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MG MGB Technical - Sticking valves

Grateful if members can shed light on a puzzle I have with sticking valves. The car is a 1966 B roadster, with a reconditioned engine (with unleaded head) fitted in 2006. A couple of years ago I had an intermittent problem with a temporary loss of power, which would recover after stopping for a minute. The cause could not be found until the poor running became permanent and could then be seen to be sticking valves. The worst was a bent exhaust valve, but two others were faulty, 1 x exh, 1 x in, with one bent pushrod. I replaced all the valves and the guides, which were professionally pressed and reamed. After rebuild, I ran the engine for 20 minutes without any trouble, but I didn't go more than half a mile on a road test before the same problem recurred. It was the same valve as the worst of the previous three (exhaust on no. 2 cylinder.) I had a new guide and valve professionally fitted and the head and all the other valves checked. The engineering firm was confident their reaming was correct. I have checked that all the water and oilways are clear, and the water pump is sound. After reassembly, I ran the engine without the rocker cover and saw that oil was present (dripping) in the rocker shaft. All the rockers feel good and move easily. After another 20 minutes running on 2 occasions, the car failed again on a road test, after 1 mile. This time it was the no.1 inlet valve. I am at a loss as to what the next step is. Very grateful for any suggestions.
I Hodges

In the early days of head conversions there were problems with certain combinations of guide and valve materials, and maybe machining. If you can (location noted) I'd say send it to Peter Burgess http://www.peter-burgess.com/

He's mentioned favourably many times here and elsewhere, he did my head a few years ago and that has been fine so far.
paulh4

I would also recommend Peter Burgess. He will solve it and tell you what is wrong.
Colin Parkinson

Any chance the shop used bronze valve guides and failed to provide for the larger clearance required for them?

Jud
J K Chapin

Mr Hodges-
I can assure you that Peter Burgess will diagnose and properly repair whatever is at fault with your engine. From my personal transatlantic experience with him over a span of some twenty years he has consistently proven to be dead honest and extremely competent. His attitude is positive and his demeanor is friendly. You won't find anyone more professional, better qualified, or easier to work with.
Stephen Strange

Thanks guys for the recommendation, I might yet have to take that up. Thanks Jud for the heads up on bronze guides. This might be the next step to explore before sending the head to the UK. I believe the replacements were bronze, and of course I relied on the engineering firm to do what was required. Stephen, I've just read your post on another thread on clearances. I'll use those numbers in discussions with the local engineering firm I used. Many thanks.
I Hodges

Valve sticking became a problem in production engines when we went to unleaded fuel. One solution was to counterbore the end of the guide slightly bigger. Effectively shortening the length of the guide wasn't too much of a problem with direct acting valvegear but with rocker operated systems there is always some side force on the valve stem. The theory was that the portion of the valve that stuck out into the exhaust port expanded when it got hot and carbon would collect in the end. When the engine cooled this would then grip the valve stem. This only seemed to be a problem with certain driving styles (short journeys starting from cold).
I believe modern engines have sintered iron guides. We know that B series has iron guides but I don't know whether they are cast or sintered. Normally Steel running on iron is good from a tribological point of view. (steel on steel is bad) Whether it's the exposed flakes of carbon in the iron or the fact that oil is retained better, I wouldn't like to say. Peter Burgess uses Brass guides (at least he did when he did my head) which are great from a heat transfer point of view but would be seen to wear out too quickly in a production engine. Having said this, I had my guides inspected after 40,000 miles when I had my engine re-bored and the guides were fine.
Paul Hollingworth

Peter Burgess uses bronze guides, not brass. He makes them himself. The work he did on my cylinder head is still good after 20 years. In my opinion there is no-one in the UK knows these engines better.
Mike Howlett

Are you using stainless valves by any chance--
William Revit

.0025" Min. stem clearance with bronze guides
.003" Min with bronze guides and stainless valves
William Revit

