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MG MGA - Occasional engine stutter

I’ve reported on this previously and had hoped that a session on a rolling road would help. The issue I have is an occasional engine stutter where I get sudden power loss and noisy engine (slight clatter best describes – no misfire) but which clears with the engine running well thereafter. This started following a professional engine rebuild including fitting an econotune cylinder head from Peter Burgess. New ignition leads, coil, electronic ignition and carb refurb saw the car recently perform well on Peter Burgess’s Rolling Road just requiring slightly richer needles. Since then the car has performed exceptionally well ….. but today within 2 – 3 miles of leaving home the stutter kicked in again. For once I managed to pull up while the engine was playing up and listened and there was a real mechanical noise occurring. After revving the engine it soon cleared and ran normal. This happened 3 times in the space of a mile or so and thereafter I able to enjoy a 40 -50 mile drive often reaching 60+ mph with the engine pulling and running sweetly. From experience, if this problem is going to occur it does so within a few mile of the start of the journey though not exclusively so, and usually when feathering the throttle not when pulling hard. Any thoughts gratefully received – with all that I’ve done chasing this problem I’m now considering something mechanical maybe a tolerance clash or initial lubrication problem.


Kevin
K Garner

Suspect a sticky valve guide.
Barney Gaylord

Thanks for the response Barney, having read your article on sticking valves it makes sense. Would there be any tell tale signs – any visual checks I could do? As a relative novice would cylinder head removal be a reasonable task to undertake?

Kevin
K Garner

When I had valve guides that were too tight, it would hang up when running at high speed with full throttle (racing conditions or passing on a highway). Let it cool down a bit or drive more casually, and it would run fine. I drove it 1000 miles in one week hoping it would loosen up, but it didn't. I finally had to disassemble it to hone the valve guides.

R&R of the cylinder head is easy enough, even for a novice. It is only time consuming, but good for sweat equity (saving labor cost). You need a new head gasket and a toque wrench to put it back together. For what you are about to investigate, a good valve spring compressor would be a BIG help to R&R the valve springs.
Barney Gaylord

Cheers Barney, thinking back to the road side situation I did get a single blow back through the carbs before the engine settled so maybe an issue with one or more of the inlet guides?

Looks like I will be enhancing my mechanical skills so thanks for the encouragement.


Kevin
K Garner

Kevin

Just a thought; you say it followed a professional engine rebuild. How long ago was that? Perhaps you still have some sort of guarantee for the work and it is up to the supplier to sort it?

Steve
Steve Gyles

Steve, without giving names out yes the engine was re-built by an MG specialist garage, probably some 18 months ago. When the car went back after the running in period I did explain the issue but as usual the car didn't play up while it was in their hands, neither did it when I recently had it on Peter Burgess's rolling road though again I explained why I wanted it tuned and the random problem I was having. Having dealt with both I dont expect to have any issues with them helping me. At the moment my plan is to remove the head and get it to them to check. As you can imagine it wasn't a cheap job in the first place.

Kevin
K Garner

With encouragement I have finally stripped the cylinder head off and will be sending it off to Peter Burgess to have checked this week. In the meantime and as a novice can I ask a couple of probably basic questions?

1. In removing the pushrods I suspect I have disturbed at least one of the tappets (no 7). Is this simply a case of removing the tappet cover and repositioning the offending tappet. Would you normally do this anyway to make sure all are in position and that the pushrods sit correctly?
2. Should I use a sealant with new gaskets for the tappet cover, heater valve and thermostat housing. I haven’t purchased a Cylinder gasket kit yet but assume the remainder are used dry?
3. While removing the head, two of the cylinder head studs released along with one of the rocker shaft pedestal studs. I suspect these were replaced as part of the engine rebuild only some 2000 miles ago so intend to re-use – do I simply double nut the studs and nip up or really tighten?
4. Once I get the head back and refit what initial setting is best for the valve clearance (my workshop manual says 17 thou hot).
5. Should I just use petrol to clean off the deposits – engine block/piston crowns, see image

Incidentally, I removed the carbs, heat shield and manifolds as one unit, not sure I will be able to replace in the same manner though.

