Best Cam belt for HC

[Alan_M]

Well I've been enjoying my Excel for a month or so now, but time to get my teeth into some servicing and improvements. I have sorted most items I need to service, but need to replace the cam belt.

So I would be grateful if anyone would be kind enough to advise which is the best belt to buy and where should I source from? Mine is an 85 registered, but I believe 86 model year, so if I'm correct this is the later HTD TYPE BELT. I will only be doing about 3,000 miles a year.

[AndyC]

This is subjective, but I'll put forward my view.

Main options, and how I see them.

Genuine- known OK, uses old belt technology but was good enough to support the warranty period.

Gates, black type- OEM supplier to Lotus but any non-Lotus one they supply will be slightly narrower (unless a special batch) but only marginally. 3% narrower probably doesn't matter, so probably good enough to last as long as genuine Lotus spec.

Gates, blue type- OEM supplier but using non OEM technology. Newer technology, proven on other manufacturers' cars just not proven on Lotus. Believe it's still 3% narrower than genuine belt, but if it's stronger then probably at least as good (probably stronger and better wear properties) as genuine.

Other belts - many of these will be made to good standards, but unless you have proof of their durability then it's an unknown.


Personal view.
If you're going to do low mileage (which you are) and change belts at least every two years, then it's likely that any would last, but probably worth going to at least the GatesOEM to safeguard an engine that's costly to repair/replace.
Blue belt technology may be an added bit of safety (I was running one of an early trial batches commissioned by a drivebelt specialist), but it's really piece of mind, it's not going to make the engine perform better.
OEM, to me, seems a waste of money given that it's just marginally different to one that I can go to a motorfactor and buy off the shelf.

[amarshall]

A few years ago, I asked Lotus about the "long life" belts developed for the US market.

Their response was that they still advise sticking to the 24k miles/24 months C service interval.

Don't ask me why, they didn't tell me. I'm just including it here for information.

[richardw]

A few years ago, I asked Lotus about the "long life" belts developed for the US market.

Their response was that they still advise sticking to the 24k miles/24 months C service interval.

Don't ask me why, they didn't tell me. I'm just including it here for information.

It's probably because they haven't evaluated the newer belts on these engines - and probably never will - therefore it is safer for them to stick to the original advice.

[amarshall]

http://www.lotusespritworld.com/EGuides ... belts.html

[Alan_M]

Thanks for replies. I think I will go genuine Lotus or the OEM equivalent Gates belt.
Where is the best place to source these?

[MrCoolA]

I’m running to the gates Blue belt and took advice from Gary Kemp who is experienced in the 9xx engines And as such very pleased to pay the extra and have his consideration that the belts will last a lot longer. I always bought Standard gates belts And have never had any issues with them, last year I decided to buy aCheaper belt and some three months post installation the belt failed and luckily for me not at high speed. Personally as I have spent £10k+ on my engine I will stick to the blue gate belts to give me that extra piece of mind but my honest opinion would be that for a standard engine bye the gates standard original spec belt. I would suggest that At each belt change check the sharpness of the teeth on the verniers As this may have contributed to my original belt Failure. I was surprised how quickly the verniers teeth Actually wore

[Esprit2]

Almost all black trapezoidal tooth timing belts are old 1960's HCR rubber technology. The change interval was 24,000 miles or 24 months, whichever comes first... and time is as important as mileage. There were essentially no main-stream improvements in materials in trapezoidal tooth belts until the recent Gates Racing blue belt, part number T104RB. It uses modern HNBR rubber, and is state of the art... well, ignoring the trapezoidal tooth profile itself. The blue belt is more expensive, but it's also much better... stronger, more durable and more stable.

The only 'black' belt exception is the HSN rubber belt that JAE special orders from Gates Racing, starting about 12 years ago. They also sell it to any other Lotus parts specialist who may be interested, so it's available through several specialists. Ask.

The black HSN and blue HNBR trapezoidal belts are aftermarket specials. There is no official factory support for those belts, so change intervals are based on opinions and collective owner experience. Most Lotus owners don't put enough miles on their cars to hit the mileage limit first, so I tend to focus on the time limit.

For the black HSN trapezoidal, 36 months is commonly used. For the blue HNBR belt, 60 months is conservative, but it's best to be conservative with the shallow trapezoidal tooth profile.

*~*~*~*
The original A-prefix part number black HTD belt also started out using the old HCR rubber. It's change interval started out as the same 24,000 miles or 24 months, but was later increased to 36,000 miles or 36 months.

In 1995, the round-tooth HTD belt was upgraded to a B-prefix part number, and used HSN rubber. It's change interval was 75,000 miles or 8 years, whichever comes first. If anyone from California is reading this, the change interval there was 100,000 miles with no time limit. HECK NO !! That was a state mandated change interval. It didn't make the belt any better, it just put the car companies on the hook for all belt related warranty costs for that time period. Now that all warranties have long expired, no owner in his right mind should ever consider trying to run a 9XX timing belt for that long. That's just dumb as a box of rocks.

