Single cylinder misfire - 3.5 on SU

z4cats · Post by **z4cats** » Mon Dec 01, 2014 8:44 pm

I am getting more confused as I go along.

With 2 Colortunes at idle, no. 8 works fine, but no. 2 just sparks.
Give it some throttle and no. 2 starts to work but very intermittently.

One thing though is that with the even rocker cover off, there can be seen a large volume of oil flowing up into the top. Would overflow the head if left running, it is also flooding over the valve / spring. This would explain the oil on the plug if it is dripping down.
The odd rocker cover has almost no oil compared to the even side, there is just a little flowing.

I am starting to think I should just get the engine out to check and rebuild it.

Got a spare 3.5 anyone?

ChrisJC · Post by **ChrisJC** » Mon Dec 01, 2014 9:16 pm

You could try swapping the rocker shafts from left to right and vice versa.
I wonder if the excess oil indicates a knackered rocker, so that valve isn't really opening.

Chris.

z4cats · Post by **z4cats** » Sat Dec 06, 2014 12:07 pm

Well, I have found the source of the problem

A bit of head scratching got me to look at what could be different for No. 2, and there it was in plain sight, the brake vacuum take off.

When I removed the hose to the brake booster and put my finger over the hole, I got ignition, on removal, just spark.

The eventual reason was that the servo was leaking air out of a fitting on the lower front half of the unit. I expect on one of the last times out, something broke the front part off, leaving an air hole.

Once this was plugged with a spare propshaft bolt, the cylinder fires correctly.

At least is was a cheap and simple fix.

Many thanks to all who contributed suggestions.

mgbv8 · Post by **mgbv8** » Sat Dec 06, 2014 8:39 pm

If you are losing that much oil into the rocker gallery the rockers and or shafts are knacked. With the rocker cover on this oil will build up and allow it to reach the valve guides and also start seeping out of the rear outer corner of the rocker cover if the gasket isnt sealed properly. It could also be starving oil from other parts of the engine if its flowing this much??