Lotus Elan

Timing chain

PostPost by: 2cams70 » Wed Nov 15, 2023 10:21 am

Hi Rohan,
Can you explain further some background information about these chains?

1. How were the engines from which these sample chains removed used -eg. race or road application?
2. Usage period - eg. hours/km were they the same?
etc.

If they are to be fairly compared we need to better understand this. From what you have shown so far however there seems to be no evidence of failure (or impending failure) of either chain. The shape of the roller around the split appears to me to be due to the forming process during manufacture rather than a fault or distortion caused from operation. You however may disagree. The two ends of the roller remain firmly butted against each other and have not separated. I do agree with you though, all other things being equal, that it's better for it not be split. Particularly when there seems to be a slight depression at the split. This would be akin to a flat spot on a tyre! Ultimately it would depend on how the geometry lines up when things roll across each other. Maybe IWIS have done the analysis, maybe not.

Also do you have photos of the sprocket wear the chains were matched with? This too is also important
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PostPost by: 2cams70 » Wed Nov 15, 2023 10:51 am

Actually thinking further about it the slight dip in the geometry at the split may not pose any problem because the tooth surface on the matching sprocket is concave........interesting.

I'd be interested in the harness readings for the respective rollers too.
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1972 Ford Escort GT1600 Twin Cam
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PostPost by: rgh0 » Wed Nov 15, 2023 10:53 am

You ask for details and history that only controlled long term engineering tests can provide. I suggest you ask IWIS to provide that detail of tests they do on their chains rather than just provide marketing BS they (and most chain companies) usually do.

The solid roller chain was used for around 5+ years on one of my competition engines. The split roller chain I dont know the history but has a similar amount of galling / pitting wear and well below the stretch wear limit.

Both chains were servicable when removed which is why I kept them. Though after this ananlysis I would not reuse either. Neither chain failed if you term failure as the chain breaking. This is an extreme interpretation. The split roller chain is clearly outside design dimensions and has failed in an engineering sense, the solid roller chain has not as it is still within dimensional tolerances

I cant link these chains to individual sprockets but in general cam sprocket wear is not an issue even with high mileage, but crank sprocket wear can be an issue even with a lower mileage engine. How this relates to chain type I cannot correlate. Ask IWIS if you want better answers.

I had many business bosses who when they did like the engineering analysis I did kept asking for more and more details trying to avoid accepting the reality.

As I said ... if you want a split roller chain in your engine thats up to you but I certainly dont. My analysis of the pins and bushes that you requested will come in due course.
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PostPost by: 2cams70 » Wed Nov 15, 2023 11:08 am

Rohan - I'm just asking questions for pure information to throw in to my rusty old computer (brain) for analysis. Nothing more. I'm finding it to be an interesting topic of discussion because I'm learning something from it.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
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PostPost by: rgh0 » Wed Nov 15, 2023 11:48 am

I will answer where I can as indicated, like you I am learning about this as I go into more and more analysis. But a full comprehensive historical analysis tracking wear over many years for different chains is not possible with the information I have, but i will do my best from the data I have to answer your questions. From now on I will keep much more detail of chains and sprockets so maybe in 10 or 20 years I will have better data :)
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PostPost by: englishmaninwales » Wed Nov 15, 2023 3:13 pm

This has been a good thread and I have learned about chain design and construction - before this in my mind a chain was a chain - end!
It demonstrates also the value of an old fashioned Internet forum (in many people’s view) over shouty social media platforms.
Thank you for the input from various contributors, especially Rohan, on the tech stuff.
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PostPost by: h20hamelan » Wed Nov 15, 2023 3:43 pm

With great sadness, I must announce I broke 5 of 6 chains yesterday while rescuing people on the top of Kokanee Glacier. Some of the links must not have been welded, or I found a few sharp rocks under the snow. So I will re-double my efforts.

On the pressing pins into links comment. I do understand the concept, and have used it on many bikes, mowers etc over 50+ years.
When pushing the pin in, I understand it should not affect the link it is being driven into, but, I always cringe when installing, like it is going to shear the link.
None of my tools have a pin carrier (to locate the pin in the link hole), and nothing I see available does.
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PostPost by: rgh0 » Sun Nov 19, 2023 4:13 am

I did a detailed examination of the pins and split bushes on the IWIS solid roller and split roller chain as requested to add to my previous posted analysis of the chain and rollers.

Both chains had stretch less than the 0.15% for new chains so there has been little or no wear on either chain.

For the split roller chain
Pin OD = 3.31mm
Bush ID = 3.38mm
Clearance = 0.07mm

For the solid roller chain
Pin OD = 3.32mm
Bush ID = 3.36mm
Clearance = 0.04mm

This extra clearance is clearly allowed for in the chain manufacture as the chain pitch of both chains is within the new chain specified tolerance and it explains the increased lateral flex observed in the split roller chains.

chain side bend compressed .jpg and



Photos of split roller chain, pins and split bushes.
WIN_20231119_14_35_58_Pro.jpg and


WIN_20231119_14_44_18_Pro.jpg and



Photos of solid roller chain, pins and split bushes

WIN_20231119_14_37_52_Pro.jpg and


WIN_20231119_14_40_33_Pro.jpg and



Note how the surface finish is much worse on the split roller chain than on the solid roller chain.

All this plus my previous posts says to me that the split roller chain is made to looser tolerances with inferior materials. None of that may matter in practical use in a Twincam in terms of catastrophic chain breakage risk but but the weaker un-heat treated links in the split roller chain will fail at a lower load but probably still within the standard minimum strength. It will matter in terms of chain life and sprocket wear and chain noise. While the split bushes distort much less than the split rollers as they are riveted into the side links the discontinuity in the bush at the split join is not great for a roller sprinning on it

cheers
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PostPost by: 2cams70 » Sun Nov 19, 2023 1:09 pm

I can’t see any wear in either chain Rohan. The split bush chain has a frosted appearance on the surface but this is not wear or fatigue pitting. If it was worn there would be scoring or polishing of the surface and there is none. We’re you able to measure the hardness?

The split roller timing chain may have even been through a special hardening process.

See link:

https://www.did-daido.co.jp/en/technolo ... index.html

If not this process it still looks to me like the split chain pins have had a special treatment process undertaken on them that the solid chain hasn’t

I think Chapman would have approved of this design. IWIS have focused only on elements of the chain design critical to function and have relaxed and made more efficient those design elements not critical to function.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2022 Ford Fiesta ST.
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PostPost by: 2cams70 » Mon Nov 20, 2023 12:35 am

1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2022 Ford Fiesta ST.
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