Philwaters7
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| posted on 28/10/13 at 11:51 AM |
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Zetec help: valve - piston clearance with hydraulic followers
Hi - looking for some zetec guru's out there.
I'm doing my first full engine build - my 2lt block is away being bored out to suit some forged pistons and I have some steel rods to go with
them. The head has been fitted with some bigger valves and thoroughly ported and I have some high lift cams which are suitable for hydraulic
followers. The pistons are pocketed, etc, etc. It should be a nice engine when finished.
However, while the block is away, I've started thinking about the next stages and I got to researching the valve - piston clearance method and
have hit a snag. When the engine is running it will have oil pressure - when I check it it won't. So, my understanding is you swap the
hydraulics followers temporarily with some solid followers so that the valve opens correctly. Along with some soft checking springs you can check the
clearance easily with some plasticine.
But - how big/thick should the solid followers be? Am I right in my understanding that the follower will be slightly pumped up even when the valve is
opening? How much is this amount? Is it constant? The follower then pumps up further as the valve lift reduces, thus taking up the 'valve
clearance' you normally shim to achieve on a solid engine. Is that right or am I missing something obvious?
My followers are drained down so I can't measure them, and even if not, how would I know I was measuring what the valve would see as lift? The
Haynes manual only states the diameter of the follower... so I'm feeling a little baffled 
Doesn't only apply to Zetec's either I guess, anything with a hydraulic follower would give the same problem. Anyway, I'm confused -
can anyone enlighten me?
Cheers,
Phil
Phil Waters
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MikeRJ
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| posted on 28/10/13 at 04:50 PM |
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The lifter only pumps up when there is no load on it, i.e. when the valve is closed and some clearance exists. As soon as the cam starts lifting the
valve the lifter should remain locked in it's last position due to a non-return valve built in. If you use solid lifters that give as close
zero valve clearance as possible to test for piston/valve clearance then you should be fine (unless your valve springs are too weak in which case
valve float will allow the lifters to "pump up" )
[Edited on 28/10/13 by MikeRJ]
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Philwaters7
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| posted on 29/10/13 at 06:17 PM |
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Thanks very much Mike, very helpful and I think I've got my head around it now 
Just need to work out how to convert some spare followers to be adjustable next... my spring will be fine, they are uprated Kent items to suit the
cams.
Phil Waters
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