Mike, you are quite right, Peters website says his guides are bronze. I wonder why I got it in my head that they were brass, perhaps it was the more golden appearance rather than the brown you would expect for bronze. Whilst brass is copper alloyed with (around 35%) zinc, the composition of bronze is less clear. Traditionally it was copper alloyed with 12% tin but now silicon has taken over as the main alloying element but of course, lead, manganese and phosphorous can also be added.
Paul Hollingworth

Thanks all, my guides are not bronze but iron. I've discussed the above with my local engineering firm and they are proposing to drill the existing guides and insert bronze sleeves, which will be reamed a fraction oversize. The sleeves apparently have very small channels to assist oil retention between guide and stem. It sounds a solution. Has anyone had experience of this?

Ian
I Hodges

As long as differential expansion doesn't cause them to come loose, will there be anything to retain the bronze liner in the iron guide?

I've no idea whether that can happen or not if not retained, but it happens with steel cylinder liners in an alloy block once things get up to temperature. They are supposed to be pressed down to flange at the bottom of the alloy bores then machined flush with the top of the block. One of them hadn't been pressed down far enough before machining so could rattle up and down with the piston.
paulh4

Yes, but-

If you have new guides as mentioned earlier it must be a clearance issue, just opening up your new guides should fix it---drilling the new guides and fitting the bronze sleves is a bit weird when it's a too tight issue. I had thought it might be a mixture or ignition timing issue but sticking an inlet valve rules that out, it'd be a hot exh. valve sticking in that case -
They're doing a bit of a sales pitch at you with the oil pockets in the bronze sleves--What actually happens there is the sleeves get pushed in then they're internally knurled to expand them to make a good tight fit then reamed to size to fit the valve. The result is a semi knurled look to the inside bore of the sleeve, yes the pockets hold some lube oil but really it's just a remainder from the knurling process--It works ok but it wouldn't hurt them to be a bit more upfront about the process-
For me it just sounds like they've got the clearance too tight---they need to be looking at .002" with iron guides and .0025" if you're running stainless valves-

willy

The pic shows what a finished sleeve looks like



William Revit

I was googling around yesterday, and I found J&E motors website (well I think it was them, I forget now) and they put bronze sleeves in their iron valve guides. The thermal expansion co-efficient for bronze is typically 17 x 10-6 whilst iron and steel are 11 x 10 -6, so as the guide gets hot the interference will increase.
A friend of mine had shuffling liners as PaulH describes on his MGB V8, but then the thermal expansion co-efficient of aluminium is 22 x 10-6.
Paul Hollingworth

Ian Hodges, do it once and do it right!

Just get a professional to sort it out.
Colin Parkinson

Hear, hear Colin. Send your cylinder head to Peter Burgess. It will come back like new with no bodges.
Mike Howlett

Hi all. The material we use for MGB guides is, nowadays, known as a high tensile brass. It used to be known as manganese silicon bronze. Brass sounds a little like horse brasses and the quality connotations thereof, the UK spec is CZ135.

From the net....CZ135 is a high tensile brass which is alloyed with aluminium, manganese and silicon etc. By alloying brass with strength-increasing elements, you get an alloy that is almost as hard as aluminium bronze, but considerably easier to process. The material also has good corrosion and wear resistance.

When fitted and in use there is rapid microscopic wear which leaves manganese silicide load bearing needles which are really wear resistant and long lived. It also dissipates heat approx 2 and a half times better than cast iron.

Phosphor bronze guides wear very quickly when used with hard valve stems. eg EN52 stem inlet valves and hard chrome flashed 21/4N stainless valves. Tuftrided or plasma nitrided 21/4N stems seem ok.

Posssibly of interest I understand the EN means emergency number and was issued during WW2.

Non chrome stemmed stainless valves gall up rapidly with cast iron guides.

The material we use is gentle even on non chrome stem 21/4N valves.

