65Mm Pistons - Ie Stock Bore For An New Rb26 Block

[djr81]

Can you tell us a little more about this comment?

I understand that a leak down was done, but the comment of pulling the motor down being pointless based on the results is confusing me.

Did it have pathetic leak down results or was it fine? What's the story?

What others are currently suggesting is that your octo breather pussy party setup may not be helping what you are experiencing.. I think you should rule this out for everyone so that we can continue to try and help. I for one do not want to encourage you to build another motor if you dont need to.

The leakdown numbers are large - too large to believe that any amount of catch can/breather set up will help the issues and too large for me to want to wind any more hp into the thing - which was the whole point of getting a built motor.

The comment was simply that I didnt think it was worth pulling the motor apart to diagnose the problem. There is too much blowby is the core of the issue. Dont need the motor in a bazillion bits to know that.

I dont want to trouble shoot the breather system. When first built it had the same breather system as the stock motor - basically a Nismo catch can and that was all.This set up was fine with the tired original motor. With the built motor it puked litres of oil into the I/C and fouled the AFM's so much that the thing would lay smoke screens down the straights. Every change to the breather/catch can system has been after establishing there was a fundamental issue. It was simply an attempt to find a bandaid fix for a motor with too much blowby. To an extent that has worked. But it wont ever be enough.

I need to build a motor with good blowby numbers in the first place. When you talk to builders over here they get all nervous and will only ever volunteer 15 - 20% leakdowns. So I have no real confidence that just doing what everyone else does is going to work well enough. Hence the 1.5mm rings which I would have been happy with. Unfortunately the ACL rings didnt fit and I cant find a piston with a similarly thick ring.

Hope that is clear?

[GTScotT]

All you had to say is that it got bad leak down results lol

You didn't need to prove that the catch can isn't the problem once you confirmed it had bad leak down. We only questions the catch can because we didn't know the leak down results.

Anyway. It has been said that other people have not had this problem before (with thinner ring piston kits).. So why not build it yourself this time? Get the block you want to used checked for bore size and follow the machinists recommendation for what size piston it needs. Buy the pistons in a kit and grind the rings to the exact specs your happy with. For reference my CP top rings had a maximum gap of 17 thou, which was good enough for me to work with. Most had a tight 16 thou.

Anyway, with any luck you could re use the ACL set with a different brand of 1.5mm rings. To get you out of trouble on the cheap. As noted some of the OEM Nissan rings look to be that thickness, have a check with your own spares and see what you can work out, otherwise buy another set.

end>thread/

[GTScotT]

Have checked stock SR compression rings today.

Both rings are 1.5mm thickness. Top ring 3.05mm width, bottom ring 3.75mm width.

now you check if those will fit in your ACL slugs and go down to Nissan if they do.

[N I B]

CP was never your problem. I guess you have a good idea what was.

[djr81]

 

All you had to say is that it got bad leak down results lol

You didn't need to prove that the catch can isn't the problem once you confirmed it had bad leak down. We only questions the catch can because we didn't know the leak down results.

Anyway. It has been said that other people have not had this problem before (with thinner ring piston kits).. So why not build it yourself this time? Get the block you want to used checked for bore size and follow the machinists recommendation for what size piston it needs. Buy the pistons in a kit and grind the rings to the exact specs your happy with. For reference my CP top rings had a maximum gap of 17 thou, which was good enough for me to work with. Most had a tight 16 thou.

Anyway, with any luck you could re use the ACL set with a different brand of 1.5mm rings. To get you out of trouble on the cheap. As noted some of the OEM Nissan rings look to be that thickness, have a check with your own spares and see what you can work out, otherwise buy another set.

end>thread/

 

Well the ACL pistons got sent back so I am currently pistonless. But I have a couple of options left unexhausted for non stock 1.5mm rings and will see how they go. Will make sure the block is viable at 86mm before I order any pistons.

