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| Cam belt replacement | Rate Topic |
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| Posted: 12-17-2015 10:51 pm |
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1st Post |
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Joenpate56 Member
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I am replacing the old belt as it is several years (10+) old. The car runs. Can i just remove the old one and put the new one on without moving any of the gears. then set the tension. Thanks
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| Posted: 12-18-2015 07:21 am |
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2nd Post |
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answerman Member
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Here. I have a very detailed explanation of how I did it (because I don't trust the gears to not turn). Probably overkill, but way less margin for error. The approach I used (got the idea from a friend who's a Lotus afficianado) was to set the engine at TDC with the 110 marks lined up, then take a bottle of WhiteOut and mark each gear (both cams, crank, and ignition) with a mark on one slot, and mark the old belt with a corresponding mark on the tooth in that slot. Once I had done that, it was a simple matter to remove the belt, line it up with the new one, mark the corresponding teeth on the new belt (counting the teeth between the marks to be sure) and then pop the new belt on in the appropriate location. Worked just fine, the whole process took maybe 3 hours from start to finish... I was in no hurry and I am sure it would go faster the next time since I now know exactly what has to be removed to get at it. For posterity, here's the order I did things (I used Greg's guide as a, well, guide, but there was more to be done than he had outlined: 1. Disconnect battery and coil wires, just because. 2. Remove top half of belt guard (I have the two piece guard) 3. Attempt to remove bottom half of guard. Grumble because it won't come out at this point, too much stuff in the way. 4. Loosen alternator, remove belt. Remove fan and pulley. Skin knuckles a bunch because of proximity to radiator. 5. Look down and realize that the lower guard still isn't going to come off. 6. Remove crank pulley. This went way better than I had expected... put a 19mm socket on my ratchet, put a pipe on the handle, and had Mrs. Answerman stand on the brake pedal (since I've never had a functioning hand brake) while I first hit my knuckle with a rubber mallet (ouch!) and then the pipe a few times to break it loose. Moved engine BACK to TDC since of course it moved during this process. 7. Now I can remove the lower belt guard. Did so. 8. Got my bottle of WhiteOut and marked one tooth/slot combination on each of the 4 gears. 9. Loosened tensioner and pulled belt off the gears. Loosened upper radiator hose clamp at top of engine, pulled hose off the fitting, and snuck the belt through there. Old belt is off! 10. Removed tensioner (that actually came out fairly easily). 11. Took tensioner to bench, followed Greg's process at http://www.jensenhealey.com/tech/bearing/bearing.html to disassemble tensioner and replace the bearings. The old ones seemed fine, but since I went this far I didn't see a compelling reason to NOT replace them. 12. Put newly assembled tensioner in place, loosely. 13. Take new belt, count teeth and make new WhiteOut marks corresponding with marks on old belt. 14. Put new belt on. Take belt off, put on again because I was one tooth off on the crank gear. Triple check all marks and deem it good. 15. Tighten tensioner till the belt tension seemed about like it was on the old one (was able to twist it about 45 degrees between the oil pump/distributor gear and the intake gear). 16. Think about it for a while and decide that I am going to be one of the 12 JH owners that still has the belt guard in place. Put the lower section back on. 17. Reinstall crank pulley and fan/pulley. 18. Reinstall alternator belt and tighten. 19. Reinstall top half of belt guard. 20. Reconnect coil wire and battery cables. 21. Say a little prayer, get in, and turn key. Starts right up and seems to run as well as she ever did. Whew.
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| Posted: 12-18-2015 08:56 pm |
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3rd Post |
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Joenpate56 Member
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Thanks Answerman: I really appreciate the detail. My belt should arrive today so maybe I can attack the project over the weekend.
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| Posted: 12-21-2015 02:14 pm |
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4th Post |
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Brett Gibson JH5 20497 Member
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I heard that one approach is to cut the belt on the engine in half, length wise, then slide the new belt onto the pulleys, once on cut the old belt off then slide the new one the remainder, have not used this method myself but maybe at some point I will give it a try.
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| Posted: 12-23-2015 09:24 am |
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5th Post |
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dwalls1 Member
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I am going to salt this one away for the future. It sounds so simple and reasonable, there must be something wrong with it.
