TIMING BELT REPLACEMENT PROCEDURE
Z31 TIMING BELT REPLACEMENT
Print and READ this before attempting to replace your belt.
I've been waiting for stickies forever.
This post should help tons of n00bs with the basic yet extremely important timing belt replacement procedure. I cannot take credit for this information, this was originally written by fa-kin-a.
"Re: Timing Belt
Posted by: fa-kin-a
Date: August 04, 2006 12:41AM
timing belt...OEM or aftermarket
tensioner and stud...OEM
thermostat...OEM...Robert Shaw...BeckArnley...no Stant?
small 90* hose
short 4 inch hose from thermostat to suction tube
both upper radiator hoses
lower radiator hose
new ss clamps
crank seal plate
CHTS and harness
new crank gear (worn?)
new OEM key...these are hard to find aftermarket?
Timing belt change . . .
Use of this "method" assumes that your car is running OK before you change the belt. If the belt has broken or sheared some teeth, you'll need to line it up from scratch.
* You also should use the any other info on the Z31 site, other sites, and in the Haynes or other manuals. If there is any disagreement, just THINK about it a while.
* The first thing I'd do BEFORE starting this job would be to start the car up from cold and let it warm up to just the point that the temp gauge hits it's normal operating temp....then shut it off. Take a flashlight and carefully look at the top side of the motor between the valve covers for any slight coolant leaks you might see...these will likely show up as some slight dampness only, usually towards the front...you'll need to stop these leaks during this job.
*No need to remove the valve covers or the spark plugs, or to rotate the engine to seat the belt, or use a feeler gauge, and I'd recommend discarding the tensioner spring, unless you can get it to work opposite the belt tension.
1) After lining up the TDC mark on the crank pulley/ dampener (be exact...see below), use a medium sized c-clamp in the *starter opening to hold the flywheel when changing the timing belt on a car with automatic (or a manual). This should just fit in the starter opening & be oriented in the direction of flywheel travel so the back of the clamp takes the load; clamp it solidly on the ring gear. Holds real well and makes sure the crank STAYS NEAR TDC during the whole job and the removal of the crank pulley/ dampener.
*After disconnecting the battery, remove the starter by backing out the (2) bolts and letting it hang on some coat-hanger wire and the heavy positive wire. No need to remove anything else.
2) The crank damper/pulley is machined from brittle cast iron and will likely chip if pried on too much. Just remove 2 or 3 bolts and use 2 or 3, 1 1/2" to 2" 6mm bolts and a steering wheel puller to remove the pulley/damper as a unit. Some might not have the holes.
*If the crank gear is stuck, the best method is probably to drill (2) 1/4-20 holes in it on opposite sides and use a puller...but you might start by trying to pry it off and possibly use a *crows-foot puller on it. When using pullers on the end of the crank, you need to be very careful not to mess up the threads in the end of it or any part of the crank surface...push against the large bolt head only.
* a cheapo puller can have the "feet" ground down quite a bit in order to just catch the edges of the crank gear...you can also use a large hose clamp to keep them on the gear while pulling it.
3) To loosen the cam gear bolts, be sure the OLD belt is reasonably tight by readjusting the tensioner. It's best to ALSO use a heavy screwdriver or prybar to hold the gear vs the head (not on a machined surface) as well as using the belt. The same method is used to tighten the cam gears to specs, using the OLD belt & prybar again. C-clamp still holds the flywheel.
4) One part that SHOULD be replaced while doing the T-belt is the small right angle *hose between the heads at the front. This hose deals with a lot of heat and mine was seriously "rotten", i. e., rubber & cord could easily be torn by hand. Same with the 4" diameter hose. While messing in this area, it's probably best to replace the several gaskets in here also.
*Look for any coolant leakage in this area BEFORE the car is FIRST torn down using a flashlight...see above.
There are also 2 bolts that look like they thread into coolant and can leak; they will need the threads gooped.
*I tested all old coolant hoses by slitting them with a knife and attempting to rip them by hand. The only other hose that was weak (other than the small elbow) was the short 4" full diameter hose right at the front.
5) I'd recommend using very light coats of Permatex non-permanent gasket sealer on both sides of any coolant gaskets that are replaced. Real cheap insurance. Clean ALL old gasket or goop off the surfaces first with a dull blade. Use a little moly grease on any bolt threads not going into coolant...don't over snug them.
