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| Joined: | 05-01-2005 |
| Location: | Minneapolis, Minnesota USA |
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The pulleys in your photo are worn and should be replaced.
A timing belt that's too tight might aggrevate the situation, but it's not the primary cause. The early J-H pulleys were not hard anodized, have a shiny appearance on the wear surface (like yours), and tend to wear relatively rapidly just because they're too soft for the task.
Later J-H pulleys, and all Lotus pulleys were hard anodized for anti-wear protection, have a dark muddy-gray-green color (almost black), and provide long service without noticeable wear. Note that not all anodizing is hard anodizing. Bright colors are not hard anodizing and offer little wear protection.
Do NOT use your E-cam or 107 MOP pulleys with your C-Cams. Nothing bad will happen if you do, but the engine will not run at it’s best.
The E-cam used a 102.5 MOP (Yellow dot) pulley.
There is no 107 MOP pulley! But there is a 107 camshaft that seems to be popular with J-H owners, and it uses a 104 MOP (green dot) pulley.
The "104" in a PULLEY name refers to the valve timing MOP (Maximum Opening Point) that the position of the keyway in it's bore produces.
The "107" in the CAMSHAFT name refers to the last three digits in it's Lotus part number.
At some time, Lotus revised the part number format for camshafts. Originally, all cams had the same part number, and each cam was identified by a different prefix letter. The C-cam was C907E0351Z. With the new format, the C-cam was given the part number F907E0101G, and should have been called the "101" cam. However, the "C-cam" name stuck, and is still it's street-name to this day. Same with the D-cam (102) and E-cam (103). The 104 and 107 cams missed all that fun, and never had prefix part numbers/ names.
It's just coincidental that a 104 camshaft also uses a 104 MOP pulley. Don't get confused by the similar number naming.
The 100 MOP (blue dot) pulley is really 97 MOP. For some reason (??) they rounded that one off, but all the other pulleys are accurate as marked. If you are ever trying to degree a blue dot pulley, use 97 degrees in order to get the math to work out.
In any case, don't use your E-cam pulleys or 107 pulleys (whichever you have) with the stock J-H C-Cam. Buy replacement 110 MOP pulleys to make the engine that run better & stronger than stock. Or, if your engine originally came with 115 MOP pulleys and 'must' still pass an annual emissions check, then buy replacement 115 MOP pulleys. But buy HARD anodized pulleys. All Lotus OEM pulleys are hard anodized.
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The stock J-H C-cams are designed to run with 110 MOP (red dot) pulleys. The 115 MOP pulleys that were stock on early J-H 907s are for reduced emissions. They reduced the valve timing overlap, reduced the power output by about 10 Hp, and marginally reduced emissions.
The later 100 Intake (blue dot) / 110 Exhaust (red dot) set-up was also for reduced emissions, but took a different approach. The ignition timing was also severely retarded, and the fuel mixture was very lean. This set-up is the original "Torqueless Wonder".
A design-correct 110 Intake/ 110 Exhaust engine easily passed the 1972 Federal emissions standards; however, the Federal gov't had already published the new, more strict standards for 1974. The 110/110 set-up would also pass the '74 standards, but just barely. So, the original 115/115 cam timing was used in order to provide a larger margin for wear and mis-adjustment. Lotus didn't wish to go through the expensive Federal Certification any more often then absolutely necessary, so the 115 Int / 115 Exh set-up was used from the very beginning of production... even though the 1972-73 cars didn't need it.
*~*~*
The tensioner has enough adjustment range that the belt can usually be tightened to spec even with worn pulleys; however, the depth of tooth engagement is reduced by tooth wear. Since the engagement depth with new pulleys is pretty marginal to begin with, the loss of any engagement due to wear increases the risk of jumping timing, and isn't acceptable. Replace the worn pulleys.
*~*~*
The twist test is a workable way of checking the timing belt tension, "IF" you have the experience required to know what it's supposed to feel like. The big problem with it is that results vary widely with an individual's hand strength and experience.
It is far better to invest in an inexpensive Krikit KR-1 tension gauge from any Gates Rubber dealer/ parts store. In North America, NAPA stores carry the Krikit KR-1. If it's not in stock at a local store, they can order it from their central warehouse. I have a NAPA receipt from my last purchase and the line-entry reads:
Qty .. Part No . Line . Descrip.. Price ... Net ..... Total .. Code
.1 .... KR-1 ..... NBH . Gauge .. 10.89 .. 10.89 .. 10.89 . T6N
Krikit on NAPA Online (under US$15.00).
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx/Belt-Tension-Gauge/_/R-NBHKR1_0006447252
… Or …
https://napaonline.com/Catalog/Result.aspx
then search for “KR1“ in the “Find a Part” dialog box
… Or …
http://tinyurl.com/odau6c3
Krikit on Gates Rubber Website
http://www.gates.com/europe/brochure.cfm?brochure=2505&location_id=2976
None of the various tension gauges directly measure belt tension. The Krikit KR-1, Kent-Moore KM-128 and the Burroughs BT-33-86J each measure different attributes, and then relate that back to belt tension. For the same belt tension, they each produce different number values. Don't get caught-up in the exact 'numbers'. Burroughs 95 is NOT the same as Krikit 95!
For the Krikit KR-1 on the J-H/ Lotus 907, use these values:
44 Too loose. Don't drive it.
50 Normal minimum before requiring adjustment.
52 Used belt – target for re-tensioning a used belt.
55 New belts – set a little tight the first time to allow for initial stretch.
58 Too tight (do not exceed 100 Burroughs / 55 Krikit).
Krikits have two scales... be sure to read the POUNDS scale !
Use at your own risk. Lotus doesn't recognize the Krikit KR-1 or the tension values given above. This is a grassroots alternative, and the tension values were obtained by direct comparison to results produced by the Burroughs gauge that Lotus specifies.
Last edited on 05-05-2014 04:42 am by Esprit2