PDA

View Full Version : to overbore or not to over bore...


timtiminy
03-15-2008, 05:31 PM
Hey guys i have a SR20DET block that i am in the process of rebuilding. one of the piston got burnt through (detonation/ lean burn) and it left aluminum on the top edge of the cylinder. the other cylinders look good other than a few lines running up and down them... they arent deep gouges as i could not distinguish a difference in surface texture when feeling it. Question i am wanting to ask is this, do you think i should see how the cylinders turn out with a light hone or just go to a .020 over bore? i am replacing the pistons with new oem ones either stock bore or .020 over bore. The only thing I worry about is the fact that the factory sleeves maximum bore tolerance is at .020 over bore and i am concerned about running the stock sleeves thin. I dont know if this should even be a concern or if its not a big deal? I only plan on pushing the motor to 300whp so i figure a oem rebuild will be plenty tough. also i am curious as to if I will have to tune for the .020 over bore? heres pics of the cylinders:
http://i41.photobucket.com/albums/e273/timtiminy/P1000539.jpg
http://i41.photobucket.com/albums/e273/timtiminy/P1000540.jpg
http://i41.photobucket.com/albums/e273/timtiminy/P1000541.jpg
http://i41.photobucket.com/albums/e273/timtiminy/P1000542.jpg
http://i41.photobucket.com/albums/e273/timtiminy/P1000543.jpg
http://i41.photobucket.com/albums/e273/timtiminy/P1000544.jpg

RedtopTech
03-16-2008, 03:56 PM
looks similar to minewhen it blew. On cylinder 3 too. Either use bore qauge or take the block to a machine shop. I had to bore .020 on mine. Good luck

blu808
03-16-2008, 10:08 PM
10 over = just fine.


overbore smoverbore.

Mi Beardo es Loco
03-17-2008, 07:08 PM
sr24 ftw lol.

KA240SX808
03-17-2008, 11:50 PM
^ Agree'd .

Xracer
03-17-2008, 11:56 PM
If you go with an overbore dont use stock pistons. (OEM pistions done come in 87mm correct?) you will be just fine with 87mm pistons aftermarket pistons. SR's aren't open deck like most honda motors.

s15specR
03-18-2008, 01:46 PM
.02 = 5mm so you'll need 86.5 pistons

fliprayzin240sx
03-18-2008, 04:15 PM
You can bore them up to 70mm. After that, they start recommending sleeves...

timtiminy
03-18-2008, 07:45 PM
they do sell 86.5mm oem pistons. $40 a piece. and they have oem rings to fit. fliprayzin240sx (http://www.zilvia.net/f/member.php?u=3466): you sure about boring the stock sleeves to 70mm? It looks like if you went 70mm you would be past the sleeve and into the aluminum block. I think i read somewhere that 86.5 is the maximum overbore you can do on the stock sleeves as recommended by the FSM. I wouldnt want to do a .010 overbore cause the 86mm pistons would fit sloppy in the cylinder. do you have to tune for a .020 overbore, or will the ecu not even be able to tell the difference?

fliprayzin240sx
03-18-2008, 09:42 PM
My current car has 87mm Greddy slugs in it since 03. HKS themselves recommends sleeving anything after 87mm.

blu808
03-18-2008, 10:04 PM
Yea tellin ya guys 10 over is fine.

As for the computer figuring out what is going on. Every engine is different, and should be tuned to each specific setup.
On a 100 % max effort build, that is running at 100% then it would need to be tuned.

If you had a completely stock sr, with forged slugs, and a t25 then it wouldn't matter.

steve shadows
03-19-2008, 10:52 AM
10 over = just fine.


overbore smoverbore.

naw .020 over + higher compression pistons

grab a power fc and good tuner

then just be ready for new sleeves if you ever blow it again :keke:


Tuning is what keeps motors from blowing (2 + years at 300-450whp stock pistons).

KA240SX808
03-19-2008, 03:06 PM
You can bore them up to 70mm. After that, they start recommending sleeves...

I'm assuming you meant 90mm? and Darton says 90mm is the limit on there Sleeves :confused:

steve shadows
03-19-2008, 05:08 PM
stock bore is 86.5

Darton's will bore out to 90mm.

