Shim or turn down cylinders.

[steve_pugh]

Have a set of pistons and cylinders and the piston sticks out the top. So it has negative deck. (This still confused me.  I'd say positive. )
Put a .090 base spacer and now have measured a deck of .023

So to get a near zero deck I will need a base spacer of .070.
You can't buy this size.  

I have the option of some long cylinders. But they are around 6mm longer than the std length ones.  

So..  Do I get the long cylinders and have them machined down to give me a zero deck.  Or buy 2 base shims to give me .070?
(A .040 and a .030 for example.  I don't like the idea of a .060 and a .010 as the .010 is thin and more likely to distort...)

I've had mixed thoughts about machining cylinders and getting them a the same.  

Cheers.  

[Andy Sykes]

machine them

[Jonny Grigg]

What Andy said. It is a no-brainer. 

[Garrick Clark]

I would machine them down also.
If you want to get a zero deck.
Machine the cylinders down in stages.
If you need say 70  thou off the cylinder bases take 50 thou off, refit the  cylinders/pistons and measure again to get your final cut measurement.
Might be an idea to get your cylinders checked for length before you start as they can vary.
If you do go for zero you might also find that the rod lengths can vary and the pistons too.
When you get close to zero deck check all deck heights and wright the numbers down,When you get close you might find the deck numbers on the 4 cylinders  are not the same.
(EVEN/ODD numbers)
In the past I have trimmed cylinders to achieve zero only  to find I had to trim 1 or more piston top down a  few thou too get all 4 pistons to zero at tdc.
Don't balance the pistons till you get true zero just in case you have to trim a piston top a tad.
Also clamp down 2 cylinders say 1 and 2 and put a quality straight edge across the cylinder top edges.
The straight edge must be flat on the cylinder edges with no rocking.
Check your measurements.
When you think you've got it right.
Check again.

[fish]

I would attest to checking individual deck height with all rods and pistons attached without rings or just get the case decked and measure everything twice before assembly.

[Jonny Grigg]

Steve,

If you didn't already check, I would measure the crankshaft centreline to the deck surface of the cylinders on the case to ensure they are both the same or within close tolerance. I would also measure each piston from the centreline if the gudgeon pin to the top of the crown to make they are all the same- otherwise you will be chasing your tail trying to get it right. Little details when building a non-stock engine make all the difference. I would not consider using shims if you have access to good quality cut-to-length cylinders- just make sure you use a competent machinist! When I did my motor, all the measuring and machining was done by Phil at Bears Motorsport. He builds Formula Vee engines and really knows what he is doing.....

Cheers, J.

[steve_pugh]

Steve,

If you didn't already check, I would measure the crankshaft centreline to the deck surface of the cylinders on the case to ensure they are both the same or within close tolerance. I would also measure each piston from the centreline if the gudgeon pin to the top of the crown to make they are all the same- otherwise you will be chasing your tail trying to get it right. Little details when building a non-stock engine make all the difference. I would not consider using shims if you have access to good quality cut-to-length cylinders- just make sure you use a competent machinist! When I did my motor, all the measuring and machining was done by Phil at Bears Motorsport. He builds Formula Vee engines and really knows what he is doing.....

Cheers, J.

Ok, that's a fair few votes for using the long cylinders.    I don't NEED or want extra long cylinders as I don't want a massively wide engine.   They would be great if I was putting an 86mm crank in with long rods.. but I'm running an 82mm with 5.5" rods and I'm only slightly out when using stock length Cylinders.

Bears are not very far from here by the looks of it.    I guess the other question is, what is the main benefit of having a zero deck?   
If I want an overall 50thou deck, and the piston is 50thou into the cylinder then is this good to go straight onto the head?  I remember you saying Jonny that I want a Zero Deck and a 50thou copper head gasket.   
The end result is identical but what is the benefit of this?  Flexibility to change the CR later by just changing a gasket?   

