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| Timing the stock cams and sprockets | Rate Topic |
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| Posted: 03-30-2009 04:48 am |
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1st Post |
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dwalls1 Member
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I am totally confused as to what I should be seeing when the cam sprockets are properly timed. My engine # is B74 078401. I have aligned as closely as possible the 115 IN and the 115 EX markings on the sprockets so that they are facing each other between the sprockets. I am not even sure what my engine number is as they are listed under A52 in the service manual. I have read the posts I could find that seemed to relate, but all in all it just makes my head hurt. Any enlightenment is much appreciated.
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| Posted: 03-30-2009 11:15 am |
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2nd Post |
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subwoofer Member
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Shouldn't you flip them over for 110/110? Hold a ruler between the centres of the cam drive retainer bolts, the timing marks should be really close. Anyway, my experience from changing the timing belt is that before the belt change it was impossible to get the mark to line up completely, while they lined up perfectly after the change. Obviously the belts stretch a little bit with use. -- Joachim
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| Posted: 03-30-2009 08:01 pm |
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3rd Post |
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dwalls1 Member
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Thank You for your response. I remain befuddled, as my sprockets are marked EX110 and IN115 on the intake cam and IN110 and EX115 on the exhaust cam. My cambelt has only been on about 2500 miles since I installed it. I'm pretty sure it was on the same way the old one was, with perhaps a slip of one tooth on the exhaust cam which I corrected yesterday. I think I shall just drive and enjoy, though I am not getting the RPM or throttle response that I thoght I was.
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| Posted: 03-30-2009 08:19 pm |
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4th Post |
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subwoofer Member
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If you flip them over, you will get markings 110in/115ex on the intake cam and 115in/110ex on the exhaust cam. That puts another 10 degrees of overlap in, which is what I thought was standard for the engines delivered in '74. At least that's what I drive, and it comes strongly on cam when you pass 4000 rpm. Not much below that, I'm afraid. There are people on this board with a lot more knowledge of these engines than me, though. I am but a mere beginner... -- Joachim
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| Posted: 03-31-2009 01:56 am |
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5th Post |
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dwalls1 Member
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Wow, this is exciting. When you say flip them over do you mean swap intake for exhaust? Or, are the markings to which you refer on the back side of the sprockets? If I can confirm what I'm doing this sounds like a great and easy hop up. It also makes sense from the engine vacuum I was getting when timing the engine with the vacuum gauge.
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| Posted: 03-31-2009 05:03 am |
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6th Post |
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subwoofer Member
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The other markings are on the other face of the sprocket, i.e. facing rearwards at the moment. No reason to swap the exhaust sprocket for the intake sprocket, although they are identical, just installed differently. -- Joachim
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| Posted: 03-31-2009 06:59 am |
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7th Post |
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Jensen Healey Super Moderator 
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Move the crankshaft to top dead center. Turn 90 degrees so no pistons can interfere with the valves. Loosen or remove the timing belt. Put the pulley on the intake side with the "110 in" marking towards the front of the car so you can read it when it's installed. Put the pulley on the exhaust side so you can read the "110 ex" when it's installed. Align the marks as Joachim says in his post. Tighten the belt. If you hear belt whine when running the engine, the belt is too tight. Try the 45^ test or tune the belt to G on the musical scale. 110 in/ 110 ex is recommended for best performance for all engines with stock cams and was standard for '74 engines. If the belt slipped one tooth, that's 18 degrees since the cam turns at half the crankshaft speed. I don't know if that's enough to cause contact between the pistons and valves. You should consider a compression check to make sure the valves aren't bent. Good luck and good wishes, Kurt
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| Posted: 03-31-2009 07:04 am |
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8th Post |
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subwoofer Member
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I know for a fact a federal spec 907 will survive 2 teeth off on both cams... It will run like utter crap and will not rev past 4000rpm, but it will run and not make any ugly noises. Not that I recommend it though... -- Joachim
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| Posted: 04-01-2009 04:21 am |
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9th Post |
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dwalls1 Member
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Thank You all for the help and encouragement . I can hardly wait 'til this weekend to get the sprockets switched and try this out . I can only speculate as to why the sprockets are the way they are. My guess is that they were changed when the car was in California to meet emissions there. I will recheck the ignition timing after the sprocket change using the vacuum gauge. If it will pull more vacuum at idle, that will certainly confirm the propriety of changing the cam timing. Thanks again and I'll keep you posted on my progress.
