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| Reversed cams effects | Rate Topic |
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| Posted: 09-09-2017 03:41 am |
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1st Post |
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tonyhawker Member
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I have just taken possession of a 74 with no compression. The head was redone by the previous owner and, upon reassembly, there is no compression. Being new to this car I have three dumb questions. Is it possible to reverse the intake and exhaust cams and/or reverse the cam towers on reassembly? If there has been a reversing of the cams has the engine been trashed? It turns over very freely Are the cams identical or marked as to their location? Any enlightenment would be most appreciated! Tony Hawker
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| Posted: 09-09-2017 02:20 pm |
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2nd Post |
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DonBurns Member
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Tony- Reversing the cams or cam towers should not result in engine damage. In the stock engine the cams are the same. But even if they are not, as in the 104 / 107 for a 912, not a problem. Just won't give the best performance. If there is 0 compression, I wonder if all of the valves were bent during assembly. It is critical that the crank is not be turned until the timing belt is on or the valves with be bent by the pistons. In any case, sounds like you need to take the head back off and examine.
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| Posted: 09-11-2017 07:28 am |
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3rd Post |
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Esprit2 Member
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As Don mentioned, the stock cams are identical. Even the cam carriers can be interchanged between the intake and exhaust sides of the head (they bolt on in either position). HOWEVER, the cam pulleys are reversed (flipped around front to back) between intake and exhaust. If the cam carriers were swapped around without correcting the pulley orientations, then the resulting cam timing would be way off. Perhaps far enough to cause a lack of compression, or worst case, to bend valves. Whenever you rotate the crank, first remove the spark plugs. It's more difficult to turn the crank with the plugs in, so you'll be putting more effort into it. 'IF' a piston hits valves, you'll probably just power right past them... bending them. With the plugs out, you can put minimal effort into turning the crank. Then any hard spot due to a piston/ valve collision will be more noticeable. Pay attention, and use a little mechanical empathy. If you feel the engine clunk to a stop, or hit a hard spot, that may well be a piston hitting valves. STOP immediately, and don't force your way past it. Without knowing more about your engine, getting into specifics would simply be conjecture. With that in mind... Start your diagnosis by confirming the cam timing with the crank at TDC. Once the timing is correct, it will be safe to crank the engine over on the starter... as in doing a Compression test. Follow up with a Leak Down test. The first step in all of that is to make certain both cam pulleys are properly installed. For each timing mark, it's IN/ EX twin is on the back side of the same tooth. Next to each mark there should be an IN (INtake) or EX (EXhaust) mark on the pulley's center web, near the rim. In early pulleys, it will be stamped. Often not very legibly. In later pulleys, it's cast in, and generally easier to read. *~*~* The timing mark next to the 'IN' should face forward on the intake pulley. The timing mark next to the "EX' mark should face forward on the exhaust pulley. If either cam pulley is reversed, that cam's timing is way off. Correct it before going any further. *~*~* The second step is to set the crank to TDC (spark plugs out as noted above), and observe the timing marks on the cam pulleys. If they are on far opposite sides of the pulleys, then the #1 piston is at BDC (Bottom Dead Center) instead of TDC. Turn the crank through one more clockwise rotation, and back to TDC. That will set #1 to TDC... ie, the only correct crank position for checking cam timing. The pulley timing marks should now align with one another 'ON' the imaginary centerline between the cams. If they align, but are a whole tooth PITCH high or low relative to the centerline, then they are still not properly timed. 