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PrecisionMike

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Everything posted by PrecisionMike

  1. Hi. Interesting stuff and I appreciate it's a couple of years after the event but think my recent experience with my oil pump rebuild may be of interest. Upon first dry assembly I found all specified clearances in accordance with workshop manual except that with one shim (gasket) fitted the pump would rotate freely for about 240 degrees and bind slightly over the rest. I measured the thickness of rotor and annulus and found them to be identical and calculated that rotor end float with 1 shim fitted was ok. I checked radial and axial runout of the rotor on its shaft after verifying the shaft ran straight and true. To my amazement I discovered an axial runout at the rotor tips which was in excess of the specified end float. It suggested the bore of the rotor was not square to its surface. I found this to be almost unbelievable since the components are all cnc manufactured . Any way the supplier was great and gave me a new annulus kit. I re measured the rotor axial float......it was Zero😁. I assembled after full re verification and the pump ran smoothly and perfectly and with full conformance to dimensional specification. My recommendation is to check every thing and never assume parts are perfect. Not just on lotus but on anything especially if it is non oem, pattern or aftermarket in any way.
  2. I've worked it all out on mine. I'll write it up and post asap. Thanks
  3. Thanks for your reply. Did you ever find a specification for valve spring installed height or valve protrusion? On mine (912 na) my exhaust valves consistently protrude 0.5 mm more than the inlet. I solved shim range issue by using new thin pad steel long skirt followers .
  4. Hi. Did you ever post the info you were after and got. I'd be very interested. Thankyou
  5. Hi again. Can I ask where the figure of 0.060 inch came from with respect to coil bind and does it mean coil to coul clearance or total additional travel from max lift.
  6. Hi. Did you ever get a figure for installed height. I'm currently building a 912 which perhaps due to excessive valve seat cut and valve facing has the resultant increase of stem protrusion and hence reduction in spring preload. It's easy to loose 0.4 mm from the valve and seat (0.2mm each) and with a spring rate of 2.25 kg/mm for the springs I'm using, that's only a reduction of 0.9 kg seating pressure which I'm not concerned about. Non the less, if data can be found then getting it right is the right thing to do, especially as it's so easy and cheap to correct. I had a new seat fitted and it cut to a seat width of 1.8 mm and I reduced my valve stem protrusion by 0.5 mm - reinstating consistency across the valves in my head.
  7. Thankyou for your response. I soaked it in wd 40 with the camshaft in the vertical position last night and thankfully with a huge sigh of relief they both cam out this afternoon. I soaked the cams in petrol and cleaned them with a long brass bottle brush. There was some debris inside so a job worth doing. Thanks once again. I must admit last night I had visions of a damaged hex with all that that entails. Oh the Joy's of Lotus!
  8. Hi, do you have any tips for removal of the grub screw. Mine seems very deep and it feels like either the allen key will break or the screw will fail. It doesn't want to budge. Thankyou
  9. Hi Rohan, I do have such a spread sheet . It's a little clumsy and I do have intent to make it more robust. I hope to doing this fairly soon and post it for consideration.
  10. Hi. Did you ever resolve that issue. Mine is the same. The engine is out so I'm looking at all hoses. It certainly appears that lotus treated the plumbing as an after thought with no consideration for production, maintenance or reliability!!
  11. Installed valve Spring height usually refers to the distance between the valve spring seat and the seat at the retainer. It is of interest since it affects the spring preload with valve fully closed and the peak load when fully open. Installed stem height refers to the protrusion of the valve stem tip beyond some known datumn. I use the mating surface at the cam tower to cylinder head. The greater the distance,the smaller the shim . As correctly pointed out it is possible to run out of shim range. I've just had one seat installed and re cut to correct exactly that, reducing stem height by 0.50 mm. The stem tip can be ground but only by a few thou as the thickness of the hardened surface could easily be ruined. To my knowledge the lotus manual does not specify either Installed valve spring height or installed stem height. If any one has these values it would be very interesting to know. Further, given a constant valve stem length, the parameters discussed affect compression ratio as for example a recessed seat or excessively ground seat on the valve itself results in pocketing the valve which increases combustion chamber volume. There are a few choices of cam follower offering reduced pad thickness which offer a solution to the shim range issue. I've seen pad thickness offered in steel long skirt followers of 4.00 , 5.55 and 6.25 mm. These are primarily or usually considered with the use of high lift cams which usually have reduced base circle diameters where otherwise very thick shims would be required. The devil is always in the detail !
