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MG MGB Technical - Pulling The Head - Diagnosing Problems

My '67 GT has been burning a tremendous amount of oil lately, over a quart every 200 miles. After downhill or high speed runs, when I come to a stop and start up again I get a huge puff of white smoke from the tail pipe. A compression check showed these results: 1/160 - 2/140 - 3/140 - 4/165. Oil pressure has been good, 60 at idle, 70-75 at speed, occasionally 80 max. Head gasket is copper. The oil burning started a few months ago and has been worsening progressively ever since.

The other day I noticed oil bubbles coming out from between the head and block above the #3 cylinder. So I've decided to remove the head and check things out. I'm through removing bits for the night and in the morning the head itself comes off. So far this is what I have found...

There is a good amount of oil in the intake manifold all the way up to the carb needles. It also made it's way into the vacuum gauge hose so I assume it has been blowing back into the manifold under pressure. The tail pipe as expected has lots of soot in it.

Is there anything in particular I should be checking for at this point or when the head comes off? What I plan to do is remove the head, visually inspect the head and copper gasket and if all looks well clean the mating surfaces and put it back together again. I'm going out of town Friday morning so I would like to have the car together tomorrow night, otherwise I might take the head for magnafluxing. (I'm not driving out of town but don't want the car sitting in the driveway in pieces).

Being inexperienced with this type of repair I would certainly appreciate any advise!
Steve Simmons

Forgot to mention the car has been pinging progressively worse as well and now pings any time I accelerate or am at speed. It idles smoothly and drives quite well other than the exhaust smoke.
Steve Simmons

Steve,
From the discription of the problem I'm thinking a cracked head allowing oil to be forced into the intake manifold. Hopefully not, but have seen this before. Compression is not bad, but oil in the intake is an indicator. Blown gasket would not let oil into the intake. I would have the head magnafluxed if a crack is not easy to see. Not sure if the pinging is related or a cause.

HTH

Ron

Ron Smith

Steve,
Is this the same car that had the "red death"? The one on which I strongly recommended that solid copper gaskets were totally unsuited to use on engines that see repeated heat-cycling as in street use? And for which I believe I sent you my dissertation on headbolts and retorquing. Whether it is or that was a different car, my guess is that the oil is leaking from the rocker feed passage and is being sucked into the back two cylinders under high vacuum conditions. Then some gets blown into the inlet manifold in the normal course of breathing. Cure is a correct gasket and retorquing, barring the bad luck of a crack.
FRM
FR Millmore

Steve - I agree with Fletcher's diagnosis. While the compression readings look all right, a leak down test may indicate leakage past the gasket. I would recommend that the head be magnafluxed to check for cracks and also have it checked for warpage. You may have to get a small amount skimmed off of it to get it perfectly flat. Get a new set of studs from APT <http://www.aptfast.com/> and a Payen gasket set when you put it together. Don't use any sealer of any kind on the gasket (take it from someone who did) and torque the nuts to the values that APT sugggests, using thier lubricant. Unfortunately, you aren't going to get this done by tomorrow, so put the bonnet down and people won't know that you are working on the car in your driveway. Good luck - Dave
David DuBois

Steve,
What do the plugs look like? Perhaps something is wrong with the "mushroom" PVC valve this also would allow oil to be drawn into the intake. Pinging could be caused by carbon build up causing a hot spot to preignite and ping. Comprssion in the middle two is a bit low, but should run fine. Let us know what you find.

Ron
Ron Smith

Isn't white smoke more an indication of coolant than oil. If that is the case I would think either blown or improperly seated headgasket and/ or cracked head with water getting into the cylinders.
Lewis

This is a different car. The "red death" car was my '65 which sadly is still off the road. This one is the uk-spec '67 GT I purchased from Bob Mason. The center two plugs looked a bit more grimey than the outer two, but none were too bad. I'm going out to pull the head in a bit.
Steve Simmons

Steve,
If it is NOT a solid copper gasket, but the old style copper cased asbestos one, a careful and correct retorque might save it. I've saved a few, and it doesn't cost anything to try. At least it should improve things a bit. I would add that I never have had any trouble with the original studs and nuts, but repros get a bunch of bad reviews.
FRM
FR Millmore

