right i will be using JE pistons in my focus rs engine. i have all the stuff now and the block has been honed to size by halesowen engines! i have measured the internal bore and i have on cyliner 1 - 86.020 cyliner 2 - 86.010 cylinder 3 - 86.020 cylinder 4 - 86.010 all in mm but im a bit lost with gapping.

the instructions say that for high performance street and strip the top ring should be gapped to bore x .0045" the 2nd ring bore x .0050" and the oil ring min .015"

now for that i am working out the ring gap of the top ring should be 3386.614 (mm converted to thou) x .0045" = 15.239" is this correct? or am i doing something wrong? so in theory the gap should be 0.0381mm? getting muddled in numbers here lol

 

Convert your cylinder bore diameter to inches and then multiply it by the given ring gap suggestion.

For example.

Cylinder 2.
86.010mm converts to 3.386"

Top ring gap calculation:
3.386 x 0.0045 = 0.0015237"

You're looking at 15thou which is about right - if you're going to give it death on the track or hit it with gas later on i'd personally make it a little larger.

Make sure the ring faces are still square to each other when they're closed up too.

 

thankyou will cleared things up! makes much more seance when you talk to someone who knows what they are doing

 

right just checked the top ring gaps and from that conversion above they should be a gap of 0.0015 they are 0.0090 so whats wrong there then? these are the rinds supplyed with the je pistons they are je rings these jobbies



0.0075 oversize on the gap seems a bit much

 

MEASURE the gap, dont try and work it out.

Put the ring into the bore and use a feeler gauge to see what the gap actually is.

 

i done my on my engine with JE Pistons took bloody ages to do all of them

 

i have mate and the gap once i have done that is 0.009 as said! and from the calculation they have given it needs to be 0.0015 easy tiger lol just after some friendly advice

 

lol did you use a file or have you got the proper tools? sounds like fun! lol dont mind if it takes a month as long as its done right! its my 1st engine build so i want everything perfect! work in engineering so have all the tools dials and measures to hand only i work in microns at work so smaller tolerances than then engines

 

proper ring grinder

 

anyone

 

where in the bore did you put the ring to measure the gap?
did you order rings to your finished bore size?

 

i put the rings in the bores a piston deep down! about half way i would say!

the rings came with the pistons and the block was honed to the piston spec stated

 

What units are you quoting in?

Cause if thats inches, then I dont believe for 1 second that the correct gap is 1.5 thou, more like 15 thou!
So I think you have got the decimal point in the wrong place.

 

yeh inches! can i pm you or have you got msn as i have seen alot of your posts on this site and it seems you know your stuff!

will has converted it for me in post #2

Convert your cylinder bore diameter to inches and then multiply it by the given ring gap suggestion.

For example.

Cylinder 2.
86.010mm converts to 3.386"

Top ring gap calculation:
3.386 x 0.0045 = 0.0015237"

You're looking at 15thou which is about right

i have checked the gap and i have currently got 0.0090" on the top rings

 

0.0015 thou is 1.5 thou which is defo not right. You currently have 9 thou which is too small imo, but it depends what the manufacturer states.

 

Just checked, Will through an extra zero in there somehow. 3.386 x 0.0045 = 0.0152 = 15.2 thou.

So i'd use a 16 thou ring gap if your not going NOS or huge boost. You need to file about 7 thou off the ring.

 

top stuff thankyou mate sounding a bit better! going to be using upto 2 bar of boost mate looking at 450 - 500hp

 

i have these pistons and rings for my zetec also

hope there not going to be a pain to fit

 

not a pain mate! just my 1st build and im just panicking lol! just want to make sure everything is done correct to the right tolerances if you have done it before im sure it would be a walk in the park

 

15-16 thou sounds just what I would expect, so just need to file 7 thou off and you are there

 

just make sure you smooth off the edges with some wetordry after you have filed

 

got 3 in! the 2nd rings were fine but the top ring needed the 7 thou taking off! started with a file and it just wasn't happening! so i had a new oil stone with course and fine side! took the material off with the course side it came off quite easy so was chuffed about that had them gaped in about a hour! and took me about 3 hours in total! put them in all nice and lubed up and positioned them to spec and put them in! nice its looking more like an engine now

thankyou for your help all that did

 

Im using this tread because i have the same quest

Building a new engine zetec turbo, with new pistons and new rings do you use the tolerance that is in the haynes book for the gap on the pistonsrings??

 

Haynes doesnt cover zetec turbo, you need to ask your piston manufacturer what they recomend if you are using forged pistons, if you are using standard pistons then add a few thou to the standard clearances quoted.

 

its forged pistons from supertech, ok so i need to contact them.....

 

Yes mate you should, although supertech are just vendors I believe so they might need to refer to the manufacturer.
You should also be asking them for PISTON TO BORE clearance as well as the ring gaps, as that will be larger than standard too. 3-4 thou or so is typical for a lot of aftermarket forged turbo pistons IME, which is double what most standard cast pistons are.

 

most new pistons should come with all the clearences on a leaflet in the box

 

how do you measure piston to bore gap?

 

With a vernier caliper and a dial gauge.

 

so you measure the piston out of thebore then measure the bore correct

 

What I do is set a vernier caliper to the size of the piston, then use a dial gauge on that, then use the same dial guage on the bore to see the difference.

 

thanks for the reply just trying to learn but you have confused me even more lol

 

Basically because you are trying to measure a several inch hole based on only a few thousands of an inch difference, you have to use a dial gauge to see this difference.

 

so chip is it wrong to measure it with a tape measure, its a good one

 

so you measure the the piston with the vernier,then measure the vernier with the dial gauge then measure the bore with the dial gauge and compare the difference?sorry to peck your head

 

You use a vernier caliper to set to the same size as the piston.
Then you use that to set a dial guage to zero.
Then you place the dial gauge in the bore and it measures the clearance.

Just ask your machine shop to do it when they bore it mate, thats your best bet probably if you havent done it before.


Lol @ tiny