Author: Pavel

Story:

This camshaft was purchased new by a customer and installed in a high horsepower SR20DET engine built for drifting purposes. Original cause of failure was not clearly determined. Camshaft sprocket retaining bolt may have not been torqued down properly leading to shearing of the camshaft locating pin, camshaft damage, as well as bent engine valves. This camshaft, although brand new, was rendered useless. The shoulder retaining the camshaft sprocket was damaged during the failure. In order to fix this camshaft, the shoulder was TIG welded ensuring only proper penetration and no overheating/warping of the camshaft. After welding the camshaft was mounted in a lathe using a 3 point support. Dial indicator used to zero-set camshaft. After shoulder machining the cam was mounted vertically in a table mill and locating pin bore repaired. During pin shearing failure the bore was damaged and enlarged. Original pin is 6mm with a light press fit. Since the bore was damaged it was decided that a 1/4 inch overbore was necessary for the repair. New hardened pin was machined with a 1/4 inch diameter pressing into the camshaft and a standard 6mm diameter to locate the camshaft gear. Pin was lathe machined using prehardened steel with a Rockwell rating of 40.

Goal:

Repair broken camshaft locating pin and render camshaft usable

Operations:

1. TIG weld camshaft shoulder
2. Lathe machine should and restore to standard dimension
3. Table mill camshaft pin bore to 1/4 pin size with light press fit
4. Lathe machine new hardened sprocket locating pin

SR20DET Camshaft Cap Bolt Upgrade Kit

ABOUT ARP

ARP is the world leader in fastener technology trusted by the industry’s leading engine builders. When it comes to your build don’t overlook one of the most important parts. Go with the best!

Camshaft positioning is critical on overhead camshaft engines and ARP makes sure that the cam towers are properly secured through use of these durable bolts. They are made from 8740 chrome-moly steel, with threads rolled after heat treat to ensure the optimum fatigue strength; far superior to OEM fasteners. These heat-treated 8740 chrome-moly bolts are nominally rated at 180,000 psi tensile strength to provide a substantial extra margin of safety over Grade 8(Standard) and Class 10.9(Metric) hardware.

WHY DO THIS?

SR20DET engine has a lot of camshafts and valve springs options. Factory M6x1.0 fasteners are designed for use with factory valve springs and cams. Installing aftermarket higher pressure valve springs and high lift performance camshafts will cause the factory camshaft cap retaining bolts to stretch and fatigue over time. This can lead to broken bolts, stripped threads in the cylinder head, and even catastrophic valvetrain failure. This bolt upgrade is similar to upgrading your engine’s head and main bolts. Increased cylinder pressure causes factory designed fasteners to stretch, causing head lift and headgasket failure. To prevent these issues you replace your factory head bolts with higher tensile strength studs. Upgraded valve springs with higher spring pressure than stock causes the same affect by lifting the camshaft out of the journal. This leads to change in journal running clearance, change in oil pressure(due to increased journal clearance), rocker arm gap(which can lead to rocker arm and camshaft lobe wear), and most importantly ignition and valve timing. Camshaft lift problem is amplified in street performance engines running high pressure valve springs and low engine rpm. During low engine speed operation the camshaft lobe spends more time pushing against a stiff springs. This longer impulse contributes to fastener fatigue failure.

EXCEPTIONS

We find this problem present in engines using M6 fasteners. Engines using M8 fasteners experience similar pressures from upgraded valve springs and high lift camshafts, but since the factory fastener already has a great cross-sectional area and higher tensile strength, this upgrade is not necessary.

MATERIALS ANALYSIS

Factory fasteners are M6x1.0 metric bolts with a preload torque rating of 8ft-lb. Using several engineering reference books, bolt dimension, and torque recommended it is possible to determine factory bolt class rating and tensile strength. We found factory bolts to be Class 9.8 rating with a tensile strength of 130,00psi. Our ARP camshaft retention kit is 27% stronger than OEM.

FOOTNOTE:

When changing from factory fasteners to high strength fasteners, clamping force and tolerances will change, therefore it will be necessary to check the bearing bores for proper size and out of round condition after installation of the bolts and align hone the cylinder head camshaft journals if necessary. Camshaft journal bores should always be align honed using the same fasteners and lubricant which will be installed during final engine assembly at the recommended preload.

Disassembly and brief look the engine in stock form can be found in this blog entry:  http://pretuning.com/2011/10/hyundai-genesis-coupe-2-0t-4b11-engine-disassembly-and-evaluation/

This is a Hyundai Genesis Coupe engine build I recently completed. As of right now, there are very few performance parts available for the engine. Although the Hyundai Theta 2.0 engine is very similar to the Mitsubishi 4B11T, the only parts that directly cross over are ARP head studs and head gaskets. Engine bearings and connecting rods are different in size and will not work even with extensive modification to either part. Below is a description of the work performed on the engine and part used, both stock and aftermarket. Enjoy!