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| Posted: 12-23-2015 04:22 pm |
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6th Post |
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Joenpate56 Member
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What would you use to cut the belt. Its pretty tough stuff.\?
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| Posted: 12-23-2015 04:37 pm |
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7th Post |
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Brett Gibson JH5 20497 Member
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I cut one up just to see how tuff they are with an "OLFA" Knife box cutter, takes a little time but slices's it up. http://www.olfaproducts.com/ProductDetail.jsp?LISTID=370000-1137370779
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| Posted: 12-24-2015 03:35 pm |
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8th Post |
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Joenpate56 Member
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i may try the cutting proceedure but i will mark everything up as Answerman detailed. thanks for all the suggestions
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| Posted: 10-14-2016 02:21 am |
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9th Post |
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JPJH Member
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Any advice on which tension gauge to use in setting the new cam belt tension?
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| Posted: 10-14-2016 02:30 am |
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10th Post |
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Esprit2 Member
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Brett Gibson JH5 20497 wrote:(Snip)... cut the belt on the engine in half, length wise, then slide the new belt onto the pulleys (Snip)...dwalls1 wrote: (Snip)... It sounds so simple and reasonable, there must be something wrong with it.That method, and using paint marks, etc-etc, are all ways of preserving the existing cam timing; however, neither makes sure the resulting timing is correct. If the timing was previously off a tooth, or more, all these methods do is preserve what was, even if it was wrong. It's not difficult to time the engine from scratch, and doing so makes sure timing is correct. Regards, Tim Engel Last edited on 11-12-2016 05:22 pm by Esprit2 |
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| Posted: 10-14-2016 03:29 am |
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11th Post |
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Esprit2 Member
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Joenpate56 wrote:I am replacing the old belt as it is several yearsThe black, trapezoidal tooth timing belt is supposed to be replaced every 24k miles or 24 months, whichever comes first. I hope the 10+ years was not running, in storage. (Snip)... Can i just remove the old one and put the new one on without moving any of the gears. then set the tension.You can, but if the timing is set to book-spec, then it's an emissions setting. You can pick-up 10 hp by setting both the intake and exhaust pulleys to 110 MOP timing. Doing that will require removing both pulleys, flipping them over, and setting the timing by using marks that may not be on your pulleys (some pulleys have dual 110/115 timing dots, and some just have one... 115 MOP). See the recent JHPS discussion, here: http://www.jensenhealey.com/forums/view_topic.php?id=1293&forum_id=2&page=4 Pick-up the discussion on page 4, message 65... onward. For detailed instructions on replacing the timing belt, go to the Jensen-Healey page on Facebook.com, click on FILES in the upper-left margin, and download the Word.doc on the how to replace the timing belt. Or just go here: https://www.facebook.com/groups/102760143109766/files/ Or PM me with your email address, and I'll send to you as a file attachment. Regards, Tim Engel
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| Posted: 10-14-2016 11:21 am |
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12th Post |
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qwerty Member 
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Me again :) You can also replace the standard belt with a gates racing belt for apparently 3x the life. Gates Part # T104RB I receieved mine, confirmed trapezoidal tooth shape.
