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MG MGB Technical - 3rd gear for 50 miles or more

SO my wife was on her way home from a long trip
She was driving her 79 MGB
Before she left it ran great no engine issues at all

She had to slow down for construction and put it in 3rd gear
After the construction she sped up but did not shift gears. She left it in 3rd and went down the highway

She got home and the engine had a loud ticking noise
I pulled the valve cover and found one of the rocker adjustment screws broken off

This weekend I will tear it apart more to see what else it wrong

Any suggestions/ideas

rsf fowler

Looks like a short stud on the pedestal. (unrelated to this prob)
What rpm did she get up to - valve float?
Art Pearse

Subject to the answer to Art's question regarding rpm - and durations of, this might just be a co-incidence. The broken rocker screw might well be the source of the ticking sound from an impacting rod.

Prior to tearing it down I'd be inclined to repair/reset the rocker assembly and see what transpires.

We need to remember these engines (even in standard and also worn condition) have been run at quite extreme rpm in lower gears - for reasonable durations, by countless sports driving fans.

Yes, you might have a problem from this but I would start with being optimistic - you can always go on to the bigger scene if it is proven needed.

Regards,
Roger
Roger T

For early cars with 5.60/14 tires, it would be about 4900@65mph. This probably has 185/70, so a bit more rpm, about 5300. (I looked up the rolling radius <11.65 vs 10.9> for both. And was surprised!)
If it is stock for 79, it would be hard pressed to go any faster.
How heavy is the Lady's foots?

Shouldn't hurt it. If it was in valve float for any time it could have beat up seats and tappets and cam. Valve float is pretty obvious and alarming, so I doubt it. Depending on mileage, all those could have been dubious to start.
It is an odd way to break a screw. Racing guys have the locknuts come loose so the adjuster backs out to the limit of the ball end. I'm inclined to think the screw was already part broken or flawed. If the screw broke from valve float, the break would be below the rocker and the pieces and pushrod would have fallen out.

I'd replace the screw and check that the pushrod is not bent. You can R&R both without taking anything apart; I wouldn't take more apart until I tried that.

FRM
FR Millmore

Shes not usually a lead foot but it was a long trip
She says the top speed she went in 3rd was 65 maybe

on the other hand the did over 1000 miles (500 or so 1 way) with no issues at all with the car until she did this.


Thanks for the help/comments

rsf fowler

"Prior to tearing it down I'd be inclined to repair/reset the rocker assembly and see what transpires."

Me too, only if that doesn't put things back to how they were would I dig in any further.
PaulH Solihull

Don't know why the adjuster screw sheared. But while you are replacing check that the push rod isn't bent also, but again don't know why it should be.
Allan Reeling

Most likely, the locknut was over tightened the last time the valves were adjusted and the adjuster finally broke in two. Replacing the adjuster will probably fix your problem. RAY
rjm RAY

I tore off the rocker assy.

Pulled the push rods.
The one in question and the rest look fine
But for some reason the one push rod that the adjustment screw broke on is different than the others.
(see the attached pics)

The one on the left is different than the others

rsf fowler

At some point in time the engine may have been overhauled and the pushrod shown was used instead of the original, probably because it was in better condition than the original one. RAY
rjm RAY

actually the engine was overhauled about 10 years ago.
That was only about 10,000 miles ago.
Its the Ol'Ladys car and she does not drive it much except for a short time in the summer

I do not remember using a different push rod but the fact is its there so I had to have.
rsf fowler

External shape doesn't really matter, but the contact surfaces do as well as the length.
PaulH Solihull

got the parts in Wednesday and installed them today
I replaced the complete rocker on the valve
Adjusted using the rule of 9
runs great
thanks for all the advice
rsf fowler

This thread was discussed between 08/06/2012 and 16/06/2012

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