Timing Belt
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Timing belts
the major weakness in the Aj-V8’s engine is the timing chains including primary and secondary tensioners. It’s a interference engine where, for compact size, the valves and pistons occupy the same space separated only by the timing of the camshafts. If the timing chain slips/breaks there will be trouble.
if you don’t know any history, change the steel timing chains and tensioners.
if you don’t know any history, change the steel timing chains and tensioners.
#7
Exhaust camshafts are operated by short "secondary" chains. The slack in these chains is managed by 2 separate tensioners which are the problem parts. The initial version was plastic, a later redesign was done, and eventually an all-metal version was issued by Jaguar for the later 4.2L engine. This all-metal unit is what you NEED. All earlier versions eventually crack and allow the slack in the chain to go uncontrolled, possibly allowing the chain to skip teeth, leading to collisions of valves with pistons. Sometimes, the secondary chain breaks, wraps around, and basically ruins the entire head. The only way to be sure is to pull the valve covers and check what tensioners are already there. If you are lucky, a previous owner will have tackled that particular job, and you will be back to normal maintenance considerations. If not, this job needs to be done as quickly as possible, likely without starting the engine again. As these cars are not worth a ton of money, major mechanical problems like failed tensioners can swallow whatever value is left in the car, unless you can do most of the work yourself, and the damage is not too extensive.
Best is to search "secondary tensioners" on this forum or others. The Jaguar engine type is generally "AJV8", with the AJ26" and "AJ27" 4.0 variants.
Another search is for the "zip-tie method" that a member detailed a while back.
Best of luck, keep us posted.
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#8
Graham
#9
The engine operates the intake camshafts with 2 separate long "primary" chains off of the main crankshaft. The slack in the chains is managed by tensioners pushing on plastic guides. Over time these parts wear out and need replacement.
Exhaust camshafts are operated by short "secondary" chains. The slack in these chains is managed by 2 separate tensioners which are the problem parts. The initial version was plastic, a later redesign was done, and eventually an all-metal version was issued by Jaguar for the later 4.2L engine. This all-metal unit is what you NEED. All earlier versions eventually crack and allow the slack in the chain to go uncontrolled, possibly allowing the chain to skip teeth, leading to collisions of valves with pistons. Sometimes, the secondary chain breaks, wraps around, and basically ruins the entire head. The only way to be sure is to pull the valve covers and check what tensioners are already there. If you are lucky, a previous owner will have tackled that particular job, and you will be back to normal maintenance considerations. If not, this job needs to be done as quickly as possible, likely without starting the engine again. As these cars are not worth a ton of money, major mechanical problems like failed tensioners can swallow whatever value is left in the car, unless you can do most of the work yourself, and the damage is not too extensive.
Best is to search "secondary tensioners" on this forum or others. The Jaguar engine type is generally "AJV8", with the AJ26" and "AJ27" 4.0 variants.
Another search is for the "zip-tie method" that a member detailed a while back.
Best of luck, keep us posted.
Exhaust camshafts are operated by short "secondary" chains. The slack in these chains is managed by 2 separate tensioners which are the problem parts. The initial version was plastic, a later redesign was done, and eventually an all-metal version was issued by Jaguar for the later 4.2L engine. This all-metal unit is what you NEED. All earlier versions eventually crack and allow the slack in the chain to go uncontrolled, possibly allowing the chain to skip teeth, leading to collisions of valves with pistons. Sometimes, the secondary chain breaks, wraps around, and basically ruins the entire head. The only way to be sure is to pull the valve covers and check what tensioners are already there. If you are lucky, a previous owner will have tackled that particular job, and you will be back to normal maintenance considerations. If not, this job needs to be done as quickly as possible, likely without starting the engine again. As these cars are not worth a ton of money, major mechanical problems like failed tensioners can swallow whatever value is left in the car, unless you can do most of the work yourself, and the damage is not too extensive.
Best is to search "secondary tensioners" on this forum or others. The Jaguar engine type is generally "AJV8", with the AJ26" and "AJ27" 4.0 variants.
Another search is for the "zip-tie method" that a member detailed a while back.
