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MG MGB Technical - Distributor drive setup
| I think all you members who are our main source of advice will remember my problems .I did find the Valve Timing out and hopefully putting this right will sort my problems out. I have now all the parts and i have started putting every thing back together again. I have fitted New timing chain and tension-er the cam looks like it is a Standard one Re checking with a DTI gauge. The Question i have is with the Crankshaft key-way at 12-0 clock the Camshaft key way at 2-0 clock as per book for Simplex chain replacement. In which position should the distributor key-way be. I have not had the cam out so there should be no way the Distributor key way should be 180 degrees out or have moved, but with the crank shaft and cam shaft in these position's my rotor arm is pointing at no 4 segment in the distributor cap which seems to mean the distributor drive is 180 out but it was not out before strip down No 1 plug lead was where it should be IE at the 2-0 clock position looking from the drivers side. Knowing me i will be having a senior moment regards Tony |
| A Basham |
| A Basham, the distributer was not taken out of the engine, when you replace the timing chain and cover manually turn the crank so number 1 piston reaches TDC,test this with a wooden spoon in the spark plug hole,the rotor arm should then point to number 1. hth phil |
| phil |
| No the distributor was not removed neither was the cam. This is what i cannot understand . The Head is still off the engine. I put the Timing chain on as per book. You cannot get the camshaft wrong as there is only one position that the dimple is in the correct position,and the key-way at 2-0 clock. But as i say with No1 piston at TDC the Crank key-way is at 12-0 clock and the Camshaft Key-way is at 2-0 clock re book. But the rotor arm is pointing to N04 segment in the cap. Is it that i am not on the compression stroke, should i put the DTI gauge on N01 pushrod Inlet turn the crank until it opens fully(Induction) the piston should then be coming upwards (compression) then at 7 degrees BTDC the rotor should be in the correct position . regards TONY |
| A Basham |
| The distributor is driven from the cam, and the cam rotates once every 2 crank revolutions, so if the pulley marks line up, the cam is as timed as it ever was on leaving the factory.(Most people recommend fine timing the actual cam events, using one of those bent woodruf keys) If the distributor points at the wrong segment, it must always have done so provided that you haven't dismantled the distributor, pulled the drive gear out or removed the cam. To correct it, you have to remove the distributor guide bush, then pull the gear out using a bolt in the threaded centre hole. Replacement is a bit trial and error as it turns as it meshes with the cam. There is a picture in the manual of the correct position for the gear. It really doesn't matter where the rotor points, as you can always move the leads around in the cap. At TDC the rotor points to the cylinder with valve clearances (1 or 4) |
| Martin Layton |
| Tony- It is possible that the distributor was 180 out when the cam was mis-timed. In other words the cam was 180 plus or minus something out from where it should be. No matter, you need to get it correct now. All turning of the engine is in the normal direction of rotation. Since the head is off, position #1 piston at TDC, Crankshaft/timing cover marks should be lined up. The frontmost pushrod is #1Exhaust, the second pushrod is #1 Inlet. Since you are working with #1 inlet, turn the engine until it - second pushrod - is fully up/open. The engine will now be at approx 110deg after TDC, the piston will be going down, and it will be approx 1" down the bore. Continue to turn the engine until #1 piston is all the way down, then back up to 7 deg before TDC, by the timing cover marks. This is the #1 firing position. The rotor should be pointing toward #1 cylinder, about the two-o'clock position, with the distributor vacuum advance pointing nearly straight up. If it is not, you need to reposition the distributor drive. Remove distributor and clamp plate - two bolts. Remove countersunk screw. Screw a 5/16-24 bolt about 4" long into the distributor drive gear. Pull the drive housing out. Pull on the bolt to remove the gear. You will note that it turns as you remove it. If the rotor was pointing at #4 plug lead, turn the gear 180deg. The slot should be pointing about 3:30, with the big segment upmost. As you push it in it will turn; The drive should wind up with the slot pointing at 2 o'clock and inline with the two bolt holes that secure the drive housing. The fatter segment will be on top. Reinstall the drive housing & bolts. The rotor should now be pointing at #1 cylinder. Set the advance unit back from straight up, and turn dist. clockwise until the points just open. Tighten the dist clamp bolt. The timing is now set static, check dynamic after you start it. FRM |