Mazworks just came out with a 90mm applicable metal HG too.

fliprayzin240sx
03-20-2008, 08:27 AM
I'm assuming you meant 90mm? and Darton says 90mm is the limit on there Sleeves :confused:

Stock block can handle up to 70mm, anything more than that, you better start sleeving.

Master Chief
03-20-2008, 06:18 PM
Stock bore is 86mm.... why do you keep saying 70mm !?!?!

Stock sleeves are about 4.5-5 mm thick. There is no need to sleeve the block, unless you plan to go over 87mm bore, or have deep bore damage and are trying to save the block.

Tomei for example use 86.5/87mm without resleeving on the motor's they sale and guaranty for reliability up to 450hp.
If they do, you can rest assure, you can , as well.

Anyway, i wouldnt take a chance on OEM pistons (wich BTW dont exist in 0.5mm over bore), and go with a set of fresh CP's - 86.5.

Good luck.

timtiminy
03-20-2008, 10:11 PM
http://www.thenismoshop.com/ikorb.php?func=catalog&category_id=1183&product_id=268
look at the drop down box for size... 0.020 overbore... (86.5mm). And why would i not do oem pistons, its not taking a chance in my oppion... Its not like i am trying to make gobs of power just a healty 300hp, havent you heard of stock block sr's making 500hp+, Its all about tuning.

infinitexsound
03-25-2008, 05:43 PM
over bore, oversized rings.... its like 80 bucks at a machine shope to bore and hone...

Master Chief
03-29-2008, 05:30 PM
The Nissan MANUAL say's there is no 0.5mm (0.020").
That web site you linked o, says that THERE IS 0.020" OVER SIZE OEM Pistons.....

Sooo..... Who do you think is right ? Some who knows what WEB SITE, or the mechanical MANUAL that came from Nissan ?

I sure hope you are going to use the NISSAN manual , and not what you read on the web.

Just so you know - Nissa offer a maximum over size piston of 0.20mm (not 0.020"). That means actualy a maximum piston size of 86.210mm.

I say you should use CP, and not OEM for several reasons.
1. I obviously know better than you and have more experience in the field.
2. OEM pistons are CAST, and are more easaly prone do damage from detonation, wich you can get even at 300HP.
3. With the CP's you can get a 86.5 SAFE bore as opposed to 86.2 with OEM pistons.
4. You go thru all the trubble of rebuilding, why not invest in some "safety" factors , as forged pistons !?
5. CP pistons are about half the weight of an OEM piston, wich will benefit even more to you increase in power, and drivtrain realibility.

etc...

BTW: The fact you hear of stories of 500hp standart oem block , doesnt mean they are reliable engines that actualy hold more than the one ocation on the dyno, where they took the reading.

Be smart, Do it right once !

timtiminy
03-30-2008, 09:45 PM
looking into Mahle pistons as they offer a 86.5mm ad its about $400 and it comes with rings so its only about $150 more than the oem pistons. Seems like their quality is top notch too.

Master Chief
03-31-2008, 04:32 PM
Mahle are a a good compromise between LOW silicone forged pistons like CP/JE.... and OEM pistons.
They are Forged, but not a strong as the Low silicone forgies.
They do have the benefith of less expanssion compare to the low silicone content once.

Make sure thoug, that you get the right pistons for the engine - i.e. pistons for SR20DET, and not SR20DE.

This is a common mistake with MAHLE, and besides the CR diference between the N/A and Turbo pistons, there is a design difference in the piston skirt.

The SR20DET has a recess in the piston skirt for the oil squirters, so they wont hit. This is not existent on the SR20DE version, as the DE's dont have the oil squirters.

i would still go with well proven CP's, but hei , each to its own.

infinitexsound
04-01-2008, 01:55 AM
since ive been gone... seems like everyone became quite the mechanical engineer.... take ur block to a machine shop...

redtop91
04-07-2008, 06:05 PM
looking into Mahle pistons as they offer a 86.5mm ad its about $400 and it comes with rings so its only about $150 more than the oem pistons. Seems like their quality is top notch too.

