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Rebuilding an Engine (VQ35)

In this article I will go over what it takes to rebuild an engine; the VQ35 will be used as a reference however this information can be applied to most engines.

If you deal with cars long enough you are eventually going to find the need to open up an engine. I have seen a lot of people try to stay away from dealing with the internals of an engine because of a couple of reasons. One, they are not familiar with the inner workings of an engine, and two, because they assume the cost associated with a rebuild is too much to afford. This is what I will be addressing. In a previous article, I explained some basic workings of an engine: https://www.fastmaximas.com/2019/01/12/what-is-engine-tuning 

Engine Anatomy

Engine lingo

A long block is referred to as a complete engine that includes the heads and the block which is where the pistons and the crank reside. A short block is an engine without the heads. The heads are responsible for providing the spark, air and fuel into the cylinders in the block. Fresh air flows in through the intake valves and exhaust gases flow out of the exhaust valves after combustion; the valves are opened and closed by the cam. The cams are turned by a gear thats connected to a timing chain or belt that is being turned by the crank. I say cams in plural because in our VQ case we have dual overhead cams. Dual overhead cams means that each head (two of them on V6’s) has two cams, one to control the intake valves and another to control the exhaust valves.

Oil distribution

Behind the crank pulley and inside the timing cover there is an oil pump that spins with the crank. The pump picks up oil from the oil pan via a pickup tube that looks like an upside-down microphone; there is a screen to block large objects from being pulled up. The oil is then pushed into the block’s main oil galley, the galley is a passage that goes across the entire block. The galley distributes the oil to the main bearings and the rod bearings. In a VQ block below the pistons, there are squirters that spray oil onto the bottom of the pistons. These squirters are mounted near the oil galley and their job is to cool down the bottom of the pistons as the pistons absorb a great amount of heat during combustion.

In addition to oil flowing to the block, oil also flows to the timing cover areas which provides oil pressure on the timing chain guides. The purpose of these guides is to put tension on the chain when the engine is running. This is what you hear often on VQ35’s; they are prone to have worn guides which cause rattle and noise. The oil passages in the timing cover also have rubber o rings and gaskets which are always recommended to be changed. Having weak seals causes lower oil pressure which is catastrophic for the engine.

Oil flows from the engine block up to the heads and out through the cam journals where the cams sit. The cams are like the crank, they spin while being held in place by a film of oil (the pressure and oil coming up from the block); cams however do not have bearings, they sit on a polished surface on the head and caps which function like bearings. Oil also flows onto the valve spring buckets which is what the cam lobes push down on to open the valves. You can see how important the quality and supply of oil is.

Bearings

VQ35 Main Bearing
Photo courtesy of Jeremy @ administrationmotorsports.com

From the galley, there are passages going to each bearing location on the block and the rod journals. Crank journals are where the rods connect to and where the crank connects to the block. The crank is suspended in space by a film of oil, which is being supplied by a hole behind the bearing. As the crank spins, oil flows out of the block into the bottom of the bearings. The bearings have a small hole which allows the oil to escape coating the bearing inner surface; oil gets between the journal and the bearing. The bearing surface stays with a constant film of oil and prevents the crank journal from touching the bearings.

Oil Clearances

Oil clearances are the space between the crank journal and the bearing. When putting an engine together it is important to measure this clearance. The reason you need to pay attention to this is that a clearance that is out of spec can cause the bearings to fail. When rebuilding the engine you should think about what clearances to go with; there are some factors to consider.

Tight clearances mean that you will need to use thinner oils so that the oil can easily feed into the tight space. One benefit of having a tight clearance is that there is higher oil pressure in the space keeping surfaces from touching; allows for more even distribution. Loose oil clearance means the is more space between the bearing and journal. Since there is more space, more oil volume flows through the bearings. Loose oil clearances are often desired because at high torque and rpm the crank can distort and if the clearance is too tight the crank can touch the bearings. A benefit of a wider gap is that oil temperature is lower because there is more volume of oil flowing through the bearings while on a tight clearance the oil has higher pressure and more friction, therefore getting hotter. Most modern engines use very tight clearances nowadays because it allows for better emissions, efficiency, and takes advantage of the advanced oils we have now. If there is too much clearance oil, pressure may be too low, and the load won’t properly be distributed on the bearing. There is a lot to this topic but I am only covering the general idea.

On a VQ35 the recommended standard clearance for rod bearings is within 0.0013 – 0.0023 in. For main bearings, the recommended clearances are within 0.0014 – 0.0018 in.