I Hodges, happy to help any way I can

Peter
Peter Burgess Tuning

Thanks for that Peter. CZ135 is definitely a brass being 37% zinc, 3% manganese, 2% aluminium, trace of lead and silicon (CuZn37Mn3Al2PbSi). It's classed as a high strength brass, as you say.
Were you using this material for guides when you did the Econotune job on my head 20 years ago? I guess it was you who told me the guides were brass. I'm not worried about material compatibility with the valve stems as they were yours too. As I said earlier in this thread 40,000 miles on and guides still showing little wear.

Paul Hollingworth

Thanks everybody for chipping in, and thanks Peter for your offer, I may yet need to take that up, but, as I live in a country with one of the most expensive courier networks, the decision to send the head across the Irish Sea is not quite straightforward! Thanks Willy, very helpful.

I am inclined to agree that with the last two episodes the problem has been insufficient clearance in the new guides, but (see original post) as I had valves sticking after 13 years of trouble free use of the reconditioned engine (ie before the new guides) I had to consider that perhaps there was some other reason that may still be present. I have clear waterways, a sound water pump, and oil clearly making its way through the rocker shaft.

PS. Just realised in my OP I said the last sticking valve was an inlet, I'm sorry it's not it's exhaust.
I Hodges

Just thinking out loud--If in fact that was an exhaust valve and your machine shop guys are confident they've got the clearance right, and because you had this issue creep up on you earlier before the head work, I'm starting to think that just maybe it's a timing or mixture issue---Could it be that the mechanical advance in the dist. has seized or the vac advance pot isn't working- Is the initial timing set correctly----Also , could it be running lean, are your idle mixtures good and healthy and set using the lifting pins to get that little rise in revs as you start to lift the pins---And-the big one--Have you fitted different air filters--if so changed the needles to suit, and/or what fuel are you running-? E5 you might just get away with E10 you need to change needles

willy
William Revit

Willy, bravo! I'm pretty happy with the timing (I have a distributor based electronic ignition) which I have checked several times, and I have reset the carbs back to basics on many occasions. But I was using bling air filters at the time of the first appearance of poor performance, but since reverted as part of tracing the fault. I have to say I didn't give much thought to E5 petrol (Ireland moves to E10 next year.) I'll have to sort out correct needles. Thanks for shining a light into a dark area for me.
I Hodges

If you're fairly confident your ign. timing is all good, maybe just for a try richen your carbs up by say a turn each and go for a run and see what happens, that should be enough mixture to change it if it's mixture related.
If you go exactly a turn on the mixtures it makes it easy to return them back after testing-
Do you happen to know what needles you have in there-?

willy
William Revit

I wouldn't expect to have to change needles between E5 and E10, I haven't run the V8 on E10 much - only during Covid for a while when E5 wasn't available. It's the octane that made the difference - E5 99 being noticeable better than E5 95 used to be. If you get flat-spotting on partial acceleration then maybe, which can happen if you change from paper filters to K&N or similar, but nothing to do with the problems discussed so far.
paulh4

Just for your info Paul
Stoich
== 14.7 for petrol-lambda 1
E5 = 14.45 --0.98 lambda
E10 = 14.2 --0.96 lambda

Not sure of your laws there, or Ireland either for that matter but here straight petrol is allowed to have up to 5% ethanol, anywhere between 0 and 5%
E5 has to have 4-5%
E10-- 9-10%
Most carburetor cars seem to cope with E5 but E10 will definitely need mixture adjustments

The cars that suffer are the early mechanical injection cars like Mercedes -Porsche that just squirt out a predetermined amount of fuel
I've actually followed an early 911 on the highway at night which had the whole muffler glowing red, pulled the guy (a friend) up and told him and while we were standing there working out why--(He had just filled up with E5) the rear plastic bumper started to melt and sag onto the tailpipe and caught fire---luckily he had an extinguisher on board .
William Revit

I Hodges if sending your head to the UK is problematic you might want to look up Hickey Race Engineering https://www.youtube.com/@HREIRL

His videos on the A-series are excellent.

best of....
MGmike
M McAndrew

Willy - same range of proportions here. BP in many parts of the country has 0% even though it has to be labelled E5. I can understand a mixture change perhaps rather than a needle change, but from my seat o'pants meter even that wasn't needed, nor when we first started to get ethanol at up to 5%. The 'agricultural' nature of these engines seems to tolerate a range either side of an ideal whereas other engines may not.
paulh4

Memory lapse there Paul, Esso not BP (see attached).

