If the chain really "jumped time", something was wrong from the start.
Think about it. If the chain only has .040 - .060 free play at the tensioner,
there is physically no way for it to slip from one tooth to another.
There just isn't enough extra chain.
It would have to have FAR more slack to get over a gear tooth.
Something was wrong, it isn't a U20 design issue.
Secondly, if a lash pad came out, the valve spring lost control
of the valve. There should be only .006-.008 clearance when the cam is
off the rocker, no where near enough room for the lash pad to slip out.
Cam timing has no relation to lash pad clearance, that just is set with
a feeler gauge. The valve/spring had to become separated from the
rocker, allowing the pad to slip out.
You lost control of the valve train do to overrev, a bad valve spring,
(valve float) or possibly bad cam/rocker/lash geometry.
I do agree here:
If the evil L breaks, its all coming apart, all bets are off.
Jim
Eric Frisbee wrote:
>
> Another thing you might want to check is to pull the valve cover and see
> if you find any of those little lash pads lying around... I've had
> this fun twice already... first time, the "evil L" shot through my valve
> cover and bent all the valves. Second time, the chain jumped time,
> bent all the valves and threw lashpads all over the place... I also had
> the very weak backfiring problems while trying a restart... good luck!
>
> Incidentally, all 2000 owners should take this into account.. ANY time
> you hear the "death rattle", you'd better get working on it!! And
> change your oil regularly... I would change about every 2000-2500
> miles. If you decide not to believe me, I hope you and one of our fine
> vendors are really good friends... After two 2000 chain throws, is
> it any wonder that I prefer the 1600???
>
> Eric
> WyCROC
> '68 2000
> '67 1600 (wifes)
> '68 + '69 1600's
>
> Andy Cost wrote:
> >
> > I had a screw come loose in the distributor at an autocross. It sputtered
> > and backfired and then would not start. The screw got jammed in the points.
> > I doubt your chain skipped. To check it crank the motor by hand or by
> > rolling the car in gear until the timing mark on the crank gear is at TDC
> > and the rotor is pointed toward the front of the motor.. At this point the
> > cam key(screw) should be at the 3:00 position. If it jumped a tooth the
> > screw will be more like 2:30 or 3:30(A.M. or P.M your choice).
> > NT
> > ----- Original Message -----
> > From: <MMccaf8697@aol.com>
> > To: <datsun-roadsters-digest@autox.team.net>
> > Sent: Sunday, July 09, 2000 11:02 AM
> > Subject: Fwd: Slipped timing chain on U-20?
> >
> > >
> > > --part1_25.810df87.2699fc0f_boundary
> > >
> > > In a message dated 07/08/2000 11:40:57 PM Mountain Daylight Time,
> > MMccaf8697
> > > writes:
> > >
> > > << Fellow roadsterites: Troubles began on a drive to a wedding tonight
> > (not
> > > mine). Upon starting from a stop sign on a steep incline, some wheelspin
> > was
> > > experienced, and when traction was gained, engine stalled. No restart,
> > only
> > > some weak backfiring. Engine seems to have some compression or load on
> > > starter. Prior to this there was some timing chain rattle at low idle
> > (about
> > > 800-900 rpm). Engine is reportedly rebuilt about 3000 miles ago and
> > previous
> > > inspection revealed newer appearing timing chain, and top gear (removal of
> > > valve cover only). Timing chain tension appears to have several washers
> > to
> > > shim shoe outward, but otherwise appears new(er). How can I quickly check
> > > for timing gear jump? Is jumping most likely at upper cam gear or
> > jackshaft
> > > gear? (I am not looking forward to removal of front cover). Assuming
> > chain
> > > has jumped at top gear, can I simply set piston #1 at TDC and reposition
> > cam
> > > and cam gear to bright link and dimple on cam gear? Advice on diagnosing
> > > this and how to proceed would be greatly appreciated.
> > > Mark McCafferty
> > > 67 1600 with U-20 and 5speed
> > > WyCROC >>
> > >
> > >
> > > --part1_25.810df87.2699fc0f_boundary
> > > Content-Disposition: inline
> > >
> > > Return-path: <MMccaf8697@aol.com>
> > > From: MMccaf8697@aol.com
> > > Full-name: MMccaf8697
> > > Message-ID: <36.85a6c19.26996a69@aol.com>
> > > Date: Sun, 9 Jul 2000 01:40:57 EDT
> > > Subject: Re: Slipped timing chain on U-20?
> > > To: -datsun-roadsters-digest@autox.team.net
> > > MIME-Version: 1.0
> > > X-Mailer: AOL 5.0 for Windows sub 109
> > >
> > > Fellow roadsterites: Troubles began on a drive to a wedding tonight (not
> > > mine). Upon starting from a stop sign on a steep incline, some wheelspin
> > was
> > > experienced, and when traction was gained, engine stalled. No restart,
> > only
> > > some weak backfiring. Engine seems to have some compression or load on
> > > starter. Prior to this there was some timing chain rattle at low idle
> > (about
> > > 800-900 rpm). Engine is reportedly rebuilt about 3000 miles ago and
> > previous
> > > inspection revealed newer appearing timing chain, and top gear (removal of
> > > valve cover only). Timing chain tension appears to have several washers
> > to
> > > shim shoe outward, but otherwise appears new(er). How can I quickly check
> > > for timing gear jump? Is jumping most likely at upper cam gear or
> > jackshaft
> > > gear? (I am not looking forward to removal of front cover). Assuming
> > chain
> > > has jumped at top gear, can I simply set piston #1 at TDC and reposition
> > cam
> > > and cam gear to bright link and dimple on cam gear? Advice on diagnosing
> > > this and how to proceed would be greatly appreciated.
> > > Mark McCafferty
> > > 67 1600 with U-20 and 5speed
> > > WyCROC
> > >
> > > --part1_25.810df87.2699fc0f_boundary--
> > >
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