Timing chain rattle? or something else...

Just been out on the 850T and it has developed a new rattle. It only starts when the engine gets hot, and comes on at around 3000 rpm. More of a rattle than a whine and it’s difficult to identify where in the engine it’s coming from, but it doesn’t sound like a failed bearing. It’s a '74 model and I don’t have much historical documentation for it, so the chain may be original. How long do they last and if I replace it, should I consider gears instead?

Also, do I need to remove the engine from the frame to get to the chain?Â

Thanks, Nick

Hi Nick

I replaced my cam chain and added a sprung tensioner when I rebuilt the engine after about 75k miles. I had the engine out to sort out the clutch. The lower frame rails bolt onto the cam chain chest so the lower frame rails may have to come off at least you will have to draw out the front engine mount bolt so that will probably mean taking the exhausts off. You may be able to prop the engine and get the cam chain chest cover off without removing anything else apart from the front engine bolt but I have never tried it.Â

As to gears I ruled them out because of the cost 25 years ago, they must be gold plated these days!

Good luck

Hi Chris

just found this article on the MGNOC site:Â http://www.mgnoc.com/print/print_article_taming_the_wild_timing_chain.html

It looks like I will need special tools though, and they make it sound like a real ball ache. Did you have much agro doing yours?

All the best. Nick


A gear puller is the only special tool, if you don’t have hire or borrow or use old screw drivers and a rubber mallet! Someone on here will have a solution.

Best wishes

Should be no need to take lower frame rails off, just chock sump then take out front engine mounting bolt. Will need alternator rotor removal tool before cover will come off. Frame rails have a tight grip on bottom of cover where bolt goes through but should succumb to leverage with a big screwdriver. You will then need a means of locking the sprockets so you can turn the nuts, usually the cam sprocket is locked. Camshaft nut is 26mm, crankshaft nut is a peg type so needs special peg socket, or as Chris suggests may be tapped around with hammer and a punch. Don’t forget there’s a locking washer behind it with one or more locking tabs that are bent forward to engage with the slots, must make sure these are completely free before trying to turn the nut. Because of the way the chain meshes with the sprockets, all have to come off / go back on simultaneously as a complete assembly.

The chain is supposed to be examined preriodically for tension, when the adjuster block can’t be moved any further to remove the slack presumably that’s when it should be replaced.

Thanks for the advice. It actually proved dead easy to get to the chain and have a look. Looks to be in good condition with the new type tensioner and the oil that I drained is clean so I don’t think it’s worn or needs replacing. i just have to figure out what the rattle is now…

Tappets ?

Nope - first thing I checked. More of a ‘grinding’ rattle than a ‘tapping’ rattle, and only when hot.

Broken clutch plate? Think this was discussed elewhere very recently…

header pipes touching the lower frame rail :bulb:

I put in a new clutch last year, and checked the UJ while I was at it, so I think that’s ok. I dropped the sump off yesterday to have a look at the bottom end and all’s fine. No sludge or nasties in the oil and the filters are both clean. Put it all back together and went for a four hour ride around the South Downs and presto! No more funny noises. No idea what was causing the rattle and it will probably come back, but simply taking it apart and putting it back together seems to have helped for now.Â

Header pipes? That could well have been it! Why didn’t i think of that?

Thanks all for the help and suggestions, that’s what makes the club special - just knowing you’re not on your own can give the confidence to have a go!

Yep! Nah worries if so

Glad you got it sorted. Symptoms suggested piston slap to me so let’s hope for the best!Â

Been a few years since I got piston slapped as I came through the front door at 3am…, I learnt my lesson.

:laughing: oh we do miss you Al…