Is the A-series (1275) more refined than a B-series, I can't remember, but I noticed going from (up to) 5% 95 octane E5 to 95 octane E10 that my midget ran leaner.

IIRC I read somewhere that Shell V-Power E5 used to be about 2-3% before E10 came in here, whether that's still the case I don't know.

Running Esso Esso Synergy Supreme+ 99 (E5 labelled) ethanol free 99 octane made the Midget sound (and seem?) noticeably smoother but no different in power and I never checked mpg, it was just better IMO and running richer.
Nigel Atkins

It's my age ... I don't use either.
paulh4

Just a lapse Peter, you remembered you don't use either, so no worries.
Nigel Atkins

Paul-Adjusting the idle mixture to suit E10 would be a very minor adjustment and as you say hardly noticeable at all for the average motorist, But, under load is a completely different situation and a needle change to suit is the only way to get it right-
It's more or less the same issue as fitting free flowing exhausts or sports air cleaners, a little tweek of the idle mixtures and it'll idle ok, but on the road it'll be lean, valves will run hot(and possibly stick or burn out) I've had the head off a B for a headgasket blow, and all the edges of the combustion chamber gone blue from heat, the result of a mixup at a servo with the wrong fuel in their bowser

willy
William Revit

I did have to change needles on the V8 way because of flat-spotting as the PO had fitted tubular exhaust manifolds and K&N filters when accelerating so I know the effect, and that was before unleaded let alone ethanol. Had nothing like that going to unleaded or either ethanol grade - the exact amount of ethanol being unknown of course. As said before it's going to E5 99 from E5 95 that has made a noticeable difference to smoothness, pickup and mileage, but YMMV as they say.
paulh4

looking at a different route for the problem, if the clearances are actually measured and not just feeling a wobble. I have seen some brasses allow the ex valves to stick under gentle use due to lack of oil on start up. We had this problem many years ago and the owner was ok if he took the rocker cover off and sprayed penetrant on the valves for first fire up. We discovered some relief valves don't work quite right and it takes too long for the oil to get up to the rockers. It should be within around 45 seconds from cold start up. One of the reasons we use ball bearing relief valves. This sticking in the guide does not occur with The CZ135.

I once fired up a B after a head fit with a huge airlock in the system. As soon as I speeded up on the rolling road an ex valve nipped in. As the engine cooled the ex valve popped back up, put some oil from the oil can on the valve stem, got rid of the airlock and all was fine....Phew!
Peter Burgess Tuning

Hi Peter
yep, there's a few possibilities with this, it'll be interesting to hear back what the cause is/was
You have bought up an interesting option which, trying to think of possibles, maybe they've fitted positive style valve stem seals to this head when it was reco'd
Not a fan of them on these engines at the best of times and specially on the exhausts
But then he had the issue before the head was done ,so I'm sticking my neck out from the other side of the planet and saying fuel/mixture is the most likely-but with the head being done mid-issue it could be a combination of mixture/fuel, clearances or lube
You need to go to Ireland for a working holiday
cheers
willy
William Revit

Hi Willy, we have been ok and had no problems with top hat-type seals causing seizures. As you say, an interesting one.
I would love to go to Ireland but I am not good at travelling apart from by car so stay on UK mainland , apart from going across a bridge to Anglesey or a bridge to Skye.....there was rumour of a road bridge from Scotland to Ireland being built but it does seem a little far fetched!
Peter Burgess Tuning