'Alignment' is not everything. They must align 'ON' the centerline. DEFINTION: One TOOTH PITCH is the total width of one tooth plus one gap. In other words, from any point on one tooth to exactly the same point on the adjacent tooth. Being off by only the actual width of one tooth is not being off "by one tooth" in cam timing jargon. Unless clearly stated otherwise, "by one tooth" should always be taken to mean by "one TOOTH PITCH". If a pulley is 'reversed', then the amount of timing error that results will vary with each MOP target. If the MOP of the timing mark being used was the early J-H's 115 MOP, and the pulley was installed reversed, then the resulting timing will be off by 24.5 pulley degrees. All cam timing events are stated in crankshaft degrees. The cams run at half crank speed, so 24.5 x 2 = 49 degrees of cam timing error. That's a big error. Similarly, if the target timing was 110 MOP, reversing the pulley will result in the timing being off by 29.5 'pulley degrees, which equates to 59 crankshaft degrees. That's huge. For 100 MOP, the error is 42.5 pulley degrees, or 85 crankshaft degrees. Humongous... and the pistons are into the valves... not much doubt about that. In any case, the intake will be retarded, and the exhaust will be advanced. The pulleys have 40 teeth, so 360 degrees in a circle divided by 40 teeth equals 9 pulley degrees per tooth PITCH (a tooth plus a gap), or 18 crankshaft degrees per tooth. So... 115 MOP pulley backwards = 49 degree error divided by 18 deg/ tooth pitch = 2.7222 tooth pitches off. 110 MOP pulley backwards = 59 degree error divided by 18 deg/ tooth pitch = 3.2778 tooth pitches off. 100 MOP pulley backwards = 85 degree error divided by 18 deg/ tooth pitch = 4.7222 tooth pitches off. At 3.0 teeth off, you may get lucky and not wipe out any valves... but you're scary close. At 4.7 teeth, keep diagnosing, but prepare yourself for the worst (bent valves)... you'll probably find it. Good luck, Tim Engel Last edited on 10-08-2017 04:18 am by Esprit2 |
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| Posted: 09-11-2017 08:21 am |
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4th Post |
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Esprit2 Member
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If you have read my previous post already, read it again. What made sense in the wee hours of the morning read a little weird after a few hours of sleep. I've edited the whole thing. Sorry about any confusion. Tony, I suppose I could have just answered your questions. tonyhawker wrote: Is it possible to reverse the intake and exhaust cams and/or reverse the cam towers on reassembly?Yes. The cam carriers themselves are identical and will bolt-on to either side of the head. The stock cams are the same, so they will also swap sides with no complaints. However the two identical cam pulleys are installed reversed... ie, flipped front to back between the intake and exhaust. That's a very significant point of difference with regards to cam timing, but one that's easily overlooked. Since the cam carriers will bolt on to either side of the head, there is no 'one way' fail-safe feature to prevent you from making a mistake. You need to know what you're doing with regard to pulley orientation, and pay attention. tonyhawker wrote: If there has been a reversing of the cams has the engine been trashed? It turns over very freely.Maybe, maybe not... read the long version. But yes, the cam timing is wrong when the cam carriers are swapped (pulleys are backwards), and depending on which timing marks were used, the pistons may have hit the valves. In that case, the entire engine is not trashed, but the head will require a rebuild. New valves for sure. Maybe new guides and seats as well. Not inexpensive. On the upside, it's possible the timing was off just far enough to kill compression without the pistons hitting valves. In that case, correcting any cam timing errors should be all that's required to 'fix' the engine. tonyhawker wrote: Are the cams identical or marked as to their location?The stock cams are identical, and not marked per their location... intake or exhaust. Look at the exposed bit of cam that's visible between the front of the cam carrier and the back of the pulley. If it's clean with no machined or stamped markings, it's the J-H 907's stock C-Cam. It was also the stock cam in all Lotus 'Federal' 907s. Requires 110, red-dot pulleys for design-correct timing. J-H early emissions timing set the MOP to 115 on both cams. Later emissions timing used 100 MOP Intake and 110 MOP Exhaust. One groove machined all the way around indicates the D-Cam. It was the Lotus 907's early stock 'non-Federal' cam, and it was never used in any stock J-H 907. Requires 110 MOP, red-dot pulleys. Two grooves indicates the later (? 1978-ish intro) Lotus 'non-Federal' E-Cam. Requires 102.5 MOP, yellow-dot pulleys. 7777777.... stamped all around the shaft indicates the 107 cam that is popular with some J-H owners. Requires 104 MOP, green-dot pulleys. 4444444.... indicates Lotus' street-performance 104 cam. Requires 104 MOP, green-dot pulleys. The "104" as used in both the cam and pulley names refer to different things. It's purely coincidental that a 104 cam requires a 104 MOP pulley... don't get hung-up on that... there's no numerical meaning/ relevance. If the cams have been reground to some other profile, then you're at the mercy of whoever did the regrind to add appropriate markings. I have two reground, unmarked cams I can't identify. For more details, read my previous message, #3 above. Regards & Good luck, Tim Engel Last edited on 10-08-2017 04:26 am by Esprit2 |
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| Posted: 09-12-2017 03:46 am |
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5th Post |
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tonyhawker Member