The Gates Racing blue HNBR round-tooth belt is a JAE special. It's probably good for 10 years, but I just get nervous thinking about running a 9XX engine for that long on one belt. Strictly my paranoid opinion, but I'd be more inclined to use the HSN interval of 75,000 miles or 8 years, and bank any longer blue time 'potential' as an insurance policy against failure. But if you must (your call/ your responsibility), then 10 years is reasonable for the blue HTD belt.

*~*~*~*
Another significant advantage of the blue belts, both trapezoidal and round-tooth HTD is their stability. Continue to check the tension on the regular service interval, but it's highly unlikely that you'll ever need to re-tension the blue belts. They just don't stretch.

The Burroughs gauge is thickness-sensitive, and the blue belts are thicker than the black ones. For the same strand-tension, the blue belts will produce higher readings on a Burroughs gauge (said another way, the correct blue tension requires a lower reading on a Burroughs).

Similarly, the Krikit KR1 is stiffness sensitive, and the blue belts are considerably stiffer. And frequency is a function of thickness, stiffness, mass... all that stuff. Bottom line, none of the tension values given in the Lotus manuals apply to the Gates Racing blue belts. If you use Lotus' tension values on a blue belt, the resulting tension will be wrong... high by a lot. And there are no factory recommendations from either Lotus or Gates for correct blue belt tensions. It's all grassroots owner experience.

The blue round-tooth HTD belt has been on the market longer than the trapezoidal, and has a good concensus on tension.
83-85 Burroughs / 35-37 Krikit KR1 (read the POUNDS scale only)(edited Dec 12, 2017).
Check/ set the tension with the crank at TDC (follow the Lotus procedure).

The blue trapezoidal belt is relatively new, and data is limited compared to the HTD.
83-85 Burroughs also works well for the trapezoidal belt.

But there's a difference of opinion on the Krikit KR1 value to use. Some say the same 45-47 works, and other's say that results in a slight whine (a belt that whines is too tight). Instead, they're using values in the 35-36 range. I suspect user technique is a factor in the different values. I'm just offering this trapezoidal tension info as hearsay, and I don't have a clear opinion of my own (I've not yet used a blue trapezoidal belt myself... just blue HTDs).

*~*~*~* Edited Dec 2, 2017
The Krikit users were right... use 35-36. 45-47 Krikit is too high, and the belt will whine. I use a Burroughs gauge most of the time, and black belt Krikit readings have always correlated at 55% of the Burroughs number value. 100 Burroughs = 55 Krikit KR1. However, the blue belts are thicker (the Burroughs is thickness sensitive) and stiffer (the Krikit is stiffness sensitive), so the old time-tested black belt correlation factor doesn't work on blue belts. For blue belts, use 83-85 Burroughs or 35-36 Krikit KR1. Okay, if you've used a Krikit, you know it's lack of repeatable accuracy makes hitting a narrow 2 pound range a little tough. Try to use 35 as a minimum, and do you best not to exceed it by much. I'm just paranoid about low tension values on 9XX engines, and I struggle to get low-30's numbers out of my mouth. Go there at your own risk, and I'll stick with 35+.
*~*~*~* End Edit

I'm not aware of any established frequency values for either blue belt. That's a shame, since I like that tension method.

*~*~*~*
The blue trapezoidal tooth belt is Gates part number T104RB, available from any Gates Rubber dealer. They may not stock it, but if you ask, they can order it for you. It's best to call first.

The blue HTD, round tooth belt is a 'special' available from independent Lotus parts vendors, but not Gates retailers. JAE paid Gates Racing to produce the Blue HTD belt, so Gates sells it exclusively to them. JAE re-sells it to any other Lotus specialist who wants it, including Lotus Cars, plc, so it's widely available.

I've installed several blue HTD belts over the last decade, and I really like them. They're more expensive, but consider the price difference insurance.

I've not yet installed a blue trapezoidal belt, so I don't have my own opinion on the optimal tension. I just recommend the highest tension that does not provoke a belt whine once the engine is up to temperature. Let me know what you find.

*~*~*~* Edited Dec 2, 2017
The consensus among private users seems to be that the tension values given above for the Blue HTD round tooth belt also works for the Blue trapezoidal tooth belt. 83-85 Burroughs or 35-36 Krikit KR1.
*~*~*~* End Edit

IMHO, the Krikit is a distant third choice behind 1) the frequency method and 2) the Burroughs gauge, so don't waste your time on the Krikit. I really recommend that you suck-up and buy the more the expensive Burroughs BT-33-86J, or the more readily available and less expensive BT-33-73F. Both are a quantum leap better than the Krikit KR1.

Regards,
Tim Engel

[Pete Boole]

Brilliant post Tim - thanks very much for all that info.

Pete

[bash]

For the round tooth belts I used early Peugeot 405 Mi16 belts with no problems. Slightly narrower than the Lotus belt but that isnt an issue.

Bash

[NickC]

Great info thanks Tim. Quick question do you know if the blue trapezoidal tooth belt (T104RB) is the same width as the original or is it slightly narrower like the Peugeot belt.

