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Piston Ring Gaps

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31 replies to this topic

#1
Bobbit

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Currently doing my first engine rebuild without any machine work done.
I'm putting in a set of Wiseco pistons (9:1 CR) in with some rods, all the oil clearances are within spec with the rods being on the tight side of spec. and now I'm down to the piston rings.

The first set of piston rings i screwed up because i decided it was a good idea to start filing rings when i was half asleep and somehow got inches mixed up with mm on the feeler gauges making my top ring gap to be 0.031" and 2nd ring gap 0.048"

So far 1 set of rings is on the to buy list.

Now to list the measurements of the rings un-filed:

Piston 2
Top 0.508mm
2nd 0.676mm

Piston 3

Top 0.330

2nd 0.610

Piston 4
Top 0.406
2nd 0.635

Each cylinder has a taper of aprox. 0.03-0.005mm

Now for the actual question:
Should i file all the rings out to the largest value (Piston 2)
or
Should i see if Wiseco makes fileback rings and file them all back to spec. Which is 0.508mm for top ring and 0.558mm for the 2nd one?



#2
MDK87

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I would usually think yes - match to the largest gap providing it's within spec. 
 

But 0.5mm seems like a very big gap..

Are you squaring the rings in the bore with an upside down piston?



#3
Bobbit

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Yeah, im putting the ring in the bore by hand and then pressing it flat with a piston down to where it approximately sits at TDC taking the first measurement then again at about the middle of the bore.

Before i did anything you could see the original hone marks in the bore with no gouges, then i went over the bores with a flex hone and cleaned all the crap out after, maybe i spent too much time honing it? but then the first ring on piston 3 shows it being tight?

 



#4
MDK87

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You would have to sit there for a long time with a flex hone to take that much meat out though.
I would think the ring gap should be around 0.15-0.2mm (?) depending on expected usage.
Best to wait for one of the guru's to chime in here. 



#5
jack be nimble

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What piston to wall clearance?
Are your bores within size to your pistons?
4g93t jumbuck conversion. PRANGED 18/3/12, CHECK MY MEMBER RIDES Page 11. no serious human injuries.
ON THE ENGINE STAND. g4cs 2.4l + Gt35r. PLUS: auto conversion + Awd coming.
thanks for parts and help: BMGTZ, EVOCPE, cwolf, Benozi, Jamo-GSR, 1JUM2NV, RXVII..much appreciated, cheers guys.
Aerodynamics are for people who can't build engines. —Enzo Ferrari
REMEMBER: you cant polish a turd, but you can roll it in glitter.

#6
Bobbit

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I wish i could tell you, but i couldn't seem to find anyone with a dial bore gauge lol and i doubt my vernier caliper would get an accurate reading.

The original pistons that came out didn't have any score marks or anything on them other than carbon.



#7
jack be nimble

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Feeler gauge between skirt and wall will tell you.

Maybe your bore is worn.
How did you measure taper? Comparing ring end gap- top, mid and bottom of bore?
4g93t jumbuck conversion. PRANGED 18/3/12, CHECK MY MEMBER RIDES Page 11. no serious human injuries.
ON THE ENGINE STAND. g4cs 2.4l + Gt35r. PLUS: auto conversion + Awd coming.
thanks for parts and help: BMGTZ, EVOCPE, cwolf, Benozi, Jamo-GSR, 1JUM2NV, RXVII..much appreciated, cheers guys.
Aerodynamics are for people who can't build engines. —Enzo Ferrari
REMEMBER: you cant polish a turd, but you can roll it in glitter.

#8
Bobbit

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Yeah measuring the ring gap top, mid and bottom.

 

Can't seem to push a feeler gauge in between the piston and bore unless i slide it down with the piston and then it's only at the very top, one measured 0.003" with some decent drag so not really sure without the proper equipment.



#9
jack be nimble

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Doesnt matter, you are using them anyway.

So at the bores smallest point that the piston travels in, thats where you want the ring gap set at the minimum gap.
Swap rings from bore to bore to get closer gaps.
I cant remember the wiseco gaps, but its on their website.
I put the file in a vice, tho a ring gap machine is faster and easier.
4g93t jumbuck conversion. PRANGED 18/3/12, CHECK MY MEMBER RIDES Page 11. no serious human injuries.
ON THE ENGINE STAND. g4cs 2.4l + Gt35r. PLUS: auto conversion + Awd coming.
thanks for parts and help: BMGTZ, EVOCPE, cwolf, Benozi, Jamo-GSR, 1JUM2NV, RXVII..much appreciated, cheers guys.
Aerodynamics are for people who can't build engines. —Enzo Ferrari
REMEMBER: you cant polish a turd, but you can roll it in glitter.

#10
jack be nimble

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I often make a wire gauge to check bores before buying pistons.
So if you know your final finish size, you can subtract you final hone to size allowance, plus a bore allowance, and make your wire gauge for that size and another for a piston size bigger. Then simply run that gauge through the bore, if it fits anywhere, you need bigger pistons.
4g93t jumbuck conversion. PRANGED 18/3/12, CHECK MY MEMBER RIDES Page 11. no serious human injuries.
ON THE ENGINE STAND. g4cs 2.4l + Gt35r. PLUS: auto conversion + Awd coming.
thanks for parts and help: BMGTZ, EVOCPE, cwolf, Benozi, Jamo-GSR, 1JUM2NV, RXVII..much appreciated, cheers guys.
Aerodynamics are for people who can't build engines. —Enzo Ferrari
REMEMBER: you cant polish a turd, but you can roll it in glitter.

#11
Bobbit

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Ended up ordering two sets of rings for the pistons, going to mix and match them until i get the clearances as close as i can.
End gaps are supposed to be top .508 and 2nd .558

If i decided to get machine work done i think it'd just make things worse with all the clearances, that and i've already got the 85mm forged pistons and don't wanna fork out for a new oversize set.
Also apparently the wiseco rings are supposed to be filed anyways so i assume the only reason gaps are so large are because of my bores.


I'm going to gap everything up and then put it all together, worst comes to worse i can always pull it apart again and save up for some oversize pistons and machine work to be done, not like its going to explode or anything? :ph34r:

 



#12
jack be nimble

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Its better to have a gap too big than too small.
4g93t jumbuck conversion. PRANGED 18/3/12, CHECK MY MEMBER RIDES Page 11. no serious human injuries.
ON THE ENGINE STAND. g4cs 2.4l + Gt35r. PLUS: auto conversion + Awd coming.
thanks for parts and help: BMGTZ, EVOCPE, cwolf, Benozi, Jamo-GSR, 1JUM2NV, RXVII..much appreciated, cheers guys.
Aerodynamics are for people who can't build engines. —Enzo Ferrari
REMEMBER: you cant polish a turd, but you can roll it in glitter.

#13
Bobbit

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Guess i just gotta remember to install a catch can and empty it.

Few more questions and i should be good to go.

Obviously i need to run in the engine, Can i run the stock ecu with my 9:1 compression ratio?
I do have a Wolf 3D that came with the car and its tuned but its only fuel and spark and i do have a wideband o2 so i could tune it if i needed to.


Have you or anyone else had experience with ECM link?  I was thinking of saving up and getting it.



#14
MDK87

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End gaps are supposed to be top .508 and 2nd .558

 

Is that what they are supposed to be or what you must live with because of your bores?

Jack what's a nominal ring gap for a stock-spec 4G63 rebuild?



#15
MDK87

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I've used ECMlink but I've not used the Wolf 3D.
ECMlink is pretty good for what it is. There is a dedicated forum as well so you can ask questions or search for common problems.
 

I'm not sure about running your 9:1 engine on the stock ECU. As the stock engine is 7.8 - bit of a difference. You might experience detonation.
Having said that, the stock (A-spec?) VR4 maps are pretty tame wrt ignition timing and pretty fat wrt fuelling. 

If you have no other option just be easy on the go pedal and run it on the highest octane fuel you have access to.


Edited by MDK87, 05 November 2014 - 12:42 AM.


#16
jack be nimble

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Is that what they are supposed to be or what you must live with because of your bores?

Jack what's a nominal ring gap for a stock-spec 4G63 rebuild?


I dont know stock ring gap. But you sort of need to go on the wiseco specs. Its on the box or on the website.

Id run the ecu, get your boot out of it if it pings, and watch the wideband.
I like my ecmlink, but will be changimg to a late evo ecu soon. Pretty easy to start with it, esp if you can get your wb to log as well. It might be hard to get the dyno guy to tune it, but you can do 80% on the road/track.
4g93t jumbuck conversion. PRANGED 18/3/12, CHECK MY MEMBER RIDES Page 11. no serious human injuries.
ON THE ENGINE STAND. g4cs 2.4l + Gt35r. PLUS: auto conversion + Awd coming.
thanks for parts and help: BMGTZ, EVOCPE, cwolf, Benozi, Jamo-GSR, 1JUM2NV, RXVII..much appreciated, cheers guys.
Aerodynamics are for people who can't build engines. —Enzo Ferrari
REMEMBER: you cant polish a turd, but you can roll it in glitter.

#17
jack be nimble

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I dont know, but ecmlink arent selling the lite version anymore, only if you have early evo or rvr. So you might have to get the full version, tho it has boost control, it is pricey
4g93t jumbuck conversion. PRANGED 18/3/12, CHECK MY MEMBER RIDES Page 11. no serious human injuries.
ON THE ENGINE STAND. g4cs 2.4l + Gt35r. PLUS: auto conversion + Awd coming.
thanks for parts and help: BMGTZ, EVOCPE, cwolf, Benozi, Jamo-GSR, 1JUM2NV, RXVII..much appreciated, cheers guys.
Aerodynamics are for people who can't build engines. —Enzo Ferrari
REMEMBER: you cant polish a turd, but you can roll it in glitter.

#18
Bobbit

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Re-Measured all the ring gaps and they are all  0.406mm top ring gap and 0.635mm second ring gap.

The min. gap spec is apparently 0.005"xBore

So 85mm to 3.34645669 Inches

Bore X Ring Gap
3.34645669 X 0.005 = 0.01673228345"

Then 0.01673228345 inches to 0.425mm


TL;DR

My current ring gap at BDC is 0.406mm but the min spec is supposed to be 0.425mm (But its recommended to have 0.4572mm)
Think it'll matter? Will it butt and break ring lands and reek all havoc?

My bore finish was also with a 320 Grit Flex hone not a 420 or what ever, maybe it'll wear enough before butting?

Also i'll be running 11 Psi at most for now but i'll run it in at 6psi or what ever the wastegate is set at.


Edited by Bobbit, 15 November 2014 - 05:20 AM.


#19
CLuTZ

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If you are gong to hone the bores then perhaps it was a better option to go a 20thou oversize piston and have your machine shop do the honing. That way you know that the pistons and more importantly the ring gaps are in spec to what Wiseco recommend. You can also have someone to blame if anything goes wrong lol. Torque plate honing is also recommended if you can get your hands on a plate or your machine shop can engineer one.

Are you going to delete the balance shafts? If so, are you going to get the entire rotating assembly and clutch balanced?



#20
Bobbit

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If you are gong to hone the bores then perhaps it was a better option to go a 20thou oversize piston and have your machine shop do the honing. That way you know that the pistons and more importantly the ring gaps are in spec to what Wiseco recommend. You can also have someone to blame if anything goes wrong lol. Torque plate honing is also recommended if you can get your hands on a plate or your machine shop can engineer one.

Are you going to delete the balance shafts? If so, are you going to get the entire rotating assembly and clutch balanced?

 

 

The bores have already been finished, those are the ring gap specs after the crosshatch has been cut in.

Balance shafts have been removed.
And already have forged rods and pistons only one rod is 1g heavier than the rest but nothing i can do about that.

Balance shafts don't actually balance anything, they just cancel out the enherant vibration of the inline 4 cylinder design, in other words.. driver comfort.




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