# Timing belt and alternator concerns 86 300zx Turbo



## Jawg (Jul 22, 2006)

Hi, John from Colorado Springs. Got my 300ZX Turbo in 1998. It was a daily driver, now it is my "collector car". Mods are KN Cold Air intake, Magnaflow catback exhaust, boost modulator. Now we are moving! :newbie: 

My beloved 300ZX is on jackstands until I can get some feedback to reassemble it. I changed my timing belt, tensioner, spring, cam/crank seals and water pump in 10/2000 at 110K miles. The parts were all OEM. All the advice I could get says to replace the belt at 6 years regardless of mileage. I still have nightmares about the timing belt job from when the crankshaft pulley bolt snapped off! It was machined and fixed successfully, but the job was more work than I care to perform or pay for, unless necessary. I now have only 119K miles and don't drive the car very often anymore. I am reluctant to change the belt every 6 years, so I decided I would pull off the top cover and do an inspection. This was so much easier than taking off both covers! The belt looks good. No cracks or fraying, still pliable, but feels a bit loose on the top section. My deflection appears to be between .563" and .625" when pushing down with my finger. Hanes calls for deflection between .512" to .571". Is my belt too stretched out?

Does anyone give their blessing to keep this belt on and inspect it every year for wear?

My other concern is the alternator. I have been going though an alternator every 1 to 2 years. The Bosh reman ones seem to last the longest. Is there a fix for this, or do I need to go back to an OE ($$$) alternator? I consider the alternator replacement to also be a pain in the back/neck.

Thanks in advance for any advice/opinions on these topics. Pictures available on request - don't know how to post them, duh.


----------



## Zen31ZR (Mar 24, 2004)

Colorado Springs , kool. I'm in south Denver, so not really a long ways from you. 
The reason to replace the belt every 6 years is because when sitting for a long time the belt takes a set, especially where it curves around the pulleys. So after sitting for 6 months and then suddenly seeing use, cracks will form in those areas. You will usually not see the cracks on the top of the belt. The belt must be looked at from the bottom, where the teeth are. There could be a lot of stress fractures in between the teeth and sometimes the teeth themselves start to flake a bit. Keep the belt on if it stays crack free. Check it every month or so that you drive it, especially after sitting for a long time

I would not rely on the Haynes manual for accurate information. Their torque spec information cost me 2 engines in another vehicle, so now when I see a Haynes manual my first impulse is to throw it away. Use as general information only and take all clearance, torque, and deflection specs with a grain of salt. The Factory Service Manual for the Z31 is very easy to find online. I beleive there was a place called Carfiche.com that had it, dunno if that site even still exists, though. Use the Haynes at your own risk. The belt may be stretched a bit, from the sound of it. Sounds like the part across the top is 1 tooth too loose. Very easy to do if you don't use the FSM suggestions for installing the belt. 
As far as using OEM parts, its always best to use the OEM tensioner pulley at the very least. 

Sounds like your alternators may be trying to charge a bad battery. How long has it been since the battery was changed. Next time the alt takes a dump, replace it and the battery and all the cables and connectors. A bad connector or cable or battery can create spikes in the rectifier and cause a failure.


----------



## Jawg (Jul 22, 2006)

Wow, Zen31ZR! Great information, thanks! Would you think that running the car weekly with at least a 5 minute idle will protect the belt from this type of wear? I was always making sure to start and/or run it at least 1x a month. I am going to get a closer look before I replace the cover, as soon as I can remember how I turned the crankshaft over last time - I couldn't find a socket in my collection that fits.

Wondering about if I missed a tooth on timing belt install. Wouldn't I know by performance? Looking at the belt now I cannot tell where the belt marks were. It seemed to line up at the time, but I bet I relied on Haynes for it.

As for the Alternator. 1 place previously did the free test with all parts in the car, running and told me it was bad. I see your reply to another post that bench testing may not show the defect.
The Battery was replaced 6/2004 at 116K miles.

