Timing Chain! Any Wisdom?

[sadao at dc.net]

Hey Good people,


I yanked my head off and rebuilt the head.

I'm about to torque the head back down.

I can put the timing chain on the cam sprockets, but I can't be sure that
I have the chain on the crank sprocket.

I can pull the chain around and spin the jackshaft (fuel pump, etc.) but
I can't seem to hook the chain on the crank sprocket.

There's probably a simple solution.. .Any wisdom out there?

-Doug Eddy 1969 Elan +2 Really Red!

[dave at tape-gallery.co.u]

Sorry, Doug...no answers - just another question re: timing chains. I
think I'm having trouble getting the tension right on my twink.

On over-run from anything over 50mph, there's a zingy kind of rattle
(not too loud), which I assumed was due to the chain being loose.

I took the cam cover off, and set the tension to give about a half inch
vertical deflection of the chain between the cam sprockets (as per my
w/shop manual). But the noise is still evident.

Should I crank the tension adjuster in further to get zero movement in
the chain, or is there a danger of over-tightening?

There is nearly 3/4" of the threaded tension adjuster clear of the
locking nuts, so I don't think the chain is stretched significantly.

As always, thanks in advance to all you experts...

David
'71 Plus 2S

[peter at rolotec.ch]

Hi David

Timing chain slack of 1/2 inch was just about right in my experience. With
car standing and engine running you can try this (assuming that you have
adjusted the chain to 1/2" before):

Set the engine speed to about 2000 RpM then slowly turn the adjuster screw
in, counting the quarter turns as you go. From a certain point you will hear
a whining noise from the chain. Now you are definitely too tight. Back off
the tensioner to the original setting. Continue loosening the screw while
varying the engine speed between idle and some 4000 RpM. At a given time and
engine speed you will hear the chain rattle against the timing cover. Now
the chain is definitely too loose. The correct position of the chain
adjuster will be near the middle of the "too tight" and the "too loose"
position and should correspond roughly with the point where you started (ie.
1/2" chain slack) Do not stay in the extreme adjuster positions too long, as
wear and tear on chain and sprockets rises sharply.

3/4" adjuster thread visible is good, ie. chain not unduly stretched, just
as you write.

You write that you hear the noise on overrun from 50mph. Are you sure it is
the engine? Is the noise related to engine speed or to road speed? Could it
be too much axial play in the gearbox or a diff nearing the end of its life?

- HTH

Peter (Elan Sprint 1971 currently being rebuilt)


----- Original Message -----
From: David Croft <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 01, 1999 11:29 AM
Subject: Re: [lotuselan] Timing Chain

[davidcroft]

Thanks, Peter


Strangely I am pretty sure the noise is road-speed related not
engine-speed, but it definitely comes from the engine compartment - not
the diff etc.

But now you mention it, I suppose a 'loose chain' rattle would be
noticeable regardless of road speed - and I should be able to make out
the noise with the bonnet open and my ear next to the front of the
engine.

Obviously the engine is starting from an 'under load' state on overrun
from high speed (much more so than with the engine just revving in
neutral) - could this explain the apparent relation to road speed?

I wouldn't know how too much axial play in the gear box would show
itself, but the 'box seems really sweet - great gearchange, no jumping
out of gear etc.

Do you think I could deliberately overtighten the chain, take the car
for a short drive and see if the noise is eliminated? Would this mean
that I am being overcautious about setting the tension? At least, if I
do run the car for a minute with the chain really tight, and the noise
remains, I would know to look elsewhere.

Regards


David

["Peter Boegli"]

----- Original Message -----
From: David Croft <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 01, 1999 3:47 PM
Subject: Re: [lotuselan] Timing Chain



Do the test I described and if it were only to "tune your ear" to the sound
of chain rattle (too loose) vs. chain whine (too tight). You might even shut
the bonnet and sit into the car to listen to it.


Do the test (50mph) once in 3rd gear and once in 4th. Is the noise any
different corresponding to the difference in engine speed?


Axial play would make itself heard as high pitched gear whining. The pitch
corresponds to the gear you are in and the road speed. And, yes, if its
really bad the gears would jump out.


I would be very careful deliberately overtightening the chain, because if it
breaks the damage will be substantial and expensive. Without any guarantee I
feel that tightening the chain to the point just _before_ the whining starts
would be safe for a short test during which the engine temperature will
remain about constant. After that please do slacken the adjuster again to
the 1/2" mark.

Could you describe the noise you hear a little bit more precisely, maybe I
can deduce a hint or two from that.

Regards
Peter

[davidcroft]

Peter,

The noise is a soft thrashy, slightly zingy kind of sound.
A soft rubbing sound with a light metallic tinkly rattle
er...running out of adjectives...

It doesn't sound like anything's about to explode...

It isn't very loud but it is noticeable. It doesn't correspond to any
particular rev range (like a loose heat shield on an exhaust, for
example, which might have a specific period of resonance).

If I hold a constant speed, even at 90+, no noise at all. If I back-off
VERY gently, and ease off the throttle over a long period of time, there
is no noise also.


Thanks again


David

["Peter Boegli"]

David,

thinking aloud and in writing:

The noise comes when there is negative torque in the drivetrain. Is its
loudness roughly proportional to that negative torque, ie. louder in 3rd
gear than in 4th? (Hard to say as the engine makes more noise, too in
3rd...) Cold it be that the noise is there in any gear, but is masked by
louder engine noise in lower gears?