The top hat valve stem seals that Peter put into my head almost completely stopped the oil consumption of my engine. It had been doing 500 miles to the pint and choking anyone who had the misfortune to follow us. I re-ringed and honed the bores at the same time as having the head 'Econotuned'. The compression values of my engine went down to 130-135 psi whereas they had been less consistent but 140-155 psi before (two top rings broken). Peter had suggested re-ringing wouldn't be too successful. The car ran pretty well though for 40,00 miles like this but then developed a clacking noise from the front of the engine below 1200 rpm. After changing timing chain and tensioner, I concluded it was either a little end or piston slap so I gave in and had the engine re-bored. The gudgeon pin bosses didnt show excessive clearance so it probably was piston slap. The engine reconditioning workshop said my bores were very worn. It had done 140,000 miles by this time.
Paul Hollingworth

Thanks again for your interest and suggestions. It will be after Xmas before the head will be reassembled and tested, but I will report back then. I am having new bronze guides fitted (not inserts) and I will be fitting No 6 needles. The latter were the suggestion of the technical dept. of SU Carbs, but they were lukewarm about changing needles because of ethanol. It would be nice to change just one thing at a time to determine the cause of the problem, but I really don't want another failure so it's going to be needles and guides together.
I Hodges

Thanks for the update-Ian-?
Could I please ask---What needles were in your SU's
William Revit

Hi Ian, what air filter arrangement?
Peter Burgess Tuning

Sorry, this is a bit like theft of a topic.
But question for Peter; "is there an issue with replacing valve guides in the Rover V8?"
A friend has been advised by someone that there is an issue and they are advising lining the CI guides rather than risk replacing them!!!
Allan Reeling

William, my needles are believed to be standard 5's, same ones that were in the car when I bought it in 1977. I will be moving to 6's.

Peter, when the sticking valve problem first appeared, I was using K&N pancakes. May I confess I made no change to the carburation other than the routine tweaking. I am currently back on standard airfilters.

There is no clear start date for E5 in Ireland, it being a gradual introduction from 2007 onwards, so no smoking gun, but in hindsight, it is not fanciful to imagine that the increasing prevalence of E5 went hand in hand with the increasing occurence of my sticking valves. The problem first arose a few years back during a long fast run down the motorway. I pulled in after some loss of power and lumpy running. After a couple of minutes pause, the engine fully recovered and ran fine. I could find nothing wrong. This started to occur more often, and, to the amusement of my pals, showed itself by a loss of power at exactly (within 20 yds!) the same spot on a hill on my way home from the golf course. Each time the engine recovered and left no indication that valves were sticking. This went on for a couple of years before the pandemic. I changed a great deal on the car trying to find the cause, Each time I looked the valves were working perfectly. It is only this year did a bent valve occur.
I Hodges

It's really interesting this--It sounds like fuel starvation but then sticking valves feel a bit like that as well, I guess you've checked fuel supply during your fault search
One point----You can't afford to take anything for granted searching for a problem--you're probably correct with the needles being 5 but really you need to see it with your own eyes--You never know who/what has been in there changing things about
How far roughly from the golf club to the drama point on the hill----If it's a fairly short distance, It'd be interesting to go for a little warmup drive first and then do the same carpark-hill drive and see what happens with some heatsoak in it--bit difficult at the moment though with no head on it and hopefully when back together it'll be all good anyway
willy
William Revit

I recall many years ago someone in Australia had his MGB cut out at the same point on a bridge every morning when going to work, didn't get the resolution of that.

Also the well-known one in America where a chaps car wouldn't restart after buying choc-chip ice-cream but did after buying vanilla, or some-such.

But on an MGB whilst weak mixture or the effects of ethanol may exacerbate sticking valves the real problem is the valves themselves, not the fuelling. If it were otherwise loads of people would be having problems.
paulh4

When running on E-10, I use the AAA needles with very good success and have for over twenty years. First suggested by Peter B.

