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MG MGB Technical cylinder head/valve stem BBS discussion at MG-Cars.info
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MG MGB Technical - cylinder head/valve stem
| Hello everyone. in my never ending quest to solve an oil leak, it was the recommendation of the group last fall to replace the valve stem seals/valve guides. This is because of black smoke on start up after sittiing for a couple of days, and on shifting. Can this be accomplished w/out removing the cylinder head? Not that it is a big deal to do, just one less step is easier. While i have things removed i will also be checking the breather case, etc. Woul dit be advisable to remove the head and take it to a shop? The engine has 60,000 miles and runs great except for oil consumption. Compression tests are all good Thanks all It's getting warmer, won't be long now!!! Ken 70 B |
| Ken Harris |
| I forgot to ask. How do you get the exhauat manifold out? I can't reach the nuts attach8ing the mani. to the exhaust? Ken |
| Ken Harris |
| Black smoke is rich mixture, blue is oil. At 60,000, a valve regrind is good practice. Or go whole hog and replace bearing shells and timing chain too. It will take only the slightest grinding to return to as new condition now, but valves start to leak slightly at this point and further running causes exponentially increasing deterioration. That means a lot (more) of material will need to be ground off the get good seating later. It's hard to convince yourself to dismantle a fine running motor, but I have seen enough in all conditions to know that this is the best overall practice. It is very nice to know that such a preemptive rebuild returns the engine to as new condition with minimal expense. FRM |
| FR Millmore |
| Ken, The first thing to do is disconnect the breather pipe from the front tappet cover and replace it with a length of pipe led down to sump level - plug the old breather pipe leading to the carbs. See if this reduces the smoke and oil consumption before worrying about valve stem seals. It is common for the tappet chest to clog up over the years and allow oil to travel up into the carbs. |
| Chris at Octarine Services |
| To get to the exhaust manifold nuts you pretty much have to remove the carbs and heat shield. I guess, given enough u-joints - on both tools and personal extremities - you can reach under and get to the nuts. Trouble is, even if you can get to them you may not be able to apply enough torque to turn them. Far better to remove the heat shield. You may need to soak the nuts in PB Blaster for a bit - big surprise there, I know.... R. |
| Rick Stevens |
| Chris, i did try the breather pipe suggestion and no difference, that is why i am thinking the valves. Rick, i have taken everything off and with my - u-joints - i justy cannot get enough leverage. I can't seem to get to them from underneath either. how the heck is it done?? I have a small hole in the exhaust, so i was thinking of just taking a sawzall, and removing it from beneath the bolts, then try to get it out and remove the bolts? Ken |
| Ken Harris |
| Ken. One does not need to remove the exhaust manifold from the engine bay to remove the cylinder head. By loosening up the exhaust system mountings, mainly by removing the attachment bracket from the head pipe to the transmission brace, it is possible to pull the exhaust manifold back far enough that the manifold studs are clear of the manifold. When removing the header pipe from the exhaust manifold, I have always used a long extension and come up from the underside. Pain in the neck. Les |
| Les Bengtson |
| To remove the pipes from the manifold is just straight extensions, and a deep socket. 3/8 drive recommended. One nut may require a bit of misalignment, but a wobble extension is far better than a uj. FRM |
| FR Millmore |
| Ok gents. I have the cylinder head off, and more questions arise? The tops of the pistons have burnt carbon type deposits on the tops, and the valves are either tan in colour or burnt blackish colour. It looks like there might be anti freeze leaking in, and there is some rust colour in the drained antifreeze Should i replace the valves, and the seals or maybe just the seals? Lastly, to get the head machined, what exactly do i ask the shop to do, or should they know as a LBC shop? Thanks Ken 70 B |
| Ken Harris |
