help!! Loud engine knocking noise... :(

[TJ 450]

To check if it has skipped a tooth, you turn the crankshaft until the two marks line up, there is one on the bearing tower and one on the camshaft itself from memory. The you compare it with the other side. If the marks on the other side are a long way off lining up, it has skipped.

Either way, you have now determined that you need to have the chain, tensioner and upper sliding rails replaced, for sure.

Tim

[Ryan1980]

One more question - as im considering giving this a go myself!

How do i know how the new chain will go on , exactly? I.e., which tooth will go where? Given that the existing chain is in the wrong spot, since it's skipped a tooth?

I've changed a timing belt before, and i remember the new one had to go on exactly the same way the old one was on... i assume this is the same?

[TJ 450]

It will be the LH camshaft that has skipped, so you will need to line up the marks on the RH cam/Harmonic Balancer and manually rotate the LH cam so its marks line up too. However this needs to be done with the chain removed from the sprocket somehow... I'm not sure how you would do this short of pulling the sprocket off altogether, although I imagine another member will know.

Tim

[oscar]

For putting the new chain on, you're going to have to have the valves assessed first IMO.   The manual states that one tooth skipped on the camshaft is equivalent to 18o turned on the crankshaft.  Around 10o is max permissible stretch prior to a new chain required.  So part of the loss of power when this event happened might not only be due to valves closing too late, but as some others have suggested, the valves contacting the piston heads in which case they may be deformed and leaking when they're closed.  I hope that's not the case.

Going back to WGB's thread, you'll note there's a masterlink in the chain.  If you can't find it after rotating the engine by hand and viewing the whole length of the chain then I've been told the chain would be original.  If it has got the masterlink in there I'd work on getting the engine at TDC and the camshafts on there TDC marks and link the chain again.  The valves will then be safe from contacting the pistons and you'll be able to do a compression test to see if valves are leaking. 



I'm going to quote an extract from WGB's thread for measuring chain stretch below.  You can't go wrong. 

The chain stretch is measured by aligning the RH camshaft timing marks by rotating the motor with the crankchaft pulley nut (Clockwise only) using a socket, short extension and a large ratcheting torque wrench which I own.



Here is a view of Right Hand Cam timing marks  - in alignment



At the same time here is the Left hand cam alignment marks showing that the chain has stretched and that the sprockets are worn as the marks do not align.



Again at the same time the crankshaft is reading 10 degrees after TDC - maximum chain stretch is 11 degrees ATDC on a 117 motor.

[WGB]

You can advance or retard the chain one tooth at a time by slackening off (removing) the tensioner and starting at one end of one cog lifting the slack in the chain and repositioning it one tooth over - clockwise looking at the cog from the front to retard it and ant-clockwise to advance it. Then move the rest of the chain over the cog in a wave-like motion.

Each tooth is 18 degrees and I would imagine if it is camshaft timing that is causing the noise that you are probably 2 teeth out on one cam based on the fact that these engines will run silently with 16 degrees of chain stretch (Almost 1 tooth) but three teeth would probably be enough to trash the motor.

The "fuse" or breakage point in the valve train is that the camshaft towers will break off as valve meets piston and be forced upwards and through the cam cover. If that hasn't happened and the problem is valve timing then it must only be a small jump of the chain.

Bill

[WGB]

I started it for a second just to check if there was oil pressure - and there is.


Im not sure how to check if it's skipped a tooth... I read in your writeup bill about checking for timing chain stretch. Is it just a matter of turning the engine until the rhs cam timing mark ( I can only see 1) lines up with a link in the chain?

http://i246.photobucket.com/albums/gg105/Ryan1980_photos/RHSchain.jpg

To check the timing chain you need a 27mm socket, a very short extension and a ratchet. If you have good belts to the power steering pump and the sparkplugs have been removed it will turn with a spanner (22mm I think) on the nut on the end of the power steering pulley.

