But on pushrod V6 and V8 engines, there isn't a chain tensioner to compensate for chain stretch. Consequently, after tens of thousand of miles, the chain loosens up, begins to make noise because it rattles in opposition to the entrance cowl, and causes cam timing to retard. At this point, the timing chain needs to be replaced.
When Parts Put on Out
Timing belts and chains carry a heavy load. They've to show the cam with sufficient pressure to overcome the resistance of all the valve springs. Belts are fabricated from artificial rubber bolstered with tough fiber cords that provide
tensile power and stop the belt from stretching. Chains are made from steel hyperlinks connected by flexible rollers. While chains are more durable than belts and typically have a longer service life, they're additionally heavier, noisier and more costly to replace. That’s why belts are used on many OHC engines.
The principle cause of belt put on is heat. As a belt wraps round and turns the sprockets, friction creates warmth (that is along with the warmth from the engine itself). Over time, this causes the rubber to lose flexibility, harden and crack. The cords inside the belt also weaken because the belt accumulates put on, rising the danger of the belt breaking.
Timing chains, by comparison, are principally immune to the effects of heat. But they do stretch as they age, which may trigger rubbing noise and retarded valve timing.
When the Cam Drive Fails
If a timing belt or chain breaks, or the cam drive gears fail, the cam stops turning, the engine loses all compression and the engine stops running. A cam drive failure may also trigger costly valve harm in “interference” engines that don’t have sufficient clearance to prevent the valves from hitting the pistons if the cam stops turning or jumps out of time.
Interference engines include most Japanese and European engines in addition to Chevrolet 1.5L and 3.4L; 1995 Chrysler 2.0L and 2.5L; 1997 and newer Chrysler 3.2L and 3.5L; and Ford Probe 2.0L and 2.2L engines.
A timing chain or belt can also soar time whether it is loose. The engine could proceed to run, but will expertise a loss of efficiency because of the altered valve timing.
Belt and Chain Alternative
The very best time for a car proprietor to switch a timing belt or chain is earlier than it fails. For mid-Nineteen Nineties and older engines, the advisable alternative interval for most timing belts is often 60,000 miles. On newer engines, the original tools belts are made of better supplies and sometimes have a really useful replacement interval of a hundred,000 miles or more.
If in case you have the heads off the engine for any cause, or if you're overhauling the engine, you should also replace the timing belt, chain or cam gears. Don’t take an opportunity reusing an previous timing belt, chain or gear set. A excessive-mileage timing chain that has stretched and is free can’t preserve accurate valve timing and ought to be replaced if play exceeds specifications. The camshaft and crankshaft sprockets also needs to get replaced along with the chain. These elements are included in a typical three-piece timing set.
Something else to contemplate is upgrading a stock timing chain and equipment set on a pushrod V6 or V8 engine with aftermarket performance parts. You can substitute the stock silent chain and plastic-covered cam gear with a single or double roller chain and a billet metal gear to improve energy and durability (though it may be a bit noisier).
Did You Know…
On some engines, the valvetrain uses each sorts of drives: a timing chain and a pair of belts. Chevy’s 3.4L DOHC V6, for instance, makes use of a timing chain to drive an intermediate sprocket that also drives two belts (one for each pair of overhead cams). This kind of setup doubles your alternative to service the cam drive
system. You may substitute the timing belts for preventive upkeep, and you can exchange the timing chain if it has stretched or is worn.
Back to the Grind
A case in point is grinding noise coming from the timing chain cowl area in 2000-’03 Ford Crown Victoria and Mercury Grand Marquis with the 4.6L V8. According to Ford Technical Service Bulletin 03-15-7, excessive wear within the timing chain tensioner arms can cause a noisy condition. The tensioner arm has an aluminum base with a nylon surface. So should you discover nylon and/or aluminum particles within the engine oil, it in all probability means the tensioner, tensioner arms, timing chains and gear set all should be replaced.
The Ford part numbers for the 2000 model 12 months tensioners are F6AZ-6L266-DA (RH) and F6AZ-6L266-CA (LH). For the 2001-’03 model years, the tensioner half numbers are 1L3Z-6L266-AA (RH) and XL1Z-6L266-AA (LH). The stress arms are 1L2Z-6L253-AA (RH) 1L2Z-6L253-AA (LH).
You need to at all times verify a database of technical service bulletins for any engine you are rebuilding to see if there are any identified points with the cam drive. Ford TSB 97-2-8, for example, describes a clattering noise at engine start-up after the engine has sat overnight that could be heard on 1995 Ford Contour and Mercury Mystique fashions with a DOHC 2.5L V6.
Oil leaking out of the chain tensioners causes the timing chain to momentarily rub towards the tensioner ratchet when the engine is first started. The noise only lasts a couple of seconds and goes away as soon as the engine builds up oil pressure.
The cure, says Ford, is to replace the unique chain tensioner parts with redesigned parts. These embrace two timing chain tensioners F5RZ-6L266-CA, the left-hand tensioner adapter F5RZ-6C275-BA, the best-hand tensioner adapter F5RZ-6C275-AA, the left-hand chain tensioner arm F6RZ-6L253-AA and the suitable-hand chain tensioner arm F6RZ-6L253-BA. The two DOHC timing chains and information assemblies also needs to be replaced on the same time.
Did You Know…
On OHC engines that use a timing chain, the timing set may additionally embrace a sequence damper or tensioner. The chain damper, tensioner, information or rails must also be replaced when the chain and sprockets are replaced as a result of these components play a vital role in supporting the chain and conserving it tight.
Out with the Outdated….
