Author Topic: Timing chain rattle after rebuild (Read 2987 times)

TheDutch · « **on:** August 20, 2009, 10:17:31 AM »

Hi all,

Having finished replacing all the timing chain components I was pleased to start the car up and be greeted with a better-than-ever idle, however was then sickened to hear that raising the revs brought with it a most unholy rattle.

I suspect it is the chain itself but cannot see why it would be doing this. I have a new tensioner which released itself as normal upon installation, and the rest of the parts are pretty much as new (but are second hand from a reputable source!)

The timing is good, and as mentioned the idle is steady and quiet. The rattle is worst around 2600rpm but diminishes over 3000rpm; very typical for a loose chain (?)

You can see the pesky blighter for yourselves in this video, note how the tensioner piston moves in and out - is this to be expected?
http://www.youtube.com/watch?v=cUXPFYcuIvA

Any suggestions welcome,

Neil

Ramblin MAn · « **Reply #1 on:** August 20, 2009, 10:46:32 AM »

Dude, what is that black goo spilling onto the tensioner? Is that oil? You are supposed to use the refined stuff!!

Seriously though, the tensioner is hydraulic so until you have oil pressue to the tensioner it will be sloppy. My chain typically rattles a lttle at idle and then quiets at about 1200 rpm.

I was under the impression that it was like that to reduce the amount of stretch that a constant pressure for a "normal" ratchet type would cause. Thats just a guess of course. I wish I could get a ratchet type.

If it is getting louder at higher RPMs maybe you aren't geting pressure to the tensioner.

3bvert · « **Reply #2 on:** August 20, 2009, 11:34:34 AM »

how many miles, how long have you owned it, did you drive it much before replacing the chain
reason I ask, is that some people, including myself, buy non running basket case cars and bikes, which can make it hard to determine what all is wrong or know the full history of the car and its conditions

used parts can be risky, I do it all the time, wtih careful exam, of all the parts though, I think a chain I would not do used, I dont think you can really tell if it is stretched with age. the guides and sprockets are easy visual to tell if good ro not

If indeed you have replaced all the parts you say, with correct parts and if after a few seconds , the car does not build enough pressure to make the chain quite, then maybe you have a oil pressure problem,

my current 318 was a basket case, it needed a head, while I was waiting for parts, I did other research on proboems ith the m42 motors. I had read about the lower oil pan bolts and suction tube bolts, a common problem and if loose or missing the car may not build correct oil pressure ( your car may not be building correct pressure). as some will start sucking air in the pick up tube instead of or mixed with oil. so I ordered a gasket, dropped the lower pan, and had 5 bolts sitting in the bottom of my pan. I had the classic problem

you can research it here, or r3v, I think , it might be a wise thing to do anyway, unless you know its been done
1 hour of time max, few bucks in parts, can equal piece of mind and good oil pressure

TheDutch · « **Reply #3 on:** August 20, 2009, 11:55:53 AM »

Thanks for the replies, and apologies for the state of the oil, the new stuff is waiting to be put in once all this is done.

I've had the car several years, now on 168k, and elected to change these parts over as it had become noisy over time and I could see the cam shaft sprockets were worn, however upon opening up the front casings it became evident that some parts had actually been changed previously, most likely 10 years/80k mls ago. As said before the replacement parts are known to be good and have only had light use.

The new tensioner 'popped' instantly (after being installed compressed), and the oil pressure light extinguishes immediately which to me suggests good oil pressure. The chain was not 'rattly' like this previously.

I've taken the lower cover off again now too but still can't see any issues. Baffled!

TheDutch · « **Reply #4 on:** August 20, 2009, 12:26:29 PM »

Turning the engine over slowly by hand shows the tensioner piston moving in and out. At it's extreme the tensioner guide rail moves to such an extent that it does not appear to be able to go any further due to the exhaust cam sprocket. At this point there is a slight amount of slack in the lengths either side of the idler sprocket.

I don't know if this is a problem, and if it is, how or why it has become one!

Ramblin MAn · « **Reply #5 on:** August 20, 2009, 03:52:33 PM »

Couple things. After a car sits for a while the lifters can bleed down and take a while to pump back up. Sometimes 20 minutes of idling. How long have you let your idle? did you let it get good and hot?

Also and this is a stupid question, did you measure the cam sprockets if you replaced them? Are you sure they are not worn or somehow wrong? If you have toomuch slack now and you didn't before, something isn't right. Also I know I have seen a measurment for a certain number of links somewhere. Did you measure the chain to see if it;'s in spec?

TheDutch · « **Reply #6 on:** August 20, 2009, 04:53:38 PM »

Well for lack of any better ideas I took the chain off again and compared it with the old one, and found the 'new' one to be about 2mm longer in length despite the much better condition of the rollers.

The old chain has been put back on and the tensioner piston protudes noticeably less, and upon starting up the racket has pretty much disappeared. Much better.

It does beg the question, how much wear or 'stretch' is permissible in these chains? 2mm does not seem like a huge percentage to me but then I've never designed an engine.