Engine parts list:

1. Manley 86.5mm forged pistons
2. K1 Technologies steel connecting rods, come with ARP 2000 rod bolts
3. ACL main and rod bearings custom made for application
4. OEM thrust bearings
5. ARP main studs, custom made for application
6. ARP head stud kit, 4B11T part
7. Cosworth 87mm bore, 1.1mm thick head gasket

Engine machine work performed:

1. Block bore/hone to 86.5mm
2. Block align hone with ARP main studs
3. Balance and polish crankshaft
4. Weight match rods and pistons
5. Hand stone block and cylinder head mating surfaces
6. Inspect cylinder head, hand-lap valves, and check seal

Engine component review:

• Block– Cylinder block is aluminum construction, die cast, open deck design. Not the best for performance. Mitsubishi 4B11T block is a semi closed deck design with reinforcement at the cylinder head mating surface. This Hyundai block can greatly benefit from a flanged sleeve or a Honda-style girdle to prevent cylinders from walking and distorting under high cylinder pressure condition. Hyundai Theta block utilizes 2 bolt main caps, while Mitsubishi 4B11T utilizes 4 bolt main caps. Piston cooling jets fed from the main oil gallery spray oil on the intake side of the piston.
• Cylinder head– Excellent design of the head. Direct bucket over valve design unlike 4G63 which was a roller rocker design. 4B11T uses very thin 5.5mm stems on the intake and exhaust valves. 4G63 used 6.5mm stems on intake and exhaust. 4B11T uses very light weight shimless buckets. Intake and exhaust camshaft use an oil pressure controlled vain-type variable valve control system. Early 4G63 had no MIVEC system and late 4G63 only had MIVEC on intake camshaft. 4B11T camshafts are chain driven versus belt drive of the 4G63. Single valve springs utilized in the 4B11T.
• Oil pump– Oil pump is mounted on the bottom of the upper oil pan girdle and chain driven off the front of the crankshaft. Oil pump is a gear-rotor design with a single stage for pressure. 4G63 used a spur gear style oil pump driven by the timing belt as an auxiliary item.
• Crankshaft– Crankshaft is forged. It uses smaller rod and main journals than the EVO 10 4B11T version. Rear of the crankshaft has provision for crankshaft position reluctor wheel, which is used by the Mitsubishi 4B11T. Hyundai engine uses the flywheel for crankshaft position. Since the rear of the crankshaft has provisions for the timing sprocket but does not use it, the crankshaft is actually out of balance. The front of the crankshaft was within 2 grams, while the rear was off by 10.5g. This required extensive drilling of the counterweight to correct out of balance. This out of balance can be detrimental to engine bearing life due to crankshaft flex at high engine rpm.
• Connecting rods– Hyundai engine uses powder steel metallurgy connecting rods. This is a cheap and effective way of production line manufacturing and adequate for the horsepower requirement of a stock factory engine. This type of connecting rod is not adequate for increased horsepower and high rpm engine. Powder steel metallurgy connecting rods usually fail catastrophically in a fracture fashion. Mitsubishi 4B11T engine uses forged steel connecting rods.
• Pistons– Pistons are cast aluminum using thin, performance-style rings. Stock pistons use a Teflon type of friction coating on the skirts.
• Gaskets– Stock head gasket is a multi layer steel design using 3 layers. Exhaust manifold gasket is a multi layer stainless steel design. Intake manifold gasket is a single layer metal design.

This is a video provided by one of our clients. Mike Gregg races a Nissan 240SX with an SR20DET engine. Mike’s engine suffered oil starvation failure and the ball bearing GT2860R turbocharger failed. Mike sent to us his GT2860R and a T28 turbos for conversions to journal bearing setup. Below is a video of the national competition he attended this summer.

PRE Tuning offers rebuilds of Nissan 300ZX T25 turbochargers. These turbos were rebuilt with all new bearings, seals, and o-rings. All bearing and turbine shaft clearances are measured using micrometers and bore gauges. Bearings housing is cleaned prior to inspection. When excessive wear is determined, it is rehoned to accept an oversized turbine shaft bearing. Rotating assembly is polished to remove any imperfections and balanced. Turbine housing is media blasted by hand and polished. After the turbo passes all clearance specification checks it is reassembled.

Compatibility: 1990-1996 Nissan 300ZX Turbo

Pictures of rebuilt turbo: