We’re in the home stretch now. I’m going to skip over the stuff like measuring the rod bearing and piston pin clearances because it’s the same as we did back with the main bearings. Same goes for the piston clearance. Measure the bore, measure the piston or pin, the difference is the clearance.
With the new rings from Arias in hand, we can set the end gaps. Generally accepted ROT (rule of thumb) is .004†(.1mm) per inch of bore is the minimum gap. This bore is 3.464†(yea, that's 88mm), so the minimum gap would be .014†or .35mm. It’s not always good to use the minimum gap. Engines that have high thermal loading like forced induction, nitrous oxide, etc., should use more gap. If you were running a fuel like alcohol, you could close up the gap a little. Don’t worry if you accidentally grind a little too much and make the gap too big. You could effectively double the gap and not see a decrease in performance. It’ll affect a leak down test, etc., but won’t really hurt performance, especially in the rpm range where you’re making power. I’ve seen engines with broken rings that you couldn’t even tell something was wrong until they were torn apart. Basically, don’t get too hung up on ring gap. Too much=OK. Too little=Very Bad.
On ring expander tools: I hate them.
First, if you have a deft hand, it stretches/tweaks the ring a lot less when it’s twisted on by hand. A ring expander that stretches the ring out enough to completely clear the piston is scary business. I used one once and threw it away. If the ring binds up, just stop and back up. People break rings when installing them in a hurry and using the armstrong method. In 25 years of assembling engines I’ve broken exactly one ring, and that was about 25 years ago.
Second, every pro engine builder I know, including the heavy-hitter mainstream guys, installs the rings by hand.
Checking the gap .016â€.
Soldiers, ready for battle. Once again, don't bust my chops about the "dirty" bench. It ain't dirty!
An army of one. Arias pistons and Carrillo rods.
The Carrillo SPS bolt. The best and strongest rod bolts money can buy.
These rod bolts torque to 65 lbs. Normally I use a stretch gauge, but it’s impossible to get in there, so for the RB it gets torqued.
All masked up and ready for paint.
Here’s the almost complete short block. Pistons in, studs in, gasket on. Check that shiny new paint job.
A few words on studs. Studs are not necessarily stronger than bolts. The main advantage to a stud is that they use a fine thread at the nut end vs. the course thread in the block. This makes for smoother torquing, and allows you to take the fastener closer to the yield point safely. For instance, say a fastener has a yield strength of 200,000 psi. With a course thread, tightening can be erratic from one fastener to the next, so the manufacturer may set the tightening torque to achieve 60% of the fasteners yield to ensure it never goes over. A fine thread like those from ARP is set at 75% of the fasteners yield. That’s 120,000 psi vs. 150,000 psi of clamp force.
You never tighten a stud in the block more than hand-tight, or just barely snug. There should be zero upward pulling or pushing of the block threads before the top nut is tightened. If a stud like those from Tomei, with an extension to bottom in the bolt bore, is tightened into the block, it pushes up on the area of the block around the stud, creating a high spot. These high spots guarantee that the seal around the cylinder is a weak one. There’s nothing wrong with the fastener, per say, but in the wrong hands… The ARP studs have a shoulder machined above the threads as a positive stop. If you were to tighten it, it would only clamp the threads together, but would still pre-stress the block in the area around the fastener. Don’t do it.
It’s much easier to lube the threads before the head is on. Lube 100% of the threads. Do not lube the threads in the block. You don’t want those turning. If you use a threadlocker or sealer with studs (only in the block), it needs to be tightened within an hour, or so, before the locker sets up.
SR20 studs can not be pre-installed like this. The head can’t slip down on the studs and clear the chain guide.
Where the power is made. This is a touge engine. The quench (squish) pads stay in place. Much better mid-range power with the pads. This head is pristine. Perfectly flat, with no imperfections, so it’s not getting cut. It’s a waste to machine things that don’t need it. My thought is that you’re taking away rebuild-ability.
The head installed.
Another shot.
Here's where people are going to bust my chops...
It's info I've been sitting on for about a decade and a half. Well, the cat's out of the bag. I know I've said I never did an extra "oil return" on an RB26, and that's true. But I never said (I don't think) I never added anything for crankcase ventilation to aid oil return through the stock pasages. Semantics...
