the flank radius 114, 116 as shown in FIG. 6, and as represented in exaggerated form by the cross-hatching in FIG. 7 while the root diameter is maintained the same. This thinning of the tooth builds in a backlash when compared to the theoretical sprocket design. Since the root land is elongated, the chain is in hard contact with the root diameter of the sprocket throughout the entire chain wrap. It will be understood that the inventive aspects reflected in FIG. 6 and FIG. 7 find equal application to both driving and driven sprockets.

In point of fact, the chain wrapped around standard non-thinned sprockets is usually in hard contact with a standard sprocket root diameter only at the immediate area of entry and exit and not over the remainder of the wrap angle. In addition, chain wear and elongation when used on these standard non-thinned sprockets further loosens the chain wrap in the non-entry and non-exit regions. Stated another way, this means there is no backlash in the standard non-thinned sprocket. Moreover, near the central portion of the wrap, the chain is able to leave contact with the sprocket. This loose condition over the central portion results in the chain rollers rattling against their bushings and against the sprocket teeth--a major source of noise. ...
I am guessing (my powers of clairvoyance are waning) that this patent is the referent of this 2017 vintage Cloyes webpage:
Occhams Razor: Pre-stretched on a rig to a spec.

I am open to further data.
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Re: -0.015" Big Block Timing Chain

Post by tenxal » Fri Nov 29, 2019 8:24 am

MadBill wrote:
Thu Nov 28, 2019 12:59 am
Post Script: Received and installed the 'dash ten' Cloyes chain (identified, as specified, by two copper-colored links) and it fits much tighter on the same sprockets as the new standard chain I removed; just enough slack to compensate for the calculated ~ 0.004" C-C greater expansion of the aluminum block.
Thanks for updating this. Going through my accumulated timing components the other day, I came across that Cloyes -.015 chain I'd posted the pic of in this thread. :)

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Re: -0.015" Big Block Timing Chain

Post by tenxal » Fri Nov 29, 2019 8:37 am

Kevin Johnson wrote:
Thu Nov 28, 2019 11:20 am
:lol: I guess I am just a bit jaded after the GM/Melling high-flow oil pump purchases.
Kevin, before ordering the -.015 chain, I spoke at length with a Cloyes technical rep that explained how they came up with the 'short' chains. They have a fixture that checks chains length as part of their Q.C. process. Anything that falls outside their length specs. gets a copper plated link to designate each .005 deviation from the minimum c-c spec. In other words, their chains aren't intentionally produced 'short'.

My need for a -.015 chain was eventually addressed by a new Dart block. :lol:

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Re: -0.015" Big Block Timing Chain

Post by Kevin Johnson » Fri Nov 29, 2019 10:55 am

tenxal wrote:
Fri Nov 29, 2019 8:37 am
Kevin Johnson wrote:
Thu Nov 28, 2019 11:20 am
:lol: I guess I am just a bit jaded after the GM/Melling high-flow oil pump purchases.
Kevin, before ordering the -.015 chain, I spoke at length with a Cloyes technical rep that explained how they came up with the 'short' chains. They have a fixture that checks chains length as part of their Q.C. process. Anything that falls outside their length specs. gets a copper plated link to designate each .005 deviation from the minimum c-c spec. In other words, their chains aren't intentionally produced 'short'.

My need for a -.015 chain was eventually addressed by a new Dart block. :lol:
Reset of my perception of the problem.

I saw MadBill's note of the center-to-center growth due to the expansion of an aluminum block and his desire for a -15 chain (dash 15 -- not minus 15). MadBill used a tilde (~) which signifies approximate in his numerical calculation of the growth.

Maybe there is confusion (even at Cloyes??) about whether the dash (-) is simply an alpha-numeric symbol of a different version or if in fact it refers to a shorter (minus) chain? If there was/is this confusion then it could be reflected in a "logical" rationalization of a deviation from a minimum center to center spec rather than a maximum.

Sorry to muddy the waters.