[GTScotT]

Sounds good mate, post your results when the time comes. Am keen to hear you sort it out.

[djr81]

Cant get the file uploader to work but if I could I would attach a quote from JE.

For for half a dozen 86mm piston. Basically a modified version of these (Modified for a thicker top ring and an 86mm bore)

http://www.jepistons.com/Catalogs/Sport-Compact/Nissan-Infiniti/rb26dett.aspx

NISSAN R32-R34 SKYLINE RB26DETT

Dome/Dish requires no deburring or preparation

2618 T6 high tensile forged aluminum

JE designs are specifically engineered for extreme applications up to, and including, professional competition. In this environment, the higher compression ratios, highest boost or heavy nitrous usage necessitate the higher tensile strength 2618 aluminum alloy.

Dome and dishes feature smooth flowing radii for excellent flame travel.

1.2 x 1.5 x 3.0mm ring widths.

.827 x 2.250 straight wall carbon steel wrist pin provided.

Pin fitting and wire locks included

Rings Now Included

Rings are as JC2904-3386 package. basically these but six not four.

http://www.summitracing.com/parts/jep-jc2904-3386

Cost is $1050 USD. Thicker wall pins are $11 ea extra. Plus shipping and GST for the lot.

Have another local option to work through too.

Edited May 2, 2013 by djr81

[djr81]

Ordered some new rings from JE - had to get two packets of four as per the above part JC2904-3386. Anyway that will give me a couple spare to send off for test.

The other avenue is rings from Pacific Engine Parts. A nice old bloke called Trevor is working up an alternative with either 1.5 1.5 4.0 ductile iron rings or the same with a steel top ring at 1.2mm.

Not sure what I will do yet - may end up with a mix and match combination.

Can get CP pistons made to suit either option.

[GTScotT]

Sounds extremely complicated for a very simple build. Just so I know, your going to this much effort just to have a 1.5mm ring, right?

[djr81]

It is mostly because I want to see what sort of difference it makes. I have come to the conclusion that RB26's have an inherent problem with oiling that is caused by blowby. Once you reach that point you kind of want to make sure you fix it and that the fix is going to last.

So rather than just follow what everyone else does and have the issues everyone else has I thought I would try a bit harder and see if I can do a bit better. Or screw it up entirely which is the more probable outcome.

Anyway the custom piston is not complicated. All you need to do is to tell them how you want the grooves for the rings done. Everythiing else stays the same.

Edited May 6, 2013 by djr81

[GTScotT]

I don't think the oil control issues experienced with RB's has anything to do with blowby mate... They are just a piston with rings on it, and piston manufacturers dont make vastly different pistons for different motors.. For example, your CP's would be more or less identical to the ones in my SR. Pin height and all that would be different but the pistons and ring design very much the same. I do not have oil control issues nor do I have blow by. The rings in my SR are exactly what came with the CP kit. There is no cursed flaw in the RB26 block.. Its just a piston in a bore, like any other motor.

Oil control issues are caused by the pump volume vs drain efficiency and blowby/leakdown is caused by worn motors or shit builds. I am sure everyone will be happy to back me up here.

Chances are you will go to all this effort only to find a quality build would have fixed it, and I bet I know what the problem is anyway.. I nearly did the same thing to mine, but you will need to pull the motor down to find out. The CP's come with an oil wiper 2nd ring. The 2nd ring is designed to wipe oil back down to the oil rings and let a little seep up to the top rings for lubrication. Get this upside down and it will wipe all the oil up into the chamber, making the motor pump smoke, plus will likely get bad leakdown results as it will work the opposite way to what its meant to.

I reckon this could be your problem, and you could save yourself a motza if you just pull that motor down and check. You might find that $500 on a new set of rings and a quick hone could save it entirely.

[djr81]

The drainage efficiency is affected by blowby. In engineering terms it can be assessed by a Froude number. Too much blowby retains the oil in the head of the motor. The issues are linked.

