omega0684
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| posted on 25/7/09 at 10:12 AM |
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Hydraulic Tappets & Solid Tappets
Whats the difference between the two? (don't say one's hydraulic)
How are they different?
What are the ADV and DisADV's of both, is it beneficial to have one or the other?
durability at high revs?
cheers
[Edited on 25/7/09 by omega0684]
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speedyxjs
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| posted on 25/7/09 at 10:20 AM |
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Hydraulic ones dont need adjusting as they dont wear as much.
How long can i resist the temptation to drop a V8 in?
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mark chandler
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| posted on 25/7/09 at 11:04 AM |
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hydraulic not good for sustained high rev's they pump up, more of an extended service interval item.
When you start extracting lots of additional power you rip and replace.
When you start looking at modern engines with the cam operating directly on the valve they make a lot of sense, no plucking out of shims and faffing
about. I do not know of any bike engines that use hydraulic items.
Regards Mark
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Canada EH!
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| posted on 25/7/09 at 05:02 PM |
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As above Hydraulics for production engines little maintenance, easier on valve train. High performance, high lift cams, Solids.
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Willie
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| posted on 29/7/09 at 09:05 PM |
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Sorry for barging in, I haven't posted in a long time, but have just started paying attention to Locost Builders again.
"Tappets" or cam followers (Referring to the bucket type) are there to follow the cam and transmit its motion vertically to the valve.
As the valves heat and cool, they expand and contract, therefore there needs to be clearance, otherwise the follower would hold the valve open when
warm, or not open it enough when cold. Exhaust valves have bigger tappet clearance than inlets, as they obviously run hotter and expand more.
Hydraulic tappets are like a bucket with a lid on it, with a hole in the side. When there is nothing in the bucket, the lid can sink down...but when
oil is forced in the side, the lid is pushed up, taking up any clearance between the valve and the cam.
The result is that hydraulic tappets allow engines to have zero clearance, and yet change their "thickness" depending on the conditions of
the engine (As the tappets reset each time the valve is closed). They're fantastic news for production cars, means nobody has to play with
feeler gauges and you don't buy a new Mondeo that sounds like a Mk3 Fiesta.
There are disadvantages, however, for performance engine installs, mostly really relating to high rpm. When you're really revving an engine
with hydraulic tappets they can stick expanded too much and you get a miss at high rpm as the valve isn't seated correctly. This is rare
though. The main problem is "air" getting into the tappets and then the tappets not taking up the necessary clearance, and you get a
thrashing noise. Commonly the Rover K-Series will do this with some hard driving on the road, you start to get a ticking/tappety noise which only
goes away when the oil has had time to recouperate. This means the cams are slapping the tappets causing wear, and the valves aren't opening as
far as they should.
Solid tappets are a pig to set up. They have shims, usually underneath, so you have to assemble the whole thing, cams and all, check the clearance
between the tappet/follower and cam, note it on all tappets, then take it to bits and adjust the shims accordingly. If one is too thick, you
won't have got the feeler gauge in...so you've to go thinner and do it again. It takes a while and can be frustrating.
If you're intending on building a real screamer of an engine, and intending to keep it at sustained high rpm, then solid tappets will be
necessary to keep the correct clearances.
Willie
p.s. Sorry for the waffle...I have just been dying to post something technical for a while
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