How do you check valve to piston clearance when you have hydraulic tappets?

I'm building a new engine with forged pistons, steel rods etc, and rather than have the valves bounce off the pistons first time out, I'd rather check how much space I have first before playing with the cam timing.

Normally I'd turn the engine over by hand with a lump of plasticine on top of a piston, then slice the plasticine afterwards and measure the thickness. However, with hydraulic tappets (it's a silvertop zetec), won't the tappet squash down and thus affect the valve lift, giving a falsely large clearance?

As the engine is dry assembled there's no oil in the tappets, which means that the tappets will compress before the valve springs. Do I need to install a soft spring for checking clearance? Try to fill the tappets with oil? Any other ideas?

Tom

Dont know about the Zetec but are Solid lifters available ?

quote:

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Originally posted by ReMan
Dont know about the Zetec but are Solid lifters available ?

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reading this, may help

look 1/4 way down page, about tappet preload.

You need to check the procedure for the Zetec not the Rover V8. Although the principle is the simmilar.

I am assuming you have a Zetec engine.
I would google it, and also check any other source.

Where did you get the Cams and pistons from? Ask them for advice.

You are right to ask, as you could do some expensive damage to your engine before you ever get to use it in anger.


I would certainly do a lot of checking first!

I'm not a Ford man (Have a Rover V8) so cant advise exactly.

Also check the valve heights are all exactly the same. I have one rattly tappet, due to me not grinding it in far enough (didn't need it from a sealing point of view).
Howver this left me with one annoying rattly tappet on tick over. It goes once the oil pressure raises with the revs.

Had a similar problem when building a head for the CVH. What we ended up doing was taking apart a lifter and shimming the two halves of it apart to make a dummy solid lifter. I shimmed it so that the thinnest feeler gauge I had (0.05mm I think) was a snug fit between the lifter and rocket once assembled, or as near to it as possible, basically so that it was touching but not a tight fit. I then used the normal plastercine method and checked the clearences as usual.

I don't know whether the same is possible with the zetec lifters.

I should probably put a disclaimer on this to say it worked for me but wouldn't want to be responsible for any grenading engines!

[Edited on 9/3/09 by andylancaster3000]

Thanks Andy, that sounds like the best idea so far.

Anyone got a spare silvertop hydraulic lifter that I can cannibalise?

Tom

either as andy said, or, probably easier on the zetec, find out the lift of the cam less the "sensible clearance", put a very light spring under the valve cap instead of the proper valve spring then depress the valve by the correct amount using a dial gauge to check as you do it, then strip and check your plasticine.