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MG Midget and Sprite Technical Timing a Cam Without Dial Gauge BBS discussion at MG-Cars.info
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MG Midget and Sprite Technical - Timing a Cam Without Dial Gauge
| Evening, Does anyone have any good tips for timing a cam using only "basic" tools. i.e. without a dial gauge? I can find TDC and upto +/- 20 degrees TDC with the markings on the timing cover. Can I go from there? I have a thought on how to do it, but will see if anyone has a tried and tested method. Cheers all, Malcolm |
| Malcolm Le Chevalier |
| And to make it more of a challenge, I don't have any rocker gear on the engine either! :-) MLC |
| Malcolm Le Chevalier |
| Malcolm. All of the cams I have checked have been within plus or minus two degrees of being correct. Without the use of a dial gauge, I doubt you are going to be able to measure with sufficient accuracy to notice any problems. In fact, the lack of accuracy of the various other methods might well lead you to believe that there was a problem where none existed. With a dial indicator, you zero the tool during that period, which lasts a number of degrees, that the piston is at the top of its stroke. Then, you continue to rotate the crankshaft, in the correct direction of rotation, until the piston is coming up to the top of its travel again. When the piston has risen to the point the dial indicator is showing .001" less than zero, you mark the crankshaft pulley. Then, you continue to rotate the crankshaft, in the direction of normal rotation, until the needle reaches zero, then just drops down to minus .001, at which point a second mark is made on the crankshaft pulley. In theory, top dead center of the connecting rod/piston combination is midway between the two marks. The only other method of determining top dead center is through the use of some form of piston stop (e.g. a bolt through the spark plug hole or a strip of flat metal bolted to the top of the block with a bolt attached to form a physical stop, not allowing the piston to rise in the bore). In such cases, the crankshaft is turned in the direction of proper rotation until the piston hits the stop and a mark made on the crankshaft pulley. Then, the crankshaft is rotated the opposite direction until the piston hits the stop again and a second mark is made. Again, in theory, the true top dead center is midway between the two points. However. With the second method, the accuracy may be considerably less than the use of a dial indicator. Also, by rotating the crankshaft in a direction other than its normal rotation, some degree of slop will develop in the exact camshaft position (due to slack in the chain, tensioner, and worn gear teeth). Also, there is some degree of force involved since you have to feel the stop prevent the movement of the piston (or think that you are doing so) which might lead to an inaccuracy of several degrees in your determined top dead center reading. Thus, I consider the physical stop method of sufficient accuracy to obtain a top dead center reading for purposes of ignition timing, )where there is commonly five degrees of allowable variation in the specifications), but would not use it for the purpose of cam timing as the inaccuracy if the physical stop method may exceed the common inaccuracies of most cams. Les |
| Les Bengtson |
| You need the cam timing figures, and put the rocker gear back. If the cam timing is symmetrical, then just set the overlap cylinder - normally #4 - valve clearances at some wide number like .045, so that you have about .010 when they are at overlap. If the cam is not symmetrical, you can work out where the overlap will be equal, usually about 5-10 deg off TDC. Then when the overlap valves have equal clearance you are at TDC or whatever offset you have come up with. The BMC books used to give this procedure, but I do not know if 1500 books still do. FRM |
| FR Millmore |
| What do you mean by "timing the cam"? If you just mean installing it the correct way up, like they did in the factory, then that's easy. If you mean making sure the timing is absolutely perfect, then you really need to unlock that wallet and buy a dial gauge. The issue with cam timing is that sometimes the cam lobes, keyways, and timing gears are ground a fraction of a degree out, and you can't know how close they are to perfect without a dial gauge. I wouldn't necessarily trust the factory timing marks, you can find true TDC easily enough using a stopper. (an old spark plug with a bolt welded into it). Bring the piston up until ti touches the stopper, mark the crank pulley, then turn the crank the other way until the piston touches the stopper again, mark the crank pulley, TDC is exactly between the two markings. I suppose you could rig some kind of stopper that worked on one of the pushrods, and find the cam lobe's nose the same way, but that's a lot of work to save £26.78 http://www.chronos.ltd.uk/acatalog/Engineering_Menu_Dial_Gauges___Dial_Indicators____Magnetic_Bases_228.html |