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Re: -0.015" Big Block Timing Chain

Post by Kevin Johnson » Sat Nov 30, 2019 10:36 am

Okay, I looked at a 2002 Cloyes catalog and it explains very clearly about the need for shorter chains due to line honing/boring.

http://www.cloyes.com/images/CloyesHigh ... t-2002.pdf

A picture of the jig used to measure the chain is shown with an outside micrometer/gauge.

So, MadBill's aluminum block has been line honed/bored and, with center-to-center expansion due to thermal growth, needs a -15. Cloyes makes clear that the -.005 (NLA), -.010 and -.015 are shorter chains.

Cloyes premium chain supplier is IWIS.

Here is an IWIS handbook with engineering information:

https://www.iwis.com/as-handbook/iwis-h ... uction.pdf

There are multiple loads that can be applied to test the length of a chain and to pre-stretch it.

My suggestion is that the chain(s) that is/are supplied to Cloyes are unstretched with the agreement that it/they will be stretched. Or IWIS stretches them in the manner below. IWIS chains are marketed as prestretched in any event.

This could be easily performed by Cloyes on the rig shown in their catalog with an adjustable spreading hydraulic ram whilst the chain sprockets rotate. A lower load is supplied for -15, a higher load for -10 and then an even higher load for standard length. In each case the chain would be meeting a published standard.

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Re: -0.015" Big Block Timing Chain

Post by Lizardracing » Sat Nov 30, 2019 1:06 pm

Easy question, How does the C-C get smaller? Wouldn't the right way be taking the material off the cap instead of the block so the C-C stays the same?

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Re: -0.015" Big Block Timing Chain

Post by FC-Pilot » Sat Nov 30, 2019 2:36 pm

Lizardracing wrote:
Sat Nov 30, 2019 1:06 pm
Easy question, How does the C-C get smaller? Wouldn't the right way be taking the material off the cap instead of the block so the C-C stays the same?
Even after taking material off the cap you still had to hone and some times bore the mains which will take off “some” material off the block. You can try to minimize it but there will be some material removed.

Paul
"It's a fine line between clever and stupid." David St. Hubbins

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Re: -0.015" Big Block Timing Chain

Post by Charliesauto » Sat Nov 30, 2019 2:41 pm

MadBill wrote:
Thu Nov 28, 2019 12:59 am
Post Script:
Received and installed the 'dash ten' Cloyes chain (identified, as specified, by two copper-colored links) and it fits much tighter on the same sprockets as the new standard chain I removed; just enough slack to compensate for the calculated ~ 0.004" C-C greater expansion of the aluminum block.
Another solution would be to use a -.005" Rollmaster set and a -.010" Cloyes chain, should net you -.015"

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Re: -0.015" Big Block Timing Chain

Post by BLOCKMAN » Sat Nov 30, 2019 4:40 pm

Charliesauto wrote:
Sat Nov 30, 2019 2:41 pm
MadBill wrote:
Thu Nov 28, 2019 12:59 am
Post Script:
Received and installed the 'dash ten' Cloyes chain (identified, as specified, by two copper-colored links) and it fits much tighter on the same sprockets as the new standard chain I removed; just enough slack to compensate for the calculated ~ 0.004" C-C greater expansion of the aluminum block.
Another solution would be to use a -.005" Rollmaster set and a -.010" Cloyes chain, should net you -.015"
I believe Cloyes uses the same change for the plus or minus timing sets are done with the gear dimensions not the chains.

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Re: -0.015" Big Block Timing Chain

Post by BLOCKMAN » Sat Nov 30, 2019 4:43 pm

Lizardracing wrote:
Sat Nov 30, 2019 1:06 pm
Easy question, How does the C-C get smaller? Wouldn't the right way be taking the material off the cap instead of the block so the C-C stays the same?
In a perfect world if you machine .003 off the caps and align hone the block in a perfect world you will be moving the C-C distance .0015 closer together.

