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

[SimonR32]

That's a drain for the excess oil that bleeds off from the VCT. If you look internally in a 25 head it lines up directly across from the oil bypass port on the inlet side of the head. If it wasn't there the factory drain holes would possibly be overwhelmed by all the excess oil from the VCT when it's not in use.

Vents are on the inlet side only and drains are on the exhaust side only in a RB engine. It's all dictated by the direction of the cranks rotation and how it pushes and pulls the crank case gases around.

I understand one side of the motor has higher pressure than the other. But it's just that, higher pressure. If there is excessive pressure everywhere in the sump the inlet side will vent pressure as it does on a rb25.

[KiwiRS4T]

Spewing out oil seems to happen only at the track during long periods at WOT . My RB25 had this problem and so did my RB30. My RB30 is a rings and bearings only build (everything else apart from the rod bolts is stock) and it spewed oil. I got a leak-down test which came out at 5% - 8% which is ok. I have an N1 pump! I fixed the oil problem by fitting 2 x 1.0mm restrictors and two sump vents on the inlet side of the engine going to a catch can - one to the top and the other to the bottom so the oil can drain back. This has fixed my oil spewing problems.I used to think that the drains at the back of the head were a waste of time but now I think that if anything they aggravate the problem by helping to blow oil out of the cam cover breathers. For others with RB26s, mines baffles have helped.

You say your leakdown test was bad - what were the numbers?

I would delete the rear head "drain" from your new build.

[skylinecouple]

So what are the standard Nissan rings made out of ? If they are good enough for the power some motors are producing then perhaps standard thickness rings and end gaps are whats required. Just need a piston to fit. On that note, what is Nismo using ? I'll wager thicker rings at 1.5mm and standard end gaps. This by the way is one of the best threads going. Some good info here. Venting and not head drain is important in a high horsepower application but I do agree with some that we are making some fundamental mistakes in material selection when assembling our engines. There is some great info in drag racing forums on this very subject. Though to be fair a 2,000hp engine may not necessarily be too worried about the extra drag of a thicker ring.

[djr81]

Spewing out oil seems to happen only at the track during long periods at WOT . My RB25 had this problem and so did my RB30. My RB30 is a rings and bearings only build (everything else apart from the rod bolts is stock) and it spewed oil. I got a leak-down test which came out at 5% - 8% which is ok. I have an N1 pump! I fixed the oil problem by fitting 2 x 1.0mm restrictors and two sump vents on the inlet side of the engine going to a catch can - one to the top and the other to the bottom so the oil can drain back. This has fixed my oil spewing problems.I used to think that the drains at the back of the head were a waste of time but now I think that if anything they aggravate the problem by helping to blow oil out of the cam cover breathers. For others with RB26s, mines baffles have helped.

You say your leakdown test was bad - what were the numbers?

I would delete the rear head "drain" from your new build.

Best was 17% out to 28%.

As an aside wrt the Mines baffles. The entry point for the oil into the system is at the back of the head which is not ideal - that is why you have to relocate the little covers for the cam lobes to the rear - to stop them flinging oil up into the entry points of the baffled system. I cant see how the Mines baffles are better than the stock items when you have a head full of oil?

Lastly there are some interesting notes from JE about side and back clearances for rings for the two different alloys commonly available. Oddly the numbers are identical.

piston_instrc2618.pdf

piston_instrc4032.pdf

[rob82]

Have you looked at total seal rings? I haven't used them myself but by design they look good. I would like to know if they are used in heavily boosted applications or just your run of the mill chevy's - which seems to be their market...

[djr81]

So what are the standard Nissan rings made out of ? If they are good enough for the power some motors are producing then perhaps standard thickness rings and end gaps are whats required. Just need a piston to fit. On that note, what is Nismo using ? I'll wager thicker rings at 1.5mm and standard end gaps. This by the way is one of the best threads going. Some good info here. Venting and not head drain is important in a high horsepower application but I do agree with some that we are making some fundamental mistakes in material selection when assembling our engines. There is some great info in drag racing forums on this very subject. Though to be fair a 2,000hp engine may not necessarily be too worried about the extra drag of a thicker ring.

From off the top of my head I would reckon the rings to be iron.

