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/
|