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Re: -0.015" Big Block Timing Chain

Post by Tuner » Sat Nov 30, 2019 4:43 pm

Somewhere in the waybachdaze in this forum was a link to a Cloyes tech bulletin that described during manufacture links are (were ?) sorted by length and separated categorically in short, long and longer, to be assembled as longer and shorter overall chain lengths. As I recall the measurement was optical (laser?) and the precision tolerance was less than .0001" per link. In another process the sprockets are (were?) measured for precise diameter and chains and sprockets are finally assembled and measured together and packaged as a set for precise fit to a specified cam and crank centerline measurement.

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Re: -0.015" Big Block Timing Chain

Post by exhaustgases » Sat Nov 30, 2019 4:52 pm

FC-Pilot wrote:
Sat Nov 30, 2019 2:36 pm
Lizardracing wrote:
Sat Nov 30, 2019 1:06 pm
Easy question, How does the C-C get smaller? Wouldn't the right way be taking the material off the cap instead of the block so the C-C stays the same?
Even after taking material off the cap you still had to hone and some times bore the mains which will take off “some” material off the block. You can try to minimize it but there will be some material removed.

Paul
Difficult ? Sort of but with the correct machine there is no reason the amount off the block should be more than a few tenths. (.0002)

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Re: -0.015" Big Block Timing Chain

Post by BLOCKMAN » Sat Nov 30, 2019 7:17 pm

exhaustgases wrote:
Sat Nov 30, 2019 4:52 pm
FC-Pilot wrote:
Sat Nov 30, 2019 2:36 pm
Lizardracing wrote:
Sat Nov 30, 2019 1:06 pm
Easy question, How does the C-C get smaller? Wouldn't the right way be taking the material off the cap instead of the block so the C-C stays the same?
Even after taking material off the cap you still had to hone and some times bore the mains which will take off “some” material off the block. You can try to minimize it but there will be some material removed.

Paul
Difficult ? Sort of but with the correct machine there is no reason the amount off the block should be more than a few tenths. (.0002)
OEM register cuts are not that flat.

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Re: -0.015" Big Block Timing Chain

Post by Kevin Johnson » Sat Nov 30, 2019 7:31 pm

Tuner wrote:
Sat Nov 30, 2019 4:43 pm
Somewhere in the waybachdaze in this forum was a link to a Cloyes tech bulletin that described during manufacture links are (were ?) sorted by length and separated categorically in short, long and longer, to be assembled as longer and shorter overall chain lengths. As I recall the measurement was optical (laser?) and the precision tolerance was less than .0001" per link. In another process the sprockets are (were?) measured for precise diameter and chains and sprockets are finally assembled and measured together and packaged as a set for precise fit to a specified cam and crank centerline measurement.
I looked through a large number of pages on the forum using simply "Cloyes" as a search parameter.

I found all sorts of interesting things (again) including the info from BHJ about the 20 to 30 degree temperature rise in the oil pan temperature of a Chevy 292 run continuously at a critical rpm.

There are patents for optically sorting morse silent chain parts to avoid misassembly.

There have been many discussions about chain quality or lack thereof and custom set creation by mixing short chains with different sized gears. Many of the links given would need to be tracked down again as websites have been changed.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


http://www.romacusa.com/tech_timing_sets.html



Re: Timing set for line bored SBC

 by tenxal » Mon Feb 08, 2016 10:07 pm
Cutlassefi wrote:That's impossible, how are you going to do that? They all use a larger diameter gear(s) to take up the slack.
The Technical person I spoke with at Cloyes told me they use a combination of gears and chains that fall on either side of manufacturing tolerances to get the final centerline distance. In other words, a custom 'short' set may have standard gears and a short chain, a standard chain and larger gears or any combination of the three. Cloyes identifies their 'short' chains by a copper colored link for each .005 the length is shortened.





Re: Timing set for line bored SBC

 by tenxal » Sat Feb 13, 2016 12:23 pm
Pic of the new .015 chain. As mentioned earlier, each .005 totallength difference from standard is denoted by a copper colored link. As measured with my Mitutoyo ball end .0001 (ten thou.) micrometer, the center-to-center dimension of all pins are the same, as are all the roller diameters. I've got the .005 'short' chain on it now and will get pics of it's deflection as well as the .015 'short' chain and post them.