I have uploaded photos of the work so far here:

http://www.lbcnuts.com/gtengine

It is a solid copper gasket. I noticed a couple spots where the upper and lower section are seperating so I guess I won't reuse the gasket. I'll get a non-copper Payen. Any sources for this gasket that I might find locally in the Los Angeles area?
Steve Simmons

Steve,
That is NOT a solid copper gasket but the composite one. The solid ones are SOLID - one piece of copper. I prefer the copper sheathed composite to all other types, but they MUST be retorqued on first heating, at 500 miles, 1000 miles, and periodically thereafter. So do all the others, although maybe not so often. Correct retorque would have prevented this. The black/greenish places are where coolant was leaking; any that go across the "fire ring" around the chambers are combustion gas leaks. There is no doubt some antifreeze in the oil. Do you still have my diatribe on head bolts and such?
FRM
FR Millmore

I believe I do, I'll dig it up today. Thanks!

I'm going to get the head magnafluxed anyway at this point since it's already off. I don't want to chance having to do this all again. I'm off to the machine shop!
Steve Simmons

White smoke is a/f or other coolant, Blue is oil and black is overly rich.

All gaskets except those marked as 'no retorque' or other wordage, need to be retorqued after the first full heat cycle and then about 500 miles after that. I retorque my head prior to the beginning of every driving season no matter how many miles I put on previously.

If you cut the bottom of the head you should try to have the top of the head cut also.

OHC engines MUST have the bottom and top cut and the cam bearing supports align bored and then shimmed to factory specs to maintain correct rocker arm patch. The same is true for 'cut' OHV engines as the rocker arms will not mate correctly and the contact angle will put undue stess on the valve train unless of course shorter pushrods are used. Correct rocker arm geometry is very important.
Mike MaGee

Steve,
Hopefully the head is OK, perhaps just a blown headgasket between cylinders. That could over pressure the crankcase and force the oil into the PVC and then the intake. Definatley HC pistons, and a standard looking small valve head. While the head is off, CC one or all of the chambers. If memory serves, stock was 43cc. Common hotrod trick was to shave the head down to give 36cc chambers. This may give an insight to the pinging issue. Overbore will add to the problem/compression ratio.

Safety Fast

Ron
Ron Smith

What I have learned from digging through the maintenance logs from the PO is that this head is using 18V Valves (72-74 intake, 68-80 exhaust). A valve job was done 8,000 miles ago (1.5 years ago) using silicon bronze valve guides. A new rocker shaft was fitted as well as valve seats, seals, shafts, etc.

My mechanic feels the silicon guides are to blame and may have been knurled too much. I gave him the complete head to send out for disassembly, hot tanking, magnafluxing and reassembly. I'm hoping this doesn't end up costing me a fortune but I really want this done properly. I do not accept that MGs have to be unreliable and so far over my 16 years of ownership I've had great luck. Well, except for one engine rebuild that went terribly wrong. But that's another story.

One additional question, anything I should be looking for while the head is off? Any tasks to perform to take advantage of the situation? Obviously I'm replacing all gaskets already and probably the thermostat, fuel and vacuum lines.

Thanks so much for all the input, it really helps!
Steve Simmons

Steve,
If the guides had been at fault, you would have had this problem long ago, likely from assembly on. Very likely, all that's wrong is that the gasket was leaking oil from the rocker feed passage into the two back cylinders, because the head was LOOSE. And no doubt was also leaking AF as well, judging by the discolored marks and the white smoke.
All 4 cylinders were leaking to/from the chambers. Both head and block show leakage of coolant.
If you do put guides in, put stock cast iron ones in.
FRM
FR Millmore

No special guides for unleaded fuel or for modern, more reliable materials? Sorry, I'm not experienced with engine internals.

One thing to note on your last post, I retorqued the head recently and the problem did not get any better. Also, this problem started as a very minor one a few thousand miles ago and has grown to be the problem it is today. I even tried overtorquing the head a few pounds to no avail. If anything, it got worse.
Steve Simmons

Probably something to be discussed by the engine gurus, but do the stud holes in the block need to be relieved slightly to prevent deformed threads (in the block, not the studs) from preventing the head being tightened fully?

