NC serpentine belt, idler and tension pulleys

Technical Area Routine Servicing
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Hi all, Iā€™m posting this up as I thought others may want to check theirs?

Recently, a good mate of mine thought he may have had the dreaded engine knock starting on his NC. A diagnosis was made by a garage who confirmed this was the case and an exchange engine was required. Ā My friend was devastated obviously and was faced with a potential bill of around Ā£2k to have a recon engine unit fittedĀ 

Anyway, as you do, he searched the Internet to see if this diagnosis was correct and found some info about collapsed, rumbling pulleys? The idea is, take off the serpentine belt, restart the engine and check if the noise disappears? It did! Confirming it wasnā€™t the engine after all,Ā 

Checking of the idler pulley and tensioner showed they were badly worn and wobbly, they were the cause of this ā€œterminalā€ noise. So, Ā£90 later, brand new belt, tensioner pulley and idler pulley purchased, fitting time approximately one hour in garage at home and hey presto car running perfect again!Ā 

When he told me the tale, I thought, Iā€™m going to do this to mine, even though I didnā€™t have the same noise, just for peace of mind. MX5Parts were quite expensive for the three items so looked at Eurocarparts. Contitech belt, SKF idler pulley and a nondescript brand for the tensioner pulley. All in for the three items was Ā£90.00. Iā€™ve done the job this morning, took longer to remove the battery tray due to rusty, seized bolts than it did to do the rest of the job! I also treated the start of some rust on the metalwork that the tray bolts to, quite pleased about that as all the bits you can see were in excellent condition, this is hidden under the tray, I also cleaned up the bolts and treated them too! I scrubbed up the battery tray and box and cleaned the battery exterior and terminal posts too whilst they were out.

Although I didnā€™t think my car was noisy in the engine department before, itā€™s certainly quieter and smoother sounding after the change! My pulleys were also on the way out Although belt appeared fine, i still changed it. Both cars have done around 60k miles and are 2007 models, 1.8 and 2.0 respectively without a/c ( slightly bigger belt needed for a/c models).

So, to summarise, a relatively easy job to tackle, for not a lot of money, giving peace of mind for ownersĀ 

i wonder if anyone else may have had the noise incorrectly diagnosed and spent a lot of money swapping engines for this easily rectified fault?

Barrie

this is good ā€œhow toā€ guideĀ 

https://forum.miata.net/vb/showthread.php?t=472887

Ā 

2 Likes
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Thanks for the heads-up, much appreciated.Ā 

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Thanks for that - hopefully nowhere near needed yet but most useful to put by!

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Useful to know, but with respect I hope your friend keeps well away from that garage. What garage diagnoses a failed engine without getting out a stethoscope and doing some basic checks of the problem?

JS

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Thanks chaps! Yes, I think my mate will give them a wide berth? I donā€™t think itā€™s a case of the work not getting done and then being charged for it all? More a case of just a wrong diagnosis? Fortunately, my mate reflected on this, searched around for other things and came up trumps with this. Mazda recommend inspection of belt at service intervals? I presume pulleys too although not mentioned? I will pass on your thanks to my mate, as without his experience and corrective action, Iā€™d not have known about this!Ā 

Barrie

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Barrie my good man, bet youā€™re sick of the sight of me! Do you have links for the parts Iā€™d need to tackle this? I know itā€™d be the tensioner pulley, idle pulley and tensioner beltā€¦ Iā€™d probably also look to change the second idler pulley as mine is a non-air con model. Cheers!

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Hi BenĀ Ā no problem mate, Eurocarpart, put your reg in and search under engine parts, then drive belts, then tensioners, idlers and dampers. Couldnā€™t find anything for the third idler pulley ( mines the same as yours, no A/C ) so that might be main dealer or possibly mx5Parts?

hereā€™s a link to my search for pulleys/tensioner.

http://www.eurocarparts.com/tensioners-idlers-and-dampers

drivebelts.

http://www.eurocarparts.com/car-drive-belt

Barrie

EDIT: currently 36% off using MID36 code.

mx5Parts for third pulley

http://www.mx5parts.co.uk/auxilary-drive-belt-pulley-mk3-35-without-aircon-p-2377.html

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Iā€™m in the middle of this job at the moment. I was originally just planning on replacing the belt on my 06/100k car, but noticed there was a lot of play in the idler and tensioner, I hadnā€™t noticed any noise yet but I figured it was only a matter of time.

Two of the four bolts at the bottom of the battery tray had rusted heavily and rounded off as soon as I put a socket near them. I managed to swap the belt without removing the tray but it needs to come out for the idler. There was just about enough room to get a Dremmel in to cut a slot in each bolt, I was then able to extract them using a manual impact driver with an 8mm slotted bit. A set of extractor sockets would probably have been easier.

Usefully MX5 Parts sell replacements for a good price:

http://www.mx5parts.co.uk/flange-bolt-battery-tray-engine-undertray-mk3-35-p-3332.htmlĀ 

Gates sell a kit containing the idler, tensioner and belt. The code wasĀ K036PK2245 for my AC equipped car, most places including Amazon sell it for ~Ā£90. I ordered mine from Parts in Motion on eBay who seem to currently be the cheapest at Ā£75:

http://www.ebay.co.uk/itm/Drive-Belt-Set-fits-MAZDA-MX5-Mk3-2-0-2008-Gates-Genuine-Top-Quality-Replacement/332252778251

Ā 

10

 

Thanks for the link! Itā€™s definitely the cheapest Iā€™ve seen it as well. My only query would be, does this fit the models without air-con? The only difference I can see from the ā€˜replacing the serpentineā€™ guide that Barrie provided was the idler pulley (15-970) vs air-con compressor. Would the belt be a different length?