Re: Some Q's on SBF timing gear & chain - thrust

 by Daniel Jones » Mon Nov 19, 2012 3:16 pm
Most vendors of timing sets do not make the timing sets they sell. Instead,
they repackage the chain and gears from multiple vendors. You need to know
who made the sprockets and chains. One of the guys on the FE Big Block Ford
forum (FE Engine Specialist Barry Rabotnick) used to work at Speed Pro. When
he worked there, they had offshore companies trying to be suppliers, so they
piggybacked some chain and sprocket testing on an OE bearing durability dyno
run. The Rolon chain from India cost them the test motor a couple times when
it failed before the test was completed. Having recently disassembled a 351C
Ford that had a Rolon chain, I can believe it. This engine had approximately
8000 miles on the chain and it was stretched worse than the one I pulled from
my 5.0L at 163,000 miles.

A summary of the test results for the chains from Barry is listed below.
Speed Pro ended up using Dynagear sprockets and Morse chain but had some
quality control issues then Dynagear went out of business. After that they
sourced the high end Cloyes sets (which used high quality Renold and Iwis
chain) and the quality control complaints went away. Take a look at the name
on the sprockets and the name on the chain and let me know what they say.
FWIW, The Ford Motorsport 351C timing sets I've purchased have used the Renold
chain and I think some of the SBF used Iwis but the last FRPP 351C chain we
examined had no manufacturer markings on the chain. The middle and top of the
line J.P. Performance sets used the Iwis/Jwis chain. I saw some Comp timing
sets that were Cloyes but that can change and you really have to open the box
to know for sure.

I was discussing the timing chain issue with a local shop that does a lot of
351C work (owner owns a Pantera and Mustang with 351C's and the builder raced
351C circle track). They use and like the Rolon chain bt only the gold color
chain. The Rolon chain that stretched on me was black in color and apparently
the gold Rolon chain is their premium line. FWIW, that shop said it was as
good as the FRPP stuff they also use and you can buy the chain separately.

Barry mentioned that the sprockets tend to come from Rollmaster (Australia),
SA Gear (US but poor quality) and Cloyes (US, not pretty but good quality).
Avon also makes some sprockets but sources others. Dynagear (US) used to make
sprockets but went out of business. A bunch of the performance aftermarket
companies are selling the poor quality chain from India (Rolon), along with
sprockets from Australia (Rollmaster, J.P Performance) or SA gear.

Chain durability testing summary:

Iwis (German) - looks very nice but was not tested, but has excellent
reputation as an OE supplier, used in high end Rollmaster
and some high end Cloyes sets
Cloyes (US) - tested OK
Renold (France) - tested excellent, used in most high end Cloyes sets but not
always
Morse (US and Mexico) - tested excellent
Daido (Japan) - tested excellent
Tsubaki (Japan) - tested excellent
KCM (Japan) - looks very nice but was not tested
Rolon (India) - failed test

Sprockets:

Rollmaster - Aus - pretty - never examined QA, good reputation
SA Gear - US - ugly - crappy
Cloyes - US - not pretty - good QA
Dynagear - US - out of business - so-so when they existed
Avon - some sprockets, buys everything else
Crane - buys everything
Comp - buys everything
Speed-Pro - buys everything
Ebrock - buys everything
Melling - buys everything
Elgin - buys everything

Note: Some of the test data was from Speed Pro, other from TRW.

Dan Jones




Re: Broken timming chains

 by Kevin Johnson » Tue Feb 14, 2017 8:21 pm
MadBill wrote:I recently read (possibly here) an interview with one of the 'name' damper companies. He talked of instrumenting customer engines to create 'bespoke' parts. He said that when they ran at critical RPMs, not only did the crank's torsional vibration increase a ton, but the oil temp rapidly rose as much as 20°. Just like a paper clip heating up when you bend it back and forth... 

Re: Harmonics V's Oil Viscosity.

