4 replies to this topic

[zero_wlv]

Just a question out of curiosity rather than any real urgency,  as this engine's going to be whipped out in 4 weeks' time when I drop a rebuilt engine in.

 

As my engine had suddenly begun to run so roughly (presumably on 3 cylinders),  I took the rocker cover off and pushed the car back and forth and noticed that the exhaust rocker on Cylinder 2 wasn't moving, even though all the other rockers were moving noticably.    The valve seemed to stay in the closed position.

 

With the rocker cover back on,  I started the engine and peered through the oil filler and could see that the rocker is actually moving,  but apparently not the full range of motion  (nowhere near as far as the neighbouring intake rocker).

 

I take it from this that the valve itself isn't actually stuck in the closed position,  but that the pushrod is bent,  thus preventing the exhaust valve from opening fully.

 

I also tried disconnecting the HT lead on Cylinder 2,  which made the engine even rougher than before,   so presumably Cylinder 2 is doing something.

 

If the pushrod's bent,  is this likely to have been caused by the exhaust valve becoming temporarily stuck to its seat?    The car's been smoking badly and burning far too much oil over the last few months so it wouldn't be a surprise if the valves are badly sooted up.

 

 

In any case I'll find out in a few weeks' time when this engine's out and I strip it down  :)

 

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Engine:   998cc completely standard

[Dusky]

Well, if your valve clearance is good this can only be a dislodged cam follower or a damaged camlobe.
You can check both by removing the tappet cover on the back of the engine and having a look.

Edited by Dusky, 14 May 2017 - 10:11 PM.

[nicklouse]

Unlikely to be a bent pushrod. They tend to need something to cause a bend.

Exhaust rockers don't move as much as inlets.

Check your valve clearances.

[Cooperman]

Sounds like the case hardening has failed on the cam lobe and the lobe has worn away. Or the follower may have broken although that is less likely.

[tiger99]

I have seen a bent push rod only once, on a small industrial diesel engine. It was caused by incorrect valve adjustment, to try to make it run quieter. At full valve lift, the valve spring went solid with the inevitable result.

An inappropriate combination of valve spring/rocker ratio/cam profile can certainly do that to an A series or indeed any pusrod engine. It invariably damages the cam and follower too.