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I just cant agree with any decomposition in a pristine belt! Entropy perhaps? Thats another topic.
It was not exposed to U.V Radiation, only perhaps to temperature changes.
After all it still smells new and is flexible.
I would agree, a properly stored belt won't deteriorate in quality for a very, very long time.

Belts deteriorate over time due to temperature changes, exposure to other chemicals (oil leaks is a classic one), and static positioning under tension (car not being driven), among other reasons. If you keep your unused belt in a constant room temperature, away from sunlight or exposure to chemicals or other environmental contamination, it'll still be good to use for a long time. Yes, rubber and plastic do deteriorate over time as the volatiles escape but that is a slow process, particularly when storage is proper.

That said, even if the belt is properly stored I'd get a new one if it's more than say seven or eight years old.
 

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Do the genuine Lotus belts have a date code on them?
 

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Yes, digits 1-3 are the day of the year, 4th digit is the year and the two letters are the manufacturing plant.

e.g. 0333DS is the 2nd February 2013, Dumfries Scotland
 

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I would never use this belt after owning 928's and all the information from you guys.
The next one will be blue along with all else that ought to be replaced.
It just seems a waste.
What did/does Lotus do then after 5 years of having belts stored waiting years to be used?
Do they just throw them away and have new ones manufactured?
I doubt it.
-btw, that waist belt is great.
 

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The belt is made in Germany by FLENNOR.
Anyone familar with that name?
 

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Yes, digits 1-3 are the day of the year, 4th digit is the year and the two letters are the manufacturing plant.

e.g. 0333DS is the 2nd February 2013, Dumfries Scotland
Thanks! How old is the one you are replacing? Are new ones from Lotus of recent manufacture?
 

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Thanks! How old is the one you are replacing? Are new ones from Lotus of recent manufacture?
Lotus buys smallish quantities that can be turned over before they get too old. The genuine Lotus branded belts are NOT just old inventory from back when the engines were current.

The unfortunate thing about the date code is that xxx3DS doesn't tell you if it's 2013 or 2003.

I have a piece of a belt marked 465DS (46th day, 2005), so clearly, a date early in the year may not start with 0 to fill in the 4-digit code.

Rubber products, timing belts included, do have a shelf life, but it's not inordinately short. The shelf-life will vary between types of belt. HCR, HSN and HNBR rubber belts, and the different cord body materials will have unique life expectations, so don't lock in too hard on one stated interval. The Gates spec mentioned above is the first time I've read anything official from a manufacturer.

Just my opinion, but the belt is cheap compared to the labor or effort that goes into installing it, and cheap compared to the damage that can occur if the belt skips timing or breaks. For that reason, I don't use an old belt from the spares bin, and I have several new-old belts in my garage that I retired un-used rather than incur any risk. I don't wish to be penny wise and dollar foolish.

The service interval clock really starts in earnest when the belt is installed and tensioned. Under stress, the belt's life drops down to that stated in Lotus' service replacement intervals... as little as two years for the trapezoidal tooth belt.

Flennor is a quality belt brand from Germany. I've never seen a Flennor belt over-the counter at a parts store in the USA, but JAE carries Flennor belts.

Gates makes most of the HTD belts in the world, not only under their own label, but also for many other brands.

Regards,
Tim Engel
 

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Think I made this post before but the 'Blue belt' is much stronger than the 'black belt' originally used. I know those fibers 'poked' my fingers whilst installing.


Robert
 

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Really great information here, my thanks to all who are sharing data and experience.

As a somewhat newbie to Lotus, I hope you don't mind me making (and stating) a few basic conclusions with respect to belts for four banger Esprits...

1. The Gates "blue belt" is highly regarded and a good belt for the Esprit because a) it's well constructed/strong, and b) has the right tooth profile, yes? The additional cost ($165 for blue v. $40 for T188) seems justified, yes?

2. The next best alternative is the Gates T188 belt as it's well made/designed and has the right tooth profile.

3. The OEM Lotus belt is an equivalent alternative to the T188 belt.

4. The trapezoidal tooth belt is a poor alternative due to both a) weaker construction/design, and b) tooth profile is poor for the Esprit cam pulley.

Is that roughly the belt hierarchy here?
 

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I've dealt with a lot of timing belt issues....and a lot of discussion of the topic...on more expensive and complex exotics than our simple four banger Esprits.

