Valve Bounce????

[jakobsladderz]

Hey guys,
Got a question someone may be able to answer me... What are the symptoms of valve bounce?
I spent some of the weekend swapping a new head onto my staz and succeeded with less skun knuckles than usual. I did manage to let the cam belt get a let loose such that the balance shaft became an unbalance shaft and the engine nearly rattled itself to pieces (was nearly 180° out of phase).
I've got a weird thing happening though. The engine runs beautifully up to about 5 grand, then it feels like the rev limiter kicks in. I checked and double checked and it's definately not the ECU rev limiting the motor. Even free revving it won't go above 5000. I get a cloud of grey smoke out the back too. With the old head (and old valve springs) it made it to 6 grand with relative ease, and nothing else other than the head and it's bits have been changed.
Could this be soft valve springs that are letting the valves bounce or float at higher RPM's so it's not making power. A mate just had a similar symptoms with a G61 in a Cordial which turned out to be valve springs.

Assuming it is the springs where is the best place to get a set of springs for these engines? I don't want no damn 150lb doubleys or anything, maybe just 50 or 60 lb to be just a bit tougher than factory to handle the 14 PSI it is to be fed.

The springs in the current head could be pushed in by hand, I don't know if that's normal or not..

cheers,
Duncan

[Cookiemonster]

Barney will be along shortly.

[jakobsladderz]

I have the bait on the end of a thread....

[Starion VR4]

Ok, just remove yr tappet cover, try to push the sping down with yr hand on the rocker, if u have to use lots of force then yr spring R ok, if its easy then of course its no good, the std spings as a general rule survive on a std cam to 6000ish, even when old. I am reasonaly sure the place that did yr head would of checked the tension of the spring. I think U need to look else where 4 yr problem. If yr springs were bouncing( usually the inlet due to weight) then a back fire in the manifold is usual. When u free rev the engine does it spin up as quick as B4? is everything the same? did U just change the head? :beer

[jakobsladderz]

It won't free rev past 5000 rpm. as it gets above that it starts to 'break down', kind of burbling sound and plenty of grey-black smoke. the turbo starts to really spool if I try with more throttle, since there's shietloads of hot, fast exhaust cruising through.. The head is the only thing changed since it used to rev happily to 6+..

It took a bit of force to push the valves open but not heaps, I was expecting more although this is the first head I've done so I didn't have a comparison..

The Cam timing may be out a smidge because the head's been shaved but with the tight side shorter the cam timing will be retarded a bit, which is better for high revs I though. The bottom of the rev range is solid, in fact it pulls hard until it bugs out at 5k.

[Starion_Turbo]

It won't free rev past 5000 rpm. as it gets above that it starts to 'break down', kind of burbling sound and plenty of grey-black smoke. the turbo starts to really spool if I try with more throttle, since there's shietloads of hot, fast exhaust cruising through.. The head is the only thing changed since it used to rev happily to 6+..


Same thing that I had happen except mine did it a lower rpm (about 4000) when I Gave it some gas to over take or reasonable acceleration, cloud of smoke viewable in revision mirror and total loss of power once hit about 4000rpm.
This was the reason I put in new piston rings with a light bore hone. After that the problem went away. Could have been a simpler fix but thats what I went with at the time.

[13secJA]

sounds like valve clearances to me (the clearance between the top of the valve stem and the and the bottom of the rocker where the two contact each other) did you set them after installing the head? with a big cam i run mine at 0.009" inlet and 0.011" exhaust. thats for a ja with solid cam not sure if all starions run a solid cam. if they are set to loose the valves open much later and close earlier making the duration smaller causing it not to rev. if they are too tight the valves get (sticky) and will stay slightly open at revs causing it to miss and pop through the exhaust at revs.

[pajeroturbo]

Hi there I had exactly the same problem with you after I changed the head gasket. I left the car like that for a month o so and after that I decided to fix it then I took the head out again and saw that I had put the valve springs wrong. the valve spring go on way .if you look at the spring you will see that at the one way the spring is closer to the other. That way goes at the bottom. After that the engine was perfect again.


'Sorry for my bad english.'

[Barney]

Sounds like cam timing to me.

[jakobsladderz]

Alright - summary so far..

I don't think it's the rings, they were fine before so why would they be any different now. Last resort maybe, but I doubt it'd be them..

Cam timing - When I reset the cam timing it didn't look that far out (maybe 1 or 2 degrees, certainly not much) and even if it was out by a couple of degrees wouldn't it be out such that the cam timing was retarded and that would be better for higher revs?

The valve springs might be upside down but the shop that did the head put it all together so I would have though they'd have got it right..

I'm going to have a better listen to it today when it does the grey smoke thing and see I can here any other signs of anythying..

lots of suggestions, thanks guys, I just want to avoid pulling the head again if I don't have too, gaskets cost a bit and there's sooooooo much stuff to dismantle to get it off.. I quite simply can't be bothered..