Bad misfire

houblebouble · Post by **houblebouble** » Sun Sep 21, 2008 11:43 pm

Hi there !

I´m new at this forum and excuse my bad English ....

Suddenly , running the V8 without any further problem or noise , there was very bad misfire over the whole revrange.
Exploring the reason I first cleaned sparkplugs , changed leads , distr. cap etc. - no way .
Removing the leads I found the misfire comes from cyl 5 - compression reduced .
Now just finished removing the rockercover and found the exhaust lifter cyl 5 has gone - can move the rocker without any restistance against pushrod.
As I´m no expert, I ´v no idea what happened - and also , more important , what to do ?

Reading a lot of threads at this forum I get a little more intelligent : change lifters AND cam !!!

The engine is a NEW 4,6 in a RRC ( ca. 15k miles ), so I peg anybody with a similar setup to help me with his experience which cam / lifters / springs to buy for best low and midrange torque.

THX

Hannes

ChrisJC · Post by **ChrisJC** » Mon Sep 22, 2008 7:23 am

I use a TorqueMax cam from RPi in my 4.6. However I do not know if it is compatible with fuel injected engines.

Yes it sounds like you need a new camshaft and followers.

You should check the valve though as the valve may have seized and caused the tappet to fail.

Chris.

houblebouble · Post by **houblebouble** » Mon Sep 22, 2008 3:27 pm

Hi !
Now stripped inletmanifold an valleygasket to have a look on cam and followers - outlet 5 no cam lobe anyhwere and the follower is without pressure .
There are only around 15K miles on this engine - what happened first : camfault and consecutiv follower destruction , or other way round.

Maybe the double springs are to strong for this valvedrive and caused this problem by destroying the weakest cam .
The other cams also are showing signs of use , but not in this amount like the 5. out

Now have to start a big job on a nearly new engine ....

Please help me to find a reliable cam ( high torque for RRC ) and tipps to solve other similar problems in the future .

The oil used was recommended 20W50 and I didn´t highrev the engine any time - so the only reason can be very low materialquality !

THX

Hannes

houblebouble · Post by **houblebouble** » Sun Sep 28, 2008 9:38 am

Hi !

Exploring the reason why the follower ( exhaust 5 )didn´t do his work , also when the cam lobe had been nearly grinded down , I found that the base of the follower had been worn down so deep, that a tiny hole was appearing in the center of the follower base , where the oil was draining out - the follower couldn´t set the pressure.

This desaster happened only on this single follower , the others had very small or no signs of wear .

2 questions please may be answered be V8 forum experts , to find what is culpable :

1. ) Tapped clearence not correct adjusted on this valve drain ? Material fault ? Lubrication problem ?

2. ) Sorely I found , that I did a fault by myself , when removing this haevy worn follower out of the cast in the wrong way : I didn´t push it down after cam stripping , but pulling it out to the top - so scratched the surface of the cast !

shame !
Will this scratches denote the next problem after fitting new cam + followers ?

I peg you guys to give me your experienced references to rescue my loved V8 !

THX Hannes

ChrisJC · Post by **ChrisJC** » Sun Sep 28, 2008 12:46 pm

Have you checked that the valve itself moves in the head? I would remove that cylinder head, take out the valve, and make sure the valve-stem and valve-guide are OK. You could have a sticky valve which has overloaded the camshaft & tappet.

Chris.

houblebouble · Post by **houblebouble** » Sun Sep 28, 2008 7:11 pm

Thanks Chris - I havn´t thought on this uncertain event , off course I ´ll do this to have a look on the valve guide - I´ll report !

Do you also have an idea on my second question - nobody here in Austria is realy common with V8 engines , especially with such a particular question .

The surface of the cast is scratched from pulling the destroyed follower out to the top ( read about this stupid fault somewhere on V8 pages to late ) . It was hard , so I used a gripper .
Is it possible to lap the alloy-surface with a very fine 3M pad a little , that the follower can slide and rotate correct - I hope that the block forgive my mistake

What can happen - to less oilpressure inside the follower , cause of to big slot between follower + block ? premature wear ? or hopefully nothing ?

I hope I explained the situation sufficient , without pictures ( I have some , but the grade of damage can not be seen very well )

Thanks

Hannes