As for timing belts, they do not stretch with age, however grow to be weak internally and should fail with no warning. Consequently, a visual inspection of the belt could not reveal much. If the mileage just isn't known, change the belt. And if the mileage is known and a belt has greater than about 30,000 miles on it, substitute it anyway.
Many OHC timing belt failures are actually attributable to faulty belt tensioners and loafer pulleys. Like belts, these elements additionally put on out and ought to be carefully inspected and replaced when the belt is changed.
Reusing previous tensioner parts will increase the danger of premature belt failure. The lifespan of many OEM tensioner components is just about 2,000 hours, or the equal of forty,000 to 60,000 miles or extra depending on how the automobile is driven. Tensioner bearings are “sealed for life” and should not serviceable, so there’s no approach to clean, examine or re-lubricate the bearings when a timing belt is changed. What’s more, it’s difficult to find out the true situation of the tensioner components as a result of they don't seem to be working under a load. Consequently, a simple visible inspection could miss tensioner bearings that are on the verge of failure.
Should you discover a belt with stripped cogs, it will tell you something within the cam drive system has jammed or caught, overloading the belt and causing it to shear tooth or jump time. The most certainly perpetrator is the camshaft, which may have seized due to engine overheating or lack of lubrication (low oil stage or loss of oil stress). Make sure to check the straightness of the cam bores in the cylinder head, and straighten or align-bore the pinnacle as needed before the head goes back on the engine.
When OHC cylinder heads get too hot, they usually swell up within the center inflicting the cam to bend or bind. In some cases, this may increasingly break the cam, snap the timing belt or shear the cam drive sprocket off the end of the cam.
…..In with the New
Comparable engines might use completely different cam drive components, so make sure you get the right alternative elements for the engine. For instance, Chevy has used three completely different timing gears for the 262 V6 since it first appeared in 1985. The flat tappet engines use a P/N 340235 gear; the non-balancer, curler cam engines use a P/N 12552128 gear; and the balancer engines use a P/N 10144121 gear. None of those gears are interchangeable.
On 1992-’ninety eight 262 engines with steadiness shafts, make sure that the 2 stability shafts are accurately phased with the camshaft. The shafts are gear-pushed off the cam, and there are two different gear units, one with extensive tooth and one with slim teeth. The extensive enamel gears were used on the earlier engines, and might be replaced with the later slim gears to cut back noise.
Chevy has additionally used two completely different timing gears on their LT1 V8 engines. The sooner 1992-’ninety five LT1 engines with aluminum heads use a P/N 10128349 cam drive gear with a small gap with sixteen splines within the center. On 1995 and later LT1s, a distinct gear P/N 10206039 with a bigger, unsplined center gap is used.
You’ll also find three different front covers on these engines. The 1992-’94 engines have a canopy with two small holes for the water pump and distributor drives, and a big gap for the crank. The 1994-’95 engines have a big middle gap for the distributor, and the 1996-’97 covers have an extra gap at the backside for the crank position sensor.
It’s also a good suggestion to examine the seal surface on the water pump drive shaft when changing the timing gears and chain on an LT1. The water pump is pushed off the cam on this engine, and if the shaft is worn, it should leak.
If you're replacing a timing chain on a late-mannequin overhead cam engine with variable valve timing (VVT), be sure you look up the meeting procedure so the VVT unit on the end of the cam is installed correctly. On GM’s Vortec 4200 DOHC inline six (introduced in 2002 on the Chevy TrailBlazer, GMC Envoy and Oldsmobile Bravada), the VVT “phaser” unit is mounted on the top of the exhaust camshaft and makes use of oil pressure to change exhaust valve timing as much as 25°.
The VVT unit is managed electronically by the powertrain control module by way of a solenoid valve that opens to route oil stress to the unit. When replacing the timing chain on certainly one of these engines, you must ensure that the VVT unit is in the right position (absolutely superior).
Be sure the replacement timing belt is identical to the original. Belt length, width, tooth profile and pitch must all be the identical, and the fabric must be the identical or better. Do not substitute a cheaper neoprene belt for one made of HSN (Extremely Saturated Nitrile). Use a high quality brand of belt because some no-identify brands use inferior materials that won’t last so long as the OEM belt or a top quality aftermarket belt.
When changing a belt, never try and “stretch” a belt over a pulley. Belts, keep in mind, don't stretch and forcing one to take action will doubtless harm the cords and cause it to fail.
Also, never pound on a sprocket to force it into place. If it isn’t sliding into place, test alignment and fit.
Misalignment problems in the cam drive may also occur if the cam sprocket is put in backwards, the fallacious thickness of washer is used (incorrect finish play), a thrust button is forgotten, or the crank sprocket isn't
positioned correctly on its keyway.
Belt rigidity is essential to belt longevity. Modify to the really helpful specifications (at all times seek advice from the guide as a result of the quantity of advisable play can range relying on the application). If the belt is too tight, it won’t last. If the belt is too unfastened, it might leap time.
Some engines, comparable to GM’s 3.4L DOHC V6, use a hydraulic tensioner to maintain the belt tight. On these engines, the tensioner must be ready before it's reinstalled by draining out the oil, fully retracting the plunger and refilling it with 5W-30 motor oil.
Additionally, verify for revised or updated belt adjustment procedures that could be more recent. An example right here is the timing belt and tensioner setup procedure that Ford initially printed for the 1998-2000 Contour and Escort ZX2, 2000 Focus, 1998-2000 Mercury Mystique and 1999-2000 Mercury Cougar with 2.0L engine. Ford TSB 99-25-four covers the revised procedure.