The RB26 doesnt have much in the way of area for drainage. Hence it is more affected by blowby than most other motors.

Anyway that is my theory.

[GTScotT]

And that is a fair theory, yet you may be trying to reinvent the wheel where over engineering your rings is not necessarily going to fix the fact the RB's have poor drainage or overzealous pumps.

I really recommend you invest some time into disassembling the broken RB and working out what it wrong for yourself. Like I said I am betting the second compression ring is upside down in at least 4 of the 6 cylinders.

[C4a0s]

I agree with GTScotT...

Blow-by is the gas that enters an engine’s crankcase during a normal combustion event or compression stroke. It happens because the seal around the cylinder is not perfect which could highly likely be caused by mixing up the top and second rings.

Poor drainage would not lead to portions of the crankcase having super low pressure so as to draw air in then out as blow-by.

[Joshbigt62r]

I also agree with GTSCOTT and c4Aos.

[r33_racer]

I do not agree with GTScotT. I have done back to back tests on both our race car and my road car in regards to rings and breathing over the last 2-3 years. The oiling issue is directly related to blow-by. RB's do not breath well at all and they don't drain oil back very well, this is very common knowledge among experienced RB engine builders.

The main fix for stopping the oil from blowing out your cam cover breathers and filing your catch can is to put crankcase vents on the inlet side of the sump (the breathing side, this is also a common fix amongst the experienced folk) to vent the excessive crankcase pressure (blow-by) directly out of the engine and into a catch can/breather can. This tells me that whilst using any standard after market piston/ring package(as this is when the problem is most noticeable, not so much with std piston/rings, though not undocumented) there is excessive blow by being generated, though it may not be a lot, it is enough to stop oil returning to the sump whilst being held under constant high rpm load like experienced in racing situations. The blow by builds up in the crankcase and tries to vent through both the internal vents and oil drains and in doing so holds the oil up in the head and starts carrying it out the cam covers and typically fills a lot of the catch can to the point where it violently pushes the oil out of the filters and make a nice big mess in your engine bay. Let me say also that having a higher volume oil pump also contributes as it is only putting more oil everywhere in the engine, however it would only be 25% of the overall issue, the rest is contributed to excessive crank case pressure.

I've looked at all the pistons we have used over the last 7 years of racing and noticed that all of them have very thin rings. Typically in the 1.0 to 1.2mm range. The common old school methodology for a reliable performance ring set was 1/16" top 1/16" 2nd and a 3/16" oil control ring. The closest metric equivalent to that is 1.5mm top 1.5mm second and a 4mm oil control ring. The increased sealing surface area drastically reduces blow by, right to the point where the oiling issue completely goes away. Even more so you will notice that the breather can filters will have almost no fumes at all. The thicker rings can handle more heat before losing tension, they also can transfer more heat into the bore. In a forced induction engine, the rings need to be able to handle the extra heat, and cylinder pressures in order to keep the bore sealed as perfectly as possible. The reality is the thinner rings just don't cut it as well as they should in a turbocharged engine. They cannot handle alot of heat and they certainly cannot handle the pressure. This is evident by the fact that by putting vents on the sump cures the pressure build up in the crank case and lets the breathing/oiling system work in a normal fashion.

I'm not really fussed if people don't believe me. This is what I have found to work and it works very well.

I reckon djr81 is heading in the right direction.

[GTScotT]

I find it more than odd that you believe this to be the issue when most people can build an RB and do the appropriate oil control mods to fix the issues stated, most to all using off the shelf piston kits with their thinner rings.

You have literally said thin rings don't cut it in a turbocharged application. Do you believe they do not seal? Do you believe everyone who has a built RB with the supplied 1.Xmm rings has a dud which will have excessive blow by? I think this is a very strongly worded opinion in light of the unending number of people who have had flawless success with off the shelf piston kits and their thin rings.