Thanks,

[Esprit2]

[quote="NickC"]Great info thanks Tim. Quick question do you know if the blue trapezoidal tooth belt (T104RB) is the same width as the original or is it slightly narrower like the Peugeot belt.[/quote]

The blue trapezoidal tooth belt is narrower at the 25.4mm (1.0") industry standard. It's the Lotus belt was the odd-man-out, at 26.5mm (1.039").

But don't worry about the blue belt being narrower. It's materials and construction make it far stronger, more stable (little or no stretch) and more durable than the OEM HCR rubber trapezoidal belts. A little bit less of a very good thing is still a very good thing.

If you use the blue trapezoidal belt, set the tension to 83-85 on a Burroughs gauge (BT-33-86J or BT-33-73F) or 35-36 on the POUNDS scale of a Krikit KR-1.

Note that in my long post dated Oct 13, 2017 I recommended 45-47 Krikit. That was determined by multiplying the 83-85 Burroughs by 55%... the old correlation factor for the OEM black belts. But it's since become apparent that the blue belts are both thicker (Burroughs is thickness sensitive) and stiffer (Krikit is stiffness sensitive) resulting in a different correlation factor. 45-47 Krikit is too high, and the belt will whine when the engine is at full operating temperature. 35-36 Krikit is more appropriate.

If any timing belt whines on a hot engine, it's talking to you and complaining that it's too tight. Back off a few pounds.

I've edited the long message to reflect the lower Krikit tension.

Regards,
Tim Engel

[Esprit2]

Angus Marshall wrote:
> A few years ago, I asked Lotus about the "long life" belts developed for the US market.
> Their response was that they still advise sticking to the 24k miles/24 months C service interval.
> Don't ask me why, they didn't tell me. I'm just including it here for information.

The "why" is because there was no "long life" belt for the US market. We used the same part number black belts that Lotus provided to the rest of the world. There were just legal mandates (Federal as well as some states... California was the most strict) that required manufactures to be responsible for the maintenance and repair costs related to certain durability and emissions control components. Sort of a legally imposed warranty. The timing belt came under the "durability" heading. The mandate didn't make the timing belt any better, stronger or more durable, it just held Lotus financially responsible for a longer period of miles and/or time. It was a mandate, not a request.

In the 1990s, California mandated 100,000 miles. No Lotus T-belt was a 100k belt, so Lotus had to pay for the replacement of the standard belt as necessary up to a total of 100k miles. IMHO, that probably has something to do with Lotus specifying a 55,000 mile change interval for the B-prefix HTD belt (A = HCR rubber / B = HSN rubber). Lotus still 'owned' the first belt change at 55k miles, but the second one was scheduled at 110k miles, beyond the 100k mandate, so the owner had to pay for that one.

Outside of California, and in DOM/ ROW markets, the specified timing belt change interval was much shorter. Now that all factory funded warranties and gov't mandates have timed out, I recommend that everyone follow the shorter Lotus service intervals. No California owner in his right mind should ever attempt to run a 9XX timing belt 100k miles just because "that's what California cars do". And even the 55k miles interval for the OEM black B-prefix belt is ill-advised without warranty back-up. The Gates Racing Blue HTD belt has a shot at it, but no black belt does.

Trying to save money on timing belt costs is a false economy that will bite you. Change on time or more often than specified, and use premium parts. The downside to going cheap is just too expensive... bent valves and a top-end rebuild.

Regards,
Tim Engel

PS... the "Quote" function doesn't work for me. If I use it, the quoted text just appears between [quote="name"] .... [/quote], not in the white background 'quote box'. What am I doing wrong? In the meantime, I'll continue to use the > character to indicate a quoted line of text.

[NickC]

If you use the blue trapezoidal belt, set the tension to 83-85 on a Burroughs gauge (BT-33-86J or BT-33-73F) or 35-36 on the POUNDS scale of a Krikit KR-1.

...

If any timing belt whines on a hot engine, it's talking to you and complaining that it's too tight. Back off a few pounds.

Borrowed a Krikit guage once but didn't get on with it, I don't think it hlped me set the belt tension any more accurately. I have always just used the 90degree twist with fingers method, seemed to get more consistent results than with the Krikit.

Any reason blue trapezoidal belt needs to be tensioned different to the 90degree twist?

[richardw]

If you use the blue trapezoidal belt, set the tension to 83-85 on a Burroughs gauge (BT-33-86J or BT-33-73F) or 35-36 on the POUNDS scale of a Krikit KR-1.

...

If any timing belt whines on a hot engine, it's talking to you and complaining that it's too tight. Back off a few pounds.

Borrowed a Krikit guage once but didn't get on with it, I don't think it hlped me set the belt tension any more accurately. I have always just used the 90degree twist with fingers method, seemed to get more consistent results than with the Krikit.

Any reason blue trapezoidal belt needs to be tensioned different to the 90degree twist?

The Burroughs and Krikit gauges do seem to be slightly primitive and inconsistent tools for the job. The engine has to be at tdc (I think) and what about temperature? Cold can mean anything between 0 and 20+ degrees and this can make a huge difference. My cambelt feels very loose in the cold weather but extremely tight when the engine is hot, which shows what a difference heat expansion makes.


I'm flummoxed as to why a decent automatic tensioner was never developed.

ATB Richard