Member Since: 06 Nov 2006
Location: In the Clubhouse
Posts: 21361
I don't know, as I just suddenly had no power, all the lights came on, when I pulled over there was no engine at all. It could have been running whilst I was slowing down, but there was no acceleration available and no power steering!! So i assume that when it broke off, the cam sensor detected something not right and shut the engine down, but not before doing some damage.....Bodsys Brake Bible
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11th Jun 2012 10:15 pm
Gareth Site Moderator
Member Since: 07 Dec 2004
Location: Bramhall
Posts: 26770
Thanks Iain, I'm trying to think of an event that could exert a sudden increase in tension on the trailing side of the belt. (I presume the tensioner is on the 'slack' side ie not the side that is pulling the cams around from the crank)
The only thing I can think is a sudden seizure of the crank, and the momentum of the cams would then tension the slack side of the belt.
However, you were only cruising at 60mph, so thats about 1600 rpm, that is a cam speed of 800rpm, so I don't think there would be much momentum to keep the cams turning enough to snap the casting.
11th Jun 2012 10:23 pm
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Posts: 21361
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11th Jun 2012 10:28 pm
stapldm
Member Since: 11 Sep 2006
Location: Swine Town
Posts: 2330
If one of the cams stopped, such as the one driving the HPFP, that would tension the belt...
Edit : OK, I thought that through again and it's actually the opposite Dr. Ian Malcolm:
"Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should."
Transgenic tomato anyone?
11th Jun 2012 10:29 pm
Bodsy Site Sponsor
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Posts: 21361
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11th Jun 2012 10:37 pm
stapldm
Member Since: 11 Sep 2006
Location: Swine Town
Posts: 2330
Yup, but if it took up extra load for some reason, even if well within the capability of the belts, it could stress the weakest point in the design, the cambelt tensioner?
Problem is, I'm finding fewer and fewer reasons that would explain why the tensioner could tension, unless the crank pulley or cam pulley effectively increased diameter momentarily by skipping a belt tooth.
Every other action on the engine seems it would relax, not tension the tensioner, including something wrong at the HPFP Dr. Ian Malcolm:
"Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should."
Transgenic tomato anyone?
11th Jun 2012 11:04 pm
buda
Member Since: 24 Jan 2010
Location: strathclyde
Posts: 334
stapldm wrote:
buda wrote:
...except perhaps the small spring (negligible)force that pushes the tensioner wheel out eccentrically towards the cambelt...
I thought that the spring was actually quite powerful and would therefore keep a constant torque on the cast mounting (not the bolt once tightened).
Valid point, one end of the spring is anchored against the casting thru the tab plate, and the other end is anchored on the inner bearing race which is bolted to the casting with the bolt. So there would be an equal force on both points I think.
Im sure that the spring force wouldnt be anywhere near as high as the torque exerted to tighten the bolt......
Reading the other posts it seems the main theory is that the belt alone could force the casting to break if the belt straightened out due to crank siezure or something...... I thought the teeth on the belt would go first.......
who knows.......
needs an expert in failure analysis to work this out.......still for you guys....
11th Jun 2012 11:43 pm
driveadisco
Member Since: 09 Jun 2012
Location: Lancs
Posts: 3
Just found this on Landroverhell.com :-
range rover sport
My 2007 range rover sport 2.7 TDV6 has just turned 60,000 miles.It has full dealer history. Yesterday it stopped and apparently (according to the Landrover dealer) Part of the oil pump casing where the timing belt tensioner bolts on has sheared off and the timing belt has slipped and the engine is trashed. And the repair quote is £9000 (yes nine thousand pounds) Which is about 50% of the things value after four and a bit years and 60,000 miles. Waiting to hear back from LR customer services......................
Not much more you can say really except perhaps a request under the Freedom of Information to Land Rover asking how many times this has happened on vehicles covered by warranty that we haven't heard about and how many have occurred since the oil casing was redisgned - a reduction in the numbers after this would suggest that LR were aware of the problem..
12th Jun 2012 2:16 pm
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cant get any info from there, it just seems to be a load of complaints, but no way of contacting the complainer or any other info.Bodsys Brake Bible
Almost all the belt jobs I have done have been in this year range and all have been ok after the belt changes so its hard to understand why as you say there looks from the outside to be no difference.
Flack
16th Jun 2012 8:11 am
Disco_Mikey
Member Since: 29 May 2007
Location: Dundee, Scotland
Posts: 20837
I am still not convinced it is the tensioner mount that fails.
Admitedly, the oil pump casing has been superceded 3 times, and beefed up fairly substancially.
Nothing explains why 07MY's have failed before and after belt changes...My D3 Build Thread
Member Since: 23 Aug 2007
Location: Kent
Posts: 10564
Would be nice to know if it is the same company that produces both the oil pump castings in the posts above and if the material used is identical. It may just be a case of a change of supplier over th two diffrent years and the second supplier is using a diffrent grade metal or even process for the casting. Hence a weaker item.MY17 D5 1st Edition Namib Orange
MY15 D4 HSE Kaikoura Stone
MY12 D4 HSE Nara Bronze Sold and gone
MY11 D4 HSE Stornaway Grey Sold and gone
D3 S spec Silver Sold and gone
Tow bar, full length roof bars, side steps, tow bar storage unit, surround camers.
D4 camera club
I am still not convinced it is the tensioner mount that fails.
Admitedly, the oil pump casing has been superceded 3 times, and beefed up fairly substancially.
Nothing explains why 07MY's have failed before and after belt changes...
Yes could be the bolt, could be something else failing on the engine, but have not most failed at low speed and when they where just tootling along, for us mere mortals its hard to pin it down..but why would LR go to trouble of changing the plate in that specific area if there was nothing wrong in that area, you only change a part design to improve it if it keeps failing or does not work..as this costs them money.
Flack
16th Jun 2012 8:30 am
amazing
Member Since: 05 Mar 2011
Location: chengdu
Posts: 1542
low speed failure
the cam drive train sees more stress at low speed as the lobes pass over centre sending little shock waves
back. this smooths out as revs rise
what material is the plate? the bolt locations are not inline with the mass of the boss which appears flush to block. thermal expansion would cause that mass to expand more than the thin connecting flange and to flex outwards when hot. stressing over time until crack propagation reaches critical. aka paris law.
just a thought from looking at picsIt is better to have and not need it then need and not have it.
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for you guys....