The fact of the matter is that it's rarely the belt that fails. In the vast majority of cases it is some other factor which is the culprit....which then causes the belt to break...such as a failing tensioner bearing, oil leaking onto the belt and degrading the belt, dirt and road debris entering into the vicinity, etc.

To think that simply putting a good quality belt on your Esprit is going to make it relatively impervious to failure is really not understanding the big picture. I would strongly encourage DIYers to look at these other factors in parallel when considering what to do to avoid a catastrophic failure.
There was mention somewhere that cam follower failure may cause the belt to break. I have heard of one person that have seen what looked like a crack and wear marks when checking and adjusting valves. Do you just change the broken one or all of them? What is the recommended service life of the followers?
 

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1. The Gates "blue belt" is highly regarded and a good belt for the Esprit because a) it's well constructed/strong, and b) has the right tooth profile, yes? The additional cost ($165 for blue v. $40 for T188) seems justified, yes?
The JAE/ Gates blue belt has the correct tooth profile (it fits) and is made of the latest, strongest materials. The high cost is more a function of it being produced in small batches for JAE... it's not a mass produced belt. Is the high cost worth it? That's for you to answer for your own priorities, but I think it is. It's like insurance. The premiums are always too high until you need the coverage.
2. The next best alternative is the Gates T188 belt as it's well made/designed and has the right tooth profile.

3. The OEM Lotus belt is an equivalent alternative to the T188 belt.
I'd disagree. The next step down from the Blue belt would be the Lotus Branded, B-prefix belt. It was introduced in 1995, uses improved HSN rubber, and has a 50,000 mile/ 5 year service interval.

The T188 and the A-prefix Lotus branded HTD belt both preceed the HSN belt, use 1960's tech HCR rubber and a fiberglass cord body. The service interval is just 37,500 miles/ 3 years. The Gates T188 is well made for what it is, but it's an early spec HTD belt using old-school materials technology.
4. The trapezoidal tooth belt is a poor alternative due to both a) weaker construction/design, and b) tooth profile is poor for the Esprit cam pulley.
Both the A and B prefix Lotus HTD belts (and their proper aftermarket cross-references) are superior to the earier 1960's tech trapezoidal tooth belt. The basic tooth shape is just a superior design. Going from trapezoidal to HTD is an upgrade. Going the other way isn't.

Any change in tooth profile requires a complete conversion, including the crank, cam and auxiliary pulleys. Do not consider running a trapezoidal tooth belt on an HTD tooth pulley, or vice versa.

Gates Rubber made all the Lotus branded timing belts and is a premium brand. You can trust the build quality. Otherwise, stick with quality name brands, and avoid internet no-name deals. If the price seems too good to be true, it probably is. Buy quality, and pay a little more if that's what it takes to get it. The Lotus 9XX timing belt is not the place to go cheap.

Regards,
Tim Engel
 

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Another point to bear in mind when considering a non Lotus belt is the alternatives are narrower which means the tensioning specification is different to the published Lotus values.

Whilst the Gates blue belt is the same width as the OE belt I expect the belt mass constant differs and therefore it too requires a different tensioning specification.
 

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There was mention somewhere that cam follower failure may cause the belt to break. I have heard of one person that have seen what looked like a crack and wear marks when checking and adjusting valves. Do you just change the broken one or all of them? What is the recommended service life of the followers?
I've seen a lot of cracked tappets in recent years. I've even had one split in two in my hand while I was cleaning it. That owner missed a catastrophic/ expensive failure by the slimmest of margins.

I've also been seeing a lot of 9XX tappets with the top wear surface breaking up (spalling... see attached photo). Chunks missing. It looks like an old concrete garage floor with areas of smooth surface material missing.

I don't know if that's a function of reduced ZDDP levels in modern oils, or if the tappets just have a limited life expectancy; but I'm now pretty quick to recommend buying replacement sets instead of replacing just the cracked ones... despite the cost. I'm getting a little paranoid about old tappets.

Early 9XX engines used chilled cast iron tappets that had a 32mm tall skirt. Around 1988 (1992??), Lotus introduced steel tappets to address apparent service life issues resulting from the 107 cam's very aggressive lobe ramps really banging the valves open and closed. Those Lotus OEM steel tappets have a shorter 31mm skirt which could make them more prone to cocking in their bores when used with more aggressive, higher lift cams. Lotus advised against using them with the Lotus 104 cam, for instance.