*In order to easily see the gear alignments, take a small brush and some quick-drying paint from a spray can, and after cleaning with lacquer thinner; MARK the punch marks on both the 3 gears and the backing plates/oil pump housing. This way, if anything moves, it will be easily seen. You also need to be aware of the parallax effect where you'll find that if you don't look straight at something when you check it's alignment, you can be pretty far off...use a small mirror if you have to.
6) Be careful when removing the old cam/crank seals. They can be difficult and you DON'T want to scratch the camshaft surfaces where the seal rides OR even the soft aluminum bore that the seal fits into. I used a medium sized flat screwdriver resting on the camshaft/crankshaft in FRONT of where the seal rides on it...you could wrap some tape on this or use some alum flashing to avoid scratching the outer shaft surface.
To install, you need to coat the rubber seal surfaces with grease and I use a little nonpermanent Permatex sealer on the outside of each seal where they press into the oil pump or heads. Will have to make something to tap the seals in straight till they are flush with the front surface, since you don't want to start them in "sideways" at all, I used some PVC tubing of the right diameter and with ends sanded square (90 degrees vs length).
* A thin film of moly grease or anti-seize should be used on the crankshaft where the cam gear goes due to potential rusting & seizure. A new Nissan key also, along with a good (or a new) plate at the back of the gear. Also a good idea to check carefully, the edges of all cam gears for burrs and dress these down with a small stone or file (by hand only) if needed.
7) If you replace the tensioner stud...you'll need to use threadlock to help hold it in the block...I used vicegrips to snug it down...maybe a couple of jammed nuts on the end would be better...don't snug it TOO much.
8) For the CHTS connections...you need to be sure you have solid contacts...I use a very small screwdriver to bend the female side of the contacts IN some...work them back and forth...and would recommend some computer type contact conditioner plus di-electric grease over this...can save some problems later.
Installing the new belt:
1) This is the last thing you do before you put the cover on and the rest back together…be sure everything is done, seals in, gears on, waterpump, CHTS, most hoses, gaskets, everything cleaned, etc…. DONE RIGHT…. before proceeding.
2) Recheck the crank gear's alignment with the mark on the oil pump housing…same with the cam gears vs the backing plate marks. Be exact here. BE SURE THE CAM GEAR IS EXACTLY ON THE MARK....
3) BEFORE putting the new belt on...you need to engage the spring with the notch or hole in the back of the tensioner...and using an allen wrench...turn the tensioner clockwise until the spring has some load on it...stop when the idler pulley is as far to the left as it will go...then tighten the nut some to hold it there.
When the belt is on...you should be able to loosen the nut and the spring on idler/tensioner will tighten the belt pretty close to the right tension.
4) The belt should have the arrow(s) facing the front of the car. All 3 lines should match the dimples in the gears...AND the notch and raised areas on the top backplate.
It is the alignment of the 3 gears and their respective backing marks in this static position that COUNTS…this process aligns the engine, the belt keeps this alignment during rotation.
5) To start...you will need to put the belt only about 1/2 way onto the gears...makes it easier to get it on the other gears. Takes some time and adjusting to get it on. Use your hands ONLY...if it won't go on...somethings not lined up....or the idle/tensioner isn't backed off as far as it will go.
6) When the belt is on the gears and the lines/dimples check out...then you should try and get the belt clear to the back and snug against the crank gear rear plate...and make sure the belt is running on the "shiny area" on each cam gear.
7) You need to put some reasonable tension on the new belt to check the alignment for the 1st time...loosening the nut holding the tensioner should allow the spring to put some tension on the belt...this should be very close to the tension needed.
Then, look at the crank gear again and check / adjust it if needed, then look at the cam gears vs the backing plate marks.
** IF you can move either cam gear one tooth vs the belt and be able to IMPROVE the alignment vs the backing plate for either cam gear…….DO IT. If you can't…it is aligned?
· The 3 lines on the belt SHOULD confirm the backing plate alignment, with the line on the crank gear mark and the other 2 lines on the cam gear marks (pass side is dotted). There should also be 40 teeth between the (2) cam lines & marks.
· There should be 43 belt teeth between driver side cam dimple and crank gear dimple.
The span (marks & lines and number of teeth between the right cam gear mark & line DOWN TO the crank gear mark & line) on the RIGHT determines your overall valve timing vs the crank; while the 40 teeth AND marks & lines between the cam gears at the TOP makes sure BOTH cams are correctly timed vs the crank gear. The tensioner span on the LEFT basically MAINTAINS the the alignment of the other (2) sides during rotation.
1) I used a paving block and a brick (glued together with silicone caulking) that weighed exactly 22 lbs (according to a baby scale> checked this against a PO scale!), glued a stick on one end (notched some to get past the FPR) and using this on the top span, got the tension close to specs. I had some minor belt noise for the first few days, but had little after this.