| Ken. Quite a lot of questions. Should I not be able to keep then straight, others will chime in and keep both of us straight. On the burnt carbon stuff, the Brits used to refer to this as "coke" and would refer to the removal of these deposits as "de-coking". Quite a wonderful term. Back in the "old days", it was recommended to use an old piston ring. Bring the piston to the top of the cylinder, lay an old piston ring on top of it and remove the excess build up. "Back then" it was a process of using wooden scrapers to remove the excess built up. Today, a wire brush, followed by a vacuum cleaner might be a better solution. The theory, back then, was that you needed a little build up around the outside of the piston to control oil loss. As to the valves, I would expect there to be slightly different colors. Cylinders one and four have their own exhaust port while cylinders two and three share a single exhaust port. This means that cylinders two and three run slightly leaner than cylinders one and four. Thus, cylinders one and four have to be slightly rich when cylinders two and three are correct. Not a significant problem and one which all of us have to live with. Condition of the valves, and their relationship to the valve seat, is something best determined by the machine shop doing the work. Best let them determine what valves may need replacing and if the valve guides need to be replaced. Same thing for the straightness of the cylinder head. If it needs to be skimmed, let them make that determination. As to "rust color in the drained anti-freeze" remember that most of the coolant is inside the cast iron block--other than that which is in the radiator. Very little, in relationship to the other parts of the system, is in the cylinder head. Thus, to diagnose a cylinder head problem, based on some discolorization of the coolant might be a mistake. Les |
| Les Bengtson |
| While the head is at the machine shop ask them to Magniflux it. This will indicate if there are any cracks that could be allowing antifreeze to leak into the cylinders. Doing a valve job without checking for this problem is Russian roulette. Ray |
| RAY |
| Ray. Good point. In my opinion, any time a cylinder head goes to a machine shop to have work done, it should be crack inspected before the work begins. I have seen too many cracked cylinder heads over the years for me to trust any untested head. Before anyone allows a machine shop to work on an MG cylinder head, they must be assured that crack inspection will be the first piece of work. It can save you hundreds of dollars. Les |
| Les Bengtson |
| Regarding the crack-testing, I concur with Ray. In fact I know this first hand - my head was ported, polished and rebuilt as part of a complete engine rebuild, and it leaked within minutes of starting it for the first time. The rebuilder did a visual check only, but there is definitely a crack above the #3 spark plug. I didn't realize how many MGB heads are cracked until after it happened to me! Regarding getting the manifold out of the car, I undid the exhaust pipe at the junction that is right near the bracket that connects to the bellhousing, tipped the manifold and pulled the it up out of the engine bay. I wasn't about to attempt the rusty bolts at the manifold/exhaust pipe from under the car - I broke off a few of those on my first MGB once. Maybe your car doesn't have a junction that close to the engine bay, so that may not work for you unless you cut the pipe. Erick |
| Erick Vesterback |
| Les, Ray thanks for the info. I am taking the head over to a shop today, adn see what happens. I will be sure to have them test it first. I have managed to get the exhaust/manifold out, and now that i have a clear view of the engine i removed the tappet covers as well. The gaskets were brittle and cracked, and there was a ton of oily crud built up around and below them. I thinking, hoping really, that that is where my oil leak has been from. Thanks again Ken 70 B |
| Ken Harris |
| Ken, Are you also getting the shop to install hardened valve seats for unleaded fuel? David |
| David Overington |
| David, i saw the note about hardened seals on the thread about de-coking the head. I didn't even think about that but yes, i wi8ll definately install the hardened valve seats. Ken |
| Ken Harris |
| ok so i'm trying to de-coke per les's directions, but i can only sem to get cylinders 2 and 3 to the top. the pistons in 1 and 4 just don't seem to want to move. they get half way up and just stop, no matter how hard i try to move them. any ideas? Ken |
| Ken Harris |
| Ken. Something is blocking the ability of the crankshaft and/or one or more of the pistons to move upwards. What happens when you rotate the crankshaft backwards? Can you, then, bring the pistons on cylinders one and four up to the top? If they bind at the same point, inspect the cylinder bores for rust. If they will move up when rotated opposite of normal engine turning direction (clockwise when viewed from the front), something is hitting something else inside the engine. This is getting interesting. Please let us know what you find. Les |
| Les Bengtson |
| As I understand this thread the the engine is still in the car and the only parts you have remvoed from the engine is the cylinder head and it's associated parts, is that correct? If you have removed other parts tell us which parts you removed. Clifton |
| Clifton Gordon |
| Les, the words "this is getting intersting" are not really what i would like to hear:) Clifton, you are right. engine in car, head and associated parts removed. the only other thing i have removed are the tappet covers. as i stand in front of the car facing back, the crankshaft will rotate clockwise as i described, when i try to rotate opposite direction it will not move. Cylinders 2+4 move down about an inch. then there is a sound like it has hit something. the sound seems to be coming from below the car, near the back of the engine. The cylinder walls are smooth and clean of any rust. Ken |