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Tim, thank you so much for taking the time for your two posts! I was vaguely familiar with the reversible pulleys but did not have all the info available to dig into the engine without possibly doing more damage. Thanks to you I now have something more concrete to go on! Offhand, are the valves specific to only the 907 engine and made of unobtanium or are there more generic replacements available? I have the machine tools to modify and regrind valves if necessary. Thanks again. Most likely "I'll be back"! Tony
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| Posted: 09-13-2017 01:27 am |
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6th Post |
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Esprit2 Member
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tonyhawker wrote:Offhand, are the valves specific to only the 907 engine and made of unobtanium or are there more generic replacements available? I have the machine tools to modify and regrind valves if necessary.Tony, The valves Lotus sold were expensive. They were very good valves, but expensive. All the 9XX intake valves were the same, until you get to the 910 in the 1995-96 Esprit S4s and the then-new Zeus head. Those intakes were 1 mm larger diameter. All the exhaust valves had the same head diameter, but the turbo 910 valves had sodium filled stems that were larger in diameter and required larger ID guides... and the larger guides required larger bores in the head. Not that you want any of that for your J-H 907, but when you're searching around, you'll know what you're looking at. Most Lotus specialists also sell aftermarket valves that are more affordable, and the J-H specialists probably do as well. I know Garry Kemp at Kemp Performance Engines has aftermarket valves available. That's pretty common. Regards, Tim Engel Last edited on 10-15-2017 01:37 am by Esprit2 |
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| Posted: 09-13-2017 01:48 am |
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7th Post |
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tonyhawker Member
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Good to know Tim. I took a closer look at my engine today. The timing mark on the crank is at 9 o'clock (Referencing horizontal). The solid cam pulleys are oriented properly. BUT! The intake is at the 9 o'clock while the exhaust is at 3 o'clock. At TDC shouldn't they be directly opposite themselves at 4:30 and 10:30? That is pointing towards each other? With the crank in the safe position I will be able to take the belt off and try to get the 110 and 116 marks about 45 degrees before opposition. Correct? I really appreciate your concern and efforts. The car is in excellent shape otherwise. Tony Last edited on 09-13-2017 01:50 am by tonyhawker |
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| Posted: 09-14-2017 05:52 am |
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8th Post |
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Esprit2 Member
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A full 4-stroke cycle involves two full revolutions of the crankshaft. If the crank is at TDC, and the cam pulley timing marks are on far opposite sides of the pulleys, then #1 is at BDC (Bottom Dead Center). Turn the crank through one more full revolution and back to TDC. The cam pulley timing marks should now align on the imaginary centerline between the cams. If not, then at least you get a real idea of how far off they are. With your crank timing mark at 9:00 o'clock, the crank is not at TDC, so the cam timing marks as they are at the moment do not reflect how the cams are timed. Carefully rotate the crank to TDC, with the cam pulleys timing marks adjacent to one another. That will tell you how the cams are currently timed... right or wrong. Setting the crank to 90 degrees before or after TDC puts the pistons half way down their bores. That's the safest position (all pistons farthest from the valves) for working on the engine with the timing belt off. It keeps you from having an Oops moment that damages valves. The stock cams have a valve lift of just 0.340", so having the pistons half way down is a large, overkill clearance margin. There's nothing magic about 90 degrees/ half way down, just a very unscientific way of giving yourself the largest possible margin for error. Simply get the pistons well away from the valves. Half way/ 90 degrees works without thinking about it too much. Regards, Tim Engel Last edited on 09-15-2017 03:14 am by Esprit2 |
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| Posted: 10-13-2017 04:45 pm |
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9th Post |
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tonyhawker Member
