Ring Gap

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MDK87

MDK87

Hyundai's can't fly!!
Joined
Dec 12, 2007
Messages
2,361
Location
Brisbane
Hi guys :)

Could someone please tell me what piston ring gap is, how to check it, and how to set it?

Thanks! :)

So far my understanding is that piston ring gap is the distance between the ends of a ring/rail once it is compressed on the piston in the cylinder bore.

I have no idea how you check it.

And all I can find so far is that it is set just by using a file.

My main qualm is how to check it relatively accurately. :p
Do you just pop the ring in the bore and use feeler guage to measure the gap?
How do you get the working surface of the ring square against the cylinder wall in this way? It would be hard to do this especially with the flimsy oil rails too wouldn't it?

Please tell me if I am on the wrong path completely!! haha

:)
 
You are on the right track... Locate the ring in the bore and then use the piston upside down to square the ring and push it down a little. Then use the feeler gauge to meausure the end gap. My rule of thumb ( if you HAVENT got the ring manufacturers specs !!) is .004" for every inch of bore diameter. That translates to around .014" MINIMUM gap for a 4G63. I repeat again, as its really important, the ring makers specs over ride anything said here for minimum ring end gap ! If the gap is tighter, then under heavy load , and lots of heat, the rings could butt up hard and crack the ring lands...

Cheers Mike
 
Oil rails - depending on the make will generally require no filing.

It is the top and middle ring that require clearance.

As you described, put the ring in the bore and measure with a feeler gauge.

Make sure you use a torque plate if you have one.

Also measure the ring towards the top of the block where they would sit at TDC. Make sure after you grind the rings that they are free from sharp edges because they can easily scratch your bore.

Also to ensure that they are square, you can just butt them up to each other and make sure the ends line up.

Only grind one side of the ring only.
Also only go in 1 certain direction, from memory, downwards.

Measure each ring to each cylinder individually. Do not mix them up.

Thats all I can remember for now!

What brand rings?
What pistons?
What grinder are you using?
 
Thanks for your reply Mike. :)

I found out that genuine rings are already gapped lol should have bought those, would save me from the chance of my handywork stuffing something up. :eek:

The rings I bought (Nippon Piston Rings) didn't come with anything at all, just the box they were packaged in.

I found a guy on the US GVR4 site with the same rings and this is what he was told to gap them to.

".019-.020 on the top. .023-.024 on the second ring"

"I use those specs on most of the motors I build. I would say I have used every ring out there with those specs. I have the NPR rings in my DD with those specs and don't have a problem running 36psi on pump daily. This motor has been in the car for a few years with many different turbos but currently runs the PT6262"

So can I ask what may be a dumb question...why do the gaps vary between 1st and 2nd ring?

And what gaps should I put on the oil ring rails?
If I can't find anything else I will just gap them using your rule of thumb Mike.

Thanks heaps! :)

EDIT: Oops just saw your post Baz! Thanks for the help. :)

I know alot of people will tell me to take it to an engine builder but I want to try learning something for myself and hey thats what GVR4's are for right!? haha

I'm just using stock gear Baz, no bored out cylinders, flash pistons etc

I am however rebuilding this motor (it was working fine on 20psi when I pulled it apart :p) in the anticipation of running 20+psi, just wanted to freshen it up a bit and stick an MLS headgasket in there, remove balance shaft etc

Thanks for all your help guys! :)
 
:huh: .....what is a torque plate Baz? ..... -_-

Is that a method of honing?

As for grinder, I was just going to use a file. Would that be ok? I don't rebuild many engines (obviously :p) so I didn't think it'd be worth getting one of those borzon grinders wheel thingys.
 
Oh I found out what a torque plate is. I remember seeing one of those in your engine rebuild pics Baz. Yeah I don't have one. :( Will have to do without.

In case there is anyone else like me who doesn't know what a torque plate is -

"Cylinder bores in engine cylinder block have as final manufacturing process a honing operation, which determines their surface finishing, cylindricity and diameter. These characteristics provide the achievement of required engine performance in terms of lubrication oil consumption, emissions, critical components wear level, besides durability and reliability.

Among the three characteristics mentioned above, cylindricity or cylinder form distortion is the most sensitive to block strain state, which means that if resources were not applied to ensure block strain state as similar as possible in the honing operation, and in the cylinder head clamping at the assembly line, the required engine performance might not be achieved.

The resource on device developed to obtain this similarity, a Torque Plate, its influence on the whole cylinder bore machining process......"

- Taken from www.sae.org

It's kind of like a pretend cylinder head that still allows access to the bores.

Now I wish I had one...
 
