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MG MGB Technical - Replacing the Valve Springs in situ

I am looking to replace the valve springs in my engine and I wondered if anyone had any experience in replacing them with the head still fitted to the engine?

My engine is a 1950cc 18v 5-bearing unit which has been gas flowed and is supposed to be safe to run to 6500 rpm. (It does have double valve springs fitted)

I was running at high revs in 4th gear and I noticed that the engine became very harsh as it reached 6000 rpm. This happened again on Peter Burgess's dyno a few weeks ago and he said that although it wasn't full valve bounce, it was just on the point of it and so I have been limiting the revs to 5500 since then. (Apparently, it is still giving around 140 bhp with very low oil consumption and so there is no significant engine wear)

This engine is beautifully smooth and revs so freely that I would rather replace the valve springs, rather than risk any top end damage.
Maybe a rev-limiter would be a good idea too.

I intend to replace the valve stem seals at the same time. Last year, on a 30 minute descent from one of the high mountain passes in the Pyrenees, I was using 2nd and 3rd gears to control the speed rather than the brakes. In the MGB following me they, noticed there was some blue smoke from my exhaust and when I got to the bottom of the mountain and pressed the gas pedal the engine would only run on 3 cylinders for a mile or so until the plugs cleared.

So I assume that the valve stem seals need replacing too.

I only have about 12,000 miles on the engine and I have already replaced the head-gasket about 6000 miles ago and so I am reluctant to remove the head unless I really have to.

I would appreciate your opinions.

Cheers
Colyn
Colyn Firth

Blue smoke when accelerating after a period on the overrun can be rings/bores as well as valve stems and guides. Seals don't do much on the MGB. Given the 30 minute descent on the gears and the low oil consumption I would have thought things aren't too bad in that area, it was a pretty stern test.

I've not done it but I've read of feeding rope into the plug holes and winding the piston up to press the rope against the valves, and also using compressed air. However I'd be concerned that with the air method the valve could get knocked and release the pressure, to drop. How far it would drop if you put the piston at TDC I don't know, but to me the rope trick is preferable.
paulh4

I would go with the rope trick!

Colin
Colin Parkinson

I would have never thought of using rope, I had envisaged some kind of gadget that would screw into the spark-plug hole that would hold the valve in place.

Thinking about it, you could push as much rope as possible in through the plug hole and then gently turn the engine until the rope stops it rotating.

Then its just a question of making up some sort of bar that bolts loosely onto a rocker mounting stud to use as a lever to press the valve springs down to get to the valve caps.

Some thinking to do here I believe.

Thanks for the input guys

Colyn
Colyn Firth

The rope trick works, but you can also use air pressure. A extension hose from a compression testor is what I use.

Your local auto parts store will have a small tool to remove the valve spring. Most have them as part of their tool loan program.
Bruce Cunha

Compressed air is the go---for me anyway---
You can't go wrong-
method--
First, tell me do you still have springs or solid spacers between your rockers-----?
William Revit

Hi William,
I had to check the rockers to be certain, I do have spring spacers on the rocker shaft.

Would you recommend replacing the springs with the solid spacers in view of the revs I use?

Also, I do have a compressor in my garage and so it will probably be easier to use compressed air to hold up the valves.

Cheers
Colyn
Colyn Firth

Colyn
Back to front answers first-
If the car were to be a racer and constantly operating up in the higher rev range, then solid spacers would be a good insurance idea but for a road car that may get a little track work and isn't constantly 'up there' they aren't really necessary---the springs are fine--
The reason i asked was to determine the best method of doing your job
My personal opinion is that it's best not to disturb the headstud tension if you don't have to---ie, leaving the rocker gear posts tensioned up has to be better than letting one side off-----specially if the cylinders are going to be pressurised-
IF you had spacers this would result in the need to withdraw the rocker shaft to remove the rockers BUT luckily, as you have springs the shaft can stay--
Method--
Back all the adjuster screws back as far as they will go
Remove the split pin,flat washer and spring washer from each end of the rocker shaft, then slide the two end rockers off the ends of the shaft (you might have to bump or lever the valve/spring down a tiddle to clear the adjuster over the top of the pushrod cup to get them off) and set them aside ready to refit later (keep them seperate/in order so they go back on in the same position)
Then working along the other trapped rockers,slide them along against spring tension till they clear the pushrod and turn them upwards 90deg. then let them slide back
Do all 6 like this, you might have to rotate the engine to get clearance on a couple as the cam will be pushing the pushrods up
Now you're ready to go, get 1/4 on tdc, into 4th gear and pull the handbrake on, pressurise the cylinder, I start at the back so it gets easier as the job progresses
Use something like a 9/16" socket and a small hammer and just go along and give each valve cap a tap to break the grip of the tapered keepers in the cap--Now get that special tool you've just made, hook it under the rocker shaft and push the spring/cap down and remove the keepers (a little stick magnet is your friend here)and release
Remove the springs/cap
The old seal will probably stay on the valve, remove it
Get your new springs/cap ready, sit it on there and compress with your magic new tool, fit the new seal down into place on the stem, fit the keepers and release the springs/cap up to trap the seal/keepers in place
Next is 2nd valve from the back/ slide the rocker against the spring to get room on the rocker shaft for 'the tool' and continue on like doing the first one
You can do cylinders 4/1 then turn the motor half a turn, in gear ,handbrake on again and do 2/3
'IF" you do happen to push a valve open there will be quite a woosh of air, don't panic, the valve can only drop probably 3/8", just pull it back up and the air will hold it, they take a fair bit to dislodge
If you're part way through and need a break just put a spring loaded clothes peg on the valve stem and the air can be turned off safely
When you're done, slide the rockers back, turn them back over and slide back over the pushrods, same again they might need the springs/caps bumped/levered down a bit to get the rocker over the top of the pushrod
Refit the end ones and adjust the clearances
----done
It sounds a long process but once you start into it it's not too bad really and doesn't disturb the headgasket at all and you've got the rocker shaft still there to work off
Two people is probably easier, one to compress springs and the other as seal and keeper man

Hope this helps-
I guess the same operation could be used using rope instead of air, but to me the less you poke in the plughole the better

willy
William Revit

Colyn, its not much more work to take the head off rather than faffing around with rope etc. You will also be able to give the head a clean up while its off.
David Brenchley

David
I had to fit a new head gasket when the original one failed after only 6000 miles and so I am reluctant to replace it after only another 6000.
So I would prefer to leave the head undisturbed if possible.

Doess anyone have any recommendations for the best quality valve springs and should I replace the caps and collets whilst I am at it?

Cheers
Colyn
Colyn Firth

KD made a valve spring remaoval tool.It clamped on the lower coil of the spring and tightned it up to the retainer. I have always use air to holdthe valve closed.
If you are worried about dropping the valve just make certain the piston is at top dead center and leave the car in 4th gear so the air pressure wil not force the piston down. That way you can do both valves on the same cylinder without turning the engine.
Sandy
Sanders

Sandy, the K-D tool is fine,I use one sometimes but you need to extend the tips of it to reach in to the inner spring--and it's fiddly getting the seal on the stem with that tool in the way, it can be done but it's a lot easier just to lever off the rocker shaft -
William Revit

This thread was discussed between 29/08/2019 and 06/09/2019

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