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| Posted: 04-04-2009 09:59 pm |
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10th Post |
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dwalls1 Member
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OK, got the cams timed with the 110 marks just right. It took a little fiddling as it's difficult to get the crank sprocket to slip a cog, but everything came together very well. I also changed the thermostat while I was at it. I installed a Cummins 180 F thermostat. Very expensive, but arguably the very best. Set the timing at 12 degrees BTDC static and it fired right off. Getting it to idle was a little tricky and I did fool with the timing at idle with the vacuum gauge pulling only 6 or 7 inches. During a shakedown run it seemed to get more RPM, but it won't idle long under 1000 RPM. At 1000 RPM it will idle indefinately with no over heating. Should I go back to 12 degrees BTDC and forget the fancy sucky gauge? Is it time to check valve clearances? It's really running good and I'm sure it's getting maximum RPM, but my tachometer is reading low. At an indicated 3000 RPM the speedometer is showing 65 MPH. I'm inclined to believe the speedometer as I have had opportunities to confirm it's accuracy. Would appreciate all thoughts and comments.
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| Posted: 04-07-2009 04:21 pm |
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11th Post |
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Brett Gibson JH5 20497 Member
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You should check that valve clearance ASAP, if one is to tight you may end up burning a valve seat, or to loose not allowing full engine breathing. 12 Deg is the book setting on a perfect engine, personally I like to set the engine timing to what makes it run the best, smooth idle, no hunting up and down, and no breaking up at higher RPM's. 1000rpm's is not a bad spot to be at as well. Whats this sucky gauge your talking about, engine vacumn or carb. draught, if it's carb draught you will need to set both carbs to match, then tweek the mixture to get the best reading of your plugs. Brett
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| Posted: 04-07-2009 09:02 pm |
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12th Post |
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dwalls1 Member
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Hi Brett, Thanks for your input, it is great to know folks are out there that share my interests and are willing to provide knowledgeable assistance. The sucky gauge is just a vacuum gauge that I was trying to use to adjust the timing. I have put it in the closet for now and just went with the 12 degree BTDC static setting. That seems to work fine. I will check the valve clearances when the car is down while I install the O/D unit I have ordered. I should probably have done that a year and 3000 miles ago, but have been having too much fun just driving it. I may get the vacuum gauge out after I get the valves dialed in, but just out of curiosity.
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| Posted: 04-18-2009 02:46 am |
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13th Post |
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mnunes22 Member
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I was in the middle of replacing my toothed belt and the bearings in the tensioner pulley. I just read this post and decided to check my cam sprockets and discovered that they are set at 115IN and 115EX when crank is at TDC. Eng.#B74 12 1073 . I've had the car over a year and it seemed to perform fine,although it does smoke when coming down a long hill. Any suggestions on flipping sprockets over and setting them at 110IN and 110EX ? Any ideas of how this change will affect the drive-ability or fuel mileage?Its easier to switch them now if it's worth the effort. Thanks, Bill Last edited on 04-18-2009 04:10 am by mnunes22 |
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| Posted: 04-18-2009 05:29 am |
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14th Post |
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Jensen Healey Super Moderator
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All stock JH's should be set at 110/ 110. The smoke is probably from worn valve guides. Kurt
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| Posted: 04-18-2009 06:46 pm |
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15th Post |
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dwalls1 Member
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I don't have enough time on mine since I switched the sprockets to make a useful assessment, but it certainly didn't hurt any and was easy enough to do. I would certainly trust the folks here to steer me right at any rate.
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| Posted: 04-18-2009 08:47 pm |
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16th Post |
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Dakota123 Member
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On 10628, the cam sprockets were replaced some time ago. Both are stamped Lotus. The intake is stamped properly, IN 110 EX 115 facing front. The one installed on the exhaust cam has no text on either side, only a scribe mark. Anybody have a clue as to what "model" sprocket this could be? The sprocket installed on the aux drive is marked 110 IN 115 EX facing front, so at a minimum I'll move this one to the exhaust cam so I know what it's timed to -- it feels a bit flat at full throttle. Mike Last edited on 04-18-2009 08:48 pm by Dakota123 |
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| Posted: 04-18-2009 08:55 pm |
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17th Post |
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dwalls1 Member
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Can't address this directly, but I did note when fooling with mine that all three sprockets were the same. I think that I would do as you are thinking and use the odd one on the distributor drive.
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| Posted: 04-19-2009 02:59 am |
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18th Post |
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Dakota123 Member
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Well, counting teeth from where "Lotus" is embossed on all three sprockets points to the mystery sprocket being a 115 EX part -- the scribe mark is located the same number of teeth from "Lotus" as is the 115 EX scribe mark on the (properly marked) aux sprocket. Not definitive, but evidence, anyway. So swapping the current aux and exhaust sprockets, and timing for 110 EX is my best bet. Mike
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