Timing chain question.

[newby]

How much slack should there be on the timing chain with the engine off and cold? I noticed while trying to check my valve clearance that my timing chain had some play in it. Perticularly on the side opposite the hydraulic tensioner. I ask because I can hear a tapping sound when the engine is on. That's why I was checking the valves to begin with.

[Nissanman]

Without any oil pressure to force the chain tensioner against the chain, there can be an "alarming" sense of free play.
If you don't know the age or mileage of the chain then it may very well be due for replacement.
However, with the engine running and oil pressure up to spec. the ticking is more likely a loose tappet, as you have already realised.
Use a stethoscope, or a long shaft screw driver, to try and locate the sound.
Alternatively, you can take off the valve cover and with the engine idling, press firmly on each tappet and see if you can stop the noise. If you can, that is the offending device
The side opposite the hydraulic tensioner is always under tension when the engine is running but can be slack when the engine is at rest.

[newby]

Thanks for the info. I used a screw driver and it sounded like it was coming from the middle some where. I know I sound completely dumb but what is a tappet?

[Nissanman]

Probably a victim of semantics between us in OZ and youse in the States
Valve lash adjuster.

[SLOroadster]

Without any oil pressure to force the chain tensioner against the chain, there can be an "alarming" sense of free play.
If you don't know the age or mileage of the chain then it may very well be due for replacement.
However, with the engine running and oil pressure up to spec. the ticking is more likely a loose tappet, as you have already realised.
Use a stethoscope, or a long shaft screw driver, to try and locate the sound.
Alternatively, you can take off the valve cover and with the engine idling, press firmly on each tappet and see if you can stop the noise. If you can, that is the offending device
The side opposite the hydraulic tensioner is always under tension when the engine is running but can be slack when the engine is at rest.

You do realize the mess you will make running the engine with the valve cover off don't you?

First off, are you dealing with an R16 or a U20? I'm assuming a U20. Does the motor have the L shaped bracket that sits in front of the cam? If there is nothing directly in front of the cam gear, no, you don't. That is a good thing. The next question, does the upper tensioner have any shims on the foot? If not, you might wish to add some. You cant shim the thing totally tight so there will be a little movement of the foot after being shimmed, perhaps a 1/4 inch or so. Even on a brand new motor, at least one shim can be fitted. It might be a good idea to rotate the motor through and see if there are any damaged chain links in the upper chain. You can sort of see the lower chain, but its not easy.

From there, look at your cam. Is there any unusual wear on any of the lobes? Likely no, but worth checking. Assuming your valve lash is correct, try and pinpoint whether the noise is from the top of the motor or not. You also might check and see if you have an exhaust leak somewhere in the exhaust headers or manifold.

My motor has an odd rattle that after two rebuilds still happens. I don't have the slightest clue what or where it is. Sometimes it goes away. It sounds like timing chain rattle, but it seems to come from the lower chain. Its got new tensioners, chains, and gears but no lower guide (known for failure so I omitted it based on the Bob Sharp manual.)

Will

[fj20spl311]

[Gregs672000]

Yep, all good info here. Do some research on the U20 death rattle. The part in front of the chain that Will mentions is a nice idea by Nissan but unfortunately gets hit by a loose chain, eventually causing it to fracture, break off and then get launched out of your motor and through the hood, thusly ending the motors life in a dramatic fashion. I have cut mine off near where it angles away from the head, and I suggest you either do the same or monitor it very closely, but keep it ONLY if it has not already been struck. I've seen some where the chain was happily sawing through. If your chains are worn out they must be replaced at some near future time, and that generally requires removing the front cover, oil pan and the head, though you MAY be able to get the front cover off without removing the head, but I think few have been successful doing that and not having it leak oil later. So, you would need a head gasket, manifold gasket as you will probably need to remove the intake and exhaust, oil pan gasket, front cover gasket, water pump gasket, collector gasket if you're running a header or a stock donut gasket, and chains. I would also suggest new head bolts or studs, but some reuse them. Oh, and buy a thread tap to clean the head bolt threads out and make sure they are not full of oil, as that will change your torque specs and you can break them. Oh, and a 10mm allen head socket to r and r the head bolts, and a torque wrench. If you have to go this far, you may want to post pics of the gears so we can tell you if they need to be replaced... Let's hope not! See, you have found the weakness of the U20, as these parts can be expensive. Then again, I'm running used gears and have for years.

Hope I did not discourage you, as I do not know of your mechanical experience, but it is better to know something about what you're looking at than to be overwhelmed and surprised. It's really not that hard, and even if things need replacement, if you get rid of the "evil L" and shim your chain it will last quite a while unless the chains are damaged. That way you can plan and save and learn. And maybe we can find someone local who can help you. I sure am going to owe Curtis for doing my wiring! What goes around comes around, and we try to help each other as much as possible.

BTW, we'll help you shim up the tensioner too!

[jrusso07]

Here's a very good write up with pics to illustrate what members have said. http://www.gordon-glasgow.org/Evil_L.asp" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

There is a chain slack checking procedure in the "what to do about it section"

I was able to change chains with the head on the motor. Take care not to damage the head gasket dring removal. Use some sealant on that portion of the gasket when reassembling.

Here is a pic http://img40.imageshack.us/img40/1648/imagemjon.jpg" onclick="window.open(this.href);return false;

[newby]

Thanks for the replies. All good information. A little background on this roadster. I had the u20 engine rebuilt last year a d they replaced most everything except the timing chains. The mechanic said they looked great so not to do it. I finally tried to get it going and the motor runs really rough. I had a different mechanic come by and he smoothed it out some but I think he might have over tightened the valve lashing trying to get rid of pigging. He set it to .002 and .003. Then he said the timing chain was too loose. But when it starts up I can hear the rattle go away. Anyway, the tapping or pinging is still there. Finally he said my plugs where fould up from trying to run it with the carbs not set up right. So im going to get some new ones later and start all over again. The only local roadster nut I know is Craig and he says he doesn't work on other people's roadsters.

[Thomcraft]

Is there a way to remove the "evil-L" without pulling the head?

[jrusso07]

You can access the evil L simply be removing the cam cover but to remove it you would have to cut it and that would allow metal chips to drop onto the chains and sprockets and ultimately into the oil pan unless you can find a way to prevent all that.

[newby]

I just got told that I should have added fuel to the carburetor since it was a new rebuild. Does anybody have a step by step instruction on this?

[SLOroadster]

I'd say, pull the positive wire on the coil and crank it till you have fuel in the fuel filter. That will also build oil pressure. Once you see fuel in the fuel filter, plug the coil back in and it should light off shortly there after.

I've done this on two new engines and haven't had any issues.

Will

[mraitch]

Phil
How did you do that 3-d photo - cool

[dbrick]

Do you know if the cylinder head was milled/cut and if so how much?