Hello everyone,
I recently bought myself a low mileage, well maintained '98 XK8 and I'm doing a general overhaul.

I've done the whole timing in the past on my x308 but I am having a bit of a puzzle with this one.

An upgraded timing kit is already installed and from the car's history it looks like it only covered a couple thousand miles.

However both primary and secondary chain on one bank seem a bit loose in some positions and perfectly fine in others while turning the crank. Could this be because of a already stretched chain or is it just due to no oil pressure in the tensioners? Chains on the left bank look tight with no slack, so it makes me wonder if a whole timing job is a wise thing to do while being already there.

Any insight would be much appreciated.

 

This seems to be a completely wild suggestion ..... but is that chain tensioner installed upside down? Try to pull the plastic runner up to meet the chain and if it doesn't move then it is upside down. If that is the case, it is one the most ham-fisted repairs I have ever seen in 55 years of spannering. You really need to replace the lot as God knows what else they have ruined.

Richard

 

They may not have removed the retaining pin from new tensioner. The one used to keep it from falling apart before installing

Jack

 

It is the correct tensioner for the RHS bank:- piston on the 'slack' side of the chain.


The variation you note could be the effects of the valve spring pressures on the camshaft in various positions.

The piston does look fully retracted so could also be as Jack notes - or it is jammed? Definitely a good time to investigate 'while you're in there'.

 

Ah yes, I'd forgotten that one is reversed compared to the other.

Rather than trying to pull the upper slider up as I suggested, try pushing the lower runner downwards with a screwdriver or similar. If if doesn't move down it's presumably jammed for some reason. I can't believe that the pin has been left in as the pins are bright orange so surely there is no way that it can be left in?

I guess it might be that you are pulling the upper part of the chain upwards and that is compressing the piston into the body. I don't think it should be that easy to pull up the chain and compress the piston unless you are using a lot of force. There is presumably no oil pressure in the tensioner but I think that the spring alone should keep it extended.

Richard

 

I've just timed my engine and observed exactly this phenomenon at certain parts of the stroke as the valve spring pressure pushes the exhaust cam 'onwards' a bit and makes the chain look loose - under running operation the chain will be pulled tight by the rotation of the engine. That's why it happens at some parts of the stroke, but not the whole time.

 

If the tensioners and guides have been replaced, and you have everything open, drop your oil pan and check the pickup for the oil pump for debris from old chipped and broken guides, mine was loaded with plastic pieces.

 

That's exactly what I observe. I guess you just left it as it was, assuming everything will work fine under oil pressure when the engine is started?

 

Yes, because it's correctly timed. The oil pressure doesn't really come into it, as the tensioner really just takes the slack out of the 'return' side of the chain. Under running conditions the cams are being constantly pulled around, so there isn't an opportunity for the springs to apply pressure on the cam lobe at a faster rate than they're already turning. If that makes sense!

 

That looks normal to me. When I did my first set of tensioners on a 98 XJR I had that result when I was finished and was sure something was off, but it was fine. Car is still running perfectly after a few years.