| FR Millmore |
| Tony, Don't take anything apart! If you didn't take the distributor out, nor the cam, then the distributor must be in the same place relative to the cam (because you haven't moved it). And unless the bad cam timing was 180 degrees out (!) then the distributor cannot be 180 degrees out. My Haynes-book-of-jokes says that No1 will be at TDC on the compression stroke when the dots on the camshaft and crankshaft sprockets are aligned and next to each other. It follows that if No4 is at TDC on the compression stroke when the crankshaft dots are aligned by the camshaft dot is around the other side (if you see what I mean). Neil |
| Neil Lock |
| Neil The cam could well have been out 180 (at cam = 360 at crank) plus or minus the error, and the plug wires rearranged to suit. That means that if Tony is trying to get it all back to original spec, the drive must be repositioned. FRM |
| FR Millmore |
| Did You change the rotor?On some the retaining pin is positioned 180° diff. Dirk |
| D. Van Ussel |
| Whoa, Guys. Listen to Neil. The timing marks on the crankshaft sprocket and the camshaft sprocket do not indicate top dead center, compression stroke, on cylinder number one. It has been a couple of years since I last had to rebuild an engine. From memory, the information Neil provides is correct. The dizzy drive is 180 out when the dots are aligned. Install the cylinder head, leave the rocker arm cover off. Rotate the engine until the second valve from the front (intake for number one cylinder) begins to close. Install the dizzy and see where the rotor is pointing. I suspect, as Neil suggests, that, at that point, the distributor drive gear will be in the correct position. I, recently, had to replace the timing chain on my 68GT, which had been fitted with the simplex chain, gears, crankshaft pulley, and timing chain cover from an 18V engine by a previous owner. (Wonderful difference, by the way, to be able to do dynamic timing without crawling under the car to do so. Highly recommended conversion.) Replaced the simplex gears and chain with the "proper" duplex chain. Replaced the timing cover gasket and oil seal. Timed the car as per my tech article on www.custompistols.com/ and had no problems. Do not think there is any problem here, except for lack of experience with MGB engines. That is corrected by practice. Most of us "learn while you go". Pay attention to what is happening, try to make sense of what is happening, and, if you do not understand what is happening, let us know. We can, perhaps as Neil has, better inform you. We, all of us, started not knowing anything. We have, as a group, learned from out mistakes and those others have made and posted. None of us are particularly special. We have learned to do a number of things on our cars, and, do them correctly. We pass on what has worked for us, hoping that others may learn more quickly than we have. Doesn't take much. Les |
| Les Bengtson |
| Les- Whoa yerself. When # 1 inlet "begins to close", that is just past full inlet open, (but it IS further down the bore than I state above, a bit past half way in fact) or about 110ATDC, the piston is still going down on intake, and is not yet to BDC. If the dist is now at #1 firing position, you are in trouble. What I detailed is correct, you want to go past BDC until #1 inlet is fully closed, then up to your chosen static advance before TDC - that is #1 firing point. Also as I stated, if the cam was out one full crankshaft turn, or 1/2 turn at the cam, plus any cam timing error previously, and Tony now has timed the cam correctly and not a half turn out, then the rotor would now be pointing at #4 when it should be pointing at #1, which is what Tony is trying to fix. That explains his puzzlement. I no longer trust aligning the timing marks "by the book" to determine firing point, because I've found a number of times that the book references are unclear or flat wrong as to whether the marks represent #1 or #4 firing point, or if they represent any firing point at all. My procedure makes no reference to the cam timing marks for that reason. I am assuming that he now has the cam timing correct. Since I am in fact not "lacking in experience", I do not depend on anybody's marks or explanations for anything other than a place to start, checking all events by first principals. Experience proves that there are frequent errors and ambiguities in published directions or the understanding of them. FRM |
| FR Millmore |
