MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Installing Renold timing chain tensioner

Good evening (US time)
This is primarily addressed to Stephen Strange in Virginia and Graham Moore in UK, because you both seem to have experience with this part, which has Jaguar pt.# EAC3629

I have acquired a new one for my MGA. It is very similar to the Rolon unit but reputed to be more likely not to expire early. However, no instructions with it. There is no hex hole for setting and releasing the ratchet.

If you can advise me on the installation and setting procedure I will be grateful.

Let me know if a photo would be helpful. Many thanks!
John Bissett
Virginia, US
John Bissett

John
2 questions
Does the inner piston of the tensioner you have, have the hex in the end or a screwdriver slot.
did your tensioner come with the plastic spacer/clip as in this pic.

William Revit

This seems to be a bit of a minefield. Renold made in France were the originals but Rolon in India produced a copy which seems to have caused problems. There were visual differences between the two such as Renold extended the edges of the slipper rubber over the ends of the base-plate where Rolon didn't and how they were shipped ready primed i.e. the screwdriver slot or the plastic spacer. However as time has gone by the distinctions between the two blurred.

I've seen some advertised as 'not Rolon' with no manufacturer markings although some look like they have been ground off one side.

I also came across this for Jaguar https://www.bighealey.co.uk/hydraulic-timing-chain-tensioner-grouped??search=timing which is said to be 'hydraulic assisted', no experience. As said it was such a minefield when I investigated my timing chain and tensioner (Renold) that I left them both alone.
paulh4

If there is no hex hole the plunger usually has a short reverse bit in the end of the spiral slot, such that when the tensioner slipper is pushed fully home into the housing the plunger bottoms out then auto releases when the slipper is released.
If you can post a photo of the plunger showing the spiral slot it would help identify if this feature is present.
Paul Walbran

Paul W. yep
If John has the plastic clip thingy on his it's dead easy as you say, just wind it up onto the last ramp and poke it in the hole with the plastic clip on the shaft and that stops it being triggered off until he's got it bolted up--then remove the clip and give the thing a little compress in and out she comes----If he hasn't got the plastic piece it's ok but you have to hold it all together compressed while getting it bolted up then trigger it.
No big deal really, just depends what he's got there.

Paul H. I used one of those later type on a mate's Jag. racer that had been gobbling up chains/tensioners etc. --seems to be ok but didn't get it off Dennis Welch though-bit too rich there with postage and all ,got him off US ebay for about 1/2 the price and looked exactly the same--works for me.
William Revit

Gentlemen,
Thank you very much for your helpful comments. I am printing them for reference. This one does NOT have the hex hole; it does have an oddly shaped hole that could be said to accept a screwdriver.

It also has the red plastic triangle, the purpose of which has completely escaped me until now!

I think I will now manage to install the thing.

Many thanks!
John Bissett
Virginia
John Bissett

Here are the 2 ends of the plunger shaft - I'm unclear on the exact location of the reverse bit in the end but I think I get it. And it does seem to work the way you describe: if I twist it into place with just the red plastic clip in place, then remove that and give it a shove to the left, it opens up. The chain is not in place yet so I can't verify it in actual position but it looks like working properly.

Thanks again,
John




John Bissett

Ok John
In your second pic. you can see the angled slope of the slot in the tube---As you wind it in against the spring pressure the angle of the slope pulls the tube inwards until it gets to the end of the slope--If you look at the shape of the slope in the pic. when it gets to the end it reverses direction which is the section Paul referred to as the short reverse bit. -Having wound it up and being in this compressed position, the force of the spring against it will hold it there in that(reversed) position until the assembly is compressed a bit which then allows it to unwind itself enough to get back onto the tapered ramp section where it normally operates.
With it compressed and the plastic spacer clipped onto the ram---This prevents it being triggered into action during fitting up to the engine -With the clip off it will compress enough to trigger it------Main thing is to make sure it's been triggered before putting the front cover on
The cutouts on the lower edge of the slot in your pic. work like a ratchet--so as the chain wears the piston gradually unwinds to take up the slack in the chain. The cutouts/ratchet prevent the piston from being pushed right back in at cranking/startup etc when there's no oil pressure to assist and simply hold the tensioner out in the correct position mechanically
The tensioner assy has an oil supply from the front camshaft bearing and the piston in the tensioner has a hole in the rubbing pad to assist with chain lubrication
Interestingly some camshafts have a groove around them that gives a fairly full oil supply to the tensioner and other cams just have a longitudinal slot that gives a reduced flow but I guess once the tensioner is full there wouldn't be a need for much flow apart from supply to the little piddle hole in the pad
Think that covers it
willy
William Revit

Ok Willy,
This is making lots of sense. It seems easy enough at the kitchen table! But I think it will work just like that in place.

I'll be taking my time as I assemble it, as I have to do - I've little practice with the innards of engines.

Thanks again to you, and everyone. I'll go back to the MGA bbs now and see what new questions arise.

Best regards and thanks,
John
John Bissett

This thread was discussed between 23/08/2023 and 26/08/2023

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now