Why do I discourage people from doing this mod? BECAUSE YOU DON'T NEED IT! And, if it's done wrong, you'll end up with more problems than you've solved. Originally, this engine turned around 11,000 rpm, boosted way over 30 pounds, and made hp north of the millennium mark. The new configuration doesn't need it, but because the mod is already done to the pan, the parts are there, etc, it's going on this engine.
The following three pictures are of the additional crankcase vent. I first started doing this mod on the 26 in the mid 90’s. It’s a common mod for high rpm engines, so it was a no-brainer for the RB26. Soon thereafter, the Internet got a hold of it and speculation as to its function ran rampant. “Additional oil drain-back†became the consensus, and consensus became fact. Now it’s well known as the additional oil drain back mod… Then it became a fact that all the oil in the engine will pool in the head and the engine will blow if you don’t have it done…
Really? Let’s examine some facts. The RB26 has been lapping the Nurburgring starting years before the R32 came out in 1989. Lap after lap at full-boogie. Since then, the R33 and R34 have been lapping the same track. The N1 GT-R that races in the N1 class doesn’t have this mod done. Super Taikyu RB26’s don’t have this mod done. I can assure you that the RB26 does not have an oil drain back problem that warrants modification to implement an additional one.
On Youtube you can find some videos of the Porsche Turbo engines in a cradle that simulate a run of the Nurburgring to test the oil system. Nissan has the same thing.
So what’s the deal??
Windage and blow-bye in ultra-performance engines. You get an RB26 up in the 10,000rpm neighborhood and lean on it with 2+ kg of boost and you have a nightmare.
See, all but one of the oil drains back into the sump on the RB26 are on the left side of the block. When we examine crank windage, that’s the side of the engine where the crank counterweights, rods, etc., are moving in a downward direction, essentially “pulling†oil back down out of the head. In the right-rear of the engine, there’s another port. This port is on the “pressure†side of the motor, and windage blows up this passage, creating an actual suction on the drain-side of the motor.
At high-rpm, high-boost, windage and blow-bye gasses can be so severe, that the single port on the right side isn’t adequate. Gasses are moving up all the ports, sometimes at high velocity. This effectively keeps oil from returning to the sump. What the large hose from the sump to the back of the head does is give the blow-bye gasses another path to the head, and allow the oil to return down the normal returns along the left side of the motor. It needs to be above the oil level in the sump, but below the baffle.
In a drag motor, if we accelerate forward at 1g, the oil in the sump will stand up at 45 degrees. It’d be neat to hear an explanation of how the oil in the head overcomes the laws of physics and somehow runs forward to the front of the engine. In a circuit/touge motor like this one, oil will indeed return down the hose to the sump because not all of the acceleration is forward. This is the reason it needs to be lower than the baffles in the pan; on that side of the engine, any oil returning will simply be picked up by the crank and added to the hurricane in the crankcase.
What we found was that under these extreme conditions, we were pumping a quart of oil out of the breathers and into the overflow in a 400m pass. Not only was it not returning, but the blow-bye gasses were pushing it out of the engine. Additional vent was added, and the problem disappeared. It needs to be said that in engines turning 9,000 rpm and boosting 1.7 bar, engines making north of 750hp, this "problem" has never presented itself. That, and the problems you can create if it's not done properly are the reason I've been so against it in more reasonable engines. An example is if you put the tube below the oil level in the pan, not only are you choking any venting action, you're giving the oil another place to go during acceleration. Like I said above, oil will leave the sump through the hose.
Hate away.
On 88mm. There's talk on the Internet that it weakens the cylinders too much... I don't know what others have experienced, but I've never had a problem. This engine made BIG power for a long time and had two failures. Dropped a valve both times. I don't recommend going all the way out the first time. I leave the bore stock with a new hone, if I can. Then it's up to 86.5mm, and so on. "Rebuildability" (is that a word?).
Next I'll write up the race head and put that on an engine like this one, but with Pauter rods, a new N1 block, and 280* high-lift cams.
This is a brilliant explanation mate, not to mention one fantastic looking motor
RB Rebuild
in Nissan RB Forum
Posted
This is a brilliant explanation mate, not to mention one fantastic looking motor