I'm with Fletcher that it appears the head was loose, but you seem to have attempted to tighten it corectly. Perhaps the damage was already done?
Alec Darnall

Steve,
Cast iron is a nearly perfect bearing material; it has free graphite in it, it is porous so it holds oil, and needs only minimum oil. It expands at the same rate as the cast iron head, so clearances to valve stems can be quite close with no problem. Tight stem clearances also guide the valve better, resulting in less wear on seats. Bronzes are good IF well lubricated, which is contrary to keeping oil from running down the guides; it expands more than the head, so the clearances must be greater to keep the hole from closing in when hot. Bronze is best suited to alloy heads (expansion rates match), and situations where maintenance is frequent and there are very high speeds and loads and a bit of oil loss is OK - race cars and air-cooled engines.
It is possible that the gasket was already on the way out when you retorqued it, it appears to have been leaking for some time. Sometimes leakage will erode the filler material between the two metal bits (separate the metal sheathing and see if there are gaps in the asbestos)- this also happens on the fiber type gaskets if they are loose. The gaskets are coated with a sealant to seal small imperfections in the surfaces; the point of timely retorque is also to stop leaks from starting and destroying this sealant in places. Retorquing then pulls the head down on the undamaged areas, still leaving leak paths. Overtorquing is not good as it distorts the head and block and can make them decidedly wavey - this may or may not be permanent. It can also result in cracks or broken studs; it is unnecessary too.
Good luck!
FRM
FR Millmore

Steve,
Iron guides seem to work best in a iron head. Not sure why the bronze guides would have been knurled. Normally this is a way to get a bit more life from worn guides. On head gaskets I have had good luck with Permatex Copper Head Gasket sealer. A very light coating seals well and does not flow to important passages. Not sure if it is still readily available. It is really neccessary to retourqe heads after 500 miles or so. If the threads on the head studs are pulled up a bit in the block they will need to be recessed (large deburr tool works fine) I have also used Felpro Umbrella style valve guide seals. The stock type will last about long enough to check if they are still there.. The exact Felpro number should be in the archives. I would try and "decoke" the piston crowns to remove all of the carbon build up left over from the recent problems.

HTH

Ron
RJS Smith

Thanks guys! Is there a preferred (safe) method for decoking the pistons? I assume sand paper is out of the question.
Steve Simmons

Steve. Quite a good bit of advice you have been given here. Alec has a good point about the need to chamfer the holes in the block that the head studs go into. Brownells, Inc. offers a tool for chamfering the muzzles of firearms and the cylinders of revolvers to make reloading easier. I purchased mine when they were somewhat less expensive than now. The tool is a piloted countersink. The hole size, for a 3/8" coarse thread is 5/16". I made up a pilot from a piece of 5/16" drill rod to fit the tool and have used this on all of my engine rebuilds over the years.

As Fletcher notes, and as Peter Burgess wrote to me many years ago, the "Payen type" resin gasket is an excellent product. Mine are from Fel-Pro which lists the gasket as "Made in England". As Mike notes, retorquing is a must. My experience is that the head requires retorquing after the initial start up and check out, then at about 100 miles, 500 miles and 1,000 miles when using new gasket and new cylinder head studs. Mike suggest an annual retorquing. I have a clicking type wrench and set it to the maximum torque specification, 50 lbft, and go over each cylinder head nut, in the proper pattern, on the annual "full tune-up" prior to emissions testing. It is interesting to note how often some of the nuts will move, just a hair, before the wrench clicks. While this is not as good a solution as backing each nut off 1/8th of a turn and torquing to full specification, it has worked well over many years.

Hope you get the problem solved and, when you do, you will report back to us.

Les
Les Bengtson

Steve. My older daughter called while I was posting and two more messages happened. I agree with the fact that knurling is only used to make oversized clearances work, somewhat properly. The system is usually used when someone is unwilling to spend the money to do the job right before selling a vehicle on to someone else. It is also used when someone wants to "just get by" with a problem and not spend the money to do the job right.

