My #3 piston actually broke (no signs of melting)
while doing 20 mph and the damage was major. Prior to
that (not even 1000 miles) , i had dropped a valve
seat which had gouged it.
Stephan
'69 2000
--- Todd Osborn <trosborn@california.com> wrote:
> Victor,
>
> Glad to here you made it home okay (I still think
> you should've got the
>
> award for best 3/4 2000, a rare '70 1500!)
>
> This burned piston got me thinking, actually I woke
> up at 6am Sunday and
>
> couldn't get back to sleep thinking about this.
> After the 80+ mph fun
>
> run I was a little worried about my car. In the
> following I would like
>
> to examine root cause (I am not trying to place
> blame, just doing a
>
> little failure analysis).
>
>
>
> Background and observations.
>
> There have been several burned pistons in the past
> few years: Jeff
>
> Kroll's '69 SPL (burned #3), Eddie's '66 (burned #3,
> I think), Victor's
>
> '70 SRL (burned #3) and perhaps Stephan's '69 SRL.
> Also Jeff & Victor
>
> were doing 100+ mph, but Eddie was only doing about
> 70. Number 3 seems
>
> to be a common thread.
>
>
>
> Candidate causes.
>
> Obviously the failure is due to overheating the
> piston. I suspect the
>
> high temp is due to a lean condition or too much
> spark advance. Not sure
>
> which is more likely. The other question is why
> number 3. I orignally
>
> thought this was due to a lean condition, the rear
> carb sees a little
>
> lower fuel pressure, so 3 & 4 should become fuel
> starved before 1 & 2.
>
> My assumption was number 3 is charge robbed by
> number 4. But I did some
>
> timing diagrams Sunday night (warning obsessive
> behavior), with a firing
>
> order of 1-3-4-2, 3 robs from 4 and 2 robs from 1.
> Given that and since
>
> number 4 sees the hottest water, one would assume 4
> is the most likely
>
> to burn. So what is going on here and how do we
> prevent it?
>
>
>
> Victor did you find anything that might have caused
> this (I don't think
>
> the 100mph is the only cause)? Spark advance (smog
> or re-curved dizzy)?
>
> Front vs rear carb mixture (are both screws set
> about the same)? Did you
>
> notice any intake manifold or carb nuts looser than
> others? Is the
>
> manifold flat? Were all spark plugs tight (may be
> hard to determine
>
> since number 3 probably had aluminum sprayed on the
> threads)? Any other
>
> thoughts? Jeff? Eddie? Stephan? Anyone?
>
>
>
> I sure hate to see this happen I would appreciate
> anyone's ideas on
>
> this.
>
>
>
> Todd Osborn (no longer losing sleep, but keeping my
> speed down)
>
> 68 DATSFUN
>
> Victor Laury wrote:
> >
> > Ok,
> >
> > The head is off. I've got a melted piston. #3 on
> the edge, by the plug. all
> > the others look fine. The cylinder wall looks
> good. maybe some light
> > scoring.
> >
> > I'm going to take a break, eat makes some
> limonade, Then drop the pan,
> > release the connecting rod and push the piston
> out.
> >
> > You are all with me.
> >
> > Victor
> > 70 SRL 31113136
> > Los Angeles
> > http://albums.photopoint.com/j/AlbumList?u=123073
> > SoCalROC http://www.ameri-eagle.com/datsun/
>
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