Hi all,
I'm thinking of car replacement and wondering what features I should look for.
Looking over several posts, it would appear that timing belts and CR diesels are a risk, but what about hydraulic tappets / cam followers ?
I understand that these are now pretty well universal, apart from perhaps the 1.2 Honda engine and old designs such as the Ford Ka. Of course without them there are the additional services costs of having clearances measured and new shims fitted.
Am I correct ? perhaps others can shed some light ..................
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I think engines from japanese manufacturers will have solid tappets - so may need shims.
Honda VTECs, Mazdas and my Nissan Primera are examples of petrol engines that may need adjustment during service. BMWs also (or is it only the M3?).
The old Ford Ka used a pushrod engine where adjustment is easy.
Incidentally, checking the valve clearance on these engines is usually reasonably quick (and therefore cheap), it's the changes that can be expensive as cams may need to be removed etc. Changes should be rare. The other problem relating to these checks is that they must be done on a stone-cold engine, so the garage must have it in their workshop from the night before.
I wouldn't worry too much about this - my mazda service manual said the first check was at 120,000KM (75,000miles) and that was to just listen to the engine. My Primera has done over 80,000 miles and shows no signs of needing work on this.
Though an M3-owning friend did say that it was very expensive when this was checked
Are you buying new ?
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Since 2002,the Ka has had hydraulic tappets,chain cam and roller followers.
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Even on those motors with bucket & shim followers, the engines usually don't rev hard or high enough to need regular checking.
On bike engines it's quite common for the valve clearances to be checked every 12K miles or so, but this reflects the fact they rev much higher and work harder.
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The shimmed tappets on Isuzu diesel engines inVauxhalls should be checked and adjusted every 18,000 miles. Many engines were not properly serviced in this regard, and the valve clearance would close up - the valve recessed into the head - and reduced compression and poor starting were the usual result.
The odd thing was that they really weren't difficult to do - it was a very good design. Even when replacing shims, you didn't need to take the cam out. One person pushing down on the bucket with a screwdriver, another with a small electronics type screwdriver to flip the shim out was all that was required - no special tools or extensive dismantling required!
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Valve clearance adjustment with screws and locknuts on the rockers is normally so easy that there's no excuse for not doing it. Takes half an hour and the engine runs better and quieter afterwards (and the wear rate, which accelerates when the clearances enlarge as a result of wear on the rocker nose or the end of the valve, is also reduced to normal). Despite the simplicity of the job, and the fact that the need for it is signalled by ticking from the valve gear, even garages used to neglect to do it and owners of course were often completely unaware of the need. Many cars went through life without this simple routine adjustment ever being done. You still hear cars that urgently need it rattling past every day.
I am surprised by NC's claim that Isuzu diesel engines suffer from valve seat recession rather than wear further up the valvegear train. I thought this only happened with petrol engines with cast iron heads and no hardened exhaust valve seat inserts when they were run at high rpm on lead-free petrol. Happened to one of my Skodas :o{
Edited by Lud on 12/03/2008 at 14:56
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>>I am surprised by NC's claim that Isuzu diesel engines suffer from valve seat recession
It happened to our W124 diesel too - the valve seats of the rearmost cyclinder sunk into the head - so far that it was losing compression, and blowing exhaust gas back out of the inlets.
New valve seats fixed it.
see;
www.shef.ac.uk/mecheng/tribology/research/projects...m
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I was interested to note that the new vvt Vauxhall petrol engines, and some diesel engines, list valve clearance check and adjustment in the service schedule. It's hardly frequent - apparently my 1.8vvt will need this at 100,000 miles or 10 years. I was a bit surprised, as most vehicles have moved to hydraulic lifters. I wondered if the adoption of variable valve timing was a factor in this - could the hydraulic lifters cause problems as the cam timing changes in operation?
JS
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