As to "decoking" or decaronbizing the pistons and combustion chambers, a wire brush in either a die grinder or an electric drill does well on the cylinder head. For this application, a "cup" type brush works well and a "coarse" brush is best if you can find one. On the pistons, the common practice is to bring the piston up to the top of its stroke and to place a "used piston ring on top of it". At that point, the carbon is scraped free of the piston top, then vacuumed up, using an aluminum scraper. Try not to damage the top of the piston (one of the reasons not to use a steel scraper) when doing this. I will admit to using a brass wire brush for this purpose in the past without damage to the piston, but, I may have been lucky.

Les
Les Bengtson

Steve,
In the past I have used a wooden (orangewood scraper) to Decoke. A bit of carb cleaner will soak the carbon and get it loose. No spray, just a dripped soak. I start when the pistons are at TDC. You can then lower them a bit and wipe out the excess. Anything that will scratch the crowns are bad. After all the carbon is gone and the bores wiped out I have polished the crowns with Autosol. Not really sure if this helps but they do look nice all bright and shiney. About to find out just how duarble a MG will be, my son has now got his learners permit and after checking insurance LOL. Moms Saturn 5 star crash rated etc etc $4650 a year for a 16 year old boy. 70 mgb roadster $1075 a year. Car now has 70K original about 20K are mine. Will see how it will hold up. Time to pass the torch on the LBC's to the next generation.

Ron
RJS Smith

Steve,

Another way of making sure that you don't get any of that carbon down the side of the pistons is to put a ring of grease round the bore near the top, raise the piston and scrape off the carbon then lower the piston and wipe out the grease.

Chris.
Chris C

I like the grease ring idea and wish I knew about it when I decoked my pistons because I didn't have an old ring when I did them. I had set up a shop vac with the nozzle placed near the piston, with the vacuum running anything I dislodged was sucked up, sort of like a dentist working on your teeth.
John

Mike Magee:Please explain in depth how takeing 20th or so, off a OHV head will change the contact angle and rocker arm mate if the valves are adjusted correctly.
Ric
R E L Lloyd

Steve As an earlier thread said use a HARD wood scraper to remove the carbon but dont remove the ring of carbon in the top of the bore. As a matter of fact I have just done mine and uses the handle of my wire brush (the end that normaly aims at me)shaped up a bit. Another thing I do that others have not mentioned is to get the top of the block and the head surface spotless. I dont mean smooth and clean, I mean clean enough to eat off. I end up using asatone (not sure how to spell it). The reason being that the resin coating in the Payen type gasket can addhere to the surface better. After you have relieved the top of the head stud holes and cleaned away all the swaff blow out the holes with compressed air and wipe out all the bores again. Water etc left in the bottom of the stud holes can crack the block. Then do the cleaning bit. Also dont forget to plug the oil supply hole while cleaning (you dont want anything down the hole that can cause problems on reassembly)and remove the plug on final clean. good luck Denis
D M HILL

'Please explain in depth how takeing 20th or so, off a OHV head will change the contact angle and rocker arm mate if the valves are adjusted correctly.'

It's the valve geometry not the lash settings. I equate it with having one shoe on and one shoe off and then try to walk. With both shoes on or off your gait is normal but if one shoe is off you walk with an abnormal gait.

Same is true for the valves if the head has been cut too much. The pushrod is being forced 'over' because it is now too long to mate up at the correct angle with the rocker arm. Bob Sharp in his Competition Preparation manual included some excellent drawings in describing the problem when cutting a head to raise the c/r for racing purposes. The same is true for street heads which have been cut too much and I've seen quite a few like that.

He suggested 2 ways to combat the problem 1 was to shorten the pushrods or 2 to use shims under the rocker assembly. Incorrect valve geometry causes a lot of wear.

One more thing - Torque Wrenches

No one torque wrench is good for every purpose. a 1/2" torque wrench with a 20# - 160# torque range is not good to use for torquing heads at 40 or 50#. A torque wrench has limited accuracy at either extreme of its rated capacity and is only really accurate in the 50% between its ratings thus a 1/2" torque wrench will not be very accurate at 40 or 50#.

