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Technical Article: Timing Chains
Tony Fox writes:

There has again been a lot of interest on various forums about the timing chains on our cars. Where a number of engine rebuilders still happily use ROLON chains in the UK, there still persist rumors in North America of chain failures, albeit mostly hearsay. However, for those of you wanting a little more confidence in an engine rebuild, there is an alternative which is to use IWIS chains. These will cost you a little more but a worthwhile investment when you consider your overall rebuild cost.

The IWIS web site is a good place to start This will give some history; hit the 'translate' button at the top right hand corner to get it in English.

Whereas most chain manufacturers are predominantly industrial with automotive tagged on, with IWIS the core business has always been automotive with industrial a close second. They have been producing chains for most main manufacturers for years, even venturing into F1.

Historically, car timing chains gave few problems and on the older engines chains lasted for many thousands of miles. Because the chains were not stressed it mattered little whether they were industrial or automotive and even the quality was not a real issue. As engines quickly increased both in terms of RPM and BHP the main producers Renold, IWIS and others generally developed a better timing chain in terms of material, engineering and design features.

This allowed companies that offered all spares for all cars to purchase solely on price. With the majority of cars using a standard chain these companies could happily buy in cheap budget chain, cut it to length and sell for the after-market. There are a few that even get their name or logo stamped into chain regardless of where it is made.

IWIS developed a chain which had an extended bush feature giving a better bearing area. It was originally designed to replace a duplex, which it did not do very well but does go quite a way to solving the Stag concerns. These chains have a much greater breaking load than others on the market; they have a smooth finish to the link edges too, which minimizes wear to the guides. The chains are marked JWIS on each link (JWIS is their trade mark).

Timing Chain

Individuals trying to source IWIS found that IWIS and their stockists had little interest in supplying and although IWIS were making the 106-pitch chain but did not do a 104 pitch (not needed on the TR7 of course, Stag only). There was also the problem that owners would search for the cheapest product and had little regard for the origin of the chain supplied to them.

There are many different chains that would work on Stags and this is one that if it fitted, would be good for many more thousands of miles compared with what is currently being offered. Although possibly the most expensive, IWIS is probably the highest quality automotive chain available and would be my recommendation. It is used in many race engines successfully including Aston Martin and Nissans. IWIS actually make a 'super chain' identified as a G67HP version, fit for the life of the engine but naturally more expensive again.

If you are buying cam chain, ask the right questions like country of origin, manufacturing company and importantly is it for automotive use. A good tip is if the chain is covered with grease or oil then it is more than likely industrial. IWIS has special steel in the automotive product and as well as being toleranced at production is also pre-run. It also differentiates between the industrial product and automotive by having blued plates on the industrial whilst the automotive has silver plates throughout. So even if you buy IWIS it might not be the correct chain unless you check for the finish. IWIS chains also do NOT have bicycle horseshoe shaped connecting links which you do see on some after market products, these are to be avoided at all costs. For more information on timing chain concerns read the Triumph Stag Essential Buyers Guide published by Veloce in the UK, go to

IWIS chains can be sourced from LD Parts in the UK.

Posted on September 2010


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