| Growler |
Is it a stock cam and stock engine, or is it high performance....if its stock ... Id think just stick it in and line up the marks According to vizard, performance cams can be way off so dont trust the marks Why not use a DTI ???.... you can get cheapos for under $20 and seem to work decent... I have 2...A high end with magnetic base and rigid connections and a harbor frieght cheapo with a flex connection and a vise grip base and i find them very valuable...i use them all the time....a great advantage to any shop...infact almost as valuable as a micrometer |
| Prop and the Blackhole Midget |
| The hard part of a DTI is learning how to use it...my advice, pre-load it, and write down the amount...i find (.050) is a good pre-load easy non confusing number...that keeps a steady pressure on the springs |
| Prop and the Blackhole Midget |
| Assuming you have established that TDC is true, if the cam spec you've been given lists the lift at TDC (which many do) then all you need to do is fit the rocker gear, set the tappet clearance for no 1 inlet to the "lift at TDC" figure, add .005". With a 5 thou feeler in the gap between rocker and valve turn the engine over until its blade is just nipped between the rocker and valve. At that point you should be at TDC, so any variation from that is the amount you need to adjust the cam gear (not forgetting to divide by 2 to allow for the difference between cam degrees and crank degrees.) This is a very accurate method, as good as with a dial indicator. You do need to check which rocker ratio the lift at TDC is specified at. |
| Paul Walbran |
| oops: Forgot to add that you also need to establish whether the lift at TDC specified is with or without the running tappet clearance |
| Paul Walbran |
| Thanks for the help guys. Yes a dial gauge is only £20 but I have the cam and was considering doing it over the weekend. Also, the rocker gear is knackered hence not on the engine/really usable at all. Looking through pictures of the strip down of the engine at home last night the cam sprocket and front plate appear to be marked with a distinct punch mark and scribe line which I can probably safely assume was to aid timing. I will see if these marks help me out. Problem is it is not a stock cam, it was re-profiled to Piper 270 spec, I shall have a play over the weekend and see! Thanks again. Malcolm |
| Malcolm Le Chevalier |
| Could someone discuss the pro's and con's of magnetic base vs clamped base dial gauges? What if any, are the trade offs for each? |
| Lawrence Slater |
| Malcom, are you timing your 1500? Have you got an uprated camshaft? - I used a std camshaft so simply used the punch marks to align - I did a sense check with a printed out timing disc and made sure the engine turned over by hand. Also be sure to check with the dial gauge that the TDC mark is accurate, mine was 1.5degrees out - trouble is I've forgotton whether it was 1.5 degrees out after or before ! If you search the archives, there is a thread started by me on cam timing the 1500 with a great response from Debs on all the technical details. Worth a read. C |
| C L Carter |
| Yep its my 1500 and cam is a Piper 270. I will go hunting in the archives Indiana Jones Styley! Cheers. Malcolm |
| Malcolm Le Chevalier |
| The punch marks on a 1500 are not accurate, and have sometimes been found to be grossly erroneous - -14Deg!. And the sprocket is designed as a vernier, so you can/do get different timings by using the "other" set of bolt holes and/or flipping the sprocket over. And a reprofiled cam will not be aligned with the original marks anyway. Lawrence - Ever tried to stick a magnet on an alloy block or head? Or get a clamp to fit around the whole block, because there is no other way to align the indicator? Or keep re- clamping for multiple measurements? Speed, ease, accuracy - both have their points. I could not live without both; even so, I sometimes make dedicated mounts, even for one time use. FRM |
| FR Millmore |