The engine should only be turned clockwise looking at the front of the pulley until the timing mark on the Right Hand cam is aligned (Left one looking from the front of the engine bay). At this point the position of the Left Hand Cam can be checked as well as the position of the crankshaft pully.

Alternatively pull the crankshaft around until it is at TDC and see where the position of the camshafts are in comparison - remembering that it takes two turns of the crankshaft for 1 turn of the camshaft so no point checking on the "back of the cam".

Your broken plastic slider is relatively light coloured and therefore should have been reasonably serviceable but has probably broken because the chain was thrashing around.

The chain was probably thrashing around because - you guessed it - the timing chain tensioner was presumably snafu.

I agree with Oscar that there may be a slightly bent valve somewhere but you are probably very lucky and a chain, tensioner and upper sliders might get you mobile.

If the engine turns over and no valve clearances anywhere are extra large it is unlikely you have bent a valve.

You will need the correct tensioner for your engine. Autohausaz sell the US and Aus one with an extra port for the airpump.

If it is a euro you will need the one without the port - I got my Euro one from M-B spares.

Bill

[s class]

Excellent advice here.  Correct the timing on the existing chain before feeding the new one in. 

There obviously is a root cause for this problem, and the prime suspect is the tensioner which was presumably not replaced during this prior head work. 

[WGB]

Happy to give advice and happy to come for a drive at some stage and look at it if you like but I guess you will be about an hour away from me.

As I see it

1) You need to ascertain that the chain has jumped, which cam and what damage was done
2) Correct the timing error (if that is the case) and check that the engine can be turned over freely and there are no problems with valve clearances suggesting a bent valve (even start engine and see if it runs freelyand quietly).
3) Replace one or all three of the upper plastic sliders (the pins can be quite difficult to remove)
4) Check the tensioner slipper liner and replace of not pristine.
5) Replace timing chain - even if near new I'm not sure I would trust it.
6) Replace the tensioner and it's gasket.

If you want me to drive up and have a look I am free tomorrow late afternoon and evening - PM me with a telephone number.

Bill

[BAR]

Given that you have identified a broken plastic guide, it would be very, very wise to have the chain and guides replaced and at the same time retension the chain.

I wasn't so lucky and the broken bit followed the chain and cause it to jump one or several teeth.  Result was bent valves.  That meant a Queen of Hearts [off with the head].

SO don't get the very expensive job of a head replacement.  Don't run the engine, just get it down to your trusty mechanic to replace the chain and search for and find all the bits of broken plastic.

[koan]

Not relevant to your problem but your photo bucket pictures are named back to front. Left and right on M-B refer to sitting in the drivers seat looking forward, not standing at the front looking at the engine.

Minor point but might catch you out when ordering parts.

koan

[Ryan1980]

thanks buddy, i was getting a little confused because of that

[Ryan1980]

any tips on how to remove the radiator? I've removed all hoses, auto transmission lines etc, it starts to come up then stops...
ive removed those metal clips too. I think the black rubber things on the sides are stopping it?

[oscar]

Those rubber mounts get caught in the square holes that the two metal clips fit into.  Just use a flat screwdriver or similar to force the rubber out of the holes and inch the radiator up bit by bit. A bit of spray lubricant in those holes gaps might help the rubber mounts slide too.

[Ryan1980]

thanks mate! got it

Okay all i want to do is turn the damn engine!! When i use the power steering pulley, the belts just slip. When i go to take the fan off, the whole thing just turns  (belts not tight enough)!  Without getting the fan off, i cant really get to the bolt on the crank shaft pulley.

After spending a long time trying to work out how to adjust the power steering pump to make the belt tighter, i finally found which bolts i need to loosen. But its going in the 'too hard basket' for now, i think its too hard for one person to do... one needs to hold the pump up whilst the other tightens the belts.  So ive given up and am going to bed..

Anyone got any other tips on how i can get this damn fan off?

[Ryan1980]

by the way - i just realised my hair at the back is covered in automatic transmission fluid. im going really well here