* It would be very easy to overtighten the belt. Since an overtight belt produces heat, and heat deteriorates rubber, it's not a good idea...not to mention the excess load on the tensioner, camshafts, stud, and the fiberglass cord in the belt...DON"T DO IT!
* I'd forget rotating the engine, and doing the feeler gauge baloney. (The engine rotation is probably recommended to enable the belt to "center" so it is positioned where it will ride....just put it back where it was running before?) If you've kept everything lined up and the engine ran before, you don't need to do all this.
* The use of the weight might seem a little dufus (hey, he's just using gravity!), but if you are doing the job alone, it is relatively easy to just balance the weight and get the right deflection vs a straight edge, since you don't need to also keep the tension correct as with a fish scale. And some say that fish scales are not accurate.
2) Torque the tensioner to specs and REDO number (4) above to verify that you have the gears aligned right...being sure to check the EXACT crank gear alignment FIRST.
3) You are almost done.
** It is recommended by some mechanics that you retighten the t-belt after around 25-30K miles...you might want to cut a hole in the belt cover at the idler so you can do this...cover with duct tape during use?
The ISSUE here is what to do AFTER a belt has broken or stripped some teeth.......WHICH is the SAFEST method to get it back in synch without doing MORE damage? With a turbo engine, you have more of a chance that there will be no valve damage, and very likely damage has already been done from out of synch rotation...but you have a chance if you are careful...especially with a low speed belt break.
You would want to avoid using a breaker bar when rotating the engine...use as little force as possible...use a box end wrench?
Since you know that the 3 marks on the gears HAVE to be lined up with the backing marks, you would do this first by moving things the minimum distance and then move the dist if needed?
Real question is, do you move the crank first or the cam gears? Maybe the shortest move for any gear to get it lined up? Move them all slightly in the right direction until lined up? Avoiding any interference during this process.
The cam gears rotate 1/2 turn for every turn of the crank. There are 20 teeth on the crank gear and 40 on the cam gear?
The dist also turns 1/2 the speed of the crank. ANY cylinder will fire again after the crank has turned (2) full turns.
Finding TDC after a broken or stripped belt.
1) The EASY method? " just align the crank mark with the oil pump housing one, then align the 2 cam ones with the 2 notches in the back plate? put the belt on and make sure the marks all coincide... all done."
2) The RIGHT method? "Best way to line up cams with crank after belt is broken is to back off the rocker shafts to fully retract all of the valves into the head, then you can rotate the cams and crank into proper position, put the new belt on and then just tighten the rocker shafts back down." Engloid (involves removing the valve covers)
3) The HAYNES method?
a) Remove the spark plugs in order to be able to rotate the engine and to be able to sense any interference as it happens.
b) Assuming the belt is off, the FIRST MOVE (to avoid any more damage) is to get the marks on the cam gears lined up with the backing plate marks by rotating the gears the shortest distance you can to accomplish this. Don't force the gears if you run into any serious resistance other than the cam lobe and spring pressure.
The real question is do you move the crank first or the cam gears? Maybe the shortest move for any gear to get it lined up is best? Move them all SOME in the right direction until lined up? Avoid any interference during this process.
c) If your crank pulley/gear woodruff key is intact and you can get an accurate indication of TDC for the crank, you then need to rotate the crank to TDC (zero degrees).
d) You MIGHT have to align the distributor with the rest of the engine, especially if you've pulled it. Find cylinder number one (look up the firing order in a manual) and trace this wire from that plug to the dist cap.
Take the dist cap off. When finding TDC for cylinder no 1, remember that the engine runs with the timing advanced, so when at TDC, the rotor will point about 15-20 degrees FORWARD (> in the direction of rotation >) of the no 1 wire contact INSIDE the cap.
There might be a couple of marks on the distributor housing to indicate the no 1 cylinder TDC postion. Get the dist in this general area so that you still have some adjustment room on either side at the base.
Might have to remove the bolt and pull the dist out & reset it to get it right. The dist has a sprial-cut gear that rotates some as you pull it or re-insert it...so you need to take this into account.
e) After putting on a new belt and snugging it up to a reasonable tightness, you'd would want to rotate the engine by hand to check for interference. Then you would try to run the engine (plugs in, hoses on, and coolant in) to see if runs OK. If it runs…then you let your breathe out slowly and do the full timing belt replacement gig. If it doesn't; test compression?
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1985 300ZX n/a
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