| Lawerance As FRM was saying, its about versatility ....id spend the good money on the magnetic base with rigid hardware and the cheap money on the vise grip with flex arm...i may have lucked out as my dials and compentents are all interchangeable with each other i can use my chicago gauge with a flex arm and the magnetic base |
| Prop and the Blackhole Midget |
| Right, to finish off the story here... I have timed the cam using the factory marks pretty much. It does assume the marks are correct but I am ok with that assumption! The full process... 1. I found TDC according to the marks on the timing cover. The piston was at the top of the bore so it can't be that far wrong! 2. Take cover off and put the cam in with lots of lube! 3. Put a tappets in hole one and two (exhaust and inlet of cylinder one) and put another tappet in upside down on top of these. 4. Using a straight edge (I used a Stanley knife blade, perfect length) I slowly turned the cam until the two tappets were level (when I couldn't see daylight through the gap). This being (roughly) the overlap point where inlet and exhaust are both slightly open when the piston is at TDC at the end of the exhaust/start of the inlet stroke. 5. Put the cam sprocket on in the same orientation it came off, it turned out that it was about 3/4 of a tooth advanced of the marks (if that makes sense). 6. Figured this must be about right, by the time I got the chain on it had moved to about 1/2 a tooth advanced according to the factory marks. Someone (I can't remember who, sorry) said its better to have it a little advanced so I'm happy. 7. Checked with the blade again, inlet slightly higher than exhaust (which makes sense as cam has moved forward a tiny bit). Also inlet is higher lift than exhaust. 8. Put rest of tappets in, then head on and torqued up blah blah blah... Should run OK eh? Might revisit things once (if?) then engine ever runs and/or when I finally get some new rocker gear. Cheers, Malcolm |
| Malcolm Le Chevalier |
| Fail FRM |
| FR Millmore |
| fail? |
| Malcolm Le Chevalier |
| Sounds good to me! |
| Growler |
| FAIL = not good enuf! You have multiple steps that could be off 10 or more degrees. Cam timing should be within 2 degrees, and 4 is noticeable easily as poor performance, bad mileage or both. Do it right! As I said, I have found factory cam installations off by 14 deg, the repro cam is not necessarily in any known relationship to any marks. You cannot judge TDC by looking at it, as there are several degrees rotation which have essentially zero effect on the vertical position of the piston. The 14 degree engine was sufficiently different after I corrected it that the customer called as soon as he got home and asked "What in the hell did you do to my car? It scared me.", and it subsequently turned out to have fuel mileage up from 27 to 33 miles per US gal. FRM |
| FR Millmore |
| Thanks for the comparison mag vs clamp, FRM/Prop. Cheers. |
| Lawrence Slater |
| Thanks for the support Growler. You are "the" Growler of drive shaft fame? I tip my hat to you sir! For clarification... TDC was found using the timing marks not by eye. It was sense checked visually i.e. piston was at top of bore, appeared to start/stop moving a few degrees before and aft of TDC mark so not an unfair to assume marks are OK. Certainly not 10 degrees out. The location of the cam was found using the straight edge across the inverted tappet bottoms, not the factory punch marks. I was admittedly dubious, but in practice it was easy to spot when sunlight was shining through between the tappet and the blade and the smallest turn of the cam either way would show up tiny gaps that you could see light through (I was working in the back of the garage, quite dim, looking forward with sunlight shining in the door). Cam sprocket was attached in old orientation (without chain) just for the sake of attaching it for something to hold on to whilst turning the cam. The factory marks were used as a sense check. I don't know how they re-profile cams, but if I were doing it I wouldn't re-profile it 90 degrees out from what is already there! I would try to add/remove as little as possible, therefore the orientation of the cam will be roughly similar to stock (assumption, but not a stupid one, but again, just for sense checking I didn't actually time it with these marks). If the factory marks had been 5 teeth not 1/2 a tooth out I would have worried. Chain then went on with sprocket in same orientation (for the sake of putting it on one way), cam moved slightly, about 1/4 of a tooth maybe. Something like 42 teeth on the sprocket (?) 