Are the engine mounts okay? The engine tilts under torque (counter-clockwise
viewed from the driver's seat and on overrun) and might touch some chassis
or body part. Are any ancillaries close to the chassis like eg. the earth
strap?

Does the gear lever gaiter have a hole? (It is amazing how much unusual
noise can enter the car through a tiny slit there, opening up when the
gearbox slightly tilts under deceleratin torque.)

Using the gear lever as an indicator - do you think its sideways movement
under hard acceleration or overrun has increased over time? This would point
to some problem in the engine-/gearbox suspension.


Do the headlamps work nork normally even under acceleration?

Do you have a fan blade sitting on the waterpump pulley? Can it touch the
radiator when the engine moves?

Sound origin location in a closed car can be tricky. So if you are not
_absolutely sure_ that it emanates from the engine compartment, do check the
differential suspension rubbers and the two torque rods, the rear wheel
bearings with the car jacked up

I hope I am not barking under the wrong tree, so let me know your findings
with these ideas. I hope they help a little.

Cheers
Peter

----- Original Message -----
From: David Croft <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 01, 1999 4:39 PM
Subject: Re: [lotuselan] Timing Chain

[jimfixit]

my noise disappeared when I replaced the sprockets (cams and crank)
Now it's quiet-er
jimbo
----- Original Message -----
From: David Croft <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 01, 1999 2:29 AM
Subject: Re: [lotuselan] Timing Chain

[BrianMartley]

Doug,

When I've done this job I've usually kept the chain on the crank sprocket,
splitting it at the top and holding it with a piece of string. The one time
I remember losing this, I managed to thread it round using a long piece of
1/8" wire (an old coat hanger) hooked at the end, with lots of fiddling.

The only other way I can offer is to drop the sump - which I bet you're not
too keen on doing unless you have to ?

Brian

[rodbean]

David Croft wrote:


I would be very careful about deliberately overtightening the chain. I
once broke a cam that way on my Elan race car. The car was too noisy to
hear the chain properly and I got it wrong, being in a hurry to get out on
the track..... cost me a lot of down time.

Could it be either the water pump (try to wiggle a fan blade) or the
generator/alternator bearings?

Here's a suggestion: Get a long screw driver and use it as a stethoscope
... handle in your ear, blade against various parts of the engine while
it's running.

Rod

[Sking06]

David....

Just a couple of thoughts... mark the inside of the cam cover above the
chain with a magic marker and then check to see if the chain is hitting the
cover. If the chain is hitting the cover the problem might also be a weak
spring in the chain adjuster that won't hold the tension even with the
proper adjustment (1/2 inch). I firmly believe that no two Lotuses are
alike, but on my Elan I can always hear what the chain is doing leaning over
the engine with the hood off between idle and about 2000 rpm. When I
couldn't get the chain to adjust properly I put in a slightly stronger
spring and solved the problem. Last, if overtightening the chain means
taking out all the spring tension I would not do it, the effect of the added
stress on the chain may not show up until it breaks. (100 miles from home,
middle of the night, etc)

Skip King

'69 Elan FHC
'61 Seven

Measure it with a micrometer
Mark it with a grease pencil
Cut it with an ax

["Peter Boegli"]

Brian,

Do I read you correctly - do you really use a timing chain with a lock so
you can split it? IMHO you are testing your luck because these chain locks
have been found to open when they shouldn't, ie. while the engine is
running. (just my 2p)

Peter



----- Original Message -----
From: Brian Martley <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 01, 1999 10:39 PM
Subject: Re: [lotuselan] Timing Chain! Any Wisdom?


(snip)

[jimfixit]

I've seen cam bearing surfaces ruined by a too tight chain/belt. It also
makes a strange howl when that happens.
To check the chain/sprocket wear, wrap the chain around the sprocket and try
to lift the chain up in the middle. If there is any movement, the
sprocket/chain is worn and should be replaced.
jimbo
----- Original Message -----
From: William "Skip" King <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 01, 1999 6:49 PM
Subject: Re: [lotuselan] Timing Chain

[Richy-dick]

David

If you are sure that you have the chain tension correct then the problem may
lie with the Slip Pad screwed to the inside of the timing chest. It is
possible that this may have worn away to the metal. It is also possible
that the rubber may have softened through the use of oil additives like STP
or Redex. This happened on my Twin Cam many years ago after I had first
rebuilt the engine. The rubber on the slip pad softened to the consistency
of Marshmallow and started to break up. Something like this could be
causing the chain to rub against metal that it wouldn't normally.
I've never seen the problem with oil additives mentioned on any Lotus list.
Has anyone else had an experience like this.

Richard A Clifton
Wakefield

[ElanS4 <elans4 at xxxx]

Richard Clifton wrote:

Now that it's been mentioned, how important is the slip pad. I
understand that it's purpose is to keep the chain from hitting the
side of the casing, but does the chain need to rub on it all the
time? Is it supposed to apply tension to the chain along the long
length of "free" chain? Does it hurt if there is a gap between the
slip pad and the chain when everything is tensioned properly?
Basically, the pad wears when the chain is loose, and when you tighten
the chain, it can clear the groves. Changing it with an engine
rebuild is a good idea, but what about in between times?

That should be enough questions for a while...

Tim Mullen
Chantilly, VA

72 Elan Sprint