| 'Whoa' everybody! If the timing marks are aligned, then the distributor drive should have the larger segment uppermost. If the larger segment is lowermost (I've invented a new word!) then you can either (i) turn it around or (ii) move all the plug leads around 180 degrees. Someone could have timed the engine 180 deg out, but why? Lining up the dots may not be the gold standard when it comes to timing the cam, but it works. Someone could have put the distributor drive in the wrong way around, which is more likely. Someone could also have dismantled the distributor and put the drive dog on the wrong way around. It doesn't really matter. Tony: - line up the dots. That'll put No1 at TDC on the compression stroke (I've checked Leyland Workshop Manual too). The rotor should be just after No1 on the distributor cap, assuming that the distributor timing was right before you took the engine apart. If the rotor is pointing at No4, and all the leads are in the right order, then the cam timing must have been 180 degrees out as you say you haven't moved the distributor. So either change the position of the drive gear or move the plug leads around two positions. Same effect, one task much easier than the other! By the way, which way is the vacuum canister pointing? Neil |
| Neil Lock |
| Neil- The crux of the matter, back in the mists of time, was that Tony's engine -bought rebuilt by unknown persons -ran like a pig. This was clearly a cam timing issue, by the symptoms he described. If they got the cam timing out, as they evidently did, then it is quite possible that they also had it 360 crank/180cam out, in addition to the poor run error, but with the dist installed to make it run with whatever they did to the cam timing. We know that moving the plug leads would rectify the wrong fire point error, but Tony either does not, or simply wants it "right". I decided to sidestep that issue and tell him how to get it back to the factory configuration, when it would then hopefully match the "book" instructions for dist. setup. FRM |
| FR Millmore |
| I have a cam in sitting in front of me, I have photographed the cam showing it's approximate position when the chainwheels are installed with the timing marks aligned as shown in the Haynes manual. Those photos are in my Yahoo photos and can be seen here. http://new.photos.yahoo.com/flash1929/album/576460762389000035 Note the chainwheels and chain in the copy of figure 51.3 from the Haynes manual. The cam key-way is pointing to about 10 o'clock. Rotating the assembly to it's normally installed position will place the key way to approximately 1-2 o'clock as specified in Haynes and the MGB shop manuals. Now look at the photo of lobes 1,2 and the cam chainwheel key-way. The photo shows number 2 lobe(intake lobe) would be opening number one intake valve and is beginning the intake stroke. The keyway is clearly visable in the photo. Consequently, the engine is NOT at TDC of the compression stroke when the chainwheel markes are aligned. Look at the photo of lobes 7 and 8. Notice that the base circle of both lobes is pointing up. This would indicate that number 4 cylinder is at TDC on the compression stroke when the chainwheel timing marks are aligned. I have also shown a photo of the cam in the approximate correct position to show I'm not inventing anything. What Tony has observed is correct, turn the crankshaft one complete turn and number one cylinder will be at TDC on the compression stroke. This problem has come up in previous threads when people installed a timing chain and didn't move the crankshaft before installing the distributor drive, they think there is a problem because it appears the distributor 180 degrees out of phase. Before someone reminds me Chris Betson's frequently asked question on installing the distributor gear reads differently, I'm aware of that, in this case he has the wrong valves showing clearance. It should read the valves in number 1 cylinder will have clearance. In the Haynes Manual on page 50 section 63 I quote in part "1. Ensure that the crankshaft is turned until No 1 piston is at TDC on the compression stroke." I haven't seen anything in Haynes or the shop manuals that states when the chainwheel marks are alighed the engine will be a TDC on the compression stroke. If it's there, where? Hope we haven't confused Tony too much. Clifton |
| Clifton Gordon |
| Clifton. Like you, I decided to find out for myself. None of my manuals, including "The MGB Handbook" by Stuart Turner and John Organ, give any information on where the engine will be when the dots on the camshaft and crankshaft sprocket are aligned properly. I remember reading, but do not remember where, that it was number four cylinder on the compression stroke. Just took a spare engine and aligned it to top dead center on the compression stroke for number one cylinder. Then, I pulled the crankshaft harmonic balancer and the timing chain cover. The woodruff key is pointing upwards on the crankshaft. The timing mark on the camshaft sprocket is 180 out from the normal installation position. This put the distributor drive shaft 180 degrees out. Thus, this is situation normal, from both of our studies, and the "problem" will correct itself when the engine is rotated so the number one cylinder is on its compression stroke. No worries. Les |
| Les Bengtson |