| Ken Harris |
| Ken. Does the crank stop only when turned counter clockwise? Or does it stop in either direction? If it turns in the normal clockwise direction and will not turn the opposite direction the cause could be slack in the timing chain allowing the cam to shift enough for a lobe to hit the crank. Since you said the engine was running OK before removing the head I would assume nothing is broken. Clifton |
| Clifton Gordon |
| Have you removed the cam followers from the tappet side covers? Ray |
| RAY |
| Ken. As Ray notes, the tappets might bind and removing them is one less thing which could cause a binding condition. However, if they were moving before, they should be moving now. Same thing for the timing chain. I had one that was loose enough that it was hitting the timing chain cover, but it did not cause the engine to bind. The engine should turn freely in both the clockwise and counter-clockwise directions. If it is not, something is binding up inside. The starter can be binding. But, when this happens, it normally does not allow the engine to be turned at all. Removing the starter and trying to turn the engine over will tell you if that is the problem. The alternator/generator and/or water pump can be seized and will prevent the engine from being turned. However, most commonly the fan belt slips sufficiently to allow the engine to move, dragging the belt across the pulley of the seized piece. Removing the fan belt and trying to turn the engine again will tell you if this is your problem. After that is where things get interesting because it will mean an internal bind within the engine block. Related to the camshaft are the tappets, the distributor drive and the oil pump. A stuck tappet can cause the engine not to want to turn over. (I would, however, have expected this to manifest itself by a valve stuck open before the cylinder head was removed.)A jambed oil pump or a jambed distributor drive could cause the engine to not be capable of being fully turned over. This would also happen if the distributor itself had jambed up in some fashion. Removing the distributor, the distributor housing (that oval shaped piece that is held into the block by one difficult to remove screw) and the distributor drive shaft would allow you to see if the distributor or its drive shaft was the problem. I would remove the distributor first, test for free movement of the cylinders, then remove the housing and drive shaft if necessary. The oil pump can only be checked by removing the sump. Between the crankshaft and cam, there are two sprockets, a timing chain, and a timing chain tensioner. If anything has come adrift within that system, it could cause a bind as a loose piece is jambed between the sprocket and chain. Inspection requires removal of the timing chain cover. The crankshaft itself offers little chance of binding unless something has fallen into the sump and is blocking its movement. The connecting rods move very close to the camshaft as the crankshaft rotates. About .018" clearance between the rod bolts and the shaft of the cam in some places. If a con rod bolt had loosened, it might be moved upwards sufficiently to strike the camshaft. Checking these means dropping the sump. It is possible that the flywheel is loose, causing some form of jamb to take place. However, the only time I had a loose flywheel, on a newly purchased car, it became quite obvious because of the vibrations it induced. More information would be of assistance in attempting to diagnose where the problem might be. Can the engine be turned a full revolution in either direction? If the bind is present in both directions, do the pistons stop at the same place each time? You mention hearing a sound as the pistons stop moving, seemingly from the back of the engine. Would it be possible to have an assistant rotate the engine while you use a stethoscope to listen to where the sound is coming from? An engine which was running properly before the cylinder head was removed should be capable of being turned over by hand easily. Hence, if this cannot be done, it becomes very interesting with a wide range of possible problems coming up, most of them requiring removal of the engine to trouble shoot. Les |
| Les Bengtson |
| Hi, take the starter out as Les suggests. If it is the pre-engaged type, it has a one way clutch which might account for the refusal to turn backwards. Sorry to be obvious, but it isn't in gear is it with the handbrake on? |
| Martin Layton |
| How stupid do i feel now???? It was in gear!!! I guess i forgot a major rule---Never overlook the obvious!! Thanks guys for your assistance, even if it was only because of a major brain cramp. Ken |
| Ken Harris |
| Good to hear it was simple. We all make obvious mistakes at times. Clifton |
| Clifton Gordon |
| Ken, There is a machine shop in Oakville that rebuilt my engine. Did a good job. I'll e-mail you the address. Ken |
| Ken Martin |
This thread was discussed between 22/03/2007 and 01/04/2007
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