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MG MGB Technical - Timing chain tensioner

While the head is off I've taken the front cover off to replace the gasket and crank pulley oil seal, as it is a bit oily round there.

While that is off I've had a look at the gears, chain and tensioner (I know, Shipwright's disease ...). No obvious wear on the teeth that I can see, the tensioner is still tensioning, but is there a maximum distance of the slipper head from the body after which chain replacement is indicated? Some pictures show less slipper shaft exposed than mine, some more.

My tensioner doesn't have the hole or screwed plug on the opposite face to where the slipper is, that most pictures show, and the WSM indicates is where an Allen key should be inserted and turned when fitting a new tensioner.
paulh4

Meant to add this

paulh4

Doesn"t look to be much wear on the rubbing pad. As there are a number of dubious quality new tensioners out there, I personally would leave well alone. Jim
jim soutar

Paul, I think the retractable, allen key type tensioner was used with the Duplex chain. The later single row chain tensioner was retractable for reassembly only.
As Jim said if the slipper material is not heavily grooved I would re-use, but, based on mileage, you might want to replace the chain.
Allan Reeling

It looks like has the metal spacer between the tension and front plate. I read it needs to be in for single chain but omitted for duplex. Yours is not centred but don’t think it matters much as long as pad fully covers chain.
Mike
Ps. Wear looks minimal to me.
Mike Ellsmore

There were two systems for releasing the tensioner after assembly. Undo the plug & use allen key as noted above, or push and release. The one shown in Paul's photo is push & release (I think the original IIRC from the days of BL boxed parts) - works by virtue of the plunger having a reverse spiral step right at the end. Once assembled the spring keeps it locked on the reverse step until the slipper is pushed further into the body, the reverse spiral turns the plunger past the apex between fwd and reverse spirals so that when released again the peg is in the forward sprial groove and unwinds itself without the need for an allen key.

It is much quicker and easier to use! Bolt the tensioner into place, flick slipper plunger and and release ... a worthwhile saving of a minute or two on the production line comapred with undoing the plug, fitting the key, releasing, doing up the plug and tapping over the locktab, all with sufficient care that the locktab stayed in the correct orientation to do its job.

The principal difference is the plunger, I recycle mine into any new tensioner I fit to my own engine.

And for what it's worth, I get good life out of the Rolon tensioners currently available but always renew a tensioner while the opportunity is there as the cost of the item is tiny compared with the effort of access. (This of course is showing my age, when I was young and stupid with plenty of time I would willing chance a weekend's repeat work to save 5 bucks.)
Paul Walbran

Paul W describes the operation perfectly. Exactly the same type is used on my 1850 Dolomite engine. The Triumph people hate the Rolon tensioners as many have suffered early failures, especially on Sprint 16v engines. When I rebuilt my engine recently the pad on the original tensioner only showed minor grooving so I put it back rather than risk a Rolon one.
Mike Howlett

Some more reading - some of what follows duplicates what Paul W says, and what Stephen Strange wrote a while ago. From the manuals it seems that only the duplex adjusters had the bolt hole for the Allen key, even though the internal parts of the two seem to be much the same and they both function in the same way, with a mechanism to ratchet the slipper out (and stop it going back in) as the chain stretches. The Parts Catalogue quotes 'alternatives' for both 3 and 5 main engines, without saying when each was used, despite the 3-main only showing the duplex chain. The single-chain type uses a spacer to prevent the slipper being pushed fully back until installed.

Give the quality of parts these days and the reputation of current-stock replacements I'm in no hurry to replace either chain or tensioner. MGB-specific items apparently come from India and have known problems, but there is a Jag alternative from the original French manufacturer that only needs the oil hole widening slightly to become identical. Googling both the original part numbers shows the same part from suppliers, with the Allen key adjuster, from the Indian manufacturer. Other sources recommend one for a Massey Ferguson tractor, but some sources quote £60 for that as opposed to about £7 for the poor item from the worst of the usual suspects, but can be had for £17. Googling the Jag item now also shows shows the poor item from the suppliers I have looked at for £22. But it's quite easy to tell the difference - the poor ones are marked 'ROLON' and have the slipper rubber bonded flat to the base, the better ones are 'RENOLD France' and the slipper rubber is longer and goes down past the ends of the base, as in the attached - poor item on the left, better (without spacer) on the right. Another thing to watch out for is that Rolon are now supplying them with the 'push to release' mechanism instead of the Allen key hole, so the lack of hole and the presence of the spacer is not indicative of the good item. Of course, if you order one online that shows the good item, there is nothing to say that is the one you will get!

