Good advice from John.
Loose chains at idle are nothing to trifle with, regardless of they "look"
with the cam cover off. You should have sufficient oil pressure at idle to
keep the chains from making noise. I personally like the chain tensioner
gasket issue problem, assuming the chains were replaced when the engine was
rebuilt. It is possible to put the gaskets on incorrectly.
Gary Ault
----- Original Message -----
From: "John F Sandhoff" <sandhoff@csus.edu>
To: <nmleeds@mindspring.com>
Cc: <datsun-roadsters@autox.team.net>
Sent: Wednesday, November 14, 2007 1:23 PM
Subject: Re: [Roadsters] U20 - Rough low idle - Chain slop
>> How much do people's U20 chains slop around at low idle?
>
> Personal opinion: they shouldn't. There should be enough oil pressure
> to maintain the tensioner.
>
>> Here are my symptoms: at 700 rpm's, even with a warm engine,
>> the idle is swinging from 660 to 740...
>
> My crystal ball points to a worn distributor. Put a timing light and
> dwell meter on the car - is timing jumping? Is dwell drifting?
>
>> The first thing we did was looked for vacume leaks
>
> Good thing to check.
>
>> Still confused, we pulled the valve cover off and ran the engine with the
>> valve cover off -- messy, but a useful diagnostic. When we looked in,
>> it looked like the timing chain was slopping all around and the
>> tensioners weren't doing such a good job.
>
> Messy, yes :-)
> In fact, if you didn't get fairly well soaked with oil, I suspect you
> have an oil flow problem. This may be your smoking gun.
>
>> The engine is freshly rebuilt. The tensioners have plenty of material
>> left on their feet. All of the oil passages were freshly cleaned when we
>> did the rebuild. We've got three theories:
>>
>> 1) The tensioner springs are shot...
>
> Nope. The springs only maintain static tension. As soon as you get oil
> pressure, the springs become quite secondary.
>
>> 2) Because the engine is so new there's just not enough oil
>> pressure to push out the tensioners are low idle.
>
> New engine = low pressure? Nope.
>
>> 3) We put on really loose exhaust...
>
> Nope.
>
>> Any ideas?
>
> Yes, actually.
>
> 1. Verify oil pressure. You better have some. Sounds like maybe you
> don't :-) Did you replace the oil pump when you did the rebuild?
>
> 2. If oil pressure and flow is good, is it possible that the gasket
> between the tensioner and the block doesn't have the little hole
> that allows oil flow? In reality, that sounds like the issue and is what
> I'd look at...
>
> The concern then is if the upper tensioner (which is easy to get to)
> has a bad gasket, what about that buried lower one?
>
> -- John
> John F Sandhoff sandhoff@csus.edu Sacramento, CA
> ________________________________________
>
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>
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