Summary

Here is a VQ35 build that I would recommend.

  • VQ35HR head gasket (If using a VQ35DE block you need to modify the coolant inlets to the block). The HR head gasket has a superior design in that there are additional coolant passages on all cylinders in comparison to the DE head gasket which has passages on one cylinder.
  • L19 head studs are some of the best studs you can get, however I personally like using Nissan Juke (MR) head bolts. Juke bolts are proven to support a decent amount of power in the 600HP range; I use them myself. HR head bolts were the budget bolts to use before the Juke ones were found to be superior; there were also manufacturing issues with the HR bolts. I used the HR bolts as well and did not have a head gasket or lifting issues.
  • Standard ACL bearings to keep the factory clearance or ACL HX bearings for a larger clearance for higher power.
  • Wiseco Pistons with your desired compression (8.8:1 is common for turbo applications and 11:1 is common for high compression)
  • Eagle Rods, come with ARP 2000 bolts.
  • To strengthen the block, ARP main studs; it is a good idea to get additional oil clearance bearings on the mains if you use the ARP studs. There may be more squishing when torquing them down compared to stock, therefore, lowering the oil clearance, so if you already use the tight clearance then bolt down with more torque, you’ll reduce the clearance to potential damaging specs.

The process

Head and Block Mating Surfaces

Take the bare block to a machine shop to get the head resurfaced (decked), doing this will ensure you have a brand new mating surface for the head gasket.
For a VQ35 I recommend you get 96mm pistons so that your cylinders can be bored and honed larger than the stock 95.5mm, this way you start with a new round surface. When getting your block bored and honed it is highly recommended that a torque plate is used. Many shops will not have a torque plate but if you look around there are folks that can rent them out. Below is a photo of what a torque plate looks like when installed prior to boring and honing the cylinders.

VQ35 With a Torque Plate installed.
Photo courtesy of Jeremy @ administrationmotorsports.com.

The heads should also be inspected to ensure they are straight, I personally like to get them resurfaced very lightly to have a fresh new area however it is not required if the heads are clean and straight. To measure the heads and block for straightness you lay down a straight ruler across the surface diagonally, then get a feeler gauge to see if there are gaps in each cylinder surface. You try to slide the gauge between the ruler and the block/head surface. If you can slide more than 0.0039 in between the ruler and the block/head then you need to resurface. There is a limit to how much material you can remove from the block and head combined, this is 0.008 in. If more removal is required then you may need a thicker head gasket.

Bore and Hone

Boring means to cut the cylinder walls to widen the cylinders and honing means lightly sanding the walls of the cylinders in cross hatch angle. Ideally, the cross-hatching should be 45 degrees and a sanding stone is used. The angles of the cross hatches determine how the oil will move, whether sticking too much to the walls(lines too horizontal) or not sticking enough(lines more vertical). Another reason to honing the cylinder after it has been bored is also to seat the piston rings. When you initially put in pistons the rings need time to move up and down the cylinders, till they have properly worn into their permanent state, a proper hone is critical here.

A torque plate is a thick plate that mimics the shape of the heads and they are torqued down to spec using the head bolts/studs. Once the plate is bolted down to spec, the cylinders can be bored out and honed. The VQ block being aluminum can change its shape and distort when the heads are bolted down, this is why it is ideal to have the plate bolted while boring. Some may say this is not necessary but I rather save money in less critical areas than this.

Another recommended machine job is to line bore the block, this is when you mount and torque down the main caps then a rod with cutting sides goes through the entire length of the block to cut and ensure all main cap bearing surfaces are lined up; The main caps are the caps that grab onto the crank. Doing this ensures the crank is completely centered. I personally have not done this in the VQ builds I have done myself but it is recommended to at least inspect the mains to see if they line up.

VQ35 Crank and Block
Photo courtesy of Jeremy @ adminmotorsports.com

Pistons

The pistons require some prepping before installing them into the block. Once the engine has been bored and honed you need to file fit the piston rings. This means that the rings are placed inside the cylinder without the piston, you push a piston upside down into the cylinder to push the ring and ensure it’s completely even all around. Then you measure the gap between the ends of the ring; this is called the end gap. This gap can be changed by using a ring filing tool that essentially just grinds off material from the ends. The necessary end gap specs are often provided by the ring/piston manufacture. This is a good time to mention what are the rings. The piston has a few rings, starting from the top is the main compression ring which is responsible for sealing the cylinder’s combustion. The second ring below that is a second compression ring which also helps in sealing combusting as well as scrape down oil that has covered the walls. Below the second compression ring are a set of thinner rings usually called oil control rings. They are two rings separated by an *accordion* ring, all three layers sitting into a single groove on the piston. The purpose of the oil control rings is to scrape down the oil from the cylinder walls.