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| Posted: 10-15-2016 07:12 am |
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13th Post |
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Esprit2 Member
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qwerty wrote:You can also replace the standard belt with a gates racing belt for apparently 3x the life.The Gates Racing blue timing belts are a definite step up in durability. The other plus is that the blue belts are very stable, and it should not be necessary to re-tension the belt for a long time. Continue to check the tension on the normal schedule, but it should rarely be necessary to make a tension adjustment. The only problem is that Lotus isn't doing any new parts development work on an engine that went out of production approx 36 years ago (907 with trapezoidal belt), and Gates Racing won't make decisions/ specs for another company's product (a Lotus engine). As a result, there is no official tension spec, and no corporate effort to establish one. There has been a Gates Racing blue belt for the round-tooth HTD belt for several years, and a pretty strong grassroots effort to zero in on a correct tension (mostly on the TurboEsprit list on YahooGroups). At the Lotus tension spec, the blue belt has a pronounced whine, which indicates it is too tight. With a lot of users reporting results, it now appears that 82-84 on a Burroughs gauge is about right for the HTD. But, the Burroughs gauge is thickness sensitive, and the blue HTD is thicker than the old black belts. So while a 'reading' of 82-84 works, I can't say exactly what the actual tension in the belt is. I suspect that it's something in the 90 range, but can't say for certain. If you really want longer belt life, then the best solution is to convert to HTD pulleys, then go with the Gates Racing blue belt. Still hold the mileage limit down to about 50k miles, but ten years should be reasonable for a time limit. Short of converting to HTD, the Gates Racing #T104RB blue belt is the best trapezoidal-tooth belt option available, but it's going to take another grassroots effort to zero-in on a consensus tension for it. Somebody needs to go first. Looks like that's you. I highly recommend that you tension it using a Burroughs gauge so that the data is easier to correlate back to accepted numbers. Set the tension as tight as possible, short of causing a whine. The belt may not whine on cold start-up, but the tension increases as the engine comes up to temperature. (A OEM black belt set to 90 Burroughs cold will end up at about 125 when the engine is hot.) Since the tension is to be set cold, it's necessary to let the engine cool down over night, then try setting the tension a few pounds lower, and let it warm up again. Repeat as necessary, one tension adjustment per heat cycle. As I mentioned above, the blue HTD is thicker than the older black HTD belts. The basic web, not the depth of the teeth. Use a vernier to measure the web thickness between two teeth, and report the thickness here. That will be helpful in trying to correlate blue vs black Burroughs readings. Once the Burroughs tension is determined, it's then possible to correlate a Krikit KR-1 tension reading. On a cold engine, take a fresh reading with a Burroughs. Then take a reading with a Krikit. If you feel energetic, change the Burroughs tension in increments of 5, from around 75 to 100, taking a corresponding Krikit reading as you go. Create a conversion scale. There's no published math formula that relates Burroughs to Krikit, so empirical measurements is the only way to go. Neither gauge actually measures the tension in the belt. They measure some other attribute, and correlate that back to tension through some formula they're not sharing. Unfortunately, each gauge measures a different attribute, so back to back measurements of the same belt tension is the only way I know of to correlate readings. Regards, Tim Engel
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| Posted: 10-15-2016 10:50 am |
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14th Post |
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qwerty Member
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Happy to be a guinnea pig, Tim are there any specs on the HTD belt (which i was looking for but can't find the crank pulley, otherwise i would have gone down that road) with regards to Hertz tuning? At work we tune all our belts using Hz or "frequency vibration" to tune belts. Thanks for the heads up on whine = too tight (<--EDITED). I will report back, also with a Hz frequecy. There are apps for the iPhone out there for frequency tuning ( i used a continental app to compare), you place the microphone over the longest part of the belt and tap the belt with the handle of a screwdriver or simply your finger. The iPhone will record and display the frequency it vibrates at, indicating tenision. I was suprised at how accurate and repeatable it is. Last edited on 10-16-2016 02:28 am by qwerty |
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| Posted: 10-15-2016 10:46 pm |
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15th Post |
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Esprit2 Member
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qwerty wrote:Tim are there any specs on the HTD belt (which i was looking for but can't find the crank pulley, otherwise i would have gone down that roadAny of the Lotus parts specialists should be able to provide you with the crank sprocket (JAE, Dave Bean Engineering, SJ Sportscars). Failing that, contact Mike Taylor at Lotusbits in the UK. He can probably set you up with a serviceable used part. Lotusbits Ltd, lotusbits@hotmail.com (Mike's a good guy, but terrible at answering email) 07866 255 614 Cell, Mike Taylor Tim are there any specs on the HTD belt(snip)with regards to Hertz tuning?Lotus issued a frequency spec for the B-prefix, HSN HTD belt. It does NOT apply to the earlier A-Prefix, HCR HTD belt, and definitely not to the trapezoidal belt. The spec changes the basic procedure from tensioning at TDC, to tensioning at 30° BTDC. The correct frequency response is 100-110 Hz. The belt tension varies quite a lot as the crank is rotated, so crank position is critical when checking the tension. The original tension specs (both J-H & Lotus) call for checking tension at TDC; and the later frequency spec (circa 2000) calls for checking at 30° BTDC. Watch what you're doing, and don't mix them up!! Thanks for the heads up on whine = too loose. I will report back, also with a Hz frequecy.Nope! Read it again... whine = too tight. A belt that whines is too tight, so back off a bit. There are apps for the iPhone out there for frequency tuning (Snip)...I use TuneIt! on a laptop (they have versions for several smart phones as well), with a slender boom mic (stick mic?... Harry Potter's wand). The mic is easier to snake in to the timing belt, while the typical phone is too bulky (more of an issue on a Turbo Esprit... not so much on a J-H). Most of the frequency apps are musical instrument tuners, and pick up the entire spectrum... meaning a lot of 'noise' outside the 100-110 Hz range. If your app has a 'set-up' option, narrow the band to little more than the target range. Something like 75-135 Hz. That will provide a much cleaner reading. Regards, Tim Engel
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| Posted: 10-16-2016 02:27 am |
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16th Post |
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qwerty Member
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Thanks for the correction Tim, I'll edit the post to keep correct information.
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| Posted: 10-16-2016 08:31 am |
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17th Post |
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qwerty Member
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Esprit2 wrote: qwerty wrote: Tim, Thickness of the Gates Blue T104RB excluding tooth height is averaging 2.35 - 2.40mm measuread at various points around the belt and on both sides. I will be able to measure a Gates HSN and JHPS belt tomorrow. Ordered a Krikit 1, now to find a Burroughs. Are you aware of anyone making HTD Red dot sprockets for the stock JH Cam without adjustability. IE non vernier. I found green dots but no red. Last edited on 10-16-2016 08:32 am by qwerty |
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| Posted: 10-16-2016 08:51 am |
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18th Post |
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qwerty Member
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Brett Gibson JH5 20497 wrote: I cut one up just to see how tuff they are with an "OLFA" Knife box cutter, takes a little time but slices's it up. http://www.olfaproducts.com/ProductDetail.jsp?LISTID=370000-1137370779 I also tried this on an old belt an noticed the belt construction on this particular belt (BANDO) brand is spiralled so if you do go down this track make sure to pull it in the direction that the belt will get wider as you tear it away rather than smaller.
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| Posted: 11-02-2016 12:32 am |
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19th Post |
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Esprit2 Member
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qwerty wrote:Thickness of the Gates Blue T104RB excluding tooth height is averaging 2.35 - 2.40mm measuread at various points around the belt and on both sides. I will be able to measure a Gates HSN and JHPS belt tomorrow.Did you ever measure the Gates HSN & JPS belts? I just measured a new Flennor 24513311 black belt, and two other used belts I couldn't identify, and the readings were all 0.088-0.089 inch (2.235-2.261 mm). That's about 0.004" / 0.1mm difference between the blue & black belts. Not as much as between the blue & black HTD belts. Stretching my memory, but for the HTD belts, I think the difference was more like 0.016-0.015"), and that made about a 3-5 lb difference in Burroughs readings. Last edited on 11-02-2016 12:52 am by Esprit2 |
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| Posted: 11-02-2016 12:42 am |
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20th Post |
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Esprit2 Member
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Brett Gibson JH5 20497 wrote:I cut one up just to see how tuff they are with an "OLFA" Knife box cutter, takes a little time but slices's it up. http://www.olfaproducts.com/ProductDetail.jsp?LISTID=370000-1137370779A friend's Esprit had the timing belt jump a few teeth, and took out the valves. When we got the belt out, we found it had been rubbing on something, and was worn down to half it's normal width. He was going to trash it, but I saved it. I then bought a large strap wrench from Harbor Freight, and replaced the strap with the narrow timing belt. Now when I want to securely hold a pulley while tightening or loosening the retaining bolt, I have a strap wrench that will actually engage the pulley teeth. It has a very secure grip. Regards, Tim Engel Last edited on 11-02-2016 12:42 am by Esprit2 |
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