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Damn...

2K views 11 replies 5 participants last post by  9psi EB 
#1 ·
Well after fitting a full chain and guide kit to my ea all has been sweet for a few weeks, then after a trip to bris ( 3 hours ) i started it the following morning and it was rattling again. Took the rocker cover off and found that I can turn the crank a little before the crank sprocket itself will turn, When I had it apart last time I replaced both the woodruff key and crank sprocket and they were a snug fit. Why is it chewing it out again?? should I replace them again and loctite the bastards there?
 
#3 ·
Could be the hydraulic chain tensioner.
 
#4 ·
The tensioner is nearly brand new and was tensioning the chain up beautifully, but as I said, if i look down through the top of the timing cover and turn the crank by hand, I can turn it about 1.5mm before the bottom crank sprocket will turn, which tells me that the keyway is chewed up again, which is strange because I replaced the crank woodruff key and also the sprocket itself, the sprocket WAS secondhand but was in excellent condition, maybe the metal was soft? or the key was manufactured too thin?
 
#6 ·
Hey, Thanks for the reply, could you elaborate a little on your last post?
The chain is fairly slack until i turn the crank a little for it to grip the crank sprocket, then shes nice and tight.
 
#7 ·
What really flogs the timing chain out is a manual transmission. On and off the throttle and up and down the gears means that the chain is being loaded up in both directions(due to valve train inertia). It generally causes the chain to stretch earlier than a automatic would that does not jar the chain.

The problem you are describing is a little strange, it seems like the woodruff key is taking excessive load in both directions to cause the key to fail. I assume that the chain was put back properly and the components are in good condition.

One possibility is something has happed to the tensioner.

The only other thing I can think of that could be causing this load is problems with the cam tunnel not being straight and the camshaft binding as it turns. This can happen if the head warps and is not repaired properly. Some people just mill the head flat, but the cam tunnel remains twisted.The head should be straightened and cam tunnel closed and honed. The head can then be milled.

You could remove the camshaft and inspect the journals for signs of a problem. Also check for valve springs binding if you have modified the head or cam in the past.

It's a bit hard to try to work our what has gone wrong as I'm not familar with the history of the car, if it's stock or what you have changed in the past.

Good luck.
 
#8 ·
Sorry I will give you a little background
The car is completely stock Im the second owner, its a 3.9l automatic and is never thrashed etc
when I bought it it had 315k on the clock but has had a new crank and head ( have seen receipts ) it did have a timing chain rattle though

Anyways I took it to a mechainc who ripped me off as the chain was never changed ( could tell by the condition of the guides and the fact that the upper guide bolt head was sheered beyond belief, it took a small blow torch to remove the bolt.

Anyway had a mechanic help me fit the brand new chain, guides and tensioner, also replaced the woodruff key and crank sprocket, though i didnt use any loctite here...

Anyway bolted it back together and all was fine for around 400k's until i took the drive to brisbane - within that period the car was driven very steadily

The weirdest part is the fact that the car was beautiful before i switched it off, then the next morning it rattled its ass off!

Im losing patience with this thing at a rapid pace, ive been driving it around and its going fine besides the rattle, just turn the stereo up

Oh and if I have the rocker cover off, and crank the engine with the key, intermittently, checking in between - sometimes the chain is tight, other times it is slack - any ideas?
 
#9 ·
To have a new chain rattle is very strange. There should not be enough slack in the thing to allow this to happen.

I don't think I would be too concerned with what you see when cranking the engine, that is probably normal. Althought a chain link could have seized(unlikely).

Assuming that oil levels and pressure are OK it sounds like something has gone wrong with the tensioner (but even a shagged tensioner to cause a new chain to rattle is strange). Maybe you should inspect it first.

Try to remember how much slack the chain had when you put the new one in, has it changed much? If the new chain has stretched then you have to start looking at what could put that much load on it. Has the camshaft sprocket been changed or is it worn?

If you get nowhere then you could probably try idling the engine without the rocker cover to see it anything looks wrong. It shouldn't be too messy.

The work that has been done to the car is interesting, why change the crank by itself?
 
#10 ·
Theres no chance that the bolt that holds the harmonic balancer on has come loose slightly? , because if it does come loose, both the chain sprocket and balancer will move without the crank moving, also wearing out the key way.
The balancer tensions up against the chain sprocket which tensions up against the inner surface of the crank.

Always loctite the bolt, and dont forget the washer on it either.
Also it wont hurt to tension it up a little more than factory specs.
To stop the engine turning when using a torque wrench on the bolt, jack the car up, or put it on stands, remove the inspection plate off bell housing and wedge a screwdriver between the flywheel teeth and the uppermost accesable corner of the block while someone else ties up the bolt.


9psi EB
 
#11 ·
thanks for that I will give it a go, I have run the engine with the cover off and the chain seems to be tight at times and slack at others. If I turn the engine over by hand the chain stays tight the whole time, its only when i use the key, on and off that it comes loose at times. The balancer bolt idea sounds like itd be worth a try, but it may be too late if the keyway is chewed up again.
 
#12 ·
Theres always Devcon.

This is an epoxy, that when set, can be drilled, tapped and something bolted to it.

If the keyway is stuffed, clean the crank, sprocket and balancer with carby cleaner, mix up some devcon, put it in the keyway, insert the woodruff key, and slide the sprocket etc on.

Just hope you never need to get it off again, and leave it to the next person who buys the car :)

9psi EB
 
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