Postby bill@bhj » Mon Jul 26, 2010 11:29 pm

I can only partly answer the question -
While testing OEM crank dampers on an inline 6, (292 Chevy) we used to make a quick sweep across the rpm range to spot the general pattern of where the torsion peaks were, then go back and go very slowly across the rpm band where the worst peaks were to get a more exact reading of where those peaks were. We wanted the frequency of those peaks for fine tuning the damper. Inline's are not alone here, I just use it as an example - They usually had several nice peaks to contend with.
If we would set the engine directly on a high peak, (say .6° p-p) we would see that peak slowly rise (~20-30%) and see a corresponding rise in the oil temperature ( say 20-30°) Since the engine owner didn't want to pursue this any longer than necessary, we never sat there to see how high either value would go.
All it proved was that the torsion was enough to make each of the bearings into a small viscous damper which would absorb some energy at the expense of heating the oil in the bearings and consequently in the pan.
This was only an issue if one were going to have the engine run right at one of the torsion peaks when these peaks might be only 100 - 200 rpm wide at the worst amplitudes.
For an engine that was up and down the rpm range and just running quickly back and forth through the peaks, it was a non-issue. NOW, for a big speedway situation where the rpm may be in a narrow rpm band for a big % of the lap, you sure wouldn't want the engine to be sitting right on a significant torsion peak. For the NASCAR size V8's this is typically in the high 6000 - low 7000 rpm neighbor hood and is usually the 2.5 order peak. In that situation, oil heating in the bearings could get significant and the oil viscosity would be going down with rising temp.
So - The torsion peaks can be influenced by the oil viscosity - and vice / versa.
Also, the high rpm track motors can certainly benefit from careful sizing and tuning of the damper to keep from having the engine dwelling on a torsion peak. All those dampers aren't the same and not enough people are measuring their effect.





Re: Timing chain; how tight is too tight?

 by MadBill » Tue Nov 23, 2010 2:50 pm
cjperformance wrote:
Rizzle wrote:I don't think .220 chain deflection becomes the same as growth amount for the block, since that has to come from both sides of the chain. However, how much does the chain grow from heat as well, since its got to generate at least a little heat?

Exactly right, slack is taken from both sides and even then .110" at the chain does not equal .110" possible movement between gear centers either. Chain angle ,( which will be determined by cam/crank centers), to cam/crank ctr/line will effect how much linear movement X amount of chain slack will allow.
You guys are over-analysing this. All that matters is the temperature change from ambient to running and the difference in expansion rate between aluminum and iron/steel. The former is ~ 13 parts per million in Imperial units for typical block material and the latter ~ 7 for most iron and common steel alloys. Since the sprockets, chain and block are all iron/steel in the first case, there is no change except for any temperature difference between them when hot.
For the aluminum block case, let's say the center-to-center distance crank to cam is 6" and the operating temperature is 200° F., an increase of 130° from ambient. The increase in c-to-c distance, and thus reduced chain slack each side is then (13-7) x 130 x 6 /1,000,000 = 4.68 thousandths.




Re: Comp timing sets...Any good?

 by Barry_R » Mon Aug 25, 2014 8:41 am
Gears & sprockets:
Dynagear has been out of business for a decade. They used to make a lot of the industry's private label stuff. Not great, but was functional for stock rebuilders - and cheap.

SA Gear is still in business. They make a lot of the industry's private label stuff. not great, but was functional for stock rebuilders - and cheap. Was not as good as Dynagear back then - and cheaper. Might be better now, but I don't know that I am willing to take that bet.

Rollmaster - a lot of the race community is enamoured with this stuff, but my observations and experiences have not been as good. We find a lot of variable tooth shape and loose fit issues. I have "fixed" at least half a dozen internet/customer "loose chain" complaints where they thought they needed a -.005 set by sending them a standard Cloyes Tru-Roller set to try.

Cloyes is an OEM supplier and manufacturer. They are the only one I am aware of from the bunch that has passed any sort of OEM level production, development, or design testing/certification processes. Does not mean that their aftermarket stuff is as good - but if I were a betting man... My luck so far has been very good.