| Clifton, Les, et al: My original explanation in this thread was chosen because: Tony had the head off and could not therefore easily examine multiple valve events, he was confused, he was setup and comfortable with a DTI on #1 intake, AND, as I observed in another post, this ambiguity, error, misunderstanding or whatever re TDC, timing marks, valve events, and distributor position has been around forever. The problem was impressed on me in my first experience with cam timing, c1960, when 15 or so "experienced grownups" could not make a 1950 Mercury run, because the marks on the gears were wrong - in fact there were two contradictory sets of marks and they were using pairs consisting of half of each set, or sometimes the factory marks. I as a 14 year old had to point out that this needed needed some exploration, and the argument went on for two weeks, much as this one is about to. In the end, they did what I said they should, figured out what was actually HAPPENING with piston, valve and distributor position, moved the gears, and started the car. Turned out the factory marks were wrong, the non-factory pair correct, and any combination of factory and non-factory also wrong. You will note that in my original post, I made NO reference to the timing marks on the sprockets, since Tony was sure he had those correctly aligned; but only to those on the timing cover, Actual TDC by the piston position, and the operation of #1 inlet, and the distributor position. It sounds as if everyone is arguing with my explanation, and confusing Tony in the process. If I'm incorrect, show me. And I think everyone who is involved here should go back and read Tony's earlier posts/threads as there is additional relevant information which does not need my repeating. They have fallen into archive heaven, but all involve low vacuum readings and poor running. Sorry I don't have the links. BTW, Clifton's link gave me a cutesy message about "we're sorry, something awful has happened", but no pictures. I love computerish. FRM |
| FR Millmore |
| Sorry for causing a little disagreement with members . To be honest both of you are correct i know this sounds silly but this is what i have found. When the crank and cam are set as per book the rotor arm IS pointing towards No4 segment in cap like i said. But this is not the compression stroke NO1 cylinder as one of you has stated. I found this out by putting the head back on and finding the compression stroke No1 cylinder by using both of your method's, plus using a compression gauge. When an MGB engine is on its compression stroke No1 cylinder the cam shaft dot is at the other side IE approx 1-o'clock IE not lined up with the crank dot as when installing the timing chain Re the manual. I really do believe either Haynes or BLMC should have pointed this out But what FR Millmore said is correct i was in a real state at the beginning . I think this engine was assembled by a blind orangutan and i did want it back to factory spec as he stated. In my first thread i found all things wrong. Low Hg at idle, bad idle, Low compression's plus wrong Dizzy everything set up wrongly (I have held up my hands that if i had listened to him and other members i would have spent less money ans saved myself worry and time) because i had a bill for an Engine rebuild i would NOT accept that the cam timing was out. Please don't fall out as we rely on people like yourselves helping people like myself out. You are all invaluable to this Forum and i think in the end all of your comments have helped. At the moment things seem to be going OK now the valve timing is correct even though i haven't got the carbs back on (waiting for a thin flange inlet manifold)the compressions have already gone up from 150 psi to over 170 Psi. The vacuum reading at cranking has gone up also. The ignition timing that was set at 7 degrees BTDC before i reset the valve timing. Was at approx 23 degrees Btdc when i had put the valve timing back correctly. Don't know how far out that would have acquainted to valve timing being out, i thought at least one if not two teeth. I have now set the ignition timing back to 7 degrees. Have put the new rocker shaft assembly ,Push rods and tappets back. I am just waiting to get the correct manifold and then the carbs back on and i hope it starts up OK and then fine tune and fingers crossed with every ones help will have sorted it out. But the previous owners bodging has reared its ugly head again, as the heater valve bolt holes in the head are stripped and the bolts fitted are far to long. Lets hope he hasn't gone into the water jacket. Again many thanks for EVERY ONES help and time without you all. I would have either sold the car or still be struggling cheers every one TONY |
| ANTHONY LINDSEY BASHAM |