AFAIK Nismo dont make a piston for the RB26 only Nissan.

From the maual:

End gaps are much smaller than for forgies.

9.4 thou to 13.4 thou for the top ring.

16.5 to 22.5 thou for the second ring.

Also

The groove gap is 1.6 to 3 thou for the top ring and 1.2 to 2.6 thou for the second.

Finding the piston to fit is as hard as finding the ring set with a 1.5mm top ring. There is only one ring set that I have found - from JE. Maybe ACL if you can find the right size. Pistons will have to be customs (Again unless you can find ACL stuff) but not very custom really as you can just use the standard designs and modify them for the different rings.

Edited May 13, 2013 by djr81

[Joshbigt62r]

Call nitto up they should be able to do you up exactly what you want. Nitto/JE custom ordered pistons.

[Joshbigt62r]

Call nitto up they should be able to do you up exactly what you want. Nitto/JE custom ordered pistons.

[Joshbigt62r]

Call nitto up they should be able to do you up exactly what you want. Nitto/JE custom ordered pistons.

[djr81]

Well the block is sorted to 86mm and the JE rings are on their way from the US.

Next up is pistons. Could someone who has some laying about help out by offering a measurement of the ring lands on a forged RB26 piston? I have attached some measurements of an ACL piston - just not sure how much they vary from brand to brand.

20130621130016.pdf

Edited June 21, 2013 by djr81

[djr81]

Well after a hopeless weekend at Wanneroo I had a rethink and ordered some other rings from Pacific Engine Parts in Melbourne. The bloke who runs it, Trevor McGregor is really good value. Anyway the ring pack is 1.2, 1.5 and 4.0mm.

Has anyone used Specialist Piston Services, also in Melbourne?

http://www.specialpistonservices.com/

[brad 110]

Colin at Sps is who you need to talk to. He can supply and a ring pack can recommend him great bloke too

[r33_racer]

Did you end up running the rings you got from JE?

[djr81]

Did you end up running the rings you got from JE?

No I realised I had coughed up on the order number and received some random rings. My fault. Most annoyed about the time that was wasted.

I figured I would go for the more known of the two options. Basically, having thought about what Trevor (and others) said about the oil ring thickness and the function of the second ring I think there is merit in the argument.

I just need confimation of the depths (waiting on an email) to then flick to the pistons mob(s).

Had an exhaust manifold gasket start to leak on the weekend so it may as well come out anyway. Just got to hustle a bit now to get it organised.

[djr81]

Ring dimensions from Pacific Engine Parts are as follows:

Top Ring .0462” (1.2mm) Wide .1270” (3.23mm) Radial

Second Ring .0582” (1.5mm) Wide .1450” (3.67mm) Radial

Oil Ring .1540” (4.0mm) Wide .1260” (3.20mm) Radial

Anyway CP offered gaps:

Top will be .048'

2^nd will be .060

3^rd will be .159 oil

So 2 thou, 2 thou and 5 thou.

Any comments?

[djr81]

Rings turned up - pretty quick turn around. I didnt go the gapless second ring but that option is available. If anyone wants Pacific Engine Parts contact.

Now need to wait for the pistons.

[r33_racer]

Looks the goods!

Will you be running a hone through lightly just to make sure the cross hatch is fresh. I think only maybe 4-5 strokes would do it for each bore, by hand ofcourse.

[noone]

Looks the goods!

Will you be running a hone through lightly just to make sure the cross hatch is fresh. I think only maybe 4-5 strokes would do it for each bore, by hand ofcourse.

would this still require the full torque plate hone etc? If you were say just re-ringing because of lack of bedding in etc as an example ?

[r33_racer]

No torque plate really, your not going to remove much material, purely just to make sure there is a half decent crosshatch there for the new rings to conform with. If you had one its not that hard to bolt it down and do it, but it wouldnt be essential. If your super pedantic you probably would though.

[djr81]

Pistons are here thanks to the kindly folk at Special Piston Services. Much easier to deal with than the Seppos. Quick turn around too.

Just got to get the motor assembled and may actually have something decent, fingers crossed. Going to delete the external rear of head return and run a pair of vents from the sump to the catch can in -10. With PEP's rings, a 1.25mm restrictor in the head and some drilled out internal returns that should be enough.