just fitted my new pistons and tightened my arp rod bolts up
the bloody pistons are 0.5mm above the top of the block!!!
had to wait 3 weeks for my rods to be polished and shotpeened and bushes fitted
may have removed too much off the block.....
what is the maximum that the pistons can protrude without interfering with the intake valve?

luckily i have another block

i will fit the head tommorow and turn it manually without the headgasket and see what happens

any ideas

 

i know that they dont sit flush mate, they all stick up a little on cvh block, dont think its nothing to worry about, but dont take my word for it.

regards.

 

mine did that aswell and its fine ,had 5 thou took off my block

 

What compression do u want? A std engine will give 2.5 mm deck height.

Mine are 0.41mm deck height, which gives 7.4:1 with my CC volume.

 

PISTONS IM USING HAVE A 10CC DISH , IM AIMING FOR 7:1

 

u will be very close to that now, obv i dont know ur CC volume. Remember, pistons that stand proud of block give good det resistance.

 

problem is , i have a std cvh block in my garage with pistons that i have been looking at , and the cut out for the intake valve seems to be a ball hair below the top of the block?

 

they miss the cutouts by miles. No one seems to be sure what those cutouts are for! like i said, std engine is 2.5mm!

To reasuure urself - why not get an old gasket, and some old bolts, and torque them only slightly. Have just one piston in, with two lifters in the head. THis makes it easy to turn over.

Dont put a belt on, and set both head and block to TDC (before u fit head to block)


then leave the head at TDC. Turn the engine by hand (will be very easy) and see if it turns freely. See how much u can turn it before it hits the valves ( an obvious resistance) Using this method u can work out the exact clearance if u want to play with cam timing later.

If they are Stainless steel valves, be extra carefil - they bend easily. Its hard to bend a cast valve!

 

cheers mate , will try tommorow

 

 

fitted both valves earlier today on no1
fiited 4.75mm of washers onto the lifter to get maximum lift
left the headgasket off
fitted 0.7mm of masking tape to the top of the piston
turned the motor by hand with the cambelt fitted

and it does not touch!!!!

cheers Rick

 

Rick

could you tell me what the compression ratio would be with 1mm deck height ?

i take deck height means how much the pistons stick out the top of the block

 

Yes it does.

I can't tell u exactly, as i would need to know what the combustion chamber volume of the head is. You need to measure this. It's a good idea to do, as you probably don't know the history of the cylinder head, and how many times its been skimmed.

It's easy enough to do. Goto the chemist and ask for an oral syrindge. These usually hold 10ml, and are accuratley graded. Lay the head perfectly level, and with the cam out or rockers slackened, see how many ml of white spirit/petrol it takes to fill the combustion chamber. Don't use pure alchold or Meths - because it evaporates too fast. To make it easier, it helps if you have a piece of glass or clear perspex with a hole in it which you can place over the combustion chamber - that way you can see when it's full.

 

thanks will do what you said and cc the head volume

so the standard pistons are deffo 2.5 mm over as i asked in a diffrent post and someone said its only 1.6mm ?

i know the head as had a 15 tho skim and the pistons are 1mm deck height

 

Easiest way to check valve clearance to piston is to place plasticine on top of the piston then dummy build the engine. Turn the engine over by hand a couple of times then remove the head. The valve's will compress the plasticine and give you an indication of piston to valve clearance.

 

why do you all whan to go such low comp??? im running @8.5.1 with a bar of boost and making 280 bhp

 

how many miles has your engine done/expect it to last?

 

just over 12000 and had no probs at all ,apart from 6 gearboxes and 3 shafts and on the 3rd clutch

 

you must have a healthy engine/turbo spec to make 280bhp at 14.7psi

also your prob only running 1 bar because thats all it can run

 

yea its realy well speced . power on a cvh comes from the turbo , head and your management . ive also got it on a custom intake and exhaust manifolds .also its only runnin 1bar because im on std rods

 

1600 and 1 bar = 280? a 2 litre YB struggles to do that, and that breathes much better than a CVH.

I made 210 @ 11psi, since then have improved intercooler and turbo. A bar of boost and 8.5:1 is fine - it's if u want to push things further, like 40psi midrange and 2bar+ held.

 

who said anything about a 1600?im running a 1840 cvh from ferridy

 

That makes sense then

 

3x Std RST 1600 cvh engines i've measured has 1.5 - 1.6mm of piston above the block.

ON the last CVH i built last march, using 0.5mm brand new mahle's the pistons were 1.65mm above block, but i cant certain the block hasn't been skimmed before i got it.


Also my old Cosworth forge CVH 7.8:1 pistons were flush with the block above. and crown hieght is 1.65mm less than a std rst piston when i measure both together.