| FRM; I have no argument about your procedure. I did read Tony's original post several times. My post was made because of Neil's last post quoted in part. "Tony: - line up the dots. That'll put No1 at TDC on the compression stroke (I've checked Leyland Workshop Manual too). The rotor should be just after No1 on the distributor cap, assuming that the distributor timing was right before you took the engine apart. If the rotor is pointing at No4, and all the leads are in the right order, then the cam timing must have been 180 degrees out as you say you haven't moved the distributor." The information in his quote isn't correct, Aligning the dots on the chain-wheels doesn't place the engine at TDC compression stroke, it's at the beginning of the intake stroke. Consequently the distributor should be aligned with the no. 4 cylinder firing position because no.4 cylinder is a TDC of the compression stroke. Tony's distributor timing could be off from the normal position, but not 180 degrees as he said in his post. With 9 teeth on the distributor spindle it could be off by one or more teeth. Your method would get it correct. My photos are supposed to be open to the public, naturally the link works for me. I'll try sending them through your email address or inviting you to see them. I just made some photos of the cam laying on my desk oriented in the approximate position it would be with the chain-wheels dots aligned. I don't have a spare cam chain-wheel to make a mock up. Clifton |
| Clifton Gordon |
| I see Tony posted as I was writing this post. Good to hear you figured it out. Clifton |
| Clifton Gordon |
| Tony, Wonderful news! Congratulations, and we hope, happy motoring soon. As I suggested off board, don't trust anyone but yourself, and check his work too! Don't feel bad about getting into this kettle of fish, I've done it a few times too. It can be a really good learning experience! Your original cam timing was one tooth out - late = 18deg, plus your static advance = 7deg, total 25deg, close enough to the 23 you measured for spark after the correction. I will recommend to anyone that you do what Tony did here, namely measure and record things before you take it apart. That way you know what's different if it works (or doesn't!) when you are done. Tony, it is likely that the heater valve bolt holes are just a bit buggered due to the excessively long bolts, and can be cleaned up with a tap. Worst case calls for a helicoil. If it has gone into the water jacket, some thread sealer will fix it, many cars have similar bolts going into water by design. Again, congrats and kudos, FRM |
| FR Millmore |
| Clifton, Referring to the method of refitting the distributor drive gear, p50 of my manual says "Ensure that the crankshaft is turned until No 1 piston is at TDC on the compression stroke [describes how to do this by observing valve gear]... Alternatively, and if the timing cover is removed, ensure that the dots on the chainwheels are adjacent and in line". My Leyland workshop manual says on the same subject, on p67 , "Turn the crankshaft until No 1 piston is at TDC on its compression stroke.... If the engine is set so that the groove in the crankshaft pulley is in line with the largest pointer on the timing chain cover, or the dimples in the crankshaft and camshaft are in line, the piston is exactly at TDC". That's where. If the manuals are wrong, and assuming many people in the UK will have replaced the timing chains in accordance with the manuals, then there is a good chance that there are plenty of cars in the UK with the leads displace by 180 degrees... As I said, it doesn't matter. Neil PS I hope that we are not all actually violently agreeing on everything apart from the numbering of the cylinders??? No 1 is at the front, right? |
| Neil Lock |
| Tony. Well done. As to causing disagreement, we have no problem with that. As long as it is done in a polite manner, everyone learns from the discussion and, quite often, information is pointed out that will be of use in the future. Glad you did not sell the car, but decided to struggle along and correct the problems. It will give you an excellent basis for understanding how things work. It can be a steep learning curve at times. However, I have found it a source of great satisfaction over the years and hope that you will both continue and find equal satisfaction in what you have accomplished. Again, a fine job and one to be proud of. Les |
| Les Bengtson |
| Many thanks every one i wont count my chickens until i have it running properly . I will say that thanks to every one on the site another MGB may be saved. And yes i am glad i stuck with it and with everyone's help hope i have won. I have told some members that i am having a lot of trouble with ill health and all the treatment and medication was making me forget the simplest of things . You would never have guessed it by some of my questions i asked but i was a time served engineer. But medication and to be honest sitting about vegetating i have lost most of my skills. And even though i may not use the car often it has made me realise how important it is to have some hobby to keep the old grey matter working it came as a shock how much i had forgotten and how easy it is to get to this state even emailing between different people talking about their own cars and work has helped Thanks every one Regards Tony |