Bearing Clearances

The standard bearing clearances for the rod to crank are 0.0013 – 0.0023 in. There are different methods of measuring this. One method is by using a plastic gauge, this is when you lay down a piece of soft material on the crank journal (a thin rubbery strip). You then install the bearings on the rods and then bolt the rods to the crank to torque spec. On an eagle VQ35DE ARP 2000 3/8th bolt this would be 28 ft-lbs; note that you MUST apply ARP moly paste to the underside of the bolt’s head as well as on the thread to get the proper torque. Once you have torqued the rod caps (the ends that connect to the rod) you then remove them and measure the thickness of the plastic gauge strip you laid down. This will give you an approximation of what your clearance is. Take note that this is a method that many do not like, mostly builders that have specialized equipment will tell you this. It is always best to use the right tools but in my experience, this was accurate as per the factory service manual specs. The bearing clearance on my last VQ35 build measured exactly what the factory service manual said, .0015; while using a plastic gauge.

You repeat this process for the main bearing clearances. You install the main bearings onto the block (the block upside down), you then lay down the crank, lay a strip of plastic gauge, place the 2nd half of the bearing onto the main cap and then mount and torque down the main camp onto the block. The factory main bearing clearance is 0.0014 – 0.0018in. When using upgraded studs for the main caps, they may require more torque than the factory bolts. This means that the bearing clearance may get smaller since the main cap will be held onto the block with more torque; this is why it is important to check the clearance. It is suggested to perform a line bore through the mains especially if using additional torque on the caps. Partly for this reason, I used the ACL HX bearings which adds .001 into the clearance so my .0015in would be .0025in with factory bolts, and then with ARP studs they would be maybe .0023 in.

Ideally, you want to have as tight of a bearing clearance as possible however there are things to consider with doing this. The tighter the clearance the thinner the oil you will need as well as the higher quality oil. The tighter the clearance the more heat is generated so the oil needs to be able to handle this heat before breaking down and allowing metal to metal contact. On a motor built from the ground up where every single spec is accounted for such as line honing the block, ensuring the crank is completely straight, a tight clearance is great. For the common budget build having more bearing clearance is acceptable because it gives you some room for flexing and distortion to occur. For example, the crank may flex as well as the rod bores may change their shape when in high torque and rpm. When using a larger clearance you also need to use a thicker oil, for example on the HX ACL bearings which give you .001 additional clearance over the factory ~.0015 in on a VQ; I use 15W40. Having a larger clearance gives you a little more cushion as well. The topic of bearing clearance and oil viscosity can go on for days and still leave you with questions, one recommendation is that you send your oil samples to a lab to get tested and see how well your engine is wearing.

Balancing

Like most steps in a build, this is a critical part, balancing the crank. When changing any component of the block such as pistons or rods, you must get the crank balanced with the new piston and rods. The crank is balanced by the factory using the weight of the piston, rods, and bearings. If you do not balance the crank after installing the aftermarket components there will be vibration due to poor balance and therefore cause failure. Balancing a crank is like balancing a rim, they place the crank on a machine, then note the weight of all components and clamp weights matching those components on the crank to mimic them. Then they spin the crank at varying speeds as the computer outputs where material needs to be removed or added. A crank has counterweights on it which is what helps the balancing; sometimes they need to remove weight from them so they are drilled. Other times weight needs to be added so they weld on more material. From my experience, when my engines have been balanced they also included the pulley and flexplate(flywheel for you manual guys).

Parts List

Revup Oil Pump – $225
Juke Head Bolts – $96
HR Head Gasket – $78
Eagle Rods – ~$590
Wiseco Pistons – $770
ACL Bearings – $90

Machine Work

Bore and Hone – $225
Resurface the block – $250
Press fit piston – $40
Balance assembly – $300
Micro polish crank – $35
File fit rings – $100
Hot tank/Jet wash (cleaning) – $150

My intention with this article was to give you insight on what is involved in an engine build and at the very least give you some points you can search for to get a deeper understanding. I hope you enjoyed it.

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