Best of luck, keep us posted.
Back when I was in undergrad and was a rookie DIY mechanic with no skill I read and did the zip tie method successfully. If I could do it back then, I’m sure anyone can do it. That car served me well for many years. When I sold it I was satisfied that I stopped that engine from meeting certain doom. The new owner is still enjoying a trouble free engine.
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Interference Type Engines versus Safe Engines
"...a couple of centimeters ...." means a lot to engine designers. Size is important and reducing the size of the engine allows a lot more than just power-weight performance. The AJV8 block is aluminium as well to save weight.
The debate between interference and safe engine designs rages on. People tend to forget that the engine block is a service part. Classic American muscle cars often have engine rebuild kits. Not so much British cars.
Consider this, safe engines have to be bigger and thus are more expensive to build. Typically safe engine designers try saving money by using only rubber belts, whereas the AJV8 engine uses the serpentine rubber belt for secondary ancillaries only, and uses steel timing chains for the critical camshaft timing. The concept was sound, albeit the chain tensioners were poorly designed at the beginning. The use of Nikasil bore liners was also a sound concept but the lining was prone to sulphur attack and led to reputational damage to the Jaguar brand. Also note that the ZF5HP24 transmission was especially made for the XK8 grand tourer.
The car was ahead of its time, but in hindsight maybe they tried too hard with new stuff.
#13
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You can pretty much classify the interference engines as performance engines and the non-interference engines as dogs. There are exceptions of course.
WOOF WOOF
Z
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JimmyL (02-25-2019)
#14
#15
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It's our bad luck that we happen to be appreciative of a car that is twice as old as it was engineered to last .
Just my 2 cents
Z
#16
Especially today with the price of cars, I expect them to last much longer than 10 years, and they do with proper care.
Most light bulbs on this car have outlasted the engine. Is that what the engineers intended? Give me cheaper bulbs and spend those dollars on the engine.
There may be a day when plastic is suitable for internal engine components, but that day has not come yet.
I was ready for an engine project so I'm not upset about changing the timing chains and tensioners,
I'm just disappointed that the engineers didn't know better.
Most light bulbs on this car have outlasted the engine. Is that what the engineers intended? Give me cheaper bulbs and spend those dollars on the engine.
There may be a day when plastic is suitable for internal engine components, but that day has not come yet.
I was ready for an engine project so I'm not upset about changing the timing chains and tensioners,
I'm just disappointed that the engineers didn't know better.
#17
#18
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Back to the engineered in obsolescence or "expiration date" idea. If cars were engineered to last, really last, from stem to stern, for say 20 years, what would that do to new car sales ? LOL. Car manufacturers would never survive that hit.
Z
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Are we living in a disposable world
As an engineer myself (civil construction), there is always the balance between cost and technical delivery. Any engineer is normally given a budget for a particular job, and then ususally he has to make compromises to fit the budget. I think there were something like 65,000 XK8s and 20,000 XKRs built. Saving a few bucks here and there would have made a difference to Jaguar's production costs.
Only enthusiastic owners like us now, continue to try and keep old cars on the road where I find getting parts, esp. the rare bits, is half the fun. Some costs though aren't much fun.
#20
I understand what you guys are saying, but how can you justify burying such a weak link in a $70,000 car?
Would it have affected sales if they raised the price of the vehicle $50 to install metal chain tensioners? No. That takes care of the bean counters.
As for the engineers, shame on them. They should have known better, which they proved that they did by fixing the problem in later years.
Remember that Jaguar was in a position to overcome a long standing poor reputation for reliability. And they did this to save the cost of a steak dinner? Absurd.
I maintain my position that there was no legitimate excuse for this oversight and Jaguar realized that later.
Would it have affected sales if they raised the price of the vehicle $50 to install metal chain tensioners? No. That takes care of the bean counters.
As for the engineers, shame on them. They should have known better, which they proved that they did by fixing the problem in later years.
Remember that Jaguar was in a position to overcome a long standing poor reputation for reliability. And they did this to save the cost of a steak dinner? Absurd.
I maintain my position that there was no legitimate excuse for this oversight and Jaguar realized that later.