| A Basham |
| Neil; No 1 cylinder is still in the front. I stand corrected on what the manuals read. Haynes did a good job until they mention that with the timing cover removed to ensure that the dots on the chain-wheels are adjacent and in line. The shop manual leaves out adjacent. I agree it makes no real difference as long as the distributor is correctly wired. It doesn't only happen in the UK, I have seen several USA threads on this subject, I'm sure it will come up again. Have a good weekend. Clifton |
| Clifton Gordon |
| My Leyland Workshop Manual *shows* the dots as being adjacent to each other, with arrows! Can't be much more specific than that. However it says the crankshaft *keyway* should be at TDC, and shows it at the top. Whether this equates to pistons 1 and 4 being at the top of their stroke I don't know for sure, but another diagram indicates that it is. Haynes has a similar diagram and a photograph of the gears in this position 'correctly assembled and ready for fitting'. I did have vague recollections of mention of both manuals having something 180 degrees out, but couldn't remember if it was the crank gear, the cam gear, or an erroneous memory. Even if you *do* get the camshaft 180 degrees out, you can *have* to end up with the distributor in the correct position if you follow the instructions for inserting the drive gear. Again Haynes says the gear wheel dots should be *adjacent* and in line although the Leyland Manual just says 'in line', but both say it No.1 piston must be at TDC on its compression stroke (i.e. irrespective of where the dot on the cam gear is) before you can turn the gear to the correct position for insertion such that when fully inserted the drive slot is in line with the distributor clamp plate bolt holes (5-main bearing engines) with the larger segment uppermost, i.e. the slot below the centre-line. So. Where *is* the dot on the cam gear when No.1 is at the top of its compression stroke? Bottom left or top right? |
| Paul Hunt 2 |
| The crank is at #1 & 4 TDC when the keyway is up. Look at it! The engine has two points in a full cycle (4 stroke cycle engine!) where #1 is at TDC, only one is the firing point/end of compression stroke. #1 is at the top=end of compression and at firing point when it is at TDC AND both valves have clearance. If both valves on #1 do not have clearance at TDC, then those on #4 do, and it is at #4 firing. Look at it! As stock, without any errors on anybody's part, the engine is at #4 TDC/firing when the dots are aligned to fit the timing gear. That's why the book say then to "turn the engine until #1 is on TDC compression", when the valves on #1 will both have clearance AND the timing dots will NOT be in the fitting position, rather the cam one will be top right, again in line with the centerlines of crank and cam. The dist drive is installed when the engine is at #1 firing, NOT in the position where the timing gear is installed -Why? - beats the hell out of me, and always has. I've made the mistake a number of times myself, because this does not make sense. All this confusation and dithering and poor writing and more poor reading and the known incidence of wrongly marked gears is why I said "go to first principles" in above posts. FRM |
| FR Millmore |
| I just completed a valve job on a '90 Trooper and it was the same. With the gears alighned and the timing marks at 12 o'clock # 4 is at TDC. Ray |
| RAY |
| So the only error in the manuals is in Haynes which says the dots will still be *adjacent* when No1 is at TDC on its compression stroke. However the Leyland Manual is causing confusion be saying/showing in-line *and* adjacent for fitting, and only 'in-line' omitting the word 'adjacent' for fitting rather than being more specific. |
| Paul Hunt 2 |
| Paul- Now you've got it. The trouble is, there are other manuals, and sundry revised versions, and versions of the procedure written by folk who have been in the middle of discussions like this - who knows what the reader gets from the writer, who got his method from reading, most likely? Or the writer who is a better mechanic than reader/writer, who knows exactly how to DO it, but forgets that ambiguities really throw those who haven't done it. Then you add in unmarked sprockets/gears - which I've seen, and wrongly marked ones, which I've also seen. First principles! (a term I think I got from you, BTW - Thanks!) FRM |
| FR Millmore |
| Improperly marked sprockets? Who ever heard of such a thing. Ray |
| RAY |
| For more on how these things happen -as if we need any more!!! - and who starts them - see my comments on the Magnette board under "timing problem" FRM |
| FR Millmore |
This thread was discussed between 06/02/2007 and 12/02/2007
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