A solution to a problem you'll probably never have ..

[ECR]

Having just “decked” the block (skimmed it flat) on my 2.0 VX I want to check the piston to valve clearance. I know this can be done by putting a thin layer of plasticine on top of the piston, turning the engine over by hand and then measuring the indent, but I’m never happy accurately measuring plasticine.

Probing the top of a cam bucket with a dial test indicator will be a far more accurate method, but it does require the fitting of a very soft valve spring on the valve to be tested. The space on top of the cam bucket is very restricted and when the DTI is fitted there is even less space. This means that pushing the valve closed by hand to make the check needs to be a very easy task  (the restricted space dictates that).

Sourcing an off the shelf soft spring of the right dimensions and strength proved to be very difficult and so in desperation I constructed a spring from washers of medium density closed cell foam cut with a hole saw. I’ve yet to make the measurements but so far the foam spring is surprisingly effective.

So that’s the solution for the problem you’ll probably never have ….

[nickh7]

I love that sort of lateral thinking, nice one 

[Wodybode]

I’ve taken these clearances with lead wire which is easier to measure with a micrometer.

[ECR]

That's a nice ithought Wodybode. Where to get lead wire of a suitable dimension?

Since making my foam springs it has been suggested that the spring from an old thermostat will do the job .....

[elie boone]

If you know the lift of your cam, you could put a o ring onto the valve stem at the correct height insert it in the head and then measure the height related to the cil. head then you can measure the distance cil. block to pocket in the piston and compare.

[SKC]

Is the engine running hydraulic cam followers? 

To measure this accurately you need to run virtually zero valve clearance if running hydraulic followers, or have your valve clearance set if running solid followers.  Alternatively you could remove the cam follower and valve spring and just put a small or O ring round the valve stem or use the stem seal. 

How much have you removed from the block face? 

Basically with a degree wheel mounted on the crankshaft and a TDC mark accurately set,  leave the cam belt off for now.  Starting at 12 degrees BTDC turn the crank in 1 degree increments, measuring the valve drop (light valve contact with the piston). Write these down in a column.  Then measure the valve lifts, starting at 12 degrees BTDC, up to TDC for the exhaust valve and then from TDC round to 12 degrees ATDC.  If you record these values in a column next to the drops, you then take the lifts away from the drops at the same crank angles.  This then give you the clearances for piston to valve.  The closest clearance is the smallest number.  It's worth taking a bit of time to do this right, getting it wrong can be quite expensive, not that I have of course.

Regards

SKC  

[ECR]

It's on solid followers ... I've only removed about 6 thou so I'm not expecting  a problem, just better to check because as you say, the consequences of getting it wrong are severe. 

Some nice suggestions there, thanks  

[metal mickey]

A short length of solder wire or plumbers lead also work well - held where you want it with a blob of grease . Works well for measuring after with a mic.

[Rob Walker]

I also use the soft spring method and push down the cam follower until valve piston contact is made and take measurements with a DT! .  I found out that the suspension springs from my old Lynn Sondek fitted perfectly and are about 8lbs/inch.  Ebay is your friend for these

[ECR]

They look ideal Rob but at £40.00 plus for three .......

I found an old thermostat spring and although I haven't tried it in anger it looks promising. it's certainly the right sort of size.