• basically, a cylinder leak-down test consists of pressurizing a cylinder with shop air and listening for leaks. fashion an adapter from an old sparkplug so you can hook up an air hose from your air compressor. rotate the engine until the cylinder to be tested is at tdc compression. be sure to get it exactly on tdc. next slowly turn up the air pressure regulator on your air compressor or slowly open the supply valve to pressurize the cylinder. go slow because the engine may try to spin - keep hands and tools clear of belts, etc. once the cylinder is fully pressurized listen for air leaks. do not confuse a "seashell" sound for a leak. air leaks will be very distinct sound and you may even feel a rush of air. open the throttle and put your ear next to the intake opening. a rush of air indicates a leaking intake valve (bent valve? misadjusted or sticking?). next put your ear to the tailpipe opening, air rushing out means a leaking exhaust valve (bent, misadjusted, sticking, or burnt?). listen at the oil filler cap. you will hear a slight hiss of air. this is normal 'blow-by' leakage. how much is normal? well, many clt tools have a flow meter to measure how much air is coming by the piston rings and out thru the oil filler cap. usually less than 15%. you probably don't have an air flow meter to hook in-line with your air hose, so instead try to remember what each cylinder sounded like and compare them to one another. engines with good compression and good rings will sound even, slightly louder than a 'seashell' and you will not feel any air rush. lastly, take the radiator cap off and look for bubbles. bubbles indicate a blown head gasket or maybe a cracked cylinder head. doing a clt along with a compression test will tell you a lot about an engine's condition.
  

• leak down test  by dennis haynes

  a number of people have asked "What is a LEAK DOWN test?" and "Can I do it myself?". first, let me explain the concept. we already use a compression test to determine an engines condition.  The problem with this test is that there are too many variables. it can only be used to check engine condition by comparing cylinders to each other or a past norm. variables such as cam profile, engine cranking speed etc, will affect the readings.

  a leak down tester uses air from a compressor and measures the rate at which it leaks through the engine. this is done with the engine not running and the beauty of this is that toy can find the source of the leakage by listening for the escaped air. internal leakage is found by air bubbles in the cooling system. tools need are a leak down tester and an air compressor. the tester is available from Milton at about $60.00. compressor should be at least 2hp and deliver 90psi.

  procedure: remove spark plugs. set engine to tdc #1. calibrate test gauge per the instructions.  Lock engine so it can not turn. connect hose to spark plug hole. connect pressurized gauge to hose connection. read leakage. if looking for coolant leaks and nothing obvious shows up, bypass gauge and connect shop air direct to cylinder. open radiator cap before this. if coolant sprays out, you have a head problem. do same test on rest of cylinders. remember to set tdc of each piston for compression stroke. this test is also great for air cooled head leaks and valve problems. note that all engines will have some leakage past the rings. i always do full pressure test when i suspect a problem. make sure engine is secured with full pressure test. it will spin violently. with gauge connected, you can rock crankshaft to see if leakage changes. if so, this is a sign that the ring lands are wearing, new engines will also do this until the rings are seated.

  i know these instructions are kind of flaky, but I hope this gives some insight as to this type of test. if having a mechanic work on your vehicle, he should be familiar with the leak down test. i would be concerned if he isn't. this is a basic troubleshooting tool that all fleets use. especially on diesels.

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pistons & rods

pistons are an aluminum alloy and have two compression rings and one oil control ring. the first compression ring and the oil control ring lands have been nitrided for durability. the second compression ring has been chrome plated and the piston skirt has been resin coated to reduce cylinder abrasion. an oil gallery has been cast into the piston and as oil from the oil jets is sprayed onto the underside of the crown, oil circulates within this gallery and cools the piston.

the same forged connecting rods are used in both the ge and gte engines, employing press fit pins with retainers on the small ends and replaceable rod bearings on the crank end. oil jets are provided on the large end for directing oil onto the underside of the piston crown for better cooling.
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1. are aftermarket forged pistons and rods a good idea?
the sellers of these components think they're an excellent idea! in reality, the stock supra pistons are as advanced a design as any aftermarket piston, and the rods are already forged. the stock reciprocating assembly "can" hang together just fine up to 8000-8500 rpm (although we're rev limited to 6900-7200) and can produce insane power levels. however, to be fair to the aftermarket, there are some weight savings and strength increases to be gained with aftermarket rods and pistons, but these become advantageous only when the engine is being prepped as a full race engine.
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crankshaft & torsional damper

the forged steel crankshaft incorporates twelve counterweights and seven main journals; the main and rod journals are induction hardened. replaceable aluminum alloy main bearings are used.  

a dual mode torsional damper is fitted to the front of the crankshaft. this is NOT an external balancer, as the crankshaft is fully balanced, rather it dampens both the axial twisting couples produced by the firing pulses, and the radial bending moment from the accessory drive belt.
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1. which type/brand of oil and filter should i use for the mkiv tt engine?
turbocharged car owners generally favor pure synthetic or synthetic blend oils over dino oils. synthetics' shear and anticoking properties at high temperatures are ideal for protecting turbocharged engines. any synthetic of the proper weight will do. don't get hung up on brand names. if your tt has a new engine or fresh short block, allow 5,000 miles for break-in with dinosaur (mineral) oil before changing over to synthetic oil. the "dino oil" helps seat rings, seals, etc.  generally stick with toyota's specification of 10w-30. however in cold climates, a change to 5w-30 may be warranted during the winter. be aware if you have a high mileage supra and switch to synthetic, your oil consumption will probably increase. despite synthetics' other very desirable qualities, some supra owners have found that certain brands of synthetic are not as friendly to valve stem seals as dino oil, and may actually accelerate wear in this area!

toyota make an excellent stock filter for the supra, and an even larger capacity filter is available with the same construction for the land cruiser or lexus, and these are good upgrades for the supra - the toyota p/n for these is 90915-20004.  In the aftermarket, Amsoil make a very good filter, as do k&n. stay away from the bargain store brands that are on sale for only two or three dollars. this is not a good area to save money.
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3. is it difficult to change the oil? how long should it take?
it isn't difficult, but the first time you do it, set aside a couple of hours to complete the task and be prepared to get messy. after you have done it once or twice, it should only take about 20 minutes and you'll have figured out how to do it with less mess. while you have the car up on stands, it's a good opportunity to check over the entire undercarriage and check the torque on the suspension mounting points both front and rear.
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6. doh, i didn't sign up for a course in heat transfer. just tell me the right proportion of coolant and water to put in my system.
okay, here's just the facts: run the "least" amount of coolant you can in your system that will provide freeze and boil over protection "for your climate", throw in a bottle of Redline water wetter too, and fill the system the rest of the way with "pure distilled" water. here's a table that's pretty accurate so you can pick which proportion will work best for your climate. all figures are in degrees fahrenheit.

           % Coolant    Freeze    Boil

            20%                 16         253
            33%                   0         256
            50%               -34         265
            70%               -90         277  

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