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MG MGB Technical - Timing chain tensioners

Hi All:
My 1967 BGT has a timing chain tensioner with an internal ratchet device to keep it under tension. The replacement that I bought has no such device but has a larger internal spring. Is the replacement ok to use? Is it as good? Pros - cons? Thanks in advance . . .
Godspeed in Safety Fast
Jc
John Crawley

I seem to remember that the actual running tension is provided hydraulically by oil pressure. The spring is there to keep some primary tension on the spring at start up. Never heard of a "ratchet device", but I've never worked on anything earlier than GG. However the double row tensioners do have a system for removing tension with an allen key, access to this is through a hole behind the piston which is blanked off by a screw and lock washer.
Allan Reeling

It is the spring that tensions the pad against the chain - the ratchet limits the amount the chain can throw the pad out, the oil feed merely provides lubrication of the pad through the small hole in its face.
Chris at Octarine Services

In my opinion
The ratchet system is necessary, especially as the chain wears and gets more movement
The ratchet stops the piston from being pushed back while the engine is off or turned backwards
If the chain gets badly worn, and without a ratchet there 'could' be timing chain rattle at startup until the oil pressure pumps the piston/pad out to tensions the chain
In an extreme case of chain wear and without a ratchet there would be the possibility of the chain jumping teeth at startup
And yes, the oil pressure does tension the chain--as well as the spring--not all pads have the lube hole
The pads wear with the current spring so I wouldn't think a heavier spring would be all that necessary or desirable for longevity
willy
William Revit

I doubt the oil supply to the tensioner is high enough pressure - it comes from the front cam bearing via the cam keeper plate.

Certainly original pads had the hole and the supply was never "designed" to provide tension in the chain.
Chris at Octarine Services

You absolutely need the ratchet device to stop the plunger oscillating. The force provided by the combination of the spring and oil pressure are insufficient to prevent this. The designers intended it to be there.
We need to consider the cyclic nature of the cam torques. When the valves are opening the torque is positive ie the crank is driving the camshaft, but when the valves are closing its the other way around and the torque is negative. I've never calculated the cam torques for B series (before my time) but I guess the torque approaches 2 +/- 20 Nm at the red line rpm. This means that the 'tight' side of the chain swaps around constantly, with the max tension being around 300 N. Considering the chain angle this would be enough to push the plunger back if the ratchet wasn't there.
The ratchet system works well for all iron engines where the block and the chain expand at the same rate as the engine warms up, but cannot be employed on aluminium engines. They tend to employ a hydraulic system with a check valve that can leak down slowly as the engine warms up.

Paul Hollingworth

John-

The camshaft drive chain tensioner is an intriguing and often-misunderstood item. Due to the fact that it receives pressurized oil from the front bearing of the camshaft, it is usually presumed to be a device that uses hydraulic pressure in order to maintain tension on the return circuit of the camshaft drive chain. In reality, it functions in a rather simple and purely mechanical manner. In fact, the pressurized oil flowing from the low-pressure circuit into it through the spigot in its rear face merely is merely ducted outward onto the slipper pad in order to both lubricate the camshaft drive chain and reduce its friction against the slipper pad, thus extending the service life of both of the components.

As the camshaft drive chain wears, it becomes, in effect, longer, and consequently will increasingly slacken on its return circuit. As the slipper plunger extends under the pressure of its compressed coil spring, the limiting peg thrusts against the smooth top of the helical slot in the cylinder and causes it to rotate. When the next indentation in lower edge of the helical slot aligns with the limiting peg, the plunger is prevented from moving back into the body of the tensioner mechanism, thus preventing the plunger from oscillating while maintaining the correct tension of the camshaft drive chain.

