44 replies to this topic

[S pack]

I think you've got that arse about. Packing the rockers UP will INCREASE the lash. 

 

Dr Terry

If you want to reduce the preload on the lifter place a packing between the bridge posts and the head pedestals. Same effect as loosening the adjusting nut on adjustable rockers.

If you want to increase the preload on the lifter then machine some off the bridge posts or the cyl head pedestals.

Edited by S pack, 14 July 2021 - 12:09 PM.

[claysummers]

I think we are just getting confused over the word lash. To me this means play in the valve train. Opposite to preload. I agree OP should remove any valve train preload from offending cylinder, and shimming is the easiest way. Ideally run adjustable rockers, but this will require head off and machining, or fitting shaft mounted adjustable roller rockers. Fiddly to set and not cheap.

early Holden nut

[S pack]

I think we are just getting confused over the word lash. To me this means play in the valve train. Opposite to preload. I agree OP should remove any valve train preload from offending cylinder, and shimming is the easiest way. Ideally run adjustable rockers, but this will require head off and machining, or fitting shaft mounted adjustable roller rockers. Fiddly to set and not cheap.

early Holden nut

Agree, valve lash is a term probably better used only with solid lifter camshafts.

 

[D-Train]

So a bent valve then?

[S pack]

So a bent valve then?

Maybe, but could easily be a faulty lifter not bleeding down fast enough so it pumps up and holds the valve open slightly whilst the engine is running.
 

[D-Train]

Thanks guys.
I pulled the rockers off cylinder 6 and the exhaust valves wear mark is a lot wider then the inlet. What does that mean?

[73SUNBURSTEXYOUWON]

Thanks guys.
I pulled the rockers off cylinder 6 and the exhaust valves wear mark is a lot wider then the inlet. What does that mean?

Picture?? Are you sure its not a flogged out valveguide too, valve not seating and maybe the stem moving about erratically causing a wider wear pattern to the rocker arm....or possibly any extra load applied to that particular rocker is causing the wider wear mark ???

[73SUNBURSTEXYOUWON]

Look at this sickly uglyness.

Effects of Solid Cam n Lifters on conventional rocker gear. Gradually smashing away at the rocker arm.

No popping here.

But just an annoyingly over noisey tappet, that wouldn't shut up - well no wonder!

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[D-Train]

Yes, when I did my first few starts to tune, the baffle in the standard vk rocker cover was touching the exhaust rocker on 6. It's a new yt alloy head and rockers with only a few dozen starts on it.
I thoughts that rubbing was going to solve my problem when I found it but no good. Could that of caused my damage?

[rodomo]

Popping through the exhaust can be caused by an air leak into the exhaust.

 

Pop diddy bang bang fart pop bang.......................but usually on deceleration

Edited by rodomo, 14 July 2021 - 09:28 PM.

[D-Train]

Pic of no 6, intake bottom exhaust top. More witness mark on exhaust.

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[73SUNBURSTEXYOUWON]

Are They Roller Rockers??
As the rocker moves up n down, the roller will move across the central area of the valve tip to create the pattern on the valve tip, re. exhaust.

The Lower intake valve tip image seems unclear to see. But same apllies.

[D-Train]

Ot is a roller rocler, but the pattern on the exhaust is bigger then the inlet and they have the same lift.

[73SUNBURSTEXYOUWON]

Ot is a roller rocler, but the pattern on the exhaust is bigger then the inlet and they have the same lift.

Ok, humour us here, measure that lift with a dial indicator to determine it is definitely the same, as a difference in lift will offer the different pattern to the valve tip.

(Edit) Pumped up lifter, was also previously mentioned will contribute to difference too.

Rule out a wiped cam lobe

Edited by 73SUNBURSTEXYOUWON, 14 July 2021 - 10:02 PM.

[73SUNBURSTEXYOUWON]

Also, extra homework.
how do other cylinder valve tip wear patterns compare to #6?

[Oversteer]

I think the compression test being dead even( It was wasn't it !?) rules out this bent/non sealing valve, eaten cam lobe hypothesis does it not ?

 

 

[D-Train]

It was all the same, but my cylinder didn't seem 100% dead either. It seemed to be firing some of the time.. I pulled the push rods out and both intake and exhaust have a slight bend in them. Not huge, but I Imagine it wouldn't take much. I'll pull the lifters and inspect/test and order some more parts.
Now should i put it back together with new rods and see if this was the prob or is there a rough way to check the valves without pulling the head and springs.

[Oversteer]

Unless the lash was wrong(holding open valve) the slightly bent push rod wouldn't likely cause any difference to idle.

 

Leak down or vacuum test on ports will tell you if valves leak.

 

It pretty easy to put it back together and test with new rods so why not.

 

Is the ECU set-up as sequential injection ? Even if it is you could swap injector driver to another cylinder and see if problem follows.

[axistr]

Have you tried to push the valves down by the palm of your hands and see if the valve springs on number 6 physically feels a bit weaker. ? At TDC number 6 compression stroke, if you can spin the push rods easy with your finger tips I wouldn't think they would be riding enough to cause the exhaust valve leakage past the seat.

 

Now you know the problem is on number 6 cylinder a few more easy checks should identify the problem. If the popping stop when you remove either the spark plug spark of remove the fuel on no number 6, and the spark plug is black (indicating rich mixture) the issue might be the extra cylinder pressure escaping past the exhaust valve when partially ignited popping into the exhaust tract. possible but more unlikely due to having good compression.

 

If the spark plug is black its not burning all of the fuel and has a rich mixture, If you can read the information on your ecu, the o2 sensor will show a very rich mixture. I had 7 stuck (closed) fuel injectors when I went to start the VR engine in the SLR for the first time. Took me a while to find that one. Maybe your number 6 fuel injector is stuck open and flooding number 6. swap it to another cylinder will quickly tell you if this is the case. Or squirt 40-50 PSI air pressure through the removed injector and check if air passes through the injector. Suggestion number 3 the spark is firing at the incorrect time. Not sure what your using as a triggering device but maybe a problem with the trigger timing on number 6 only. I had a problem with a V6 Holden the harmonic balance trigger plate has a bit missing on the problem cylinder. To confirm a problem with number 6, use a timing light hooked up to number 6 spark plug lead and see how many degrees on the harmonic balance it firing at, if its after top dead centre there's your problem and the mixture is still trying to burn as the exhaust valve starts to open. Last check is the configuration of the ecu on number 6. don't know what program your running but maybe a timing offset on number 6 has been set incorrectly of something simple like the firing order set ect. I would probably check all cylinders spark plug timing and see where they are all firing as a starting point.

 

I reckon if you do the above checks you will find the problem.        

[UCSLE]

had a bent valve in my 308 and it still had good compression , the way to tell is not by the final reading but how the compression gauge pumps up 

 

a rough way to check after the compression test is to bolt a spanner on where the rocker gear goes and press on the valve 

preferably a smooth spanner so it doesn't damage the valve