I wouldn't use Mahle. A friend of mine's SR was build with Mahle pistons, which lack a notch for the oil squirters even in the turbo compression ratio. He found out only when the left over bits ended up in the lower oil pan. The pistons themselves are great though, but that omission makes me not trust them just yet. Mahle is supposed to be fixing them though. Just beware if you go with Mahle. The pistons appear to clear on assembly.... As far as overbore goes, .040 or 87mm is as far as I'd go on the stock sleeves. And OEM overbore pistons do exist, the FSM for the SR's mention them. Just don't ask me how to buy them.

timtiminy
04-10-2008, 09:36 PM
i am aware of the mahle piston to oil squirter clearance issue. I plan to get the notch machined in them if i dont get a set of revised ones.

timtiminy
05-19-2008, 10:01 AM
when doing an oem rebuild is it advisable to get new oem rods or should the used ones be okay?

timtiminy
05-29-2008, 09:48 PM
http://www.thenismoshop.com/ikorb.php?func=catalog&category_id=1183&product_id=268
thats the link to the nissan oem pistons, and right there it says they are available in .020 overbore and i wrote them and they tols me it was .020 inches which is .5mm overbore

SR20DET OEM Pistons question

hello, I am in the process of rebuilding my rwd SR20DET motor, i am
looing into getting oversized pistons and saw that you carry oem
oversized pistons. I have some questions about them, first off i have
heard that the nissan oem oversized pistons are 86.2mm (being a .2mm
overbore) then i see on your site that they are a .020 oversized,
which would make them 86.5mm correct? i wanted to know the actual size
as i need to find out my machining costs for the cylinder honing. I
also wanted to ask if the wrist pins come with the pistons as well,
Thank you,
Tim

Reply

Justin Ngamthonglor to me

Yes these are 86.5mm, all OEM pistons come with wrist pins. They just don't
come with piston rings.

Justin N.
West Covina Nissan
www.thenismoshop.com (http://www.thenismoshop.com)
205 N. Citrus St
West Covina CA 91791
626-732-1000 ext 6375
626-732-3700 fax

Master Chief
06-18-2008, 02:46 PM
Again with that site, and again i ask - who do you think has more chance of beeing wrong about that ? Nissan, or whoever sells those pistons ?

I dont even see what the arguing is all about.
Nissan DO NOT MAKE 86.5mm PISTONS for the SR20DET !

The Nissan OEM , ONLY, over size piston is a 0.20mm.

Here i went out of my way and attached the relevant page of the manual
and for your convenients - the OEM Part Numbers :

http://www.max-tuning.com/gallery/mypics/sr20det/oem_piston_size.jpg



http://www.max-tuning.com/gallery/mypics/sr20det/oem_piston_size2.jpg

If somone on that site wants to argue some more, i sugest they call Nissan.

timtiminy
06-21-2008, 07:11 PM
master chief: let me ask you this. i need to go overbore as one of the sleeves is damaged on the block. I dont know how big of a bore i need to go, but lets say i get the 86.2mm oem overbore pistons, what would i bore the cylinders to? they would have to be a bit bigger than 86.2 correct? whats the actual clearance needed?

Master Chief
06-22-2008, 12:48 PM
A simple question my friend - before you even start in thinking about a rebuild - DO YOU HAVE/READ THE NISSAN SR20DET MANUAL !?!?!?!?

All the info, relevant for an OEM rebuild, is there....

Anyway, to your questions.

First of all, the correct proccess of boring/honing a cylinder is as follows :
1) Meassure the piston intended to be used in the specific cylinder.
2) Determine the PISTON to CYLINDER clerance needed (usualy info got from manufacturer)
3) Add the Piston meassurment to the piston-to-cylinder clearance. This will give you the NOMINAL cylinder bore you need.
4) Before borring the cylinder, remeber to allow for about 0.03mm for honing.
5) Final boring cylinder meassurment will be:
NOMINAL cylinder bore - Honing allowence.


Look at the manual.....
Oversize piston meassures to between : 86.180mm - 86.210mm
Add the needed OEM clerance : 0.010 - 0.030mm
This will mean , depended on the actual piston dimention, that your cylinder bore should be somwhere between - 86.190mm - 86.240.

Again, depended on the actual MEASSURED piston diameter - dont go by just what it says on the box.


As you can see the OEM clerances are very small, wich means, amongs the rest, that its very easy to make mistakes.

Again, as before, i recomand going with CP pistons, or simmilar proven 86.5 mm FORGED pistons.
Among the obvious benefits of forged pistons, the top manufacturers here, offer good quality control, the pistons will usualy be weight matched as a set, and size matched - allso you will recive info on exactly how much you need to bore the cylider etc....