I pulled the alternator today and returned to Pep Boys - where I bought it, tested good. Then I took it to my other parts store for 2nd opinion, tested good. I am going to clean and lube the plastic connector (tab is broken) on the back and reassemble. If I am still getting flickering in all my lights I will look for a loose ground, or just take the whole car back into Pep Boys for their complete diagnostic of electrical system. It would be heaven to replace the connecting wires with longer ones. Replacing those wires sounds like it would be difficult.


As for Haynes; yes, I have cursed their name several times! Some of their books and fixes are certainly better than others. I thought about renewing Alldata.
Thanks for your info!


----------



## Zen31ZR (Mar 24, 2004)

If you are going to start the car, take it all the way through the warm up cycle and let it run for 20 minutes or more. This will burn off most of the fuel and other combustion residue that will cause harmful deposits later when the car sits. This procedure should also help prevent the belt taking a set, yes. It will also prevent the fuel injection system from developing problems. I do hope that you are using some form of fuel stabilizer, gasoline looses most of its octane after 28 days and begins to revert to its turpentine base. The fuel stabilizer prevents that and also prevents corrosion in the injection system and filters.

The problem with bench testing an alternator is that it is not under the same loads seen when driving the car. Best to take the entire car to the shop and have it tested. Even that isn't very enlightening, an engine at idle or revved up while not under a load is not the same thing as driving. I've seen alternators pass these tests that failed under otherwise "real world" conditions. 

Perhaps the timning belt is not 1 whole tooth off, probably more like 1/2 a tooth. The correct belt install and tension procedure is outlined in the FSM, and I will give you a hint, the passenger valve cover has to come off.......

All-Data is good stuff, but I'd still use the correct Nissan FSM. And best of all its free if you look in the right place.


----------



## Jawg (Jul 22, 2006)

Good reminder on the fuel stabilizer. I will start adding it since a tank of fuel lasts me up to 6 months. I pay for the 91 octane (Colorado highest pump octane) and would like to keep all of it. I add it to my lawnmower and Yamaha XT350, so why not my cherished Z. I will give the car a 20 minute run weekly also. My 6 year old son loves this car and thinks it is the coolest since he can sit up front and his window goes all the way down. 

I got it all put together yesterday and runs well. Alternator seems to be functioning normally now, so it could've been a loose wire. I will go give the car a hard drive today on a sushi run. I do need to add a boost gauge so I know how much I am running. I did add the adjustable pop off valve and guestimated a setting at 10psi. I saw you were running 12 in one of your posts.


----------



## Zen31ZR (Mar 24, 2004)

12 psi was probably a long time ago. After I added a proper mechanical boost controller I was running 16 psi on a daily basis. About 3 psi more than I should have been with the completely stock fuel system, and ultimately leading to the untimely demise of my engine. I completely did away with the pop-off valve and capped that area with a pipe plug. From what I saw with my own boost guage the stock POV kicks in at around 9-10 psi. My car saw high 13s at Bandimere with cheap street tires and the worthless open diff the 85's had. Bandi's starting line is super slick and I had to bog it down a lot just to get going. I have no doubt I was in the 12s on regular pavement, which was a much better launch pad. You car should be quite capable of that and more.


----------



## Jawg (Jul 22, 2006)

I thought my stock POV was opening at around 4# to 6#, it was an utterly lame amount of boost. Yes, I also did the $1 pipe thread plug and ran that way for a year. Until a mechanic friend made a good point about blowing the engine if there was a mishap with too much boost. I decided to spend the $80 or so and got the adjustable one so I could stop worrying about it. Thanks for the help. I think I will check my timing belt every 3 to 6 months for cracks and replace it one of these days. I may make some more performance mods in the future, but for now it is fast enough to get me in trouble.


----------



## Zen31ZR (Mar 24, 2004)

Stock, the turbo runs about 7 psi. The POV on mine opened at 9 psi, as I recall. The wastegate is what prevents the engine from building too much boost. The POV is a needless affectation and you'll notice the Z31 is one of the only cars from that era that has one. With any serious mod, you need to pay close attention to how the engine behaves on daily basis, making the POV useless. The POV is for people that can't be bothered to pay attention for themselves, and to make up for a lack of proper equipment. Overboost would be immediately apparent on a *proper* boost guage, which unfortunately the Z31 does not have stock, thus the need for the POV. Notice I said proper........


----------