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Tim, I have been busy on other projects that take priority over my "winter project" so little progress. I purchased a cheap Blow Down gauge and discovered that advancing the crank beyond TDC the leakage decreased to 15-20%. This tells me the cams are retarded and the valves undamaged. The car came with an extra set of well used cams and towers. I plan to take one of the pulleys off and hold it up to the engine cam pulleys to visually determine how much they are retarded. 3 teeth retarded seems to be in the ballpark as I remember. With the crank at TDC I will remove the belt, reverse both pulleys and manually set the cams where the blow down just ceases and check the mark alignment. If they are now within a tooth or two I plan to match the marks and put the old belt back on and check the compression. I figure advancing the cams 3 teeth while at TDC will do no damage. If all seems well I will put the new Gates 104 belt on and proceed with other checks. Don't want to damage a $116 belt, don't you know! I really appreciate the replies from you and the other gentleman. It really helped keeping me on the right track. Tony
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| Posted: 10-15-2017 01:51 am |
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10th Post |
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Esprit2 Member
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Tony, Before you go making changes, how about posting clear, close-up photos of the present pulleys. Clean them so that any markings stamped on them are legible. From that, I can tell you if they're installed with the correct side facing forward. If they are correct, and the timing marks are correctly aligned, then that's all you need to worry about. It's NOT about three teeth, or anything like that. Just install the pulleys and properly align the correct timing marks, and all the rest will take care of itself. If you follow correct procedure and get the pulleys and the belt installed correctly, and the compression pressures and/or leak down rates are still bad, then the problem is in the engine somewhere and messing around with the cam timing won't fix it... but it can make it worse. The 907 is an interference engine, and timing errors or experiments gone wrong get very expensive in a split second. This isn't the place for guessing, or 'taking a shot at it'. Show me good pictures. *~*~* Out of curiosity, where did you buy the Gates T104RB belt? Regards, Tim Engel Last edited on 10-15-2017 01:54 am by Esprit2 |
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| Posted: 10-17-2017 08:22 pm |
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11th Post |
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Esprit2 Member
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tonyhawker wrote:If all seems well I will put the new Gates 104 belt on and proceed with other checks. Don't want to damage a $116 belt, don't you know!I think that price is way too high. I've not tried PepBoys or O-Reilly's, etc, but I have searched some reliable internet sources. I consistently see T104RB prices (no shipping or tax) in the $64-$70 range. When I saw that you paid $116, it just rocked me back on my heels. If it's still in the package, see if you can return it. I just checked RockAuto.com, and they list the Gates T104RB Blue belt for $64.79, plus shipping. http://www.rockauto.com/en/catalog/nissan,1986,maxima,3.0l+v6,1211263,engine,timing+belt,5716 Scroll down to the bottom... last entry. RockAuto doesn't list it under Lotus or Jensen-Healey. The link above is to the 1986 Nissan Maxima with the 3.0 V6... it uses the same 133 tooth by 1 inch wide trapezoidal tooth belt. Later model years went through a progression of several different round-tooth profiles (not all of which were HTD), so stick with 1986 for a trapezoidal tooth belt. If you ever have trouble with a local parts counter guy failing to find a belt for a JH or Lotus 907, just direct him to the 'early' 3.0 V6 Maxima. Regards, Tim Engel Last edited on 10-17-2017 08:35 pm by Esprit2 |
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| Posted: 12-11-2017 01:47 am |
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12th Post |
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tonyhawker Member
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For you, Tim, and any other followers of this topic, I found the exhaust cam sprocket was indeed reversed but indexed correctly at the 110 marks. Reversing the sprocket eliminated the nearly 100% cylinder leak down readings and now are in the 10-15% region. Compressions are up over 100 lbs. on cold dry cylinders. Now that I have heat in the trailer I can jack up the car and install the exhaust pipe and bleed the brakes. Any attempt at starting has to wait on some wiring cleanup. Thank you again Tim for your guidance. Keep your fingers crossed! I know I am! Tony
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| Posted: 12-12-2017 07:23 am |
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13th Post |
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Esprit2 Member
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It's good to hear the compression has improved. Spec Compression Pressure for 8.4:1 cr are: 110-130 psi COLD = Jensen-Healey spec. 150-170 psi HOT. = Lotus specifies checking HOT. What cylinder pressures are you getting now? I'd still like to see a photo of the cam pulley timing marks with the crank set to TDC. All things considered, I think one last look is reasonable. Regards, Tim Engel Last edited on 12-13-2017 04:44 pm by Esprit2 |
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