Of the cracked tappets I've seen, the cast iron and steel versions both seem to be cracking. It's not like one tappet is the problem, and the other is the solution. In a friend's X180R, all but 4 were cracked... we replaced the full set.

JAE sells an aftermarket tappet that is steel, and has a 33mm skirt, 2mm longer than the current Lotus service replacement part. It's also available in several crown thicknesses. Inside the tappet there's a raised pad that actually contacts the shim. In the JAE parts, that pad is available in several heights. If your old valves have receded, or the valves have been re-ground and lapped in to the point that the necessary shims are getting really thin, then select a thinner tappet to allow the use of thicker shims once again.

I do think it's critically important to check the tappets for cracking at every opportunity. But waiting until you see a crack is probably going to make any corrective action too late... you'll find the crack during the autopsy.

Regards,
Tim Engel
 

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Really great information here, my thanks to all who are sharing data and experience.

As a somewhat newbie to Lotus, I hope you don't mind me making (and stating) a few basic conclusions with respect to belts for four banger Esprits...

1. The Gates "blue belt" is highly regarded and a good belt for the Esprit because a) it's well constructed/strong, and b) has the right tooth profile, yes? The additional cost ($165 for blue v. $40 for T188) seems justified, yes?

2. The next best alternative is the Gates T188 belt as it's well made/designed and has the right tooth profile.

3. The OEM Lotus belt is an equivalent alternative to the T188 belt.

4. The trapezoidal tooth belt is a poor alternative due to both a) weaker construction/design, and b) tooth profile is poor for the Esprit cam pulley.

Is that roughly the belt hierarchy here?
1. I don't know why anyone would use anything other than a new blue belt.

2. Not really. The OEM is the next best.
A912E6697F - HCR, 26.4mm wide, Curvilinear tooth profile. Old OEM belt superseded by B912E6697F circa 1995.
B912E6697F - HSN, 26.4mm wide, Curvilinear tooth profile. Current Lotus OEM belt.
T188 - HCR, 25.4mm wide, correct Curvilinear tooth profile. Gates lists for 89-91 Peugeot 405.
T249 - HSN, 25.4mm wide, incorrect Modified Curvilinear III tooth profile. Gates lists for 94-up Nissan 3.0L and 3.3L V6.

I contacted Gates and they do not recommend any belt as a replacement for the B912E6697F or A912E6697F in spite of the fact that they are an OEM supplier. I was told this is because Gates OEM and aftermarket operate as separate entities and that Gates aftermarket is legally prohibited from selling a branded version of the OEM belt due to an agreement between Lotus and Gates OEM division. I was also told that Gates racing is yet another division that isn't bound by the same agreements and was able to re-engineer the belt (that the OEM division produced for Lotus) to sell to JAE.

...This all seems extraordinary but I was a product engineer for Fram/Bendix/Autolite for many years and it's really the norm in the automotive industry.

3. The current OEM (B912E6697F) combines the profile of the T188 with the increased durability of the T249 and is 1mm wider than either.

4. Yes, a very poor choice indeed. The trapezoidal belt was for older engines (pre '86 I believe). Different pulleys, totally incompatible.
 

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Another point to bear in mind when considering a non Lotus belt is the alternatives are narrower which means the tensioning specification is different to the published Lotus values.

Whilst the Gates blue belt is the same width as the OE belt I expect the belt mass constant differs and therefore it too requires a different tensioning specification.
The original Lotus OEM belt is 26.4mm wide, while the similar industry standard belt width is 25.4mm... that's a nice, round 1.0 inch wide, and 1mm narrower than the Lotus belt.

While it's reasonable to presume that in a destructive tension test, the narrower belt will fail first, for the task at hand, the difference is probably not significant. That is to say, both belts would exceed the anticipated stress by several factors of safety.

However, greater width does equate to greater mass, and frequency response is a function of mass (and other factors). Lotus frequency spec for tensioning the timing belt was based upon their own OEM belt, so the results may vary if a narrower/ lighter belt is used.

It would be nice to have more data on that so we can be more anal retentive about tensioning the belt. However, to the best of my knowledge, that data hasn't been published.

Also, I'm not certain the Gates Blue belt's width has been published. It's not a "Lotus" belt, and it may have been made to Gate's standard width. Just a thought. Anyone care to measure theirs? Regardless, it's still the strongest belt available.

