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Edward · Alfa 33 Joined: 21 Sep 2003 Posts: 307 Location: Bristol

You may have read the earlier post regarding note about the problems with hydraulic tappets - can someone explain this process to me in simple english. I am reasonably technical but I guess without seeing this in motion I am finding it a little difficult to understand from guesswork alone. How is the so called hydraulic process different from a cam pushing onto the top of a upside down bucket on top of a valve - if it is so poor why did Alfa go for it in the first place??? I have them in my car and regularly rev the nuts off it and it seems to go fine - could someone please explain the process, the weaknesses (and the benefits of solid lifters????) and why hydraulic tappets / lifters seem to have such bad press?

I would welcome your comments.
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The faster the better.

bobbber · Posted: Mon May 16, 2005 9:07 am Post subject:

The advantage of hydraulic tappets is that 'they need no adjustment'. None, not even a bit. In actual fact, due to the design they can't be adjusted!!!

I always think of the hydraulic lifter as being two thimbals (yes, those things used for sewing!).

One thimbal is on the end of the valve stem - and the other fits on top of it (like stacking them).

Oil is pumped into the gap between the two, which takes up the 'slack' between the 'top' thimbal and the cam.

How's that so far?

Rob
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Fiat Bravo 165 Sport

ChrisC · Alfa Sprint Joined: 13 Mar 2003 Posts: 152 Location: Frome

Hey, I understood that idea Very Happy

i did however get stuck at the point of wouldnt the resistance vary depending upon the oil pressure....
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Alfa Sprint QV - Gone to a better home and in happier health for it
Silver Lancia Beta HPE Volumex - under restoration

bobbber · Posted: Mon May 16, 2005 9:45 am Post subject:

Yeah, well I'm originally from Bristol - so I think we all speak the same lingo on this post me babbers! Laughing

I understand the gap between the two thimbals can leak out oil - this would cause a tapping noise, as all the slack between the top thimbal and the cam would not be taken up.

I'm also guessing, as you said chris, that lack of oil pressure can cause the thimbal "not to pump up correctly/fully".

I'm no expert on these things - haven't even seen them, but understand the "thimbal" explanation to be a good way of understanding the principle.

Perhaps the use of solid lifters, mostly in racing scenarios, is due to the oil pressure breaking down under excessively constant "reving the nuts off of it". I'm sure someone on here can explain this?

I also understand hydraulic tappets is common practice on European Cars - due to the 'zero adjustment' required.

Incidentally - I have leaking hydraulic 'ticking' tappets...

By using thicker oil - I've made them shut up. Guess the thicker oil is less likely to leak through an apature than thin... think that's common sense????

Hope this helps,

Rob
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Fiat Bravo 165 Sport

tvatavuk · Posted: Mon May 16, 2005 9:46 am Post subject:

It would somewhat (if you lack pressure), and because of that it isn't smart to rev engine on start.
There are also two springs outter and inner which push lifter/valve up or give resistance on way down?
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Tino Vatavuk
Little black dress which replaced Alfa Romeo 33 S 16v Permanent 4 GMo

bobbber · Posted: Mon May 16, 2005 10:18 am Post subject:

Yes, the springs make the valves close - i.e. press the valves into their seats.

Rob
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Fiat Bravo 165 Sport

tvatavuk · Posted: Mon May 16, 2005 3:39 pm Post subject:

Info I have is that hydro-lifters from 8v 1.3/1.4 boxer are same as on VW?
That could explain somewhat their life time when used on more powerfull boxer.
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Tino Vatavuk
Little black dress which replaced Alfa Romeo 33 S 16v Permanent 4 GMo

Eddie W · Posted: Tue May 24, 2005 11:21 am Post subject:

The weakness of hydraulic lifters for performance is that they can pump up at high revs thus holding the valves off the seat. Not that I've ever noticed that happening in our 33 1.7. My main objection is that I've yet to come across a 1.7 that doesn't have lifter rattle and having seen some in bits the lifters and cams were worn to buggery. Replacing this gear is not cheap and yet the solid lifter stuff of much the same or more mileage that I've seen has had no wear. Seems like a good economy to me to change when the opportunity arises.
Regards Eddie
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GaryUK · Guest

My 1.7 did 190k miles and no lifter rattle at all(mind I bluprinted it myself Rolling Eyes

.)

The lifters also let oil in very easily but don't let it out. When you are rebuilding a hydraulic lifter top end you have to put the lifters in a hefty vice to compress them and get the oil out so you can refit the cam easily. So the oil pressure takes up the slack but once this slack is taken up they no longer require the oil pressure(short term) to maintain the required lift(unless f-ed).