You have mentioned that experienced builders gain success by having breathers in the right spot, which I must agree is probably the real trick to it all. Yet you have also noted that standard motors (which have 1.5mm rings) don't have this issue, like a built motor with 1.5mm rings wouldnt, when in fact they do. It is known fact that a 'tracked' internally stock RB26 should have all the drain/breather mods done and should over fill the sump by 1L to stop it puking its guts out and nuking itself.

I agree that the thicker rings would work for a stronger motor (better heat transfer plus outright ability to take heat and not fail, which would make for a stronger motor when building for extreme application), but can't for a moment believe that running thinner rings 'just won't cut it' in terms of providing a seal and stopping blow by.

I still believe we are simply discussing poorly built motors.

[djr81]

I find it more than odd that you believe this to be the issue when most people can build an RB and do the appropriate oil control mods to fix the issues stated, most to all using off the shelf piston kits with their thinner rings.

You have literally said thin rings don't cut it in a turbocharged application. Do you believe they do not seal? Do you believe everyone who has a built RB with the supplied 1.Xmm rings has a dud which will have excessive blow by? I think this is a very strongly worded opinion in light of the unending number of people who have had flawless success with off the shelf piston kits and their thin rings.

You have mentioned that experienced builders gain success by having breathers in the right spot, which I must agree is probably the real trick to it all. Yet you have also noted that standard motors (which have 1.5mm rings) don't have this issue, like a built motor with 1.5mm rings wouldnt, when in fact they do. It is known fact that a 'tracked' internally stock RB26 should have all the drain/breather mods done and should over fill the sump by 1L to stop it puking its guts out and nuking itself.

I agree that the thicker rings would work for a stronger motor (better heat transfer plus outright ability to take heat and not fail, which would make for a stronger motor when building for extreme application), but can't for a moment believe that running thinner rings 'just won't cut it' in terms of providing a seal and stopping blow by.

I still believe we are simply discussing poorly built motors.

There are any number of things that can be argued about - indeed there are 46 pages of oil control for RB motor discussions in another thread that would suggest people arent entirely on top of the issue.

I dont want this thread to fire off into the wilderness as I am trying to sort out a piston with good sealing - better than the average aftrmarket package.

But I would offer the following observations.

That forged piston and ring combination tend to be less tailored to individual motors than the manufacturers would have us believe.

There are very few built motors with rings that are fatter than 1.2 1.5 3.0. ACL were one of the few vendors and they stopped making them some years ago. If you dig about you will find some endorsements of their product.

The overfill of stock sumped RB26's is as much about the small oil capacity (four and a bit litres) and reducing oil surge as anything else.

The contention is that for a similar amount of blowby as another turbo motor (pick one it doesnt really matter) and RB will suffer from oiling issues to a larger extent (Because of the small cross section of the oil return drains). So the idea is to have less blowby than other motors. A reduction in blowby will reduce the amount of oiling mods needed or alternatively allow the motor to run for more kms until they become an issue. That is my contention anyway. If I am over engineering the rings/pistons then so be it but if there was one area of an RB26 you would want to over engineer it would be that.

Edited May 7, 2013 by djr81

[Joshbigt62r]

+1 ^^^ again.

[GTRsean]

A few people overlook the all important 'torque plate hone', especially when using head studs in their engine build...

For those that don't know a torque plate is a thick piece of aluminum or steel with holes drilled in it for head bolts to go through and holes larger than the bores of the block. It simulates a cylinder head being bolted down and makes the threads in the block tension to their fitted position, this in turn makes the bores take their 'normal' shape when the head is torqued down.

Then the honing can take place and remove any high or low spots in the bore, typically next to the bolt holes...

I actually got an engine rebuilder/machinist to get one made up for the builds I was doing as they didn't have one for the RB's, they footed the bill

The bore can be up to and over .001' out of round when the head is torqued up, and this will mean a poor ring seal and guaranteed blowby!