Regards,
Tim Engel
 

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I do think it's critically important to check the tappets for cracking at every opportunity. But waiting until you see a crack is probably going to make any corrective action too late... you'll find the crack during the autopsy.

Regards,
Tim Engel
I know its a strange way to look at it but in a way I am thankful of this problem as I probably would not have my car if not for the cracking and failure of the tappet.
 

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B912E6697F - HBNR (Same as HSN?), 26.4mm wide, Curvilinear tooth profile. Current Lotus OEM belt.
No. The B-prefix belt was introduced in 1995, and is HSN (Highly Saturated Nitrile) rubber, not HNBR.

The JAE/ Gates Racing blue belt is HNBR rubber, which is the current leading edge technology.

HCR = High-Temp Chloroprene Rubber (similar to neoprene, but better) -- 1960s technology.
HSN = Highly Saturated Nitrile Rubber -- Introduced in 1995.
HNBR = Hydrogenated Acrylonitrile-Butadiene Rubber -- Current materials technology.

How 'bout editing item 2) in your post, deleting the part that says the b-prefix belt is HNBR... just to minimize confusion for future readers.

I contacted Gates and they do not recommend any belt as a replacement for the B912E6697F or A912E6697F in spite of the fact that they are an OEM supplier. I was told this is because Gates OEM and aftermarket operate as separate entities and that Gates aftermarket is legally prohibited from selling a branded version of the OEM belt due to an agreement between Lotus and Gates OEM division. I was also told that Gates racing is yet another division that isn't bound by the same agreements and was able to re-engineer the belt (that the OEM division produced for Lotus) to sell to JAE.
All true. Gates is THE OEM belt & hose supplier to Lotus. And I'm certain Gates makes an HSN version of the Curvilinear HTD1 belt (ie, Lotus OEM B-prefix belt, but 1" / 25.4mm wide), we just need to find the number. But due to Gates OEM's exclusive contract with Lotus, they cannot reveal the 1.0"/ 25.4mm standard belt's model number. And that's understandable.

If you ever get a talkative Gates tech rep on the phone, do NOT mention Lotus. Just speak in generic terms and ask for an HSN version of the Gates T188. A Curvilinear HTD1 belt with 133 teeth.

OR, just buy a belt from your favorite independend Lotus vendor. We need their support as much as they need our business. Just to pick a name out of the hat... JAE can sell you a Lotus branded belt, and it's more expensive than a Gates/ Goodyear/ Dayco cross-ref over the counter. But ask, and JAE can also sell you a Gates or Flennor belt for a price very close to NAPA's... plus shipping. If you can send a simple order for a timing belt their way, do it. Keep them in business with your business, and we all come out a head in the long run. I really don't understand the active effort to avoid buying from them.

Trapezoid owners...
Note that HNBR rubber isn't a Gates option for that belt, since the factory with that mandrel is not set up to run HNBR rubber. However, they can run HSN rubber, which is an incremental improvement over the default, old-school HCR rubber. To that end, JAE has also struck a deal for a small order of HSN trapezoidal belts. Again, it's a short-run, special order, so the price is higher than a plain old HCR belt. But the trapezoidal tooth belt is the weakest belt ever spec'd for the 9XX, and any improvement in durability is a very good thing.

Debating between HSN and HNBR for the HTD belt is playing with what flavor frosting you want. Switching from HCR to HSN rubber in the trapezoidal belt is changing the cake itself... much more significant.

Regards,
Tim Engel
 

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I's been using the 25.4mm belt, and tensioning using the acoustic method to 100-110Hz, and it's been working fine, without whine. I also replace my belt often! Much more often than 18k in fact.

Here are my tappets at 74k, when I discovered the original cast iron exhaust tappets were cracked and were worn so that they weren't spinning any more. The spinning would help equalize the wear on the face, but once they stop spinning, then they will wear much faster, and are much more likely to crack.

Exhaust tappets


Here you can see the groove from wearing in the same spot, due to not spinning. You could feel this groove, and there appeared to be a crack on the inside.


Intake tappets



I replaced all of the tappets with new stronger nitrided steel versions from JAE.

This required all new shims, since the new tappets are a different thickness. Couldn't even use my old shims to get a baseline, so I made fake cast iron shims just for the measurements.

BTW, I have always used Mobil 1 15W-50, but not sure what the PO's used for the first 41k miles.
 
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