[fish]

The piston's location at TDC either below (0.050) or above (-0.050) deck/cylinder to head mating surface will be one of the determining factors of dynamic and static compression ratio and a crucial part in the turbulence and combustion occurrence not to mention proximity to making sweet violent love to the head of your.....valve, also dependant on the cam+rocker lift.

The beauty of having zero deck is that NO combustion occurs within the cylinder walls while also creating a good quench depending on the heads in use, although a 0.050 deck which is the norm will work just fine whichever way you come to that figure. You are right about it being easier to change comp ratio if using a copper head gasket, make sure you lap the cylinders to the head.

Here's a good compression calculator
https://www.uempistons.com/index.php?main_page=calculators&type=comp

[steve_pugh]

There seems to be around 50/50 on the schools of thought about combustion in the actual cylinder itself.
I can achieve the .050 by running the cyls as they are with a .023 deck at tdc and a .030 copper head gasket.   The end result is similar and there is no complicated machining to do.

Just spoke to Bears and they said that they can do it but that it's risky as the lathe bit can 'bite' and then grab the cyl.   They use a new bit each cyl (which makes it expensive) to minimise this but make no guarantees.   
His thoughts were that he would leave the small amount I have in the cyl and achieve the extra deck height required by use of a gasket.   
We are looking for a CR of about 10:1 with an FK10 Cam so with a .050 deck we need 54ccs in the heads.

[Mike Lawless]

Personally, I believe you are over thinking this, unless you are after absolute perfection. If it were me, I'd just run a .060 -.065 overall deck. You can get there with your .023 deck and a commonly available .040 copper gasket.

Far more important is to have both barrels on any side the exact same length so it doesn't distort the barrel when torqued down. Better to live with a small amount of difference in deck and CR that risk having the barrels becoming out of round from uneven clamp loads.

I have run everywhere from .045 to .075 on my race motor, and it doesn't run appreciably different.

I also like the Cima Mahle barrels over the commonly available long cylinders. The long cylinders seem to be softer and wear quicker.

[steve_pugh]

Personally, I believe you are over thinking this, unless you are after absolute perfection. If it were me, I'd just run a .060 -.065 overall deck. You can get there with your .023 deck and a commonly available .040 copper gasket.

Far more important is to have both barrels on any side the exact same length so it doesn't distort the barrel when torqued down. Better to live with a small amount of difference in deck and CR that risk having the barrels becoming out of round from uneven clamp loads.

I have run everywhere from .045 to .075 on my race motor, and it doesn't run appreciably different.

I also like the Cima Mahle barrels over the commonly available long cylinders. The long cylinders seem to be softer and wear quicker.

I really don't want to over-complicate this.  I would like the very best perfect engine avail but within the confines of an amateur builder.   My next engine will be more complicated. :-)   I also use the car on the street so it can't have a crazy CR.   
We are checking and double checking every measurement and I guess my original reason for asking was I don't have the ability to keep machining them down bit by bit and keep measuring and then final machining.   The parts would have to go back and forth to the machine shop for that.   

I'm using AA Cylinders and AA forged Pistons.   

I will double check the length of each Cyl with a straight edge and also the face of the case.   It's a shame that there isn't more material on the case as this would seem simpler to machine down rather than Cylinders.

[Old Guy]

Steve,

Go with Mike Lawless' suggestion.  You failed to mention that you would have to PURCHASE the long cylinders. 

[steve_pugh]

Steve,

Go with Mike Lawless' suggestion.  You failed to mention that you would have to PURCHASE the long cylinders. 

Sorry Ron.   I put I have the 'option' of some, but yeah, I should have specified I need to buy them...
Btw thanks for all your help via email with the AA stuff.   Massively helpful.   

[Andy Sykes]

Speak to Alan at GAC he can do any go the machining and it very helpful and knows his flat fours, is also only in Aylesbury, he builds all of Danny's engines , don't skimp at this stage it end in tears