Good to know that thereā€™s a healthy supply of bolts for the battery tray as well! 

 

Edit: Answered my own question, there are differing parts numbers for the belts re cars with and without air-con. Shame the above wonā€™t fit my car but good to know for those who do need to change it!

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I thought, but I might be wrong, that the only difference would be a shorter belt. Unfortunately it doesnā€™t look like Gates offer a kit for non-AC cars, although they do sell a shorter belt individually:

Ā 

https://www.gatesautocat.com/drive/MAZDA/MX5/NC18/LFG7-LFG8-LFY7/06-05_12-14/19257

Ā 

I thinkĀ 6PK2160 is the belt for the NC1 non-AC cars andĀ 6PK2245 for AC. The last four digits are the length in mm, so 2160 vs 2245.

Ā 

The kits are essentially just three Gates products bundled together, so I should receive aĀ 6PK2245 belt aĀ T36263 idler and aĀ T38408 tensioner. You can buy the idler and tensioner for reasonable prices individually on Amazon (Ā£25 and Ā£37 I think), so you could put your own ā€˜kitā€™ together for a reasonable price, assuming the idler and tensioner are the same on non-AC cars.

Ā 

Looking at the Gates tech pages forĀ T36263 andĀ T38408 they donā€™t appear to suggest that those parts work for AC, non-AC, 1.8 and 2.0 cars, so I think youā€™d be fine to order individually.

1 Like
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Is there a specific interval when the belt should be changed? There is nothing in the service book or Haynes. Mine looks OK with slight glazing on the plain side but it doesnā€™t squeek, however it is 11 years old with 62000 miles.
My local tame mechanic showed me a volvo he had that bust is auxiliary belt, the cam shaft then sucked in the stringy bits of the belt into the bearings which then threw the timing out and trashed the engine. Ouch.

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I donā€™t think so, Iā€™ve seen reports of people doing it at 104k miles and 50k miles. Iā€™m going to be doing mine at 11 years and roughly 68k (within the next couple of months) for peace of mind. If itā€™s not necessary and has lasted 11 years when you change it, at least youā€™re going to get roughly 11 years thereafter, right? 

14

 

You are indeed correct! I found that info immediately after asking the question. 

For those interested, the belt required for non-ac cars is part number 6PK2160. Iā€™ve just done amazon searches and the contitech version of this is Ā£8-odd. I.e. you can get the kit from amazon for circa Ā£80 buying the items separately.

The eBay seller quoted me Ā£85 for the three parts following some random discounting. 

 

Edit: need to learn to read before my 3rd coffee of the morning. Absolutely correct about the part number for the belt, sorry for overlooking that.

The bundle using the parts with prices quoted by yourself and the Contitech belt are Ā£70, delivered. Ordering now. 

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Benz3ne, i agree, think ill just do it anyway for peace of mind as you sayā€¦as for it lasting another 11 yearsā€¦i dont think the car will last that long anyway!

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I was spurred on to swap mine after talking to another MX-5 owner who had had a track day ruined by a snapped belt and was cursing himself for not carrying a spare. For the sake of Ā£10-15 Iā€™d definitely change at least the belt. If thereā€™s minimal play in the idler and tensioner and theyā€™re not noisy you could probably skip them. Saying that I didnā€™t think mine were noisy, but now theyā€™re swapped thereā€™s definitely a reduction in noise.

The factory belt does seem to be good quality. The last aux belt I changed was a BMW belt at around 6 years and 50k, that was heavily cracked. The belt I just removed from my Mazda at 11 years and 100k isnā€™t showing any signs of cracking! However holding it in my hand next to a new belt it feels a lot thinner, lighter and flimsier.

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Had the same issue with my NC as well, so I replaced theĀ serpentine belt, idler and tensioner pulleys a couple of days ago. For the pulleys I went with the Gates kit and for the belt with the Contitech one.

No longer have the annoying noise at low rpm and the steering feels lighter now. I guess they were pretty worn after all!

18

Greetings.Ā  Sorry for this revival but have a similar problem (potentially) and it prompted me to lookĀ  for info regarding. Brilliant thread and maybe others can benefit as well.Ā 

After a day when unrelated disaster struck by a new 5 litre tin of roofing felt adhesive tipped up in the passenger footwell, lid sprung, and tin vomited, I arrived home and heard that scraping and rumbling noise from the top/front of the engine at low revs.

A magic listening dowel placed on the housing of the top pulley gave the impression that all was not well (muted whisperings).Ā  I presume new carpets will solve the sticky problem on the passenger side but am concerned about the possibility of pulley failure.Ā  The major hurdle is the diagnosis.Ā  Is it or isnā€™t it? The NC is 2006 2.0 with a paltry 35000 miles and seems early to have such things go wrong.Ā  From the excellent advice in this thread I am confident I can diy but an accurate diagnosis seems essential! Any views/suggestions would be gratefully received. Ā 

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To test, remove the belt start and let the engine run for a few seconds, noise gone it would point to the tensioners/belt.

20

Agreed.

Also have a look at the Alternator, Power Steering, Water Pump and Air-con bearings.  Engine off, no belt and turning them by hand; they should be silky smooth, any roughness or catching will be noisy and require attention.