That Yank guys ring end gaps seems a little excessive... nice and safe , but would contribute to a lot of blowby. The name of the game is to keep the end gap as small as possible without the ends touching... Any gaps and combustion gas can escape into the crankcase ie blowby.

Be very careful filing rings ! Its a bit of an art. See if you can borrow a special rotary disc.. it makes things lots safer. Otherwise, put a fine cut file in a vice and then as per Bazeng description.

The second ring has more gap ( slightly)than the top ring. I think its because the piston transfers more heat to the ring in that area ?? therefore the ring gets hotter and grows a little larger .

I made my own torque plate... its more important to use it in the final plateau hone. And the bores do distort a little when they are torqued up. I assume you are keeping the original bore and not going oversize ?? The hone is a very important part of the ring sealing process. Betta get it right !

Cheers Mike
 
Yes I'm keeping the original bore size. I was just going to get one of those expander claw honing things from supercheap in case the cylinder walls have become a little glazed, that was about all I was going to do in regards to honing. Never planned to bore them out.

EDIT: Which reminds me, what is the lubricant you use when doing that? I think last time we used mineral turps or something but I forget. That was just on a 4G61.

:)
 
For a performance build.. which your 4G63 is at 20psi boost, I would very strongly recommend an engine machine shop hone the bores. It is super critical to get it right . I personally only use the Supercheap honers on "supercheap" re ring jobs on old crap boxes. I get the professionals , even with my experience, to hone the horsepower blocks. Their honers and experience isnt all that expensive to use, compared to pulling your engine out to redo the job after the disappointment of a smokey, oil burning breather after an attempt to to a "cheapy" at home. Just my opinion...

Mike
 
Good point Mike, I was half thinking of getting UMR engines to hone the block and perhaps shave a little off the top as well. Maybe they will have a torque plate! :)

I'm not sure how the experts do it, but if I get it honed, won't that increase the bore diameter a little, leading to increased blowby? Or is that what the purpose of gapping rings is, so that the piston rings can take up the slack?

I just get confused and am not sure if honing is the same thing as boring when you take it to a shop. E.g "20thou" bored block is not an example of "honing" right??

Also when postioning the gap on the pistons, you set them 90 degrees apart right? So for example the gap in the 2nd compression ring is 90 degrees clockwise in relation to the gap in the first one. The 1st oil rail is then another 90 deg clockwise ontop of that and the 2nd oil rail is then another 90 deg further clockwise.

Sorry for all the noob questions guys... :unsure:
 
yeah, honing does increase the bore diameter marginally. Thats why you have to be a little careful... It all depends on bore wear, but usually 4G63's arent too bad for that, especially if you can see the old hone pattern, and not shiney worn sections. Ring gapping should control the blowby, but there will be more piston to bore clearance. This will just make things a little clackier until it all heats up.
Decking the block is a good idea as it can take a cut of up to .005" to get things flat again... crucial for MLS head gasket sealing.

I like to set my rings 180 degrees apart ... Gives the gases the hardest path to escape. Theoretically, rings rotate over time, so it only really helps on firing up . Not sure how they prove how fast and how they rotate though !
 
I think I'm out of questions for now. :p

Thanks a million for all your advice Mike! :thumbsup:
 
Great thread.
Im no expert but i also read somwhere that the ring gaps are dependant on the ammount of heat you expect the motor to make. So you know how much they should expand. Makes perfect sense.

Higher boost, or nitrous ect makes the rings expand more so you run more gap.
Pump fuel with say 25psi boost will need less gap than that bloke running 36psi for eg. Or some 600hp motor, so you wouldnt nessicarily follow what a really big hp build would do.

It was posted up on here or galantvr4.org.au in the last few weeks. Along with a list of suggested ring gaps according to the fuel and boost used.
 
milkandoj said:
Great thread.
Im no expert but i also read somwhere that the ring gaps are dependant on the ammount of heat you expect the motor to make. So you know how much they should expand. Makes perfect sense.

Higher boost, or nitrous ect makes the rings expand more so you run more gap.
Pump fuel with say 25psi boost will need less gap than that bloke running 36psi for eg. Or some 600hp motor, so you wouldnt nessicarily follow what a really big hp build would do.

It was posted up on here or galantvr4.org.au in the last few weeks. Along with a list of suggested ring gaps according to the fuel and boost used.
Click to expand...

Hey Gerard,

I've been searching for threads regarding this stuff to no avail (except the US site). Mike has pretty much sorted me out now, but it would be good to read this thread you're speaking of.
Would you be able to provide a link champ?

Cheers. :)
 

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