360/42/4 = 2 degs (ish) shift on cam sprocket, which will effectively 4 degs out on the crank. Check with straight edge over tappets again inlet is slightly higher than exhaust, therefore must be advanced. As per FRMs advice in other thread it is better to have it advanced as chain will settle in etc. But perhaps 4 degs is too much... But... lift on inlet is higher than lift on exhaust for Piper 270 cam, so setting them level in the first place means it is maybe slightly retarded anyway. When I have rocker gear I will check it, (the old stuff went in the bin it was so knackered). Maybe I will come to eat my words, but if the car ever runs, even with 1 horsepower and doing 1 MPG I will be happy and can move the timing by half a nats cock then. In the mean time I have many more and larger fish to fry! i.e. piles more welding, drivers sill is next up! Just "Fail" helps no one. Phew, long may ye rest in the archives! Bye for now, Malcolm |
| Malcolm Le Chevalier |
| I just dont agree with this thread.... Here in the states we start our boys in early life with the phrase, right tool for the right job...i can remember that as far back as kindergarten and my uncle telling me that For the amount of work repkacing a camshaft.. i dont understand not spending $20 for a DTM ...im sure you a discount tool store with in a resonable distance or pyou couldnt call several people to locate one to barrow I just think this is a lot of risk in time and .money and performance trying to reinvent a good basic concept thats easy to do with great accuracy with a DTI...with chain flexion from rocking back and forth can easily soak up 7 degrees ...i know that for a fact ... I had a heck of a time until sime one said to move the chain in one direction only... But you also using the old chain and gears...that has wear on it I just think your taking a really long trip with lots of risk just to save the equivalant of 2 liters of fuel I just hope your not using molegrips in place of sockets and rapid eye blinking in place of a timing light |
| Prop and the Blackhole Midget |
| If the chain can flex 7 degrees each way I may as well just put it in anyway round as it will flap about so much as timing rendered useless. I said nothing about using the old chain. Sadly where I am in the world there aren't an abundance of £10 gauge shops. On the plus side there aren't many MacDonalds either. But I have sourced one I can borrow and (for the third time) check what I have done. Altering timing if its bolloxed degrees out = a dozen timing cover screws move cam, put chain back on. |
| Malcolm Le Chevalier |
| Malcolm, don't forget its a Triumph lump you're working on and its got the stupidest chain tensioner in the cover I've ever seen ;0) Check your readings with a little pressure on the slack side of the chain, it'll almost certainly make a degree or so of retard impact. bash on... MGmike PS. stop avoiding the welding by doing other stuff you can do later...... |
| M McAndrew |
| This was a quick interlude from welding because I was bored of hacking at rust and don't have the new panels I need anyway as I'm feeling poor this month! It all has to get done eventually! Cheers Mike, Malcolm |
| Malcolm Le Chevalier |
| I'm sure what you've done will work just fine- anything that's an improvement on the Haynes "line up the dots" method is a bonus. However I'd go back and dial it in accurately before stitching the engine up, as I'd go mad wondering how much extra power I could be enjoying if I'd timed it accurately. Having to crack open the timing case to change the timing is a huge pain, and I've been spoiled by modern engines with their easily-accessible timing voodoo. |
| Growler |
| I told you how to do it accurately without the DTI, and since you cannot use the engine without rockers, what is the rush? You can even do it without a degree wheel if you use your head - the one with fur on. I've set up many cams with nothing but feeler gauges and a bit of math. You have not given any indication that you know the cam timing figures, or whether it is a symmetric timed cam; I do not know. When cams are being reprofiled, it is commonly necessary to move the lobe peaks a few degrees to save material and get the timing as desired without reducing the lobe overall size too much- that changes timing relative to any marks. Smart ass remarks about moving the lobe 90 are not much help either. The chain could have 7 feet of slack and it makes no difference to timing, which is done in one direction with all slack on the slack side, how about that? It is not uncommon to find TDC marks out as few degrees, along with any other marks. Why would you do all this and give away 5 or 10 or 20 hp? And the Post will deliver tools for less than the cost of a few litres of fuel. FRM |