Allso, mind the fact the boring only 0.2mm might not clear the problem you have with the cylinder and you wont have any choice, but to go bigger.

I am getting the fealing that you would be better off just leting some machine shop doing the work, and you simply pay the bill.

Remeber again what i said many times before - Do it right, the first time.
Dont cheap out on a few buks just for the sake of cheaping out.
If you need to save another month to get the extra couple of buks to buy the appropiate set of pistons for the job - wait another month.

Good luck !

burnsauto
06-22-2008, 06:48 PM
if you're just going up a small amount in piston size, its not boring...its just honing it out a little. Boring requires you removing large amounts of material.

Master Chief
06-24-2008, 05:21 AM
To add to that, from experience, honing for more than 0.03mm-0.04mm, even with a torque plate installed, will cause diferences in the bore diameter, at diferent hights of the cylinder.

Because of the honing machine moving up and down, honing for to long periods (that would be needed to remove more than the 0.04mm material) will cause the middle of the cylinder to be wider than the top, and especially bottom, where the honing machine cant pass thru deep enough.

For best results, honing should be kept to no more the 0.03mm.

(All this depends offcours on what machine, proccess and what stones are used, etc...)

timtiminy
06-25-2008, 12:35 PM
To add to that, from experience, honing for more than 0.03mm-0.04mm, even with a torque plate installed, will cause diferences in the bore diameter, at diferent hights of the cylinder.

Because of the honing machine moving up and down, honing for to long periods (that would be needed to remove more than the 0.04mm material) will cause the middle of the cylinder to be wider than the top, and especially bottom, where the honing machine cant pass thru deep enough.

For best results, honing should be kept to no more the 0.03mm.

(All this depends offcours on what machine, proccess and what stones are used, etc...)

So you are saying that one should not overbore past .03mm to ensure a consistant bore diameter? then why would you suggest going to an aftermarket piston of 86.5mm. that would mean overboring the cylinder .5mm, that would be overboring almost 17x as big as you recommend. this isnt making sense to me.... anyhow thanks for your advice. I am going to save up till i can get a set of aftermarket forged pistons.

Master Chief
06-27-2008, 05:10 PM
Boring is one thing, and Honing is a totaly difrent process.
In my last post i was talking about HONING, not BORING !

Its clear that you dont know the difference.
Look up the terms on Google.

I sugset you take the motor to a copetent machine shop, as its obvious you do not have enough knoledge to take matters into your own hand.

Good luck.

timtiminy
06-28-2008, 05:00 PM
sorry i was confused on the boring/honing i thought you were talking about boring. i understand now. Thanks

timtiminy
09-09-2008, 12:30 PM
If i am going with aftermarket 86.5mm pistons do i need to take them to the machine shop with me so that they know how large to bore the cylinders with the correct clearance, or do i just have the cylinders bored to 86.5mm and the "86.5mm" pistons are compensating for the clearance by being a little under 86.5mm?

Master Chief
09-09-2008, 02:20 PM
Take them with you !

The correct proccess is to have the Piston meassured, as per the piston makers instructions, at 20 Deg. C room tmperature - using a micrometer.
Than use the micrometer, fixed at the meassure taken, to zero a bore gauge.

The zeroed bore gauge, should be used to meassure the bore.

The cylinder should be bored, until the bore gauge shows the desired piston to wall clerance (-about 0.03mm honing alowance).

The block offcours, should be at the same room teperature, as the pistons.

It only takes a small error in meassure, or a small temperature difference, to under bore or over bore the block, byond the desired clerances.

Allso, the pistons are not always exactly as advertised, and its smart to have things checked (although i never had a problem with CP's beeing off).

timtiminy
09-09-2008, 05:10 PM
Thanks master chief. Now the only dilema i have is whether i need to get 87mm pistons in order for the overbore to get rid of the scoring on the cylinder wall... or if 86.5mm pistons will be adequate. what is your expericence with overboring cylinders to clean them up from detonation and blowing a hole through the piston where the ring lands where blown through and the rings gouged into the cylinder wall?

Master Chief
10-03-2008, 05:01 PM
Thats something that needs to be seen to know.
An experienced machine shop, should be able to determine how much would you need to bore, to clear things up.