As mine pushes all the way back against spring pressure and comes out again, I'm going to have to remove and investigate it, at least.


paulh4

Paul
Probably an optical illusion, or my wobbly old eyes - but on the rh side of the pic, the first pin on the timing chain just appearing under the cam sprocket--
I've blown the pic up as far as I can but can't see it clear enough to decide--
Is the roller missing off that pin or is it just the way I'm looking at it
willy
William Revit

I know what you mean but the rollers are reflecting differently. Just taken these two, the lower one with a bit of paper shoved behind.

paulh4

Price is not an indicator of quality.

There is nothing wrong with the Rolon tensioners which I have used for years.

The overlap of rubber on the Reynold item is not an indicator of quality - rather that the steel plate behind the rubber is smaller.

Chris at Octarine Services

Just passing on what others have said.
paulh4

FWIW: http://mgaguru.com/mgtech/engine/cs103a.htm

http://www.mgexp.com/phorum/read.php?41,2502263
paulh4

That mgaguru link that Paul posted is exactly what I meant when I mentioned the problem that Dolomite Sprint owners have with Rolon chain tensioners. I found this photo which shows a Rolon tensioner after less than 4000 miles driving. The owner fortunately caught it in time. Others have had the chain disintegrate. This owner found the majority of the slipper pad in the bottom of the timing case.

Mike Howlett

I may possibly be the person paulh4 refers to above.
I had a new Rolon timing chain tensioner fail in under 1200 miles on a newly built engine; the rubber pad had separated from the blade of the tensioner.
My now retired mechanic who built my new 18V engine (with two row timing chain) that we installed into my MGA has extensive experience with Jaguars but also, living where we do, with large diesel engines and farm machinery (and car, and then later power boat racing experience). He noticed that he could substitute a used Jaguar XK engine tensioner that he happened to have lying around for the failed Rolon MG tensioner, but before discussing it with me, he ordered and installed a new Rolon tensioner This has now been fine for about 3,500 miles.
My mechanic explained that with the short B-series engine timing chain, the tensioner "doesn't have to do much". But in contrast the Jaguar in line 6 XK series engine has a very long timing chain. He'd come across two catastrophic engine failures where the shaft of the tensioner blade had fallen right out of the body of the tensioner. He in turn had noticed that the Massey Ferguson tensioner had a longer shaft than the Jaguar item which would preclude this happening to a Jaguar engine and he had successfully used the Massey Ferguson tensioner in Jaguar engines.
I didn't ask if he routinely substituted the Massey Ferguson item in Jaguars. I'd imagine regular maintenance would be a better solution.

Photos and summary of my experience are here:
http://mgaguru.com/mgtech/engine/cs103a.htm
T Aczel

Took the tensioner off and apart today - Renold I'm pleased to say. On reassembly the 'stepping' mechanism works correctly, so I don't know why it had what seemed like excessive movement before. Negligible wear between piston and bore, air pressure very evident when moving it in and out with the oil hole blocked. Slipper pad barely worn as in the attached, note that the piston is offset to the same side as the wear marks, although not quite as much as is evidenced by the position of the oil hole. Ironically without the spacer plate that is fitted with single chains, the piston would be more central to the chain!

The mechanism hold the slipper almost fully into the body if you turn the 'slot' in the end of the spring retainer with a screwdriver as you press the retainer in, until it locks behind a recess. Once fitted, just push the slipper back the remaining distance, and it pops out to tension the chain. Why the Rolon ones have the faff of an Allen key I have no idea.

Incidentally this is not a 'hydraulic' tensioner that you will see it described as elsewhere, the oil simply flows through the lubricate the chain, the tension comes from a spring.


paulh4

My experience differs - never had a failure.

However I do know that overtightening the two bolts can cause the plunger to bind in the barrel - now that would certainly lead to failure.

Chris at Octarine Services

This thread was discussed between 22/01/2018 and 04/02/2018

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