| FR Millmore |
| Malcolm I picked up a dial gauge for a few quid on Ebay. Its your engine and you're entitled to do it anyway you want, but anyone who has done this job a few times with reprofiled cams will know that they vary widely - you may well have lucked in to something close to correct or you may be 20 degrees out... If it doesn't run properly once you put it all together, FRM will rightly point out 'I told you so...' Regards James |
| James Bilsland |
| Paul I tend to use the lift at TDC method but not as you do Most of the cam grinders here supply that spec.as an inlet lift at tdc, measured at the lobe ie - lifter rise Using your method would result in a mistimed cam in this case IF the spec was for eg. 90thou at tdc at the lobe this would be say 135 at tdc with 1.5:1 rockers fair difference Just sayin Willy |
| William Revit |
| Willy Agreed you have to establish whether the spec given is at the lobe or at the valve. Piper and others specify the TDC lift at the valve. This introduces assumptions about rocker ratios being accurate and needs recalculating if the rocker ratio changes. there is also the question of establishing whether the lift is off the base circle (zero clearance) and if not then at what clearance it is. I myself always reference it to the cam lobe as you do, set up on full lift and then check lift at TDC - all with a dial indicator. My earlier post was to set out an accurate way of timing without a gauge. I have had to use this on the odd occasion when I've gone offsite to help someone and left my kit behind :-( Checking later has confimred the accuracy, it does work very well so long as you get the rocker ratio right. |
| Paul Walbran |
| Cheers Paul Wouldn't it be great if all cam grinders used the same referance method, like lift at the lobe OR lift at the valve, then it would be great if all cars had the same oil filter-------- Have a nice weekend - Willy |
| William Revit |
| Yep, would make life lots simpler. I have to confess that the reason I use both full lift and TDC methods each time is that it's a good way of checking the cam is what it is supposed to be ... occasionally it isn't. Usually (but not always) because it's been handed on between owners and gathered a bit of mystique! |
| Paul Walbran |
| Yeah, I like to double check, I've found some cam grinders grind to spec which is fine and a couple grind 2-3deg. advance into them, which is also fine but you need to know I can remember having an experimental grind done for a "B" once and it was 8deg. out just because he had to move the cam around to get the grind on. It worked out well but would have been a real fizzer if it wasn't checked Cheers Willy |
| William Revit |
| If anyone is still interested in what I did with my engine, I borrowed a DTI from Mark (thanks!) to check what I had done. Whatever your opinions of me and my methods are, dealing in facts, full cam lift occurs on my engine at 108 crank degrees ATDC. Seemingly spot on what is specified by Piper. Some will say it's luck, some will say I have just made this up to prove a point! But in my case what I did appears to have worked. Tested it a few times, same result each time. As James said, its my (or your engine) I can do what I like. In my case what I did appears to have worked. Cheers all, Malcolm |
| Malcolm Le Chevalier |
| Melcolm, Sorry man, i didnt loose any sleep thinking about your cam replacement... It didnt even stop me from going to red lobster the other night for endless shrimp ....i guess im just not the friend you thought I was But considering you value what I think of you...can I barrow $20....hahaha ..... Hahaha and LOL. Nah... Seriously, im glad it worked out for you, the true reward is the peace that comes from ""KNOWING" that the cam is timed correctly....now that is something that would keep me up late at night...the not knowing Im looking forward to hearing how the new cam performs |
| Prop and the Blackhole Midget |
| Hmmm... My tone on my above comment didnt come off quite right... I meant it to be humorous, not condecending nor ...obtuse?? But i certinly never saw your thought and idea as a negitive, quite the contrary, im glad you raised the question, i found the debate stimulating and interesting....but then agian ive always liked new ideas and reinventing the wheels, and now look at me, people cant wait to hear of my next new modifcation idea....people truely value what I say.....hahaha Seriously... You have always had the respect of this forum, i dont think anyone thought ill of you, my interputation of peoples comments where more of wanting success for for you and concern of failure... You have to remember new ideas take some getting used to, new ideas are in a word "Targets"... If you make your self a target people will shoot at you Thank god that whole, round earth idea never caught on, now that was a stupid idea, who ever came up with that idea was an idiot Prop... Chapter president of the flat earth socity |