The Original Equipment chain tensioner was manufactured by Renold in France, as was the camshaft drive chain. However, they no longer manufacture them for the BMC B-Series engine. Currently, there seems to be only one remaining manufacturer of this item, Rolon in India. However, the quality control of Rolon has been known to occasionally slip. Regrettably, the Indian-made Rolon unit has a stronger spring than that of the Original Equipment MGB unit, which can cause faster wear of the slipper pad. Fortunately, Renold of France still manufactures the chain tensioner for the Jaguar XKE DOHC six-cylinder engine (Jaguar Part # EAC 3629 or C10332), and, with the exception of an easily modified minor detail, it is identical to the one that it produced for the BMC B-Series engine. The oiling passageway inside of the body of the chain tensioner of the French-made Renold Jaguar XKE DOHC six-cylinder engine has a diameter of approximately 1/32". Simply enlarge the diameter of this single oiling passageway to a diameter of 1/8" (0.125" / 3.175mm). The bonding plate of the Original Equipment camshaft drive chain tensioner has a bevel on both its leading and trailing edges, and the edges of the slipper pad is wrapped around them.

The tensioner body of the Indian-made Rolon unit is a little different from that of the Original Equipment French-made Renold unit. It does not have the drilled dowel on its back which on an MGB serves basically as an oil restrictor, instead it has just a simple open oiling hole which results in over-oiling of the camshaft drive chain and reduced oiling of the front camshaft bearing. The slipper pad material of the Indian-made Rolon unit feels more like plastic than like rubber, and is bonded flush with the ends of the plate. Its lack of edge support has been known to allow separation from the bonding plate under the greater cyclic stresses that are incurred upon the material of the slipper pad when used with a high-performance camshaft. On the other hand, the slipper pad of the French-made Renold unit feels more like real rubber and is bonded to the steel pad differently, being overlapping and bonded on both the top and bottom as well. The French-made Renold unit has the machine bolt on the back side of the body for releasing the Allen head bolt spring assembly and unlocking the slipper pad, while the Indian-made Rolon unit requires that you must unlock it prior to installing it, making installation a rather cumbersome affair.

New camshaft drive chain tensioners are usually supplied with a spacer plate. The spacer plate is appropriate for simplex (single-row) camshaft drive chain mechanisms, and should be omitted when employed with duplex (double-row) camshaft drive chain mechanisms. Note that the metal sleeve on the back of the 'foot' of the camshaft drive chain tensioner is not centered in the tensioner, but is offset to one side. This sleeve is centered on a simplex drive chain by means of the spacer plate, but when using the duplex chain both the foot and this sleeve are centered on the duplex chain by omitting the spacer plate. It is, however, important to use a gasket between the tensioner and the front engine mounting plate.

When assembling the camshaft drive chain tensioner, it is very important that all of its components be clean. Install the new plunger into the camshaft drive chain tensioner and check that the mechanism is functioning properly. Be sure that the high end of the slider ramp of the slipper pad is presented to the feed side of the camshaft drive chain. Also, be sure to inspect the bore of its adjuster body for ovality (+ 0.003" / +0.0762mm maximum). Should it prove to be worn out, a new one can be obtained from Advanced Performance Technology (APT Part # BCT-1).

Insert the coil spring into the plunger and place the helically-cut cylinder onto the opposite end of the coil spring. Compress the coil spring until the helically-cut cylinder enters into the plunger, then use an Allen wrench to hold the coil spring static while you rotate the helically-cut cylinder clockwise until its end is below the limiting peg of the plunger and the coil spring is held under compression. Now, remove the Allen wrench and slide the assembly into the body of the tensioner. Be sure that you have cleaned all of the threads first; otherwise, you will get a false torque reading. With its backplate against the front plate of the engine, install the camshaft drive chain tensioner along with its tab washer (BMC Part # AEC 340), torque the machine bolts to 10 Ft-lbs (dry), and then bend over the lock tabs against the flats of the machine bolts in order to secure them.