I use a 3/8" drive rated at 15 - 80# to torque my heads. The pull must be at least 15# for any accuracy in torquing up the initial installation of the head.
Mike MaGee

Head is going to be done in a few days... any tips on painting? Is it best to primer first or just shoot the main coats?
Steve Simmons

Pulling the head!

Pulling!

Head!

Fnarrr! Fnarr!
Finbarr Saunders

Finally heard back from the machine shop. The head passed the magnaflux, yay! The guides were found to be silicon bronze and were the culprit in my oil problem. The previous rebuilder may have knurled them a bit much apparently.

He is going to surface the head, install cast iron guides and machine the top of the guides for "hat seals". Finally he will be machining a 3-angle valve seat, if memory serves.

Does this all sound good?
Steve Simmons

Steve,
Glad to hear the head was OK. Again can't think why the guides were knurled in the first place. If clearance was a problem (too small) then they should have been reamed. Knurling is used to make a large hole smaller. The hat or umbrella seals are what I meant by Felpro style. They will last much longer than the original style. Ask the machinist to CC the chambers, it is alwasy nice to know how far the head has been skimmed in the past. 3 angle is the best for valves. As to paint, I just sprayed the Moss MG red/maroon on the clean head no primer.

Safety Fast

Ron
Ron Smith

Steve - I would highly recommend new studs be installed before you replace the head. I like the ones from ARP, available from APT <http://www.aptfast.com/> click on APT parts then on B series and then Fasteners and components. These studs are about one grade up from what is available from other places. Good luck - Dave
David DuBois

I will repeat that I have never had a problem with original studs/nuts on all the cars I've done, even some that were pretty badly pitted that I wanted to replace but didn't have parts for. But 1/8 thick hardened washers are most desireable - the Moss HD ones are OK.
FRM
FR Millmore

my 2 cents FWI: 1. Great to have the picture record to eyeball for clues. Very nice job. 2. Lawrie Alexander recommends a slight smear of silicone on the outboard side of the head gasket ( sparkplug side) and two strands of #18 wire spiralled together and set on the outside between the edge and water jacket about 15 inches long when twisted. He did this on an engine built for me 7 years ago, and it has never exuded any coolant. I thought it hookey at the time, but now use that rig and copper head gasket spay on every head gasket change. I'm unaware of any head gasket that does not require retorgueing at 100, 500, and 1000 mas or menos. Finally: 3. If you can't afford ARP head studs, at least go with the Brittex, or Moss stock replacements. I've measured many thousnads of stretch in old head studs. Makes little sense to me to reuse the stock studs given the effort of having to redo it later
vem myers

Thanks guys. I'll probably pick up new studs unless I can find a receipt for the ones in there and it shows they are new-ish.

Sorry for the delayed response. I've been running from a hurricane for the past 27 hours.
Steve Simmons

Call ARP directly and they'll be cheaper. I just bought a kit for $95 plus shipping, but I do get a discount as a very repeat customer.

It should be noted that the kit comes w/ 4 5/16 3.75" studs which would not allow my aluminum valve cover to seat correctly. I called and they sent me the factory length which is 3" for the 2 middle rocker studs.

1-800-826-3045.
Mike MaGee

Steve,
Hopefully the creek won't rise to far. The ARP part number is 206-4202 BMC B-series head stud kit w/12 point nuts and washer. 190,000 PSI. Also try Summit racing and some of the others. ARP is more popular with the V8 hotrod folks but any big retailer will be able to get this part number as a special order. Usally much cheaper than Moss etc. I have a set on the 18GB engine you saw. Be sure to oil the threads slightly per directions when you torque them down.

Stay Safe

Ron
Ron Smith

Thanks! If my old studs have 20K miles on them, should they be replaced? Looks like that's how long they have been used.
Steve Simmons

Got the head back today, still waiting for studs and gaskets to arrive. The head is a thing of beauty! Thanks to all who offered advise. Maybe I'll post some photos when I start putting it together.
Steve Simmons

Steve,

Is your head inserted valve seat ?
Renou

It had hardened seats already so we left them in place. It was also machined to 3-angle.
Steve Simmons

This thread was discussed between 18/08/2005 and 08/09/2005

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