Cheers Kevin….


K Garner

Seems your picture is flipped, unless you took it in a mirror!

My thoughts, I am sure you will get more or this wouldn't be a forum!

1. The tappets normally drop in ok, but if you are not sure then you can do that easily through the covers for peace of mind.

2. you shouldn't need any sealer with the cork gaskets, but I usually smear a bit on to help them stay in place. Hopefully the rocker cover gasket is still in good condition and stuck to the cover?

3. just nip up

4. 17 thou then readjust after re-torquing the head once hot.

5. I would probably just wipe the pistons and block to remove any loose debris.

Easy enough to refit everything after the head is in place.
N McGurk

Thanks for the comments Neil. And yes photo was flipped and now hopefully unflipped.

Kevin

K Garner

Kevin - It might be worth checking what sort of valve guide material has been used. I had my head done by an excellent cylinder head specialist and he wouldn't fit the normally recognised bronze valve guides as they have a much larger contraction rate than the cast iron head and can cause seizure. This means they require a much larger clearance on the valve stems. He insisted and very successfully fitted cast iron guides with bronze liners for me. I often get complimented on the engine's quiet tick-over.
Suggest also before you screw the head studs back in, very lightly countersink the studs tapped holes in the block to ensure there is nothing sticking up above the block's face.
I used Wellseal on all my gaskets including the head.
Pete
P N Tipping

Reactivating this post to say that following advice from the forum I checked all the pushrods and ultimately replaced only the damaged pushrod and for safety the associated follower although visually this looked un-damaged. As usual one job lead to another and another so have now fitted a single 12 volt 202 Varta Battery and Stub Stacks courtesy of Steve Gyles design. After negotiating flood waters in the local lanes today I was really impressed with engine performance so hoping this has cured my sticking valve problem – guess time will tell. A couple of questions, I set valve clearance 17 tho cold (1500 engine) do I really need to reset hot and what sort of mileage do I need to do before re-torquing the head.


Cheers Kevin
Newport Shropshire
UK
K Garner

You can re-torque the head (hot) after the first engine run at normal operating temperature. Check/adjust valves after any re-torque.
Barney Gaylord

Hi Kevin. Glad you enjoyed the performance. I had my car out today for an airing. She danced and skipped down the damp country lanes; no floods thank goodness. Exhilarating. It blew some of the dampness out off the car. Opened up the garage door the other day and the car almost melted in condensation.

Steve
Steve Gyles

Kevin:

If you fitted stub stacks, I recommend getting back to Peter Burgess' rolling road for a readjustment. The stacks should lean-out your mixture a bit so you will want to readjust for maximum power. Good luck.

M.D.
'57 Coupe
M. D.

Hi Kevin, Glad to hear you are up and running.
Two questions :-
1 Did you get any feed back or explanation as to what, if anything , was wrong with the head , and what was done to cure the problem?
2 You say you replaced the damaged pushrod. What was the damage and how did it occur?
David
D C Grahame


Hi David, I only noticed the damaged pushrod when i came to refit the head so when I first returned the head to the workshop I was still not 100% sure that I had a real problem with a sticking valve/s so it was more out of hope that I returned it. Very subjectively while I watched the head being stripped I got the impression that at least one valve, visually at least, put up more resistance when being removed. The shop asked if the engine had ever overheated, which since a full rebuild it hadn't, and there was some speculation about poor lubrication. Regardless, the guides were re-honed and the head reassembled. Incidentally the guides were bronze based made up to the shops own spec and I know there are mixed feelings about bronze guides. My suspicion was that at least one of the guides had been missed from the final machining.

The image below, see also archive post title "Push Rod Damaged", clearly shows the damage to the knuckle on the pushrod No 5, it is clear it had been bouncing around in the tappet socket, I was surprised it hadn't come entirely adrift. Visually the shaft looked perfectly straight. I've got fingers crossed that the problem is resolved and that no permanent damage done.

Cheers Kevin


K Garner

This thread was discussed between 29/09/2012 and 10/01/2013

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