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MG MGB Technical - Timing Chain Tensioners

I understand MG owners are now experiencing the same problem with the rubber of the slipper pad parting company with the metal piston component of aftermarket chain tensioners that us Dolomite Sprint owners have been living with for the past 12 years?

The tensioners in the two cars differ slightly in that to release the tension in our OE tensioners it is a 'press and release' action, whereas in yours' an allen key needs to be inserted to release the spring. As a consequence, the chassis of the tensioner differs in that yours' has a blanking bolt in a tapped hole to provide access for the allen key, whereas ours are a blind casting.

We have found that your style of tensioner 12H3292 fits our cars, but the problem of the poor adhesion of the slipper pad rubber has caught up with you too.

We had been using a similar Jaguar part number EAC3629, but a number of specialist Jaguar suppliers are superseding that part number to the same poor quality aftermarket item and if you can get hold of original Jaguar parts they have recently more than doubled in price to Ł81.00!

As a solution, I have acquired a small quantity of new old stock BL/BMC slipper pads for the 12H3292 tensioner which at one point in time were supplied separately, part number 17H31, and these are of a quality of manufacture where the adhesion of the rubber pad to the metal piston is durable in use. Dolomite owners are now using these new old stock items either substituting the slipper pad in the aftermarket MG item, or machining our original chassis components to receive a blanking bolt. Ours are interference engines where if the chain breaks, the engine is likely to suffer significant and very expensive damage.

I'm making these slipper pads generally available to those folk who need/want them, but when they are gone, there will be no more.

Ł35 to include UK postage.
A Nicholas

It's been a known issue on MGBs for a few years now, and there have been two types available with different priming/release actions as you say. At one time there was a clear distinction between the original French Renold item and the Indian Rolon copy in the slipper pad which went over the ends of the backing plate on the former but not on the latter. The oiling hole was also different, larger on the latter which could steal oil from the front cam bearing.

Last time I looked they were available at anywhere from £7 for a Rolon from the usual suspects via EAC 3629 or C10332 Jaguar parts to £200 for a 826113M1 for a Massey Ferguson! (I've always said ours are basically tractor engines). It's complicated by the priming method, slipper pad and oiling hole changing over the years on the Rolon, with some suppliers claiming theirs is 'not Rolon' but not having a manufacturers mark and in fact looking like what was there has been ground off. There also seem to be two different types of overlap at the ends of the slipper pads - a full rectangular overlap both ends on original Renold items and an angled overlap on later Renold and Rolon.

Going by what you can see of the manufacturers mark here Renold don't seem to be totally immune from losing the slipper pad, with angled overlap. I had occasion to investigate the timing chain and (clearly Renold with rectangular overlap) tensioner on mine as I thought the latter wasn't doing it's job, but all seemed fine to I put them back rather than replace.


paulh4

Hi Paul,

From my first experience of this in 2010 we have had not one failure of a Renolds produced item. If Renolds were not available, we would re-use an existing tensioner rather than risk any other brand or brandless items. Originally we had the simple solution of the Jaguar part EAC 3629 which at the time was available trade to us at about £25 and was always Renolds brand and made in France, but slowly we found the aftermarket Jag specialists superseded to aftermarket items whilst the price from Jag increased; from my trade account I'm aware that Triumph specialists now selling at Renolds at £81 are making very little profit on each one.

The simple fact is with Chinese manufacture it is all too often "can you make something that looks like this?' There is little if any understanding of function, and whilst the first offering may have an element of quality, unless you have reliable QA representation at the factory, the standard is quickly reduced to minimal; I speak from experience of having dealt directly with Chinese manufacturing mindset. We have had similar problems with engine mounts and carburettor mounts where the knowledge of how to stick rubber to metal simply isn't being correctly used, and whilst you may see correlation between the angle of overlap, it is not the cause of failure.

Often described as being 'tight', us Triumph owners baulk at paying £81 for a tensioner that used to be a fraction of the cost, so continually looking for more economic solutions, I've found the current offering, albeit of limited supply. having seen our own forum discussions on this linked to various MG sites, I'm extending the opportunity to all old car owners rather than hoarding what we have for ourselves.

By the time I had heard and investigated the issue on my engine in 2010, over 90 of the chain rollers had been split and fallen into the sump. That was an engine which I had spent nearly £5k on in parts, machining and balancing and labour, which was probably only a few revolutions of the chain from being completely written off!
A Nicholas

There is one particular MGB supplier that is always cheaper than the others but after several problems with different parts I refuse to use them, especially when they start arguing the toss and expect me to take it up with their supplier. Doesn't stop many owners on the MGOC forum saying that is their source, so equally 'tight'. For 'mission critical' stuff (this being an example) I wouldn't use cheap from anyone.
The more expensive sources are not immune from problems, their response is very different, but I doubt they would entertain consequential costs.

I'm not saying the different angle of overlap is the cause of problems, but it is an indicator. Only time would tell.
paulh4

Anyone tried the paddle type from SC parts--bit expensive but looks foolproof
William Revit

I'm not a cheapskate but £331.56 is a bit steep, although it looks well made.

https://www.scparts.co.uk/sc_en/timing-chain-tensioner-1-62818.html
R.A Davis

Not seen that before. Looks good!
Colin Parkinson

A mate got one for his Jag. somewhere a lot cheaper ,I'll give him a call and find out
William Revit

From- Denis Welch Motorsport 130 UKpounds (haven't got a pounds thingy on my keyboard)

https://www.bighealey.co.uk/hydraulic-timing-chain-tensioner-grouped&search=timing%20chain%20tensioner
William Revit

Interesting it is described as 'hydraulic' which it quite likely is. SNG Barret describe theirs as hydraulic https://www.sngbarratt.com/English/#/UK/parts/2d43d916-7dd0-4231-8f9a-744dd6adcb06 despite showing the original type and part number, so highly unlikely. Telling that the cheapo version is out of stock unlike the 'original', also showing this 'slipper' version priced between the two others.
paulh4

That's the highest price I've seen for the Jag part!

I'm wondering how the hydraulic version maintains tension when the engine isn't running...the Dolomite with its much longer chain couldn't cope with a slack start up without the chain trying to jump a tooth and as standard our pistons have cut outs to receive the valve interference!
A Nicholas

This thread was discussed between 05/07/2022 and 07/07/2022

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