| Prop and the Blackhole Midget |
| Seriously Prop. What drugs DO you take? lol. |
| Lawrence Slater |
| What drugs do I take ??? Mostly just asprine, but I only take those when im wild mushroom hunting... |
| Prop and the Blackhole Midget |
| Malcolm Interested - Yes , that's why we post on here,to try and help, right Prop You have set your cam up using one method and checked it using another with the same result - all good - that's all you need to do Willy |
| William Revit |
| Yepp... Willy, Thats the message i wanted to convey...but i really failed my 1 st attempt... Then missed the 5 min window tryimg to clean my pist up Nd got stuck with a rather condecending and borish thread Something to be said for breavity |
| Prop and the Blackhole Midget |
| Prop, my brother tried magic mushrooms too. He didn't get stoned though, just a gut ache. Wrong mushrooms. lol. |
| Lawrence Slater |
| I think your supposed to "chase" the mushrooms by licking the exit fun hole of a bull frog.... Kind of make you wonder what the muchrooms are for Hahaha Prop |
| Prop and the Blackhole Midget |
| Malcolm- Great! As Prop said, the knowing is important, especially if you have mysterious problems later. None of the comments were meant to belittle you, or even your methods, but this is a critical point in performance (or stock) engine building. Couldn't tell you how many times I've found things wrongly assembled after guys spent weeks or months trying to get one sorted. An early lesson was watching 15 or 20 guys try to get a flathead Ford to run after replacing the cam, for about a month. I asked them what they were doing and it seemed one (dominant) group wanted to use the factory marks, while the losing group wanted the "new" marks. I suggested that maybe the "new" marks were made because the factory ones were wrong. A half hour later it was running. And do not forget that just because you were correct this time, it does not mean the "rough checks" will work next time. I once idly decided to measure the timing on every valve, and found one lobe out by a significant amount - some machine setup error. While I do not usually do that, I do often check my setup by checking #4 valves to see if they duplicate the #1 settings as they should. Will be interested in knowing how it works - I will be fitting next week the Piper 270 Mr Burgess so kindly supplied, in a 1300 Spitfire I built in 1996, in which the Kent cam committed suicide. FRM |
| FR Millmore |
| Malcolm, I've not read every comment here. But I would ignore those of the 'purists' - I think you'll find they're engines won't run any better than yours cos they'll have forgotten something silly - like, their timing gun is probably remarkably inaccurate, and thier dizzy probably has loads of play - and their tacho is probably 20% out... and their tdc marks are probably a degree or 2 out. Like I said, I just put mine back in using the standard marks - and orientated everything the way it came off. It runs beautifully. |
| C L Carter |
| Carter- Not bothered to read it and you are making such remarks? Old racing saying - "Half-assed is half fast - if it finishes at all" After you learn to read and do us the courtesy of listening, and after you rebuild a few hundred of the same engine and can explain why some cars of "identical" spec run better or worse (sometimes MUCH better or worse) than others, come back and tell me. If you can catch me in the same car. FRM |
| FR Millmore |
| Carter... And i thought i lived a dangerous life For modern day cars id not have an issue with just trusting factory marks... But we are talking 40 year old tech, i dont think there was much computer tech in manufacturing back in the day But congrats on your cam change just the same and i hope the best for you, but please becarful encourging that type of enginerring... Id hate to offer that kind o advice and have someone destroy there engine As far as a purist goes.... If because i own and use a torque wrench, a micrometer and a DTI, ... Then yes... Ill wear the title Prop |
| Prop and the Blackhole Midget |
This thread was discussed between 23/08/2012 and 05/09/2012
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