Some engine questions.. (more added plus video)

[adam73bgt]

So basically I've got a few things I've been wondering about my engine, and rather than make lots of different threads I thought I'd consolidate them into one thread

The car in question is my MGB GT, standard 1800cc B series engine except for K&N filters

Firstly, the car usually idles around 800-1000 rpm regardless of engine temperature, but in warm weather this can go up to 1300 or even 1500 rpm. The temperature gauge stays below the midpoint of the gauge (where it usually is) and oil pressure reads about 30psi at idle. So I'm wondering what could be causing this? Vacuum leak or something?

Secondly, I think I've got a bit of wear on the rocker shaft, there was a fair bit of valve noise going on so I checked the valve clearances. They're all fine but theres still a fair bit of valve noise, plus some of the rockers felt a bit 'wobbly' on the shaft (I'm guessing this is an indication of the shaft being worn?)

So if the rocker shaft is worn, should I get an oversized shaft and have the rockers machined to fit? or should I look to replace the whole rocker assembly with new rockers and shaft?

If I were to get new rockers would I then need new pushrods or anything? are they matched through wear or something?..

Once I know what I'm doing with the rockers I'll probably have more questions about how to go about changing the shaft etc.

Thanks in advance for any help

[AtomicRooster]

As for idle, is it on waxstat carbs?

[ChasR]

From memory, it should be on fixed jet carbs, but with the changes owners make over the years it could have anything (even HIF4s!).

I would say it is most likely down to the waxstats playing up or leaks at the throttle spindle (the latter you can identify with a can of carb cleaner and a nozzle carefully pointed at the spindles.

If the former, a rebuild kit should do the job. If on Waxstats you can get conversion kits to go to fixed jets. Depending on who you ask, Waxstats are not too terrible (in theory, your MPG can improve with them when working correctly), to being the creation of Satan. If the latter, you may get away with a full rebuild kit on both, but the body may need rebushing, which can make life a little trickier without a reamer etc.

On two of my BL cars, they had the same symphoms as you (I actually wound the idle level off the lever, the spindles were that bad (the idle would shoot down with carb cleaner).

It could also be down to poor or cracked carb gaskets/connectors to the inlet manifold. Again, carb cleaner should reveal this.

[adam73bgt]

They're HS4 carbs so I'm not sure about whether they're waxstat or not? I do know throttle spindle wear can be a problem with them though so I'll have a shoot with some carb cleaner. I've also got a new jet kit somewhere so I think I'll be fitting that when I'm back from uni too.

With spraying carb cleaner at the throttle spindle, should I be listening for a drop in revs? .. though I suppose any change in revs would indicate a poor seal...

Also do either of you have any experience with changing rocker shafts at all? thats the bit that worries me the most, although I do keep getting bad thoughts about using a worn rocker shaft as an excuse to fit some roller rockers....

[Seth]

Changing a rocker shaft should be no bother at all. It is hard to know whether it really needs it though without hearing/looking at it. The rockers should be free to move sideways a little as they are only spaced apart by light springs but they should not be able to rock other than in the direction they should, if you see what I mean. You can probably remove the front or rear rocker from the shaft without unbolting the shaft from the engine which might help determine condition of the shaft.

If you do unbolt the shaft work in a logical order like you would with cylinder head nuts.

Be aware that there was a change in design of the oil feed to the rocker shaft in the middle of MGB engine production. You ought to be able to determine which you have from your engine number but it is possible the cylinder head might have been changed leading to an engine that ought to have a 'centre' feed having an 'offset feed' and visa versa. Its easy to see which you have once you take the rocker shaft off though.

Don't mess about with roller rockers unless the rest of the engine is something extra special. It would be pointless cost.

[adam73bgt]

Thanks for the reply, I think I got a bit scared by reading an MGB forum thread that mentioned having to loosen off the head bolts as well when changing rocker shafts

I get what you mean about the rockers being able to move a bit, I think I've got a video of the engine running which I shall have to try and post on here at some point, the main thing that struck me was how the engine still sounds a bit clattery (though i realise they're not the quietest of engines) after valve adjustment

Aye I'll be careful to get the right rocker shaft if I do change it, being around the middle of production and not having the original engine can provide a little bit of a challenge, I'll need to probably remove the shaft to get the locking screw thing in anyway as that had somehow worked its way out

Oh and thanks for dissuading me from roller rockers, not sure why I seem to get the irrational need to upgrade things while I have them apart

[Seth]

Four of the nuts that hold the rocker shaft pedestals are head nuts too but on something as ancient as a B series engine you will probably get away with it fine. I know I have done in the past. Just be sure to torque up properly afterwards.

Its the rear most rocker pedestal that has the oil drilling in a different place and must match the position of the hole in the top of the head.

[adam73bgt]

Mm, with them being head nuts should I be draining the coolant system? Or is the iron head too stiff to be affected by the removal of just the rocker pedestal nuts?

[Seth]

No, I wouldn't bother, just keep an eye on things. I think it very unlikely that the head seal will be affected. I know I have done this to an A series with no problems and the likelyhood is I've done it to a B series too.

If you are worried then you could just take the head off altogether as gasket sets aren't that expensive anwyay, allowing you to see what the rest of the top end is looking like too.

[adam73bgt]

Hmm I'm not too sure I want to see what the rest of the top end is looking like.. I could easily see myself spiralling into a full on engine strip which I don't really fancy doing too much. Though it would be interesting, I'm not sure i trust myself to put it all back together properly

[adam73bgt]

Right I think I've sorted a video of the engine running after I did the valve clearances, not sure if anyone will be able to tell if this is normal valve noise or a symptom of a worn rocker shaft but here it is



Other engine related issues have started popping up as well now The ignition warning light is coming on at idle and lower revs, but the light goes out with increasing revs, the voltmeter doesn't appear to be going above 13 volts, so i think this is some sort of problem with the regulator or something inside the alternator? I think I'll be getting an uprated one soon in any case

And also I need a new oil cooler as mine is split, lovely how all these issues are popping up at once...