  12. Aluminium adhesive backed reflective tape! Its electrically conductive so should provide screening. B&Q sell it (uk)
  13. Oh. I am sorry to hear that. I read many of his posts. He was clearly very knowledgeable and eager to share that knowledge. Thankyou for the information on the sealant.
  14. Hi mr molemot. What zero thickness gasket goo do you recommend
  15. Hi. I'm in the process of dimensional verification of my 912 build using Omega high compression pistons and would be very interested to know what exact piston you had. I'm measuring clearances of .0025 / .0033 which I feel are to small and are certainly smaller than the Omega recommended and am in the process of deciding what to do next. If you had the 9mega part number off the crown or a photo that yould be brilliant.
  16. Hi Giorgio, you mentioned a front crank cover modification.......what was the mod?
  17. Thankyou to all, job done! Very careful scraping with new razor blade after a soak in rust remover did the trick. With the blade held slightly away from the surface and pushed into the corner the fillet radius of rust and crude is gone. Thanks also due to PNM Engineering for advice!
  18. Spot on! As a mechanical engineer but not an expert in vibration and harmonics this is the root of the matter. There are two scenarios to design for a) the harmonics and resonance that may cause excessive deflection in belt runs and b) the loss of tension caused by counter clockwise rotation which can occur during engine switch off. Where there is a potential for resonance, dampers are usually employed and for the kick back situation I observe that many tensioners in high reving motorcycle engines often have a one way device which allows forward motion of the tensioner but limited reward motion. As an expreiment I've rotated my engine backwards through 10 degrees and it is shocking how the tension on the drive side disappears, leaving the belt slack for the next engine start event. If that slack is not enough to cause belt creep ( which it appears not to be) then it's not an issue. For that situation, the fixed tensioner is theoretically better .....Its all a compromise and the point has been well made here that overthinking the issue is a real danger and that for well maintained set ups both solutions are ok. I do observe from work on various "modern" machinery with a cam belt however, that the use of hydraulically damped spring loaded tensioners seem common.
  19. Thanks, but I was rather refering to the mound of rust like crud that fills the corner radius in the counter bore where the liner sits. It is tough and looks like it needs a chisel and sandpaper which of course , though tempting would ruin the engine. ...I'm currently soaking it in rust remover which is slowly helping.
  20. pullies well, and feels sturdier than the others, but no guarantees! If the HTD pullies were priced better, I'd go with them, but this was an inexpensive upgrade for the time being. Rockauto.com lists them under $60USD. Thanks snowrs...do you mean Nissan 200....I had a 300 zx twin turbo years ago (fantastic machine...some to rag stole it and burnt it) and that was a v6 with a single cambelt 6 yards long!
  21. Looks like a fantastic job. Do you have any tips for cleaning the liner seating area in the block.
  22. I have been considering this too but feel some small range of spring compliance would be beneficial in coping with thermal expansion and contraction. I will give the matter further thought and post my solution when ready.
  23. Hi, I've been thinking about such a mod..Some sort of threaded rod passing through the adjuster. How were you planning to do it? Excellent and thankyou Lovely looking engine !
  24. Please dont get me wrong, I love lotus and I've owned mine for thirty years....I'm nit sure lotus had a strategy for solving an early belt jump problem.....I think in the early days thet lurched through a field of iterations in hope that the "next mod" would fix it. I've worked on various high reving Ferrari, alfa and Landis all of whom use auto damped tensioners!! Who really knows?????? We need a direct line to CABC!
  25. Hi. I had understood that after 1986 / 7 the 900 series standardised on htd with fixed eccentric tensioner and not the auto tensioner?
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