timing chain keeps losing tension

[j16jrf 0]

I have replaced the chain and guides etc on my 2.9 vr6.

Twice now the chain has lost tension and resulted in bent valves, why is this happening?

 

I have checked everything and it all seems ok its just baffling me.

 

I have even replaced the oil fed bolt that pushes into the top of the chain to give the tension.

 

Can someone PLEASE help me.

 

Thanks

Jamie

[dr_mat 0]

Bummer..

 

The only explanation can be that the tensioner bolt isn't getting any oil fed to it while the engine is running. That means either your oil pressure is too low or you have a blockage somewhere.

[j16jrf 0]

Yeah thats what i thought, so i have ordered a new oil pump too to see if it cures it.

 

fingers corssed this time

[Kevin Bacon 5]

When you replaced the chains, the little green O ring in the side plate for the tensioner bolt oil feed didn't drop out did it?

 

Been there, done that :lol:

 

With the cam cover off and everything checked, pull your plugs and crank sensor and turn the motor over on the starter until the oil pressure light goes out.

 

Get an assistant to do that whilst you watch the cam chain. It will go slack and drop each time the valve springs push the cam lobes round for about 10 seconds until the oil pressure builds up, and then the chain should be taught at all times. Run it for about 30 seconds on the starter and providing the chain stays taught, it will remain that way.

 

If it stays slack, you have an oil leak somewhere, or a very weak pump as Mat says, but if that were the case you would unlikely get any oil in the head. Check around the oil filter housing as the oil is distributed around the engine from there.

[j16jrf 0]

thanks very much i will try that one ;)

 

hopefully get it sorted soon.

[dr_mat 0]

On the upside, if you're becoming an expert at reconditioning VR6 heads, you can do mine .. :)

[j16jrf 0]

pmsl deffo not going to be an expert, its a mechanic doing it for me lol

 

he is a very good mechanic and this is just boiling his brain. I phoned storm developments and they say the oil filled bolt that gives the best tension at the back of the head could be to blame.

 

turns out this was the issue, no worries all built up and running now very sweetly.

Great to have it back on the road again cant beat that noise

[efil4sbuD 0]

When you replaced the chains, the little green O ring in the side plate for the tensioner bolt oil feed didn't drop out did it?

 

Been there, done that :lol:

 

 

 

Cheesewire, you say you lost your O ring once, what was the result of that? Did you have any problems with oil pressure or did you refit it before starting the engine again?

[Toad 0]

Are you still having this issue then?

[efil4sbuD 0]

Are you still having this issue then?

 

I'm not the original poster. I was searching for oil pressure problems and found this thread.

 

I just came across the bit where Cheeswire said the O ring fell out and wondered what happened because of it as i forgot to put mine in and now have low oil pressure. I can't see that it can cause that but i'm kind of stumped and i don't know what the cause is.

[Kevin Bacon 5]

Sorry, didn't notice the replies to this....

 

Yeah I ran it on the starter motor and couldn't get the chains to stay taught. When I dismantled the chain cover again, that's when I noticed the green O ring was missing from the cover. I always stick them into the cover plate with silicon now.

 

You won't lose total pressure as the machining tolerances on the cover are very tight as it's a gasketless fit, but it won't hold the right pressure.

[efil4sbuD 0]

Ok, maybe that's been my problem then. After doing the chains i built it back up so quickly that i forgot the O ring. I realised my mistake but ran the engine anyway.

The oil light came on immediately and the buzzer came on at about 40MPH, though not when revving to 3k RPM at a standstill, curiously.

I only did a couple of miles to the MOT station and back so hopefully no damage.

 

I have now got the O ring back in place but the battery is flat so i'm yet to check if it's now cured.

[Kevin Bacon 5]

Sounds about right. I didn't run mine as I could see with the rocker cover off that the chains stayed slack after a few mins of cranking.

 

You should be OK I reckon!

[diggerbucket 0]

Where exactly is this o-ring? When you say tensioner bolt is that the thing that's screwed into the back of the head? I'm sure my chains could be a bit tighter....

[efil4sbuD 0]

Yep, there are a couple of tensioners, one for the top chain and one for the lower.

The upper one screws into the back of the head (actually the upper chain cover) and keeps it's tension with oil fed in from the side. The O ring sits around this oil way between the main head and the upper chain cover where the tensioner is screwed into.

 

You can't see if from the outside but when you remove the upper cover it will most likely be sitting in a recess on the head.

[Kevin Bacon 5]

Yeah it sits in the chain cover adjacent to the tensioner.

 

It's easy for it to fall out when reinstalling the chain cover, so I would hold it in with a dab of silicon personally.

[efil4sbuD 0]

Well, refitting my O ring didn't make any difference to oil pressure (unless it fell out again when i wasn't looking), still flashing and bleeping.

 

I'm thinking i must have a wiring fault. I've had the head off so all wiring was undone but there's only a few places that could be venting and i think i've covered those:

The Oil filler cap

The breather on the valve cover

The tensioner

The crank oil seal

Top and bottom chain covers

The oil filter housing

 

I have also changed the crank oil seal but that was tight so would not have come off.

 

Has anyone got any ideas why else i'd have a loss of pressure? There's fresh oil on the top of the cams so the pump is working.

 

*** Edit ***

Fixed now, it was a wiring problem.

 

 

James