When the camshaft drive chain tensioner is newly-installed, its spring-loaded ratchet mechanism must be released after fitting in order to properly tension the camshaft drive chain. If this is not done, then the ratchet mechanism will not maintain the camshaft drive chain under proper tension after the engine stops and the oil pressure ceases, whereupon the camshaft drive chain will rattle at idling speed when the engine is restarted. Release the plunger by inserting and rotating the Allen wrench clockwise. Under no circumstances should you either attempt to rotate the Allen wrench counterclockwise (anticlockwise) or attempt to force the plunger outwards. If the slipper pad is tensioned by means of forcing the ratchet through via turning the ratchet mechanism itself, the Allen key drive will then become detached. The spring will then become displaced and the tensioning mechanism will be free to float up and down, defeating its purpose. Once the camshaft drive chain has been properly tensioned, you may proceed to fine-tune the timing of the camshaft.
Stephen Strange

Stephen:
Wow! Great explanation . . . Thanks so much event though it means that I have to pull everything apart and remove the spacer plate.
Much appreciated
Jc
John Crawley

Interested in this as I think I have timing chain rattle that needs investigation.

You still need to be careful with the Jaguar part, I think, as David manners for one is showing two versions of EAC3629, one at £13 and one at £25. Looking at the detail the cheaper one is described as 'Replacement part' and the dearer 'Genuine part'. Other vendors show just one, typically around £13, so I suspect they are the Rolon part. However MG suppliers are showing the Rolon part at £7-£8.
paulh4

Thr Rolon ones in the red boxes are fine. A word of caution, the little plate with the hex hole for releasing the tensioner is press fit. If you wind the tensioner with the Allen key you can loosen the plate, the tensioner will cease to work and the spring is the only mechanism applying tension. I hold the tensioner pad against the chain and gently turn the hex plate until the tensioner adjustment releases. Ease a little more pressure onto the pad and you will feel the ratchet mechanism set the tension. Not too tight a tension as you can cause rapid wear of the pad.

Peter
Peter Burgess Tuning

my rolon failed within 2k miles. snapped inside.

bought the jag one - from my local jag main dealer - for £15

G

Graham Moore

& the old one...

i don't recall it coming in a red box. just a bag (MGOC)

Graham Moore

Graham
Was that on a new chain--It's badly worn on the end like what happens with a badly worn chain

willy
William Revit

I wonder if yours failed as I have explained above? The spring and cam chain movement may well wear the pad rapidly as shown as the ratchet system cannot work. It can be difficult working out which part of the tensioner failed first. Was the washer with the allen key hole separated when you stripped it? We have fitted around 300 of these Rolon B series tensioners and only seen pads sheared off on two different full race engines which may have been us over tensioning the slipper to start with. I 'killed' the first one I fitted by forcing rotation with an allen key alone and not relieving the strain by easing the pad out with a screwdriver levering between back of pad body and tensioner block.

Peter
Peter Burgess Tuning

For my sins I also own a Dolomite 1850. Reading the Triumph Dolomite Club forum, many owners have had failures of Rolon tensiones on both 1850s and Sprints. On that forum the word Rolon is like a swear word.
Mike Howlett

Hi All:
I have pulled off the engine front cover, removed the spacer plate and voila the tensioner fit to the chain is now perfect. Thanks for the heads up!
Jc
John Crawley

Oh Peter! Levering out with a driver?

Seriously, I have found that some of the rolon ones are a bit tight on clearances, to the point that tightening up the mounting bolts causes the barrel to bind.

I only ever turn the adjuster to lock the snail while its apart before fitting and then once fitted to just unlock the snail - never to wind it down ....
Chris at Octarine Services

At least I am honest and admit my deviations :) :) I keep minimum pressure to unwind/unlock the tensioner hence the screwdriver. You are quite right, a few have been tight in the hole in the front plate, although one turned out to be a minute burr in the front plate!!!!
Peter
Peter Burgess Tuning

This thread was discussed between 24/10/2017 and 07/11/2017

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