Chains:
Cloyes purchased the Dynagear chain operations 10 years ago from the bankruptcy. They use that chain product in all their inexpensive and replacement timing sets. But they use outsourced chain in their top of the line sets - either Renold or JwiS. Probably a message in there

JwiS - German chain used in the top of the line Cloyes and Rollmaster sets. Seems to be very, very good.
Renold - French chain that used to be used in the top of the line Cloyes sets. Was very, very good - no idea whay Cloyes changed
Morse - American based OEM supplier. Used to see a lot of it, not as much anymore. Was very, very good.
Tsubaki - Japanese chain. Used to be used in older TRW sets. Was very, very good.
Daido - - Japanese chain marked "DID". Still found on occasion in some private label stuff. Very, very good.

Rolon - made in India. Used in most private label and low cost timing sets. I have had exactly two timing chains fail on me in perhaps 40 years of screwing around with cars. One failure cost me an OE engine bearing 100 hr durability test. One failure cost me a ton of valves and assorted parts in an SOHC Ford. Both occurred during dyno testing in fairly well controlled environments. Neither engine showed any sign of distress right up to the failure point and ran without issue once the damaged parts were replaced along with chains from an alternate source. If I find a Rolon chain in the shop I put on rubber gloves, pick it up with pliers and dispose of it in a doubled up plastic bag clearly marked as "hazardous waste". After sealing the bag I throw out both the gloves and the pliers.
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www.survivalmotorsports.com

WD for Comp, Manley, Blue Thunder, Diamond
Probe, Holley, Clevite, Federal-Mogul, Scat....





Re: Degreeing Cam Chain Stretch?

 by Kevin Johnson » Mon May 02, 2016 3:15 am
digger wrote:The op is not talking about wear it's a new chain is how I read the post. Of course parts wear over time leading to the thing getting longer. Maybe it pays to shakedown the chain by loading it a few times before installing? When you do strain and displacement measurements on real structures you're supposed to load it and unload a structure a few times before recording measurments to get rid of relaxation kind of like running it in

A survey of literature from chain manufacturers reveals that many are quick to point out that their products are pre-stressed, pre-strained and/or pre-stretched and this is a sign of quality. Of the surveyed manufacturers, Timken is the most specific as to the process used.

http://www.timken.com/en-us/products/do ... atalog.pdf

FACTORY PRE-LOADED AT 50 PERCENT MUTS
Timken drives chains are preloaded to 50 percent of minimum ultimate tensile strength (MUTS) which is especially important for applications involving fixed center-to-center sprockets without take-ups. Applications can withstand shock loads up to 50 percent of the chain’s tensile strength without premature elongation.


https://ec.kamandirect.com/content/reso ... erview.pdf

During the assembly process, our roller chain is pre-stressed to avoid excessive early chain wear leading
to less frequent take-up adjustments.


http://www.rotek.no/en/kjeder-og-kjedeh ... chain.html

Pre-stressed for higher accuracy.


Roller chains are prestressed to minimize chain stretch during initial running periods and for long lasting durability. Prestressing minimizes tolerance variations by providing balanced loading among all parts and avoiding premature fatigue failure. Shot peening increases resistance to fatigue. case hardening of pins and bushings means longer life for Browning chain.

http://www.globalindustrial.com/g/motor ... ller-chain


~~~~~~~~~~~~~~~~~~

Often the same or similar terminology is used when describing elements involving wear. It is open to discussion whether physical elongation of individual elements due to shock loads in use constitutes wear.

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Re: -0.015" Big Block Timing Chain

Post by exhaustgases » Sun Dec 01, 2019 12:07 am

BLOCKMAN wrote:
Sat Nov 30, 2019 7:17 pm
exhaustgases wrote:
Sat Nov 30, 2019 4:52 pm
FC-Pilot wrote:
Sat Nov 30, 2019 2:36 pm


Even after taking material off the cap you still had to hone and some times bore the mains which will take off “some” material off the block. You can try to minimize it but there will be some material removed.

Paul
Difficult ? Sort of but with the correct machine there is no reason the amount off the block should be more than a few tenths. (.0002)
OEM register cuts are not that flat.
And likely not many after market ones either, all depending on what is bolted to it too. But again with the correct machine it will compensate for that. If that is the desired result.

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