The claim is "sticking valves", but what does this mean and how was it determined? It was noted that there was one bent valve, but what was the cause of the valve being bent and where was it bent? It can take a rather significant amount of force to actually bend a valve, and I would expect to see a bent pushrod (with is mentioned in passing with very little other information) and a damaged rocker arm included with a bent valve.

It has been noted that the rocker arms seems to work properly. But, how was this decision made? If the decision was made by tearing down the rocker arm system, inspecting it visually, then measuring the OD of the shaft and the ID of the bushings, that is one thing. If the decision was made after removing the rocker arm from the cylinder head and simply seeing if the rocker arm moved freely on the shaft, the analysis might be as good--the stress from valve operation is on the underside of the rocker arm shaft and the top of the bottom portion of the rocker arm bushing. Unless they are properly inspected, a false reading may well be obtained.

It is noted that oil shows up on the rocker arms when the engine is running. Many years ago, I decided to try and set the valves with the engine running, as is done of some US cars, rather than the factory procedure of warming up the engine, then setting the valve clearances with the engine off. I quickly learned that running the engine with the rocker arm cover off allowed oil to be thrown everywhere. A lot of clean up required. Thus, is there sufficient oil flow at the cylinder head under investigation?

As I have read this thread over the last few weeks, I have wondered (as Willy recently did) whether the root cause of the problem was a fuel supply issue. But, without more accurate information on what is actually happening, it is difficult to make suggestions. However, I will agree with all of the other owners of Peter's modified cylinder heads--they are a work of art and everyone should own one once in their life.

Les
Les Bengtson

Hi Allan
No problem with changing V8 guides. We struggled for years heating heads up and panicking when we drifted in mew guides as nothing is 90 degrees to use a press. Queue my friend Terry at HMB making me a beautiful jig to press in new guides. They press in the same as MGB or Mini gyuides now. Only waited 36 years for this :)


Hi Ian
Running std needles with k&Ns will give you, most likely, a weak mix which wouldn't help 'sticking' situation if conditions were close to causing a problem....another nail in the coffin scenario. Add something like retarded ignition and you are well on the way to having an ex valve run too hot.
Peter Burgess Tuning

Ian
Still trying to think out of the square--
Before you refit your cylinder head it might just pay to measure the distance from the exhaust valve heads to the gasket surface of the cylinder head
Depending on which head you have and/or also because it's had inserts the valves may be running out of room and hitting the top of the engine block

willy
William Revit

Hi all, apologies for the lengthy radio silence, but circumstances intervened. Just wanted to let you know that the engine has been reassembled and road tested over some pretty steep hills without incident. Fingers crossed the problem has been solved. Thinking it over, there is just too little evidence regarding the last two bent/sticking valve episodes to point conclusively to any one cause, and consequently to be able to say that my new bronze guides or my no. 6 needles are the sole solution. But the car was running very successfully before I started using E5 petrol. Before you all cry post hoc ergo propter hoc, I had examined and changed an awful lot on the car before coming to believe E5 was the root cause of my problem. Thank you Willy for the heads up. But also thanks everyone for your interest and suggestions, and I’m perfectly willing to believe there were other small factors which, together with E5, contributed to the sticking valves. Thanks again. Happy motoring.
I Hodges

May have been covered before but fuel in the UK at least was always E5 or less before E10 became available. Maybe you changed from 95 to 99, as I did in the V8 with only positive changes, when 95 became E10. The roadster has always run on 99/E5. According to this Ireland doesn't have E10 yet although it is imminent https://www.breakingnews.ie/ireland/e10-petrol-to-be-introduced-at-irish-filling-stations-within-weeks-1438746.html
paulh4

Hi Ian - Thanks for the feedback on your issue
Congrats, it sounds like you have a win and as you say possibly a mix of causes, but you've looked at it openmindedly and achieved the result you deserve for doing so.
It'll be a disappointment for your golf club buddies, what will they talk about now---"He's made it to the top of the hill."

willy
William Revit